Missed Dose of Heart or Seizure Meds in Cats

Name: Missed Dose of Heart or Seizure Meds in Cats
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

If you miss a dose of your cat's heart or seizure medication, the right move depends on the drug and how late you are. For most once- or twice-daily feline heart and seizure drugs, a dose missed by a few hours can usually be given as soon as you remember, while a dose missed by many hours is often skipped until the next scheduled time. Doubling up is almost never safe, and with pimobendan for cats a missed dose should never be "made up" by giving two pills at once.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

Give a late dose only if your veterinarian or the prescription label says it is safe, and only if the next scheduled dose is still several hours away.
If it is almost time for the next dose, skip the missed one and resume the normal schedule. Do not give two doses together.
Never double a dose of pimobendan, benazepril, or phenobarbital to catch up. Each of these drugs can cause real harm at higher-than-prescribed amounts.
Call your veterinarian the same day if your cat misses a seizure medication dose, because seizure control can slip quickly.
Call an emergency clinic right away if your cat has a seizure, collapses, breathes with an open mouth, or seems to be in heart failure after a missed dose.

What These Medicines Are and Why Your Cat Takes Them

Heart and seizure medications in cats fall into a few groups. Each one works differently, and each has its own rules for a missed dose.

Heart medications

Pimobendan is a phosphodiesterase III inhibitor and calcium channel sensitizer. In cats it is used off-label, meaning it is not approved for feline use, but veterinarians prescribe it for certain cardiomyopathies. Potential benefits include improved left ventricular systolic and diastolic function, reduced platelet aggregation, reduction in left atrial size, and improved left atrial and auricular systolic function [1]. It is most often used when congestive heart failure is linked to systolic dysfunction, including dilated cardiomyopathy, restrictive cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and some nonspecific phenotypes [1].

Benazepril is an ACE inhibitor. It lowers blood pressure and reduces the workload on a failing heart. It is one of several drugs used to manage feline cardiovascular disease, where the goals are to limit damage to heart muscle, control fluid buildup around the lungs, improve circulation, regulate heart rate and rhythm, support blood oxygen levels, and reduce the risk of blood clots [2].

Diuretics such as furosemide are also common. These increase urine output and remove fluid that accumulates in cats with heart disease. A diuretic can be life saving when a cat is in a crisis caused by heart failure [2].

Seizure medications

Phenobarbital is a maintenance anticonvulsant. It has high bioavailability and is rapidly absorbed, which is why it can also be used in cluster seizures, reactive seizures, or status epilepticus to prevent further seizure activity [3]. In an emergency, if seizures continue after repeated doses of diazepam, a maintenance anticonvulsant such as IV phenobarbital should be started as a preventative [3].

Levetiracetam is another anticonvulsant used in cats. In dogs, rectal administration has reached adequate therapeutic concentrations within 30 minutes in most cases, and high-dose oral levetiracetam has been used by owners who cannot reach emergency care [3]. Your veterinarian will decide which drug and route fit your cat.

If your cat takes seizure medication, these guides may help: What Are the Side Effects of Seizure Medication in Cats? and What to Do If Your Cat Has a Seizure: Medication and Emergency Response.

How These Drugs Work in a Cat's Body

Pimobendan makes the heart muscle contract more forcefully and relax more completely. It also has an antiplatelet effect. In one study, healthy adult cats given oral pimobendan at 0.625 mg per cat twice daily for one week, then 1.25 mg per cat twice daily for one week, had their platelet function measured by whole blood aggregometry and a platelet function analyzer [4]. This matters because cats with heart disease are at risk for arterial thromboembolism, and pimobendan may reduce that risk in addition to helping the heart pump [1].

Pimobendan also has electrical effects. A pilot study in five healthy cats found that an intravenous bolus of 0.15 mg/kg twice daily for three days significantly increased total 24-hour heart rate, and reports indicate an increase in arrhythmic events after oral administration to healthy cats [5]. This is one reason dosing is not something to adjust on your own.

