TANYA'S

COMPREHENSIVE GUIDE TO

FELINE CHRONIC KIDNEY DISEASE

 

 

ALL ABOUT HYPERTENSION (HIGH BLOOD PRESSURE)

 

ON THIS PAGE:


What is Hypertension (High Blood Pressure)


How Common is Hypertension


Why Monitoring Blood Pressure is So Important


Symptoms


Diagnosis


At What Point is Blood Pressure Too High


Frequency of Blood Pressure Testing


Treatment


The Best Treatment: Amlodipine


If Your Vet Suggests Other Treatments


Studies Into Use of Other Medications for Cats with Hypertension (Including Telmisartan)


 

 

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Home > Key Issues > Hypertension

 


Overview


  • Hypertension (high blood pressure) is very common in CKD cats, and can have some very serious side effects, including a stroke or blindness.

  • Therefore if at all possible, you must ensure your cat's blood pressure is checked regularly.

  • Hypertension can usually be easily controlled using medication.

  • The best medication is amlodipine (common trade names are Norvasc or Istin). It is effective, is unlikely to make blood pressure fall too low, and in some cases may even reverse blindness caused by hypertension.


What is High Blood Pressure                                                                                Back to Page Index


 

Hypertension means the pressure (or tension) in the arteries is elevated. This creates more work for the heart, and can eventually lead to damage to blood vessels.

 

For many years it was thought that hypertension in cats was the result of another condition, such as CKD - this is known as secondary hypertension. According to Heart disease in the older cat (2006) Simpson K Presentation to the FAB Conference (page 3), other conditions that may cause hypertension include hyperthyroidism, hyperparathyroidism, diabetes and anaemia.

 

Whilst it is true that hypertension is more common in cats with these conditions, it is gradually becoming clear that primary hypertension does exist in cats, and may in fact contribute to the development of CKD. If the blood vessels within the kidneys are damaged because of hypertension, eventually CKD can result. The National Kidney & Urologic Diseases Information Clearing House explains more about this. Feline hypertension: risks and management (2005) is a presentation by Dr Clarke Atkins to the World Small Animal Veterinary Association Thirtieth World Congress, in which he states "adding to the confusion in understanding the pathogenesis of hypertensive renal disease, renal disease begets hypertension and hypertension begets renal disease."

 


How Common is Hypertension                                                                                Back to Page Index


Prevalence of systolic hypertension in  cats with chronic renal failure at initial evaluation (2002) Syme HM, Barber PJ, Markwell PJ & Elliott J, Journal of the American Veterinary Medical Association 220 pp1799-804), found an incidence rate of high blood pressure of only 20% in cats at initial diagnosis of CKD. However, since the risk of high blood pressure developing increases as the CKD worsens, it appears that at least one third of CKD cats have high blood pressure. In fact, as Maggie Scherk reports in Blood pressure: a critical factor (2008), a Presentation to the World Small Animal Veterinary Association World Congress, some estimates actually put the incidence of high blood pressure in CKD cats at more than 60%.

 

Cats with hyperthyroidism (an overactive thyroid) are also prone to developing hypertension (87% in one study were found to have hypertension), so you need to be particularly careful if your cat has both hyperthyroidism and CKD. Using corticosteroids may also lead to hypertension.

 


Why Monitoring Blood Pressure is So Important                                            Back to Page Index


 

Untreated hypertension can affect the brain, heart, kidneys or eyes. That is to say, it may make the CKD worse, and can cause blindness, strokes or heart problems.

 

Hypertension is not usually visible so blood pressure needs to be measured, but unfortunately many vets do not routinely check CKD cats for hypertension, even though CKD patients are at increased risk of hypertension.

 

Long Beach Animal Hospital has a section on hypertension in cats.

Newman Veterinary also discusses hypertension in cats.

Centennial Valley Animal Hospital - information on hypertension in cats.

Mar Vista Vet has an overview of high blood pressure in cats.

The American Veterinary Medical Association has an audio presentation about hypertension in cats which lasts about five minutes.

 


Symptoms of Hypertension                                                                                                       Back to Page Index


 

There are a surprising number of possible symptoms of hypertension in cats. Some of these symptoms are more serious than others. If you see less serious symptoms, your cat still needs to see the vet but it can wait a short while (a day or so) if necessary. However, if you see any of the urgent symptoms below, I would seek veterinary help as soon as possible. If you think your cat has had a stroke in particular, I would go to the ER or out of hours vet. If you think your cat has gone blind, the sooner you start the medication, the more likely that s/he will regain the lost vision, so I would go to the vet as soon as they are open, but if it is the weekend or a holiday, I would go to the ER or out of hours vet.

