Symmetrel: Effective Antiviral and Parkinson's Symptom Management
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Synonyms | |||
Symmetrel (amantadine hydrochloride) is a well-established antiviral and antiparkinsonian agent with a unique dual mechanism of action. As a synthetic tricyclic amine, it demonstrates clinical efficacy against influenza A virus strains while providing symptomatic relief for Parkinson’s disease, drug-induced extrapyramidal reactions, and fatigue associated with multiple sclerosis. Its neuropharmacological profile includes dopaminergic facilitation and NMDA receptor antagonism, making it a versatile therapeutic option under appropriate medical supervision. This comprehensive product card details its pharmacological characteristics, clinical applications, and essential safety information for healthcare professionals.
Features
- Contains 100 mg amantadine hydrochloride per capsule
- Rapid oral absorption with peak plasma concentrations within 2-4 hours
- Extensive tissue distribution including penetration across the blood-brain barrier
- Primarily renal elimination with elimination half-life of approximately 12-18 hours
- Stable shelf life of 36 months when stored properly
- Available in 100 mg capsules with distinctive identification markings
Benefits
- Provides proven prophylaxis against influenza A virus infections when administered prior to or following exposure
- Reduces parkinsonian symptoms including rigidity, bradykinesia, and tremor through dopaminergic enhancement
- Mitigates drug-induced extrapyramidal symptoms caused by neuroleptic medications
- Demonstrates efficacy in managing fatigue associated with multiple sclerosis
- Offers flexible dosing regimens adaptable to individual patient needs and renal function
- Establishes therapeutic effects typically within 48 hours of initiation for parkinsonian symptoms
Common use
Symmetrel is primarily indicated for the prophylaxis and treatment of respiratory tract illnesses caused by influenza A virus strains. In neurological practice, it is employed as monotherapy or adjunctive treatment for Parkinson’s disease, particularly in early-stage disease or to manage levodopa-induced dyskinesias. Additionally, it finds application in managing extrapyramidal symptoms secondary to neuroleptic drug therapy and off-label for fatigue management in multiple sclerosis patients. Clinical decision-making should consider the patient’s renal function, concomitant medications, and specific symptom profile.
Dosage and direction
For influenza prophylaxis in adults: 200 mg once daily or 100 mg twice daily. For influenza treatment: 200 mg initially followed by 100 mg daily or 100 mg twice daily. For Parkinson’s disease: Initial dose of 100 mg daily, increasing to 100 mg twice daily after one week if necessary. Maximum daily dose should not exceed 400 mg in divided doses for patients with normal renal function. Dosage must be adjusted in renal impairment: CrCl 30-50 mL/min: 200 mg first day then 100 mg daily; CrCl 15-29 mL/min: 200 mg first day then 100 mg every other day; CrCl <15 mL/min: 200 mg every 7 days. Administration with food may minimize gastrointestinal discomfort.
Precautions
Monitor renal function regularly during therapy. Use with caution in patients with history of seizures, cardiovascular disease