Tanya's Comprehensive Guide to Feline Chronic Kidney Disease

Hypertension 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 be easily controlled using a medication called amlodipine (common trade names are Norvasc or Istin).

What is High Blood Pressure Back to Page Index

Hypertension means the pressure (or tension) in the arteries is elevated. As the National Kidney & Urologic Diseases Information Clearing House explains, this creates more work for the heart, and can eventually lead to damage to blood vessels. If the blood vessels within the kidneys are damaged as part of this process, eventually CKD can result.

Unlike humans, primary hypertension is uncommon in cats. Usually it is associated with other diseases. According to Heart disease in the older cat (2006) Simpson K Presentation to the FAB Conference (page 3), other conditions that may be associated with hypertension include hyperthyroidism, hyperparathyroidism, diabetes and anaemia.

Why Monitoring Blood Pressure is So Important Back to Page Index

Untreated hypertension can affect the brain, heart, kidneys or eyes. This means it may make the CKD worse, and can cause blindness, strokes or heart problems.

A 2002 study (Prevalence of systolic hypertension in cats with chronic renal failure at initial evaluation, Syme HM, Barber PJ, Markwell PJ, Elliott J, Journal of the American Veterinary Medical Association 220 pp1799-804) indicated 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 as high as more than 60%.

Cats with hyperthyroidism 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 a hyperactive thyroid and CKD. Using corticosteroids may also lead to hypertension.

Hypertension is not usually visible so it 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.

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 dayor 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

Other symptoms

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."

Although cats with hypertension who have occasional seizures do not normally require anti-convulsant medication, cats who have had a stroke and are having continuing seizures may require such medication.

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).

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.

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 opthalmologist, 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.

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).

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.

Bleeding Eyes (Retinal Haemorrhage)

These may also be a sign of hypertension. The Feline Advisory Bureau 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 Reglan (metoclopramide) 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 on appropriate blood pressure medication, it was possible to stop the phenobarbital 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 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 phosphorus levels, high or low potassium levels, calcium imbalances (especially head twitching), a hyperactive thyroid or Vitamin B deficiency. Twitching may also be caused by 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.

Blood in Urine

This can be a sign of hypertension. It may also indicate the presence of a urinary tract infection, or bladder 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).

KV Vet Supply sells a product called Health Alert which can test for blood in the urine.

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

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), an appetite stimulant, or anabolic steroids, such as stanazole (Winstrol), can make a cat become vocal. Metaclopramide (Reglan), used for stomach problems, 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 Metaclopramide (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

Blood pressure measuring equipment

How to measure blood pressure

How often to measure blood pressure

At what point is blood pressure too high

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.

If you live in the middle of nowhere with no blood pressure testing equipment, at the very least do the following:

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.

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 Health Care has instructions on how to take the femoral pulse.

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. The usual type is Doppler equipment, and with a Doppler, only the systolic pressure is measured.

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.

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 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.

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

Burtons in the UK sells the 811 Parks model for £733. 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.

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 showing the symptoms of hypertension described above, or cats with proteinuria (in Management of chronic renal failure: beyond the can, a presentation to the Atlantic Coast Veterinary Conference 2001 (scroll to No. 3), Dr MS Wallace mentions that hypertension may promote proteinuria) or whose bloodwork has worsened are considered to have existing target organ damage. 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. So 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 you are giving Epogen, Procrit or Eprex for anaemia, I would check it each time you check the anaemia.
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 (Norvasc or Istin)
Veterinary links recommending amlodipine
If your vet recommends other treatments

The Best Treatment: Amlodipine Back to Page Index

Why amlodipine is the best treatment
Target blood pressure
Commonly used dosages

How to cut amlodipine

Other methods of administration

Possible side effects

Interactions with other medications

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 reason why amlodipine is the best choice is 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 CKDs 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 opthalmologist, 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 is 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

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.

The worst side effect 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.

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

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 University of Zürich Institute for Veterinary Pharmacology and Toxicology warns (in German) that amlodipine should not be used at the same time as maropitant (Cerenia), a treatment used for nausea and vomiting.

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 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."

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 (see below).

Hypertension in cats and dogs (2002) Stepien RL is a presentation to the Waltham/OSU Symposium: Small Animal Cardiology 2002. It mentions that amlodipine "is the current antihypertensive medication of choice for cats", according to a report from the Hypertension Consensus Panel, American College of Veterinary Internal Medicine entitled "Current recommendations for diagnosis and management of hypertension in cats and dogs". Dallas, TX, 20th Annual Veterinary Medical Forum, 2002.

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 2004 discusses using amlodipine in conjunction with enalapril or benazepril for cats who do not respond to amlodipine alone.

Study Into Use of Telmisartan for Cats with Hypertension Back to Page Index

Although amlodipine is widely used to treat hypertension in cats, the University of Pennsylvania School of Veterinary Medicine is seeking volunteers to take part in a study to evaluate the efficacy of another medication called telmisartan (Micardis) for controlling hypertension in CKD cats. 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. Drugs has some information about the use of this drug in humans, as does Patient UK.

Cats with CKD who are otherwise in good health are eligible. The study will last for five days, and you must be able to go to Penn because your cat needs to be an in-patient for at least the first three nights of the study, but preferably all five days (four nights). All testing will be free, plus you will be given a US$300 American Express gift card for completing the study.

Penn Veterinary Clinical Investigation Center has more information about the study, including contact details.

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, but although these medications can work well in dogs, they are 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. But in most cases, you should 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.

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This page last updated: 26 October 2011

Links on this page last checked: 29 November 2011