Urgent Symptoms of Hypertension


 

Stroke


In the worst case, a cat with untreated hypertension may have a stroke. A stroke means that the blood supply to part of the brain is cut off. Symptoms of stroke include an inability to walk properly (which may also be caused by low potassium levels, high phosphorus levels leading to secondary hyperparathyroidism, or heart problems), weakness on one side of the body (which may include the head tilting to one side), circling and blindness.

 

A stroke is a medical emergency. If you think your cat has had a stroke, you should go to the ER or out of hours vet because, according to Veterinary Partner, starting amlodipine (the best treatment for hypertension in cats) within six hours of the stroke "appears to be protective to neurologic tissues."

 

Seizures are relatively common in CKD cats with untreated hypertension, but these normally resolve once the hypertension is under control, and do not require treatment other than blood pressure medication. However, occasionally cats who have had a stroke will start to have seizures, and in such cases anti-convulsant medication may be required.

 

Don't give up hope: Vet Info states that "on average, most feline patients recover and return to normal in two to three weeks after the stroke."

 

Davies Veterinary Specialists have some information on strokes in cats and dogs.

 

Blindness, Particularly Sudden Blindness (Retinal Detachment)


Unfortunately this is a relatively common occurrence in cats with untreated hypertension. The hypertension causes the retinas to detach, so the cat becomes blind.

 

You may notice a change in your cat's eyes, such as dilated pupils or uneven pupils, or you can try moving your hand towards your cat's face and see if s/he reacts (a positive menace response) or not (a negative menace response). Another option is to get your cat's attention, then drop a cotton wool ball and see if the cat follows the ball with his/her eyes.

 

Blindness may also manifest itself in a less obvious manner. e.g. your cat may no longer jump and climb, which you might ascribe to weakness, when in fact it is caused by an inability to see where s/he is jumping. Your cat may also walk differently, perhaps keeping to the side of rooms, or walking through food (because s/he cannot see it).

 

Even if your cat's retinas detach because of high blood pressure, if treatment is started quickly enough (usually within three days of detachment), there is an approximately 50:50 chance of the retinas re-attaching and your cat regaining some sight. Even if you do not start amlodipine immediately, there is still hope: I know of one CKD cat who went blind but regained his sight, even though treatment was not begun for some weeks; but obviously the sooner you begin treatment, the better your cat's chances.

 

If you can see a veterinary ophthalmologist, s/he may be able to suggest other measures in addition to the use of amlodipine to increase the chances of the retinas re-attaching; but many people just use amlodipine with the help of their general vet and see an improvement in their cat's vision.

 

If your cat's retinas do not re-attach, do not despair, cats cope far better with blindness than humans do, and I would not consider blindness in itself to be grounds for euthanasia. 

 

One other possible cause of blindness in cats is the use of an antibiotic called Baytril, though this is extremely rare if dosage guidelines are adhered to.

 

Sometimes cats can appear blind after seizures and you will get a negative menace response, but this should not last for long, and in fact they are not normally blind - Harpsie had a negative menace response after his seizures and several vets were convinced he was blind, but he could still see and play with Cat Dancer.

 

Diagnosis and management of chronic renal failure in cats (c. 2000) Sparkes A, has a photo on page 2 of a cat with this problem.

Pet Place has an article about detached retinas, including information on other possible causes (no need to register to read this, just click Close at the bottom of the annoying pop-up window).

Understanding blindness in cats (2010) Mitchell N Irish Veterinary Journal 63(12) pp760-765 discusses blindness in cats and how to help your cat cope if it cannot be reversed.

Feline hypertensive retinopathy (2007) is an article by Christi Benigni of Washington State University.

Davies Veterinary Specialists has advice on how best to help your cat cope with blindness.

Your Cat Care Guide has tips on helping your cat cope with blindness.

 

Bleeding Eyes (Retinal Haemorrhage)


These may also be a sign of hypertension. The International Cat Care has a photograph of a cat with this problem.

 

Less Urgent Symptoms of Hypertension


These still need treating, but you do not need to rush to the ER. On the other hand, I would not accept an appointment a week or two into the future either. If you see these symptoms, try to be seen within a maximum of three days, but ideally faster, of course.

 

Worsening Kidney Values


Since hypertension can adversely affect the kidneys, one possible symptom is a worsening of kidney values in bloodwork, particularly if it appears to occur quite suddenly. I recommend always having blood pressure checked in any cat whose bloodwork worsens unexpectedly.

 

Seizures


These may be a symptom of hypertension. Seizures may take a number of different forms. There may be the classic jerking and loss of consciousness, but being "spaced out" or mentally absent, may also be a type of seizure. Harpsie' s website has more information on what seizures may look like.

 

Seizures in CKD cats may also be caused by high potassium levels, calcium imbalances, high levels of toxins, or metabolic acidosis. The use of metoclopramide (Reglan) for stomach problems or Advantage for fleas may lower the seizure threshold. Other possible causes of seizures include epilepsy or a brain tumour, but the causes mentioned above are far more likely in a CKD cat and should therefore be considered first.

