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Cisapride is a prokinetic drug, which means it gets the digestive tract moving again. In cats it's used mostly for chronic constipation and megacolon, and the usual dose is 2.5 mg for a cat under 5 kg or 5 mg for a cat over 5 kg, given every 8 hours about half an hour before food.1,6
It's a drug I prescribe often and it does good work. It's also rarely the whole answer on its own.
Key Takeaways
Feline dosing is set per cat rather than calculated per kilogram, which is unusual for a drug and makes it easy to remember.
| Cat's weight | Dose | Schedule |
|---|---|---|
| Under 5 kg (about 11 lb) | 2.5 mg per cat by mouth | Every 8 hours1,6 |
| Over 5 kg (about 11 lb) | 5 mg per cat by mouth | Every 8 hours1,6 |
| Calculated by weight instead | 0.5 to 1 mg/kg by mouth | Every 8 to 12 hours7 |
Give it roughly 30 minutes before a meal. The drug needs to be working by the time food arrives, and timing it to the meal is the single easiest thing to get right at home.
Follow the label on your own bottle rather than the table above. There's wide variation between cats in how quickly they clear cisapride,1,5 so two cats of the same weight can genuinely need different amounts. If your cat is still straining on the starting dose, that's information for your vet, not a reason to double up on your own.
It's compounded, so it arrives as a capsule, a tablet or a flavoured liquid depending on what the pharmacy makes. The liquid is easier to measure accurately for a small cat. Compounded medications also carry a shorter expiry than commercial ones, so check the date on the bottle and ask whether yours needs to go in the fridge.
Cisapride triggers the release of acetylcholine from nerve endings in the myenteric plexus, the nerve network sitting in the wall of the gut.1 Acetylcholine is the signal that tells smooth muscle to contract, so more of it means stronger, more frequent contractions and faster movement of food and stool through the tract.
At the receptor level it acts as an agonist at 5-HT4 and 5-HT2 serotonin receptors and an antagonist at 5-HT3 and 5-HT1.1 Those receptor effects differ between species, which is why feline data is worth more here than the human or canine literature.
The esophagus is where that species difference gets practical. Cisapride is usually described as working by tightening the sphincter at the bottom of the esophagus. In an in vitro study of feline esophageal tissue, it increased contraction of the esophageal body to 190% of baseline but had no meaningful effect on the lower esophageal sphincter itself.1,2 The cat's esophagus is mostly cholinergic and the sphincter isn't, so a drug that works by releasing acetylcholine moves one and not the other.1,2
So in a cat, cisapride helps the esophagus push food downward rather than clamping the valve at the bottom shut.
Dogs don't get that benefit. The canine esophagus is striated muscle with no smooth muscle for the drug to act on, and there's no evidence cisapride helps canine megaesophagus.1 Cats are built differently, which is why the drug has a place here.
Chronic constipation and megacolon are the two accepted uses, and they're accepted because the feline evidence exists rather than being borrowed from another species.1
Two studies from the University of Pennsylvania tested cisapride directly on cat colon muscle. The first showed it stimulates contraction in healthy feline colonic smooth muscle.4 The second did the same using muscle taken from cats with idiopathic megacolon and found it still produced contraction in both the ascending and descending colon, working largely on the muscle itself and depending on calcium moving into the cell.3 The second study is the more useful one, because it means the drug can still do something in a colon that has already stretched and gone sluggish.
If your cat is straining in the box, producing small hard stools or skipping days, that's the picture this drug was made for. Our article on constipation in cats covers what to try first and when it stops being a home problem.
Megacolon is the more advanced version, where the colon has dilated to the point that it no longer empties properly. Cisapride is a core part of managing it medically, and in many cats it delays or avoids surgery altogether.6
Esophageal motility problems and acid reflux are the second tier. The USP monograph rates cisapride as potentially effective for feline esophageal dysfunction and for reflux, on weaker evidence than the colon work.1 I do use it for these, and I'd tell you honestly that the support behind it is thinner than the support for constipation.
If your cat is regurgitating rather than vomiting, the difference is diagnostic and worth sorting out before reaching for any drug. A barium study is often how we tell the two apart.
A stool softener, in almost every case. Cisapride pushes, and something else has to make the stool soft enough to be worth pushing. Lactulose is the usual choice at 0.5 mL/kg every 8 to 12 hours, adjusted up or down until the stool is soft rather than liquid.7
Diet comes next, and the right answer depends on how far along your cat is. In milder constipation where the colon still has some push left, added fibre helps. Once the colon is dilated and motility is poor, fibre just adds bulk the colon can't move, and a highly digestible canned diet that leaves less residue behind is the better call.
Hydration is the one owners underestimate. A dehydrated cat pulls water back out of the colon and hardens the stool, which is why constipation and kidney disease travel together so often. Canned food, water fountains and subcutaneous fluids at home all help, and for a cat with kidney disease the fluids usually do more for the constipation than any drug will.
A cat who has stopped eating needs that dealt with first. Cats go downhill faster than dogs when they go off food, and a constipated cat is often a nauseated one.
Low potassium is worth checking too, because it weakens smooth muscle and makes constipation harder to fix. Hypokalemia shows up on routine bloodwork and is straightforward to correct once you know it's there.
