Amantadine

# amantadine ## Overview - **Classification**: Antiviral (Influenza A), Antiparkinsonian - **Mechanism**: Blocks the M2 ion channel of influenza A virus, inhibiting viral replication. In Parkinson's, it has dopaminergic and anticholinergic properties, increasing dopamine release and blocking reuptake. ## Primary Indications 1. **Parkinson's Disease (PD)** - Treatment of signs and symptoms. 2. **Drug-Induced Extrapyramidal Symptoms (EPS)** - Treatment of symptoms caused by antipsychotic medications. 3. **Influenza A Prophylaxis/Treatment** - For susceptible strains when vaccination is not feasible/effective. ## Adult Dosing ### Standard Dosing **Parkinson's Disease / Drug-Induced EPS** - **Dose**: **100 mg** - **Frequency**: Twice daily (BID) - **Route**: Oral - **Duration**: Chronic for PD/EPS - **Max Dose**: **400 mg/day** (rarely used, typically **200 mg/day**) **Influenza A (Treatment & Prophylaxis)** - **Dose**: **100 mg** - **Frequency**: Twice daily (BID) - **Route**: Oral - **Duration**: 10-14 days for treatment; up to 90 days for prophylaxis. - **Max Dose**: **200 mg/day** ### Dose Adjustments - **Renal Impairment**: Amantadine is renally eliminated. - **CrCl 50-60 mL/min**: **100 mg** once daily. - **CrCl 30-49 mL/min**: **100 mg** every other day. - **CrCl 15-29 mL/min**: **100 mg** twice weekly. - **CrCl <15 mL/min**: **100 mg** once weekly. - Hemodialysis: Administer **24-48 hours** after dialysis. - **Hepatic Impairment**: No specific dose adjustments required. - **Elderly Patients**: Start with lower doses (**100 mg once daily**) due to decreased renal function and increased susceptibility to CNS adverse effects. ## Pediatric Dosing ### Neonates (0-28 days) - **Not Recommended**: Safety and efficacy not established. ### Infants (1-12 months) - **Not Recommended**: Safety and efficacy not established. ### Children (1-9 years) **Influenza A Prophylaxis/Treatment** - **Dose (<40 kg)**: **4.4-8.8 mg/kg/day** - **Frequency**: Divided twice daily (BID) - **Maximum**: **150 mg/day** - **Dose (≥40 kg)**: **100 mg** - **Frequency**: Twice daily (BID) - **Special Notes**: Higher incidence of adverse effects in children. Not for unconfirmed influenza A. ### Adolescents (10-18 years) **Influenza A Prophylaxis/Treatment** - **Dose**: **100 mg** - **Frequency**: Twice daily (BID) - **Maximum**: **200 mg/day** - **Special Notes**: Same as adult dosing. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to amantadine or its components. - **Absolute**: End-stage renal disease (ESRD) for some indications due to accumulation risk. - **Relative**: History of seizures, severe congestive heart failure. ### Common Adverse Effects - **Very Common (>10%)**: Livedo reticularis (skin discoloration), dizziness, insomnia, nausea. - **Common (1-10%)**: Dry mouth, nervousness, blurred vision, constipation, peripheral edema. - **Serious but Rare**: Neuroleptic malignant syndrome (upon withdrawal), seizures, heart failure exacerbation, psychiatric symptoms (hallucinations, confusion), QT prolongation. ### Key Drug Interactions - **Anticholinergic Agents**: Increased risk of anticholinergic side effects (e.g., dry mouth, blurred vision, urinary retention). - **CNS Stimulants**: May enhance CNS stimulation, leading to nervousness, insomnia, or irritability. - **QT-prolonging Drugs**: Concurrent use may increase risk of QT prolongation and torsades de pointes. Avoid if possible. - **Trimethoprim/Sulfamethoxazole (TMP/SMX)**: May reduce renal clearance of amantadine, increasing its levels. Monitor for toxicity. ## Monitoring & Follow-up - **Before Treatment**: Baseline renal function (CrCl). - **During Treatment**: Monitor for CNS side effects (confusion, hallucinations), edema, Livedo reticularis. - **Clinical Signs**: Watch for changes in mental status, new or worsening psychiatric symptoms, signs of heart failure (edema, dyspnea), and seizure activity. For Parkinson's, monitor motor fluctuations. ## Clinical Pearls - 💡 **Timing**: Doses are typically given in the morning and early afternoon to minimize insomnia. - 💡 **Withdrawal**: Abrupt discontinuation can lead to severe Parkinsonian crisis or neuroleptic malignant syndrome-like symptoms. Taper slowly. - 💡 **Livedo Reticularis**: A common, benign, reversible skin discoloration. May resolve with dose reduction or discontinuation. - 💡 **Renal Function**: Extremely important to adjust dose based on kidney function. Overdosing due to renal impairment is a common cause of toxicity. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.