 

I am really surprised how many vets do not seem to realise that seizures may be caused by hypertension or other CKD-related causes. I have lost count of the number of cats I've heard about who have simply been put on phenobarbital, an epilepsy medication, rather than having their blood pressure measured. In every single one of these cases, once the cat was given appropriate blood pressure medication, it was possible to stop the phenobarbital (which should always be done gradually) and the seizures never returned.

 

Headaches and Head Pressing


Humans with high blood pressure often report having a very bad headache. There is no way to know if our cats have a headache, but I have heard of a  couple of cats pressing their heads against walls, which might be indicative of a headache. Such behaviour is sometimes also seen in cats with brain tumours.

 

Lethargy


Cats with hypertension may be lethargic. Anaemia may also cause lethargy, as may high or low potassium levels, heart problems and fluid retention.

 

Nosebleeds (Epistaxis)


These may be a sign of hypertension. Dental abscesses or a low blood platelet count may also cause nosebleeds.

 

Pet Place has some information about nosebleeds (no need to register to read this, just click Close at the bottom of the annoying pop-up window).

Heart disease in the older cat (2006) Simpson K Presentation to the FAB Conference has a photo of a cat with a nosebleed caused by hypertension (page 4).

 

Red and/or Hot Ears


A number of people have reported this symptom over the years. In all cases, the cat has turned out to have hypertension, often with a systolic reading over 200. Alternatively, red ears are sometimes seen in cats with food allergies.

 

Twitching


Twitching may be caused by high blood pressure. Other causes of twitching include high or low potassium levels, high blood pressure, high phosphorus levels, calcium imbalances (especially head twitching), hyperthyroidism or Vitamin B deficiency. Twitching may also be caused by high toxin levels. If your cat only twitches while you are giving fluids, it is probably caused by either the type of fluid used or by giving cold (room temperature) fluids.

 

Pharaoh's Shakes is a video showing a CKD cat twitching.

Pet MD mentions that twitching may be caused by kidney disease.

 

Blood in Urine


This can be a sign of hypertension. It may also indicate the presence of a urinary tract infection, or kidney stones. There is a condition called "benign renal haematuria" which means there is bleeding from the kidney but the cause is not known; however, this is rare in cats.

 

Severe or ongoing haematuria may cause or worsen anaemia, so you should always take your cat to the vet if you see this symptom.

 

Persistent haematuria and proteinuria due to glomerular disease in related Abyssinian cats (2008) White JD, Norris JM, Bosward KL, Fleay R, Lauer C & Malik R Journal of Feline Medicine & Surgery 10(3) pp219-29 discusses how in Abyssinian cats with haematuria, the cause may be glomerular disease.

Long Beach Animal Hospital mentions (under Physical Exam) that blood in the urine may be a sign of hypertension.

Pet Place has some information about haematuria in cats (no need to register to read this, just click Close at the bottom of the annoying pop-up window).

The Pet Checkup is a product that checks for blood in urine, and which may also be used to check for other issues, such as diabetes.

Health Meter Cat Litter can detect blood in urine, and also checks urine pH. 

 

Howling, Especially at Night


This may be a symptom of hypertension, or may be caused by toxin levels. However, it may also have other causes such as deafness, hyperthyroidism, or occasionally just old age and possibly cognitive dysfunction (senility).

 

Certain medications such as periactin (Cyproheptadine) or mirtazapine (Remeron), both appetite stimulants, or anabolic steroids can make a cat become vocal. Metoclopramide (Reglan), sometimes used for nausea and vomiting, may also have this effect.

 

Inability or Reluctance to Walk


If the hypertension causes a stroke, the cat may find it hard to walk, and may want to stay in one place, or may seem to have weakness in the legs. Other causes of weakness in the legs include low potassium levels or high phosphorus levels leading to secondary hyperparathyroidism. Muscle wasting may also be caused by metabolic acidosis, while weakness in the back legs is occasionally caused by low magnesium or low calcium levels.

 

General weakness may be caused by anaemia, or because the cat is simply not eating enough. It is essential that cats eat, because if they do not eat, they are at risk of developing a potentially life-threatening condition called hepatic lipidosis; Mar Vista Vet has more information about this. The Persuading Your Cat to Eat page has tips on persuading your cat to eat.

 

If your cat is diabetic, back leg weakness may be caused by diabetic neuropathy.

 

Pacing or Restlessness


Sometimes cats with hypertension will pace up and down or just act restless generally. This may also be a sign of hyperthyroidism or of pain. Cats on certain medications, such as metoclopramide (Reglan), cyproheptadine (Periactin) or mirtazapine (Remeron or Zistin) may also exhibit these symptoms, especially if they have been given a high dose.