Surgery becomes the answer, and it's a better outcome than owners expect when they first hear it.
Most cats with idiopathic megacolon eventually stop responding to medical management. When that happens, subtotal colectomy is the procedure of choice, and clinical signs lasting longer than six months have been linked to colonic changes that won't reverse on their own.7 Waiting too long narrows the options rather than preserving them.
Cats do well afterwards. Expect soft stool or diarrhea for up to two months while things settle, and constipation returns in around 35% of cats in one study.7 For a cat who has been blocked up and repeatedly enema'd for a year, that's usually a trade worth making.
I raise this early rather than late, because the conversation is much easier when surgery is a plan rather than an emergency.
Most cats tolerate cisapride well, and this is one of the better behaved drugs I hand out.
When something does show up it's abdominal cramping, vomiting or diarrhea, and it's usually tied to a dose that's too high for that particular cat rather than to the drug itself. If your cat is uncomfortable or vomiting after doses, call rather than pushing on. The dose can come down.
The cardiac history is worth explaining, because owners find it when they search the drug name and it reads alarmingly out of context. Cisapride was pulled from the human market over fatal heart rhythm disturbances. In animals, there have been no reported cases of serious arrhythmias caused by cisapride.1
That history still shapes how it's prescribed. Medications that prolong the QT interval or drop potassium quickly are avoided alongside cisapride, including quinidine, procainamide, sotalol, phenothiazines such as acepromazine, and furosemide.1 If your cat is on a heart medication or a diuretic, say so before starting.
Don't give cisapride to a cat with a suspected obstruction, a perforation or bleeding in the gut. Stimulating peristalsis against any of those can do real harm.1 This is the reason a constipated cat who is vomiting, painful or flat needs to be examined rather than started on a prokinetic at home.
Liver and kidney disease call for caution rather than avoidance. Cisapride is processed by the liver and leaves in bile and urine, so a cat with reduced function in either organ may need a lower dose.1 Mention any history of jaundice or abnormal liver values.
Drug interactions run in both directions. Drugs that block liver metabolism raise cisapride levels, including ketoconazole, itraconazole, fluconazole, cimetidine, erythromycin, clarithromycin and azithromycin.1 Going the other way, faster gastric emptying changes how other drugs are absorbed. Digoxin absorption drops when cisapride is given with it, which is the opposite of what you'd assume.1
Give your vet the full list of what your cat takes, supplements included, before the first dose.
If your cat is straining in the litter box, going days between stools, or already on cisapride and not improving, give us a call at (519) 896-0532.
Cisapride is dosed per cat rather than per kilogram. A cat under 5 kg (about 11 lb) usually gets 2.5 mg by mouth and a cat over 5 kg usually gets 5 mg by mouth, every 8 hours, given about 30 minutes before a meal. Some vets calculate it by weight instead at 0.5 to 1 mg/kg every 8 to 12 hours. Cats vary widely in how quickly they clear this drug, so two cats of the same weight can genuinely need different amounts. Follow the label on your own bottle rather than a general guide. If your cat is still straining on the starting dose, that's a conversation with your vet, not a reason to increase it yourself.
The drug itself starts acting within a couple of hours, but the result you're watching for is a bowel movement, and that depends on how backed up your cat is when you start. A mildly constipated cat may pass stool the same day. A cat with a colon full of hard stool often needs an enema or deobstipation at the clinic first, because no oral prokinetic can move a mass that's already impacted. Once your cat is cleared out, cisapride helps keep things moving. If there's no change after two or three days, call your vet rather than continuing on the same dose.
Give it when you remember, then carry on with the normal schedule from that point. If you're already close to the next dose, skip the missed one instead. Never give two doses together to catch up. Cisapride is usually given three times daily, which is an easy schedule to lose track of, so a repeating phone reminder helps. A single missed dose isn't an emergency, but several missed doses in a row can be enough to let a cat back up again.
Yes, and many cats do. Cats with megacolon or chronic constipation are often on cisapride for life, alongside a stool softener and a diet change. It's well tolerated over long periods. Your vet is watching whether it's still working, because most cats with idiopathic megacolon eventually stop responding to medical management. Keep track of how often your cat passes stool and what it looks like. That's the record your vet will want at the next recheck.
Because there's no commercial cisapride product on the market in Canada or the United States. It left human pharmacies years ago and no veterinary version was ever licensed, so a compounding pharmacy makes up every prescription as a capsule, tablet or flavoured liquid. That means you can't pick it up at any pharmacy and it usually needs to be ordered. Compounded medications also carry a shorter expiry than commercial ones, so check the date on the bottle and ask whether yours needs refrigeration.
Cisapride was withdrawn from the human market because of fatal heart rhythm disturbances. In animals, there have been no reported cases of serious arrhythmias caused by cisapride, and it's considered well tolerated in cats. That history still shapes how it's prescribed. Your vet will avoid pairing it with medications that prolong the QT interval or drop potassium quickly, including quinidine, procainamide, sotalol, phenothiazines such as acepromazine, and furosemide. Tell your vet if your cat is on a heart medication or a diuretic before starting.
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