Mysoline

Mysoline is an anticonvulsant that is used alone or with other medications to control seizures in adults and children. Mysoline is used alone or with other medicines to treat people with: generalized tonic-clonic (grand mal) seizures, complex partial (psychomotor) seizures, partial (focal) epileptic seizures.

Product dosage: 250 mg
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Synonyms Primidone

Mysoline (primidone) is an established anticonvulsant medication primarily indicated for the management of seizure disorders. As a barbiturate derivative, it exerts its therapeutic effect by depressing the central nervous system and raising the seizure threshold, thereby reducing the incidence and severity of epileptic episodes. Its long-standing presence in neurological therapeutics offers clinicians a well-understood option for patients with grand mal, psychomotor, or focal epileptic seizures. This product card provides a comprehensive overview for healthcare professionals to ensure informed prescribing and patient management.

Features

• Active Ingredient: Primidone
• Pharmacological Class: Anticonvulsant, Barbiturate derivative
• Available Formulations: Scored tablets (50 mg, 250 mg) and oral suspension
• Mechanism of Action: Enhances GABAergic inhibition, suppresses neuronal excitability
• Bioavailability: Rapidly absorbed from the gastrointestinal tract
• Metabolism: Hepatic, to active metabolites (phenobarbital, PEMA)
• Elimination Half-Life: Primidone: 10-12 hours; Phenobarbital (metabolite): 53-118 hours
• Excretion: Primarily renal

Benefits

• Provides proven efficacy in controlling tonic-clonic (grand mal) and complex partial (psychomotor) seizures.
• Offers a therapeutic option with a long history of clinical use, allowing for predictable patient response.
• The active metabolite, phenobarbital, contributes to sustained anticonvulsant activity, supporting stable plasma levels.
• Can be used as monotherapy or as part of a combination anticonvulsant regimen for refractory cases.
• Available in multiple strengths and formulations (tablet, suspension) to facilitate precise dosing and administration across different patient populations.

Common use

Mysoline is indicated for the control of grand mal, psychomotor, and focal epileptic seizures. It may be used either alone or as an adjunctive therapy in the management of seizure disorders that have not been adequately controlled by other anticonvulsants. Its use is determined following a comprehensive neurological evaluation and diagnosis.

Dosage and direction

Dosage must be individualized based on the patient’s age, weight, renal and hepatic function, seizure type, and concomitant medications. Therapy should be initiated at a low dose and gradually titrated upward to achieve optimal seizure control while minimizing adverse effects.

Adults and children over 8 years:

• Initial dose: 100-125 mg at bedtime for the first 3 days.
• Increase gradually: May increase by 100-125 mg every 3 days until therapeutic response is achieved.
• Maintenance dose: Usually 250 mg three times daily to 500 mg three times daily. Doses exceeding 2 g daily require careful monitoring.

Children under 8 years:

• Initial dose: 50 mg at bedtime for the first 3 days.
• Increase gradually: May increase by 50 mg every 3 days.
• Maintenance dose: 125-250 mg three times daily, or 10-25 mg/kg/day in divided doses.

Elderly or debilitated patients: Initiate at lower doses due to increased susceptibility to CNS depression. Administer with or after food to minimize gastrointestinal upset. Tablets may be crushed if necessary. Do not abruptly discontinue; taper gradually to avoid withdrawal seizures.

Precautions

Patients should be monitored for signs of drowsiness, dizziness, or ataxia, especially at initiation of therapy or following dosage increases. Use with caution in patients with hepatic or renal impairment, as this may affect drug metabolism and elimination. Periodic assessment of hepatic function, complete blood count, and primidone/phenobarbital plasma levels is recommended during long-term therapy. May cause drowsiness that impairs mental or physical abilities required for hazardous tasks (e.g., driving, operating machinery). May have habit-forming potential; caution in patients with a history of substance abuse. Abrupt withdrawal may precipitate status epilepticus.

Contraindications

Mysoline is contraindicated in patients with:

• Hypersensitivity to primidone or any component of the formulation.
• Hypersensitivity to barbiturates.
• Porphyria.
• Severe respiratory depression with hypoxia.
• Severe hepatic impairment.

Possible side effect

Common side effects may include:

• Drowsiness, sedation, dizziness
• Ataxia, vertigo
• Nausea, vomiting, anorexia
• Fatigue, emotional disturbance

Serious side effects requiring medical attention:

• Megaloblastic anemia (may respond to folic acid)
• Stevens-Johnson syndrome, toxic epidermal necrolysis
• Significant mood changes, suicidal ideation
• Severe dermatological reactions
• Hepatitis, hepatic dysfunction
• Hyperkinesia in children

Drug interaction

Mysoline has a significant potential for drug interactions due to its metabolism and enzyme-inducing properties.

• Enhanced CNS depression: with alcohol, other anticonvulsants, sedatives, hypnotics, anxiolytics, opioids.
• Decreased efficacy: of oral contraceptives, anticoagulants (warfarin), corticosteroids, cyclosporine, tricyclic antidepressants, many antipsychotics, certain antifungals (e.g., itraconazole), and some antiviral agents due to induction of hepatic enzymes (CYP450).
• Increased levels/toxicity of primidone/phenobarbital: with valproic acid, isoniazid, monoamine oxidase inhibitors (MAOIs).
• Variable effects: with other anticonvulsants; combination therapy requires careful monitoring of plasma levels.

Missed dose

If a dose is missed, it should be taken as soon as remembered. However, if it is almost time for the next dose, the missed dose should be skipped, and the regular dosing schedule resumed. Doubling the dose to make up for a missed one is not recommended.

Overdose

Symptoms of overdose are primarily those of CNS depression and may include:

• Profound drowsiness progressing to coma
• Respiratory depression
• Hypotension
• Hypothermia
• Pulmonary edema

Management is supportive and symptomatic, focusing on maintaining adequate ventilation, blood pressure, and renal function. Hemodialysis may be beneficial due to the drug’s renal excretion. There is no specific antidote.

Storage

Store at room temperature (20-25°C or 68-77°F), in a tight, light-resistant container. Keep out of reach of children and pets. Do not use after the expiration date printed on the packaging. The oral suspension should not be frozen.

Disclaimer

This information is intended for educational purposes and for use by healthcare professionals only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider with any questions regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The prescribing physician is responsible for determining appropriate dosage and monitoring therapy based on the individual patient’s condition.

Reviews

“Mysoline has been a cornerstone in my practice for managing certain types of refractory epilepsy. Its dual action via primidone and its active metabolite provides a reliable pharmacokinetic profile. While sedation can be a challenge initially, careful titration often yields a favorable balance between efficacy and tolerability.” – Neurologist, 15 years experience

“In our pediatric epilepsy clinic, we use Mysoline judiciously. It’s effective, but requires vigilant monitoring for behavioral side effects and potential hematological changes. The availability of a suspension formulation is advantageous for precise weight-based dosing in younger children.” – Pediatric Neurologist

“For patients who have failed first-line agents, adding or switching to Mysoline can sometimes provide the seizure control we need. The drug interaction profile is extensive, necessitating a thorough review of the patient’s entire medication regimen before initiation.” – Clinical Pharmacist Specialist in Neurology