 


Diagnosis of Hypertension                                                                                       Back to Page Index


Hypertension is often known as the silent killer because it is not usually apparent and can be hard to detect. Below are a couple of possible subtle signs you might be able to detect; but the ideal preventative measure is for your vet to monitor your cat's blood pressure regularly with proper equipment. 

Unfortunately, not every vet has the equipment with which to check blood pressure unless they work in a veterinary hospital. If your vet does not have the necessary equipment, encourage him or her to purchase it. An alternative is to call around other vets in your area - some are happy to do a one off blood pressure check for non-clients for US$25 or so. My vet charges about GBP16.

Tests to Use if Blood Pressure Measuring Equipment is Not Available


Although the following tests are no substitute for the proper measurement of blood pressure using dedicated equipment, if you live in the middle of nowhere with no blood pressure testing equipment available, at the very least ask your vet to perform them:

 

Retinal Examination


Firstly, you and your vet should regularly examine the retina (a fundic exam) - often there are retinal changes caused by hypertension prior to retinal detachment occurring. An older cat's pupils may not dilate and contract the same as in a younger cat so you should try to ascertain how your cat's pupils respond to light i.e. what is normal for your cat. Permanently dilated or unevenly dilated eyes, or bleeding eyes, require urgent veterinary assistance.

 

What your vet sees during an eye exam on a cat is a video presentation by Dr Wendy Zimmerman.

Femoral Pulse


You can also try to become familiar with the way your cat's femoral pulse feels (this is the pulse in the femur, the thigh bone). If your cat has hypertension, the pulse will usually feel stronger than the norm for your cat. Your vet can teach you how to assess this.

 

You can also watch for jugular pulsing: slightly elevate your cat's chin and watch in the jugular area (in the neck) - you shouldn't see any pulsing.

 

Pet Education has instructions on how to take the femoral pulse.

 

Enlarged Aorta


The aorta is the large artery running from the heart. A chest x-ray may show that it is enlarged, and in Feline cardiology: back to the basics, Dr JM Bright states "This change is often noted as a normal aging change in cats; however, an enlarged aortic root may also indicate systemic hypertension."  This was what alerted my cardiologist to the fact that my cat's hypertension was in fact not controlled.

 

Blood Pressure Measuring Equipment


Most vets use what is called indirect blood measuring equipment, which is wrapped around the cat's tail or a paw, rather like the equipment used on a human's arm to measure blood pressure. Some vets use oscillometric equipment but Doppler ultrasound equipment seems to be more popular, perhaps because, as Evaluation of Doppler ultrasonic and oscillometric methods of indirect blood pressure measurement in cats (2004) Habermann, CE, Morgan JD, Kang CW & Brown SA International Journal of Applied Research in Veterinary Medicine 2(4) pp279-289 found, the Doppler method is the more reliable method in conscious cats. With a Doppler, only the systolic pressure is measured.

 

Measuring Blood Pressure at Home


Some people with CKD cats have purchased blood pressure monitoring equipment for home use, and been trained in its use by their vet; this is not only cheaper in the long run and more convenient, but it also avoids the problem of "white coat syndrome", where a cat's blood pressure appears to be higher than it is because of the stress of being at the vet's. The following can be purchased for home use:

 

Parks Medical (model no. 811) is a popular brand which has been used by a number of people dealing with CKD over the years. You do need a vet's prescription to buy one. It costs about US$620, essential accessories (cuffs etc.) cost extra.

Vmed Vet Dop Doppler is another brand which several people with CKD cats have purchased. With all the extras, it costs about US$1000. I own this model, but I have to confess, I have never truly mastered it. My vet tells me she has trouble finding my Indie's blood pressure too, but still, I think in retrospect I would have saved my money.

Matrix Medical sells the Critikon Dynamap brand. The models for sale are refurbished and are therefore reasonably priced, though I must emphasise, I do not know anybody who has used one. If you mention you are a member of Tanya's Support Group, model number 8100 (item number 1582) complete with two cat-sized cuffs should cost US$200 and the XL (item number 1584) costs US$250 with two cat-sized cuffs. Shipping for either model costs approximately US$20.

Thames Medical sells a CAT doppler blood pressure kit for £735.

Burtons Veterinary Products in the UK sells the 811 Parks model for £859. You may need to ask your vet to order it on your behalf.

 

How to Measure Blood Pressure


Blood pressure is often measured using the cat's tail, though my vet uses a front paw. Cats can suffer from "white coat syndrome", where their blood pressure rises from the stress of the vet or hospital visit, so it is best to make sure your cat is as relaxed as possible before any tests are run:

  • you should always try to be present when blood pressure is taken.