Phenobarbital raises the seizure threshold in the brain. It does not cure the underlying cause of seizures. It reduces how often seizures happen and how severe they are. Because it is absorbed quickly and thoroughly, it can be used both for long-term control and in some emergency situations [3].

Benazepril blocks an enzyme that tightens blood vessels and retains fluid. The result is lower blood pressure and less strain on the heart. It works gradually, so a single missed dose is usually less dramatic than a missed seizure medication dose, but your veterinarian still needs to know.

Pimobendan for Cats Missed Dose: Dosing Basics and What to Do

Who decides the dose

Your veterinarian does. Pimobendan is not approved for cats, so there is no standard label dose for you to follow [5]. The dose is calculated from your cat's weight, heart condition, kidney values, and other medications. Never change the amount or the timing on your own.

How it is given

Pimobendan is usually given by mouth, often twice daily. Some cats get it on an empty stomach, some with a small amount of food. Follow the instructions on your bottle. If your cat vomits soon after a dose, call your veterinarian before repeating it.

If you miss a pimobendan dose

Less than half the dosing interval has passed (for example, you are 3 hours late on a twice-daily schedule): give the dose now if your veterinarian has told you this is acceptable.
More than half the interval has passed: skip it and give the next dose at the normal time.
Never give two doses at once. Pimobendan can increase heart rate and provoke arrhythmias, and a double dose raises that risk [5].
If your cat is showing trouble breathing, open-mouth breathing, or weakness, treat it as an emergency and go to a clinic.

If you miss a benazepril dose

Benazepril is often once daily. If you remember within a few hours, give it. If it is nearly time for the next dose, skip the missed one. Do not double up, because a double dose can drop blood pressure too low. If your cat is already on a diuretic, watch for weakness, wobbliness, or unusual tiredness after any dosing error.

For cats on other heart drugs, see Atenolol Cat Heart Dose: Beta Blocker Feline Heart Protocol.

If you miss a phenobarbital dose

Phenobarbital is usually given once or twice daily. If you miss a dose and remember within a few hours, give it. If you are close to the next dose, skip it and call your veterinarian. Do not double up. A sudden gap in phenobarbital can lower the seizure threshold and trigger a seizure, especially in a cat with a history of cluster seizures or status epilepticus [3]. Your veterinarian may want to check a blood level if doses have been irregular. For more on that, see Therapeutic Monitoring of Antiepileptic Drugs in Dogs and Cats.

If your cat takes thyroid medication too, the same "do not double up" rule applies. Here is a guide: What to Do If Your Cat Misses a Dose of Thyroid Medication.

Side Effects to Watch For

Side effect	How common or serious	What to do
Vomiting or drooling after a pill	Common, usually mild	Give with a small treat or food if your vet approves. Call if it happens with every dose.
Loss of appetite	Common with heart drugs	Call your vet if it lasts more than a day or your cat stops eating.
Increased heart rate, restlessness	Possible with pimobendan, seen in a study of healthy cats given IV pimobendan [5]	Call your vet. Do not give another dose until you talk to them.
Weakness, wobbliness, collapse	Serious, can signal low blood pressure	Emergency visit now.
Increased thirst and urination	Common with diuretics	Expected to some degree. Call if your cat seems dehydrated or very tired.
Worsening seizures, clusters, or a seizure lasting more than a few minutes	Serious, especially after missed doses [3]	Emergency visit now.
Trouble breathing, open-mouth breathing, blue gums	Serious, can signal heart failure or fluid around the lungs [2]	Emergency visit now.

Who Should Not Take These Medicines and What Interacts With Them

Pimobendan is not approved for cats, so it should only be used under direct veterinary supervision [5]. Cats with certain arrhythmias, severe outflow tract obstruction, or unstable heart rhythms may not be good candidates. Your veterinarian will weigh the risks.

