Symmetrel

Symmetrel (amantadine hydrochloride) is a well-established antiviral and antiparkinsonian agent with a unique dual mechanism of action. Originally developed as an antiviral medication, its efficacy in managing Parkinson’s disease symptoms and drug-induced extrapyramidal reactions has made it a valuable therapeutic option in neurological and infectious disease practice. This medication demonstrates particular utility in early-stage Parkinson’s management and influenza A prophylaxis, offering patients improved motor control and antiviral protection through its distinct pharmacological profile.

Features

• Contains amantadine hydrochloride as the active pharmaceutical ingredient
• Available in 100mg capsule and syrup formulations for flexible dosing
• Exhibits both antiviral and dopaminergic activity
• Demonstrated efficacy against influenza A virus strains
• Provides symptomatic relief for Parkinson’s disease
• Shows activity against drug-induced extrapyramidal symptoms
• Established safety profile with decades of clinical use
• Multiple administration routes including oral and liquid formulations

Benefits

• Reduces severity and duration of influenza A symptoms when administered prophylactically
• Improves motor function and reduces rigidity in Parkinson’s disease patients
• Decreases tremors and bradykinesia through dopaminergic enhancement
• Helps manage levodopa-induced dyskinesias in advanced Parkinson’s disease
• Provides alternative therapeutic option for patients with medication intolerance
• Offers rapid onset of action compared to some antiparkinsonian medications

Common use

Symmetrel is primarily indicated for the prophylaxis and treatment of respiratory tract infections caused by influenza A virus strains. In neurological practice, it is extensively used for the treatment of Parkinson’s disease, particularly in early-stage management where it can provide symptomatic relief without the complexity of levodopa regimens. Additionally, it finds application in managing drug-induced extrapyramidal symptoms caused by neuroleptic medications. The medication has also shown utility in cases of fatigue associated with multiple sclerosis, though this represents an off-label use. Clinical practice often employs Symmetrel as monotherapy in early Parkinson’s disease or as adjunctive therapy with levodopa in more advanced cases.

Dosage and direction

For influenza A prophylaxis in adults: 200mg daily as a single dose or divided as 100mg twice daily. For treatment of influenza A infection: 200mg daily initiated within 24-48 hours of symptom onset and continued for 24-48 hours after symptoms disappear. For Parkinson’s disease: Initial dose of 100mg daily, increasing to 100mg twice daily after one week if necessary. Some patients may benefit from 400mg daily in divided doses, though this requires careful monitoring. For drug-induced extrapyramidal symptoms: 100mg twice daily, with possible increase to 300mg daily in divided doses if needed. Dosage adjustments are necessary for patients with renal impairment, elderly patients, and those with congestive heart failure. Administration with food may minimize gastrointestinal upset.

Precautions

Patients should be monitored for signs of congestive heart failure, peripheral edema, and orthostatic hypotension. Those with history of seizures require careful supervision as amantadine may lower seizure threshold. Psychiatric manifestations including depression, anxiety, and hallucinations may occur, particularly in elderly patients. Caution is advised when operating machinery or driving until response to therapy is established. Sudden discontinuation may lead to parkinsonian crisis or neuroleptic malignant syndrome. Regular renal function assessment is recommended during prolonged therapy. Patients should maintain adequate hydration to minimize the risk of livedo reticularis.

Contraindications

Hypersensitivity to amantadine or any component of the formulation. Severe renal impairment (creatinine clearance less than 15mL/min). History of angle-closure glaucoma. Concurrent use of live attenuated influenza vaccine. Patients with uncontrolled psychosis or severe psychoneurosis. Known hypersensitivity reactions to adamantane derivatives. Pregnancy unless clearly needed and benefits outweigh risks. Breastfeeding mothers due to secretion in human milk.

Possible side effect

Common adverse effects include nausea, dizziness, lightheadedness, and insomnia. Less frequently reported are depression, anxiety, irritability, and hallucinations. Peripheral edema and orthostatic hypotension may occur, particularly in elderly patients. Livedo reticularis (a purplish network pattern on skin) appears in some patients after several months of therapy. Anticholinergic effects such as dry mouth, blurred vision, and constipation may be observed. Rare but serious side effects include congestive heart failure, psychosis, leukopenia, and seizures. Most side effects are dose-dependent and reversible upon dosage reduction or discontinuation.

Drug interaction

Concomitant use with anticholinergic drugs may enhance anticholinergic side effects. Alcohol may increase risk of CNS effects such as dizziness and confusion. Co-administration with CNS stimulants may exacerbate nervousness, insomnia, or anxiety. Thiazide diuretics may decrease amantadine clearance, increasing the risk of toxicity. QT-prolonging agents may have additive effects on cardiac repolarization. Memantine should not be co-administered due to similar mechanisms and increased adverse effect risk. Triamterene-hydrochlorothiazide combination may reduce amantadine renal clearance by approximately 20%.

Missed dose

If a dose is missed, it should be taken as soon as remembered unless it is nearly time for the next scheduled dose. In that case, the missed dose should be skipped and the regular dosing schedule resumed. Patients should not double the dose to make up for a missed administration. Consistent dosing is important for maintaining therapeutic levels, particularly in Parkinson’s disease management. For influenza prophylaxis, missing a single dose may reduce protective efficacy, and patients should contact their healthcare provider for guidance.

Overdose

Amantadine overdose may manifest as agitation, hallucinations, psychotic behavior, cardiac arrhythmias, and hyperthermia. Severe cases may progress to convulsions, coma, and respiratory depression. Treatment is primarily supportive with careful monitoring of cardiac and respiratory function. Gastric lavage may be considered if presentation is early after ingestion. Activated charcoal may be administered. Acidification of urine may enhance elimination but is contraindicated in patients with myoglobinuria or renal impairment. Hemodialysis may be effective in removing amantadine from circulation. Management should include cardiac monitoring for arrhythmias and appropriate symptomatic treatment.

Storage

Store at controlled room temperature between 20-25°C (68-77°F). Protect from light and moisture. Keep container tightly closed. Do not freeze the syrup formulation. Keep out of reach of children and pets. Do not use after expiration date printed on packaging. Do not transfer capsules to other containers as this may affect stability. The syrup formulation should be used within a certain period after opening—consult product packaging for specific guidance.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Individual patient responses may vary. Healthcare professionals should exercise their own professional judgment when considering the use of this medication. Full prescribing information should be consulted before initiation of therapy. Patients should not make changes to their medication regimen without consulting their healthcare provider. The information presented here may not include all possible uses, directions, precautions, or interactions.

Reviews

Clinical studies demonstrate Symmetrel’s efficacy in reducing influenza A infection rates by approximately 50-70% when used prophylactically. In Parkinson’s disease management, approximately 60-70% of patients show significant improvement in motor symptoms. Many patients report improved quality of life and functional capacity. Some reviews note the benefit of rapid onset of action compared to other antiparkinsonian medications. However, some patients report tolerance development requiring dosage adjustment. The livedo reticularis side effect is frequently mentioned as a cosmetic concern though typically benign. Overall, Symmetrel maintains a favorable risk-benefit profile in appropriate patient populations.