  • try to have blood pressure tested as soon as you arrive at the vet's, and definitely before any other testing or handling is done.

  • if your cat is prone to stress at the vet's, it can sometimes help to cover the cat's head with a towel or blanket. This would probably make humans more stressed, but it does help some cats: we used to do this for Harpsie whenever he had blood taken and it definitely made him calmer.

It is normal to take several readings and average them out in order to have an accurate reading. ACVIM Consensus Statement: guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats (2007) Brown S, Atkins C, Bagley R, Carr A, Cowgill L, Davidson M, Egner B, Elliott J, Henik R, Labato M, Littman M, Polzin D, Ross L, Snyder P, and Stepien R Journal of Veterinary Internal Medicine 21 pp542–558 recommends discarding the first measurement, then measuring blood pressure at least three more times, preferably 5-7 times, to produce readings which show less than 20% difference overall. The average of these readings is the cat's blood pressure measurement.

 

Cats get high blood pressure too: monitor it is a video by Dr Andrew Sparkes which clearly demonstrates how to measure blood pressure in cats.

Purdue University College of Veterinary Medicine also has a video showing how to measure a cat's blood pressure.

The Cat's Meow Veterinary Hospital explains very clearly how to measure blood pressure in cats.

 


At What Point is it Hypertension?                                                                           Back to Page Index


 

For cats, hypertension is usually considered to be present when systolic pressure is over 145 mmHg (Doppler machines only measure systolic pressure). Many vets start treatment when systolic pressure is over 160mmHg.

 

ACVIM Consensus Statement: guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats (2007) Brown S, Atkins C, Bagley R, Carr A, Cowgill L, Davidson M, Egner B, Elliott J, Henik R, Labato M, Littman M, Polzin D, Ross L, Snyder P, and Stepien R Journal of Veterinary Internal Medicine 21 pp542–558 provides the following suggestions for animals with what they call target organ damage (TOD).

 

What do they mean by TOD? Cats are considered to have target organ damage if they:

  • are showing the symptoms of hypertension described above; or

  • have bloodwork which has worsened.

The chances of target organ damage occurring in the future increase once blood pressure is consistently over 160: ocular (eye) problems have occurred with blood pressure as low as 168. The risk of ocular and neurological problems (seizures, stroke etc.) is much higher once blood pressure is over 180.

 

Average Systolic Blood Pressure Measurement

Risk  of Damage to Organs

Treatment Plan

Under 150

Minimal

No treatment necessary.

150-159

Mild

Treatment is not normally necessary. However, it may be appropriate to begin or increase blood pressure medications if ocular or neurological signs are present.

160 - 179

Moderate

Begin or increase blood pressure medications.

Over 180

Severe

Begin or increase blood pressure medications.

 

The goal is a blood pressure reading between 120 and 149.

 

I have heard that some vets refuse to measure or treat blood pressure in stressed cats, claiming that the results will be inaccurate. Whilst stress may indeed affect the results, it will only do so by 20 or so points. In addition, according to Dr M Scherk in Blood pressure: a critical factor (2008), Presentation to the World Small Animal Veterinary Association World Congress, the usual method of measuring blood pressure in cats (doppler) tends to understate the result by around 14 points. Thus, declining, for example, to treat a cat with blood pressure over 200 is extremely unwise. Personally I would want to treat any cat of mine whose blood pressure was over 170 on more than one occasion.

 

Sometimes a cat's blood pressure will "spike" (increase dramatically, then reduce to normal levels) at intervals, which means you may notice symptoms of hypertension in your cat but tests at the vet appear normal. This is a tricky situation, but it does usually indicate that hypertension is in your cat's future. It therefore is probably worth treating for hypertension in such cases, because the best treatment for hypertension in cats is considered unlikely to cause the opposite problem of hypotension, and you avoid the risks of untreated hypertension.

 


Frequency of Blood Pressure Testing                                                                 Back to Page Index


The following suggestions are based on the ACVIM Consensus Statement: guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats (2007) Brown S, Atkins C, Bagley R, Carr A, Cowgill L, Davidson M, Egner B, Elliott J, Henik R, Labato M, Littman M, Polzin D, Ross L, Snyder P, and Stepien R Journal of Veterinary Internal Medicine 21 pp542–558.

 

For cats with hypertension: 

  • The goal is a blood pressure reading between 120 and 149.

  • If you are starting or changing medication, you should check blood pressure 7-10 days after starting, or 1-3 days if the cat is exhibiting ocular or neurological problems. Once the blood pressure has reduced to a safe level, you should check blood pressure again in 1-3 months.

  • If the blood pressure has reduced too far (below 120), you should decrease the dose or frequency or change the medication you are using. You should then check blood pressure 7-10 days after starting, or earlier if you are concerned about your cat's health. Once the blood pressure has increased to a safe level, you should check blood pressure again in 1-3 months.

