Primidone
Also known as: Mysoline, Neurosyn
> **Crucial for Success:** Strict compliance with therapy is essential for successful epilepsy treatment. Give the medication at the exact same times each day. * **Behavioral Changes:** Your dog may seem anxious, agitated, or unusually sleepy when starting this medication. These effects are often temporary and may resolve as their body adjusts. * **Increased Thirst/Appetite:** You may notice your pet drinking, urinating, and eating more than usual. Monitor their weight and discuss diet management with your veterinarian. * **When to Call the Vet:** Contact your veterinarian immediately if your pet develops severe lethargy, loss of appetite, vomiting, yellowing of the eyes/gums (jaundice), pale gums, or if seizures are not well controlled. * **Do Not Stop Abruptly:** Never stop giving this medication suddenly without veterinary guidance, as this can trigger severe, life-threatening seizures.
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
What it is used for
- Seizure control
- Seizure control
- Seizure control
How it is given
Possible side effects
- Anxiety and agitation (especially during initiation)
- Elevated liver enzymes (ALT, ALP, GLDH)
- Decreased serum albumin
- Hepatic lipidosis
- Hepatocellular hypertrophy and necrosis
- Extramedullary hematopoiesis
- Depression and sedation
- Ataxia
- Polydipsia (PD)
- Polyuria (PU)
- Polyphagia
- Anorexia
- Tachycardia
- Dermatitis
Cautions & contraindications
- Severe liver disease
- Demonstrated previous hypersensitivity to primidone or barbiturates
- Nephritis (large doses contraindicated)
- Severe respiratory dysfunction (large doses contraindicated)
- Cats (considered contraindicated by many clinicians due to high toxicity risk)
- **Species Warnings:** Use with extreme caution, if at all, in cats. Primidone is considered highly toxic to felines. **Patient Conditions:** Use cautiously in patients who are hypovolemic, anemic, have borderline hypoadrenal function, or have cardiac or respiratory disease. **Drug Transition:** When converting dogs from primidone to phenobarbital, it is suggested to do this slowly (tapering 1/4 of the dose each month) to prevent withdrawal seizures. **Laboratory Interference:** Barbiturates may cause falsely elevated bromosulfophthalein (BSP) retention. Primidone/phenobarbital can alter thyroid testing (decreased total and free T4, normal T3, normal/increased TSH); wait at least 4 weeks after discontinuation to perform thyroid testing. May cause a false-positive low-dose dexamethasone suppression test.
Drug interactions
- Acetaminophen: Increased risk for hepatotoxicity, particularly with large or chronic doses of barbiturates.
- Carbonic Anhydrase Inhibitors (e.g., acetazolamide): Oral administration may decrease the GI absorption of primidone.
- Monoamine Oxidase Inhibitors (e.g., amitraz, selegiline): May prolong phenobarbital effects.
- Phenytoin: Barbiturates may affect phenytoin metabolism, and phenytoin may alter barbiturate levels; therapeutic monitoring indicated.
- Rifampin: May induce enzymes that increase the metabolism of barbiturates.
- Antihistamines: May increase the CNS depressant effects of phenobarbital.
- Chloramphenicol: May increase the effects of phenobarbital; phenobarbital may also decrease chloramphenicol levels.
- Opiates: May increase the CNS depressant effects of phenobarbital.
- Phenothiazines: May increase the effects of phenobarbital; phenobarbital may decrease phenothiazine serum concentrations.
- Valproic Acid: May increase the effects of phenobarbital.
Frequently asked questions
What is Primidone used for in pets?
> **Crucial for Success:** Strict compliance with therapy is essential for successful epilepsy treatment. Give the medication at the exact same times each day. * **Behavioral Changes:** Your dog may seem anxious, agitated, or unusually sleepy when starting this medication. These effects are often temporary and may resolve as their body adjusts. * **Increased Thirst/Appetite:** You may notice your pet drinking, urinating, and eating more than usual. Monitor their weight and discuss diet management with your veterinarian. * **When to Call the Vet:** Contact your veterinarian immediately if your pet develops severe lethargy, loss of appetite, vomiting, yellowing of the eyes/gums (jaundice), pale gums, or if seizures are not well controlled. * **Do Not Stop Abruptly:** Never stop giving this medication suddenly without veterinary guidance, as this can trigger severe, life-threatening seizures.
Is Primidone safe for my pet?
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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