Medication Name

Amantadine

Mechanism of Action

Amantadine functions by blocking the viral M2 protein, disrupting the viral replication cycle. Additionally, it modulates the release of dopamine, acting as an indirect dopamine agonist.

Indications

Indicated for the treatment of Parkinson’s disease, amantadine helps alleviate motor symptoms. It is also used for prophylaxis and treatment of Influenza A virus infections. Amantadine mitigates symptoms of drug-induced extrapyramidal reactions.

Dosage Forms

Available in immediate-release capsules, extended-release capsules, and syrup formulations. Immediate-release capsules generally contain 100 mg of amantadine, while extended-release formulations range from 129 mg to 193 mg per capsule. The syrup form includes 50 mg/5 ml concentration.

Pharmacokinetics

Amantadine is rapidly absorbed from the gastrointestinal tract. It has a bioavailability of approximately 86%-90%. Peak plasma concentrations are achieved within 2-4 hours post-administration for immediate-release forms. The half-life ranges from 10 to 31 hours, influenced by renal function.

Metabolism and Excretion

Undergoes minimal hepatic metabolism. Primarily excreted unchanged in the urine. Renal excretion includes both glomerular filtration and tubular secretion processes.

Dosing Guidelines

For Parkinson’s disease, the recommended initial dose is 100 mg twice daily. For Influenza A prophylaxis, 100-200 mg daily is suggested, with specific attention to dosage adjustment in patients with renal impairment. Pediatric doses typically differ from adults and must be carefully determined by a healthcare provider.

Contraindications

Contraindicated in persons with a known hypersensitivity to amantadine. Should not be used in individuals with untreated narrow-angle glaucoma. Advised against use in severe renal impairment without appropriate dose adjustments. Patients with a history of seizure disorders should use amantadine cautiously.

Interactions

Might interact with anticholinergic agents, enhancing their effects. Co-administration with CNS stimulants may increase risks of adverse nervous system reactions. Potentiates the effects of dopaminergic agents. Concurrent use with live attenuated influenza vaccines can reduce vaccine efficacy.

Laboratory Monitoring

Regular monitoring of renal function is recommended during long-term therapy. Periodic liver function tests may be warranted. Monitoring for signs of neuroleptic malignant syndrome is advisable in Parkinson’s disease patients.

Storage Conditions

Store amantadine at room temperature, away from moisture and heat. Extended-release capsules should be kept in their original packaging to maintain stability. Avoid exposure to light for liquid formulations.

Pharmacodynamic Considerations

Exhibits dose-dependent effects on dopaminergic pathways. Shows antiviral efficacy by inhibiting the uncoating of Influenza A virus. May improve motor control in Parkinson’s disease through upregulation of dopamine pathways.

Patient Counseling

Instruct patients to take medication exactly as prescribed. Emphasize the importance of adherence to dosing schedules to mitigate symptom fluctuation. Advise patients to report any unexpected side effects or symptoms of toxicity immediately. Explain the necessity of dosage adjustments in renal impairment to avoid accumulation and toxicity.

Special Populations

For geriatric patients, careful dose titration is essential due to increased susceptibility to side effects. In pregnant women, the benefits should be weighed against potential risks as amantadine crosses the placenta. Lactating mothers should be informed about the drug’s excretion in breast milk and potential effects on the infant.

Adverse Reactions

Common side effects include dizziness, anxiety, gastrointestinal disturbances, and peripheral edema. Some patients may experience livedo reticularis, a mottled purplish skin discoloration. Central nervous system effects such as confusion, hallucinations, and insomnia have also been reported. Infrequently, serious adverse reactions such as orthostatic hypotension and leukopenia may occur.