  • If the blood pressure remains too high, you should increase the dose or frequency or change the medication you are using. You should then check blood pressure 7-10 days after starting, or 1-3 days if the cat is exhibiting ocular or neurological problems. Once the blood pressure has reduced to a safe level, you should check blood pressure again in 1-3 months.

  • If your cat does not have hypertension, it should be in order to test blood pressure every quarter.

  • In all cases, if your vet recommends testing more frequently, then I would do so.

 


Treatment of Hypertension                                                                                      Back to Page Index


 

Hypertension is usually easily controlled with medication. Your vet may also ask you to restrict your cat's sodium intake. The International Renal Interest Society states on page 5 that there is no evidence this is helpful for cats, and that it should certainly not take the place of medication, but if you do opt to do this, you should do it gradually. The food data tables provide information about the sodium content of many cat foods available in the USA and UK. Please see the Nutritional Requirements page for more information about sodium and whether to reduce your cat's intake.

 

Since hypertension can damage the kidneys, getting it under control has the pleasant side effect in some cats of improving their kidney values.

 


The Best Treatment: Amlodipine                                                                         Back to Page Index


Why Amlodipine is the Best Treatment


The good news is that hypertension is very easily controlled in most cases by means of medication. The best treatment is a drug called amlodipine, which is actually a heart medication in the calcium channel blocker family. You may be offered generic amlodipine or you may be given a branded version - I have used both with no problems. Brand names include Norvasc in the USA and Canada and Istin in Europe and Australasia.

 

The main reasons why amlodipine is the best choice are because it works extremely well at controlling hypertension in cats, takes effect quickly (usually within a week) and is a safe treatment with very few side effects. Blood pressure in small animals Part 2: hypertension target organ damage heart and kidney (2009) Carr AP & Egner BE states "Adverse side effects from a rapid drop in blood pressure (weakness, syncope, organ failure) are rarely reported. Amlodipine (0.625 to 1.25 mg/cat/day) reduces systolic blood pressure by approximately 40 mmHg. The higher dose is usually needed in heavier cats."

 

The other crucial reason why amlodipine is the treatment of choice is because, even if your cat's retinas detach because of high blood pressure, there is an approximately 50:50 chance of the retinas re-attaching and your cat regaining some sight if treatment with amlodipine is started quickly enough (usually within three days of detachment). Even if you do not start amlodipine immediately, there is still hope: I know of several CKD cat who went blind but regained their sight, even though treatment was not begun for some time, in a couple of cases not for 2-4 weeks.

 

If your cat is blind and you can see a veterinary ophthalmologist, s/he may be able to suggest other measures in addition to the use of amlodipine to increase the chances of the retinas re-attaching; but many people just use amlodipine with the help of their general vet and see an improvement in their cat's vision.

 

Target Blood Pressure


The goal is a blood pressure reading between 120 and 149.

 

Dosage


The usual amlodipine dose for cats is 0.625 mg per day but you should be guided by your vet; some cats need double this dose (1.25mg). In most cases, however, you should start at the lower dose.

 

It can take up to a week for amlodipine to work, though you may see results more quickly. Your vet should check blood pressure 7-10 days after starting amlodipine, though personally I prefer to check it after a week. If blood pressure remains severely elevated, the dosage may be increased to 1.25mg per day. See Frequency of Blood Pressure Testing for more information on when and how to consider dosage changes. Any changes (especially reductions) in dosage should be made gradually, to give the cat's body time to get used to the lower dose.

 

If your vet does not have the necessary equipment to check blood pressure, but strongly suspects that your cat has hypertension, it might be worth trying amlodipine and seeing if your cat improves. Generally speaking, as mentioned by Veterinary Partner, amlodipine is a pretty safe drug and is unlikely to cause the opposite problem of hypotension (low blood pressure), even in a cat whose blood pressure is not overly elevated.

 

How to Cut Amlodipine into Cat-Sized Doses


The usual dose is 0.625mg per day, but since the tablets dispensed are often 5mg, this means you need to break the tablet into eight, a tricky thing to do. One method of doing this is to use flat-edged tweezers:

  • Snap the pill in half with your fingers.

  • Take the half-pill and grip it firmly in the tweezers so that the edge of the tweezers are gripping the piece right in the middle. Then just grasp the other half of the piece with your other hand, and snap it off. 

  • Repeat step 2 until you have eight pieces.

This method also works for the 2.5mg tablets.

 

Generic amlodipine recently became available in the USA, but these pills are even smaller than brand name Norvasc, so you may find that overall there is no advantage because you waste more of the lower priced pills.