Benazepril should be used with care in cats with kidney disease, dehydration, or low blood pressure. It interacts with diuretics and with other blood pressure drugs, and the combination can drop pressure too far.

Phenobarbital interacts with many drugs because it changes how the liver processes them. It can also cause sedation, especially in the first weeks. Cats with liver disease need careful monitoring. Never add a supplement, herbal product, or over-the-counter medicine without asking your veterinarian first, because complementary products can affect how well seizure drugs work and how consistently they are taken [6].

Tell your veterinarian about every drug, supplement, and topical product your cat receives, including flea and tick preventives.

Overdose and When to Call a Veterinarian or Poison Control

An overdose is different from a missed dose. Signs of a heart medication overdose include collapse, extreme weakness, vomiting, a very slow or very fast heart rate, and trouble breathing. Signs of a phenobarbital overdose include heavy sedation, trouble standing, wobbliness, and slowed breathing.

If you think your cat got too much medication, call your veterinarian or an animal poison control hotline right away. Have the bottle with you so you can read the drug name, strength, and how many pills may have been eaten. Do not wait for symptoms to appear.

Limitations and When to Contact a Veterinarian

This guidance covers common situations, but your cat's case is specific. Only your veterinarian can tell you whether to give a late dose, skip it, or change the schedule.

Call your veterinarian the same day if:

Your cat missed a phenobarbital or levetiracetam dose.
Your cat missed two or more doses in a row of any heart or seizure drug.
Your cat vomited a dose and you are not sure whether it was absorbed.
Your cat seems more tired, wobbly, or less interested in food than usual.

Go to an emergency clinic now if:

Your cat has a seizure that lasts more than a few minutes, or has more than one seizure in a short period [3].
Your cat is breathing with an open mouth, breathing fast at rest, or has blue or pale gums [2].
Your cat collapses, cannot stand, or seems to be in pain.
You gave a double dose by mistake.

Schedule a routine visit if your cat has had several missed doses over the past month, even if they seem fine. Your veterinarian may want to check drug levels, kidney values, or an ECG.

Frequently Asked Questions

Can I give my cat a missed pimobendan dose at the next meal?

Only if your veterinarian says the timing is safe. If the next scheduled dose is close, skip the missed one and give the normal amount at the normal time. Never combine two doses into one meal.

What happens if my cat misses a phenobarbital dose?

A single late dose is often not a crisis, but a gap can lower seizure control. Give the dose if you remember within a few hours, skip it if the next dose is near, and call your veterinarian. Watch closely for seizure activity for the next day or two.

Is it safe to double a heart medication dose to catch up?

No. Doubling a heart medication can cause dangerously low blood pressure, a fast or irregular heart rate, or worsening heart function. Call your veterinarian instead and follow their instructions.

How long can a cat safely go without seizure medication?

That depends on the drug, the dose, and your cat's seizure history. Cats with a history of cluster seizures or status epilepticus are at higher risk when levels drop [3]. Do not wait to see if a seizure happens. Call your veterinarian.

Should I stop giving the medication if my cat seems fine now?

No. Heart and seizure medications usually control signs instead of cure the disease. Stopping suddenly can cause a relapse, and with seizure drugs it can trigger a seizure. Talk to your veterinarian before making any change.

References

Use of pimobendan in cats: a practical evidence-based review. Journal of feline medicine and surgery, 2025.
Treatment of Cardiovascular Disease in Cats - Cat Owners. Merck Veterinary Manual.
Anticonvulsants for Emergency Treatment of Seizures in Dogs and Cats - Pharmacology. Merck Veterinary Manual.
Effects of orally administered pimobendan on platelet function in healthy adult cats. American journal of veterinary research, 2023.
A pilot study of the proarrhythmic effects of pimobendan injection in clinically healthy cats. Veterinary research communications, 2024.
Exploring the relationship of complementary therapy use and medication adherence among patients with epilepsy. Journal of pharmaceutical policy and practice, 2025.