 

Other Methods of Administration


In the UK a cat-sized version of amlodipine (0.625mg), made by Summit Veterinary Pharmaceuticals Limited, became  available in 2011. I am using this for my own cats, with no problems. The downside is that this form of medication is far more expensive (more than twice the price of generic amlodipine). The upside is that you know your cat is getting the exact dose every day.

 

In the USA it is possible to have medications compounded (made specially for your cat in cat-sized doses, sometimes in flavoured form) by a compounding pharmacy. Capsules or liquid suspensions (a liquid form of medication) are available, but if you opt for this, make sure you use a reliable compounding pharmacy. If you use a compounded amlodipine suspension, you should keep it in the fridge and discard it after 14 days.

 

Some people have amlodipine made into a transdermal medication, but I would not recommend this, because it is hard to know how much of the medication is being absorbed when it is given in this way. In fact, a couple of Tanya's Feline CRF Support Group members have found that the transdermal amlodipine they have used has not successfully controlled their cat's blood pressure, whereas the more usual commercially available form has.

 

Since amlodipine is such an important medication, if at all possible, I would use the commercial tablets.

Amlodipine: Possible Side Effects


The worst side effect of using amlodipine generally appears to be that some cats may become a bit lethargic when first starting amlodipine, but this should wear off as their bodies get used to the medication - most cats eventually seem brighter once their blood pressure is under control. However, if in addition to lethargy you see any of the symptoms linked to low blood pressure mentioned below, contact your vet.

 

Other possible side effects include constipation, upset stomach and, rarely, dental problems (gingivitis), low potassium levels, swelling of the limbs or an increased heart rate. You should contact your vet if you notice an increased heart rate.

 

Amlodipine appears to be a safe medication for the vast majority of cats, and does not seem to lower blood pressure too far as may happen with some other types of blood pressure medication. Possible signs of low blood pressure include lethargy, fainting, drinking more, nausea, pale gums, and fast and shallow breathing.

If you are at all concerned about any of the symptoms you see, contact your vet who can check to see if your cat's blood pressure has fallen too low (below 110).

 

The US National Library of Medicine has some information about possible side effects in humans.

 

Amlodipine: Interactions with Other Medications


Plumb's Veterinary Drug Handbook mentions that cyproheptadine, an appetite stimulant commonly used in CKD cats, may also have calcium channel blocking effects and cause low blood pressure: there is a risk that this in combination with amlodipine  could reduce blood pressure too far, so it is probably safer not to use these two drugs together. 

 

The European Medicines Agency says (clause 4.8 on page 9) that "Cerenia should not be used concomitantly with Ca-channel antagonists as maropitant has affinity to Ca-channels." The University of Zürich Institute for Veterinary Pharmacology and Toxicology also mentions this (in German). In principle this means that amlodipine should not be used with maropitant (Cerenia), a treatment used for nausea and vomiting. 'Concomitantly' has a rather vague medical meaning in that it means during the same time period, but in this context I don't know exactly what time period the EMA is referring to, i.e. do they mean at the same time or on the same day? Both of these medications tend to be given once daily, so they have a relatively long effect. I suspect that giving them both on the same day but 12 hours apart (i.e. one in the morning and one in the evening) would probably be acceptable, but check with your vet.

 

If you are using cimetidine (Tagamet) to control stomach acid, it may increase the effects of amlodipine (thereby possibly reducing blood pressure too far), so it would probably be safer to use another histamine H2 antagonist such as ranitidine (Zantac 75) or famotidine (Pepcid AC) instead.

 

As reported by The US National Library of Medicine, products which contain glucosamine and chondroitin (used to treat arthritis), such as Cosequin, have been known to raise blood pressure temporarily in some human patients, so speak to your vet about whether to continue using such products if your cat has hypertension. It is possible that the sodium base of some of these products may be a factor, so try to obtain a product without a sodium base if possible.

 

One study, Feline hypertension: diagnosis and management (2002)  Elliott J, 27th World Small Animal Veterinary Association Congress 2002, indicates that treating hypertension with amlodipine sometimes reduces potassium levels, so you should ensure your cat's potassium levels are monitored and supplementation begun if necessary.

 

Veterinary Links Recommending Amlodipine


 

In Chronic renal failure in the cat (2006) Sparkes AH Presentation to the World Small Animal Veterinary Association World Congress, Dr Sparkes states "in cats monotherapy with amlodipine (a calcium channel blocker) is generally regarded as the treatment of choice for systemic hypertension."

 

How I treat hypertension (2012) Atkins CE Veterinary Focus 22(1) pp17-23 states "the literature and clinical experience leads one to conclude that amlodipine is the single best agent for managing feline systemic hypertension", although he does also mention that in some cases he uses it in conjunction with other medications (see below).

 

Hypertension in cats and dogs (2002) Stepien RL Presentation to the Waltham/OSU Symposium: Small Animal Cardiology 2002 mentions that amlodipine "is the current antihypertensive medication of choice for cats."

 

Effects of the calcium channel antagonist amlodipine in cats with surgically induced hypertensive renal insufficiency (2002) Mathur S, Syme H, Brown CA, Elliot J, Moore PA, Newell MA, Munday JS, Cartier LM, Sheldon SE & Brown SA American Journal of Veterinary Research 63 pp833-9 indicates that amlodipine has an anti-hypertensive effect in cats with renal failure and hypertension, which may improve the prognosis for such cats. (Note: the cats in the study did not have naturally occurring CKD).

 

Treatment of systemic hypertension in cats with amlodipine besylate (1997) Henik RA, Snyder PS & Volk LM Journal of the American Animal Hospital Association 33 (3) pp226-234 indicates that amlodipine appears to be a safe and effective treatment for hypertension in cats.

 

Feline hypertension: clinical features and therapeutic strategies (2004) Bright JM Presentation to the World Small Animal Veterinary Association World Congress discusses using amlodipine in conjunction with ACE inhibitors such as benazepril or enalapril for cats who do not respond to amlodipine alone.

 


If Your Vet Suggests Other Treatments                                                                 Back to Page Index


 

Some vets prefer to use heart medications known as ACE inhibitors, which include enalapril (Enacard) and benazepril (Fortekor/Lotensin), to treat high blood pressure. They may wish to do this simply because they think it is the best treatment, but they may also want to do so because of something known as the renin-angiotensin-aldosterone system or RAAS. There is more information about this here.

 

Although ACE inhibitors can work well in dogs, they are often not the best choice for cats because:

  • they are less likely to lower blood pressure. In Heart disease in the older cat (2006) Simpson K Presentation to the FAB Conference, Ms Simpson says (page 5) of ACE inhibitors that "as a group they appear fairly unreliable at decreasing blood pressure."

  • unlike amlodipine, they do not seem able to reverse blindness caused by high blood pressure;

  • they may cause increases in creatinine levels when first begun.

However, for really severe cases of hypertension which do not respond to amlodipine alone, it may sometimes be necessary to give ACE inhibitors in addition to the amlodipine. I had to do this for my non-CKD cat with hypertension. But in most cases, you can try amlodipine by itself first. If your vet is reluctant, you may wish to print out some of the links above.

 

Feline hypertension: diagnosis and management (2002)  Elliott J, Presentation to the 27th World Small Animal Veterinary Association Congress 2002 also discusses the use of ACE inhibitors in addition to amlodipine in cats who do not respond to amlodipine alone, but recommends checking bloodwork if ACE inhibitors are added, since these drugs may cause an increase in creatinine levels.

 

Feline hypertension: clinical features and therapeutic strategies (2004) Bright JM Presentation to the World Small Animal Veterinary Association World Congress 2004 discusses using amlodipine in conjunction with ACE inhibitors such as benazepril or enalapril for cats who do not respond to amlodipine alone.

 

Feline hypertension: risks, diagnosis and management (2007) Atkins CE is a presentation to the World Small Animal Veterinary Association World Congress 2007 which states that "the literature and clinical experience would, nevertheless, lead one to appropriately conclude that amlodipine is the single best agent for the management of feline systemic hypertension", although he does also mention that in some cases he uses it in conjunction with other medications.

 


Studies Into Use of Other Medications for Cats with Hypertension


 

Study Into Use of Telmisartan for Cats with Hypertension


Although amlodipine is widely used to treat hypertension in cats, the University of Pennsylvania School of Veterinary Medicine has recently completed a study it began in 2010 to evaluate the efficacy of another medication called telmisartan (Micardis) for controlling hypertension in CKD cats. I will report on the trial's findings once they are available.

 

This medication has been used in humans, but has not been widely used in cats, although one small safety study found it appeared to be generally safe. However, telmisartan, under the trade name of Semintra, was approved in December 2012 for the treatment of proteinuria in CKD cats in Europe. You can read more about this here.

 

Other Studies


I am occasionally contacted about a trial regarding a hypertension medication for cats on a website called My cat can help. Apparently this trial is FDA approved. Unfortunately the website does not share any meaningful information, such as the name of the medication being tested, nor does it have any contact details. This may well be a legitimate trial, but with so little information to go on, I cannot comment further, other than to point out that the site mentions your cat may not receive the medication, which presumably means a placebo is given instead, not a chance I would personally want to take in a cat with hypertension.

 

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This page last updated: 16 September 2013

Links on this page last checked: 20 April 2012

   

*****

 

TREATING YOUR CAT WITHOUT VETERINARY ADVICE CAN BE EXTREMELY DANGEROUS.

 

I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who has lived through CKD with three cats. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.

 

If your cat appears to be in pain or distress, do not waste time on the internet, contact your vet immediately.

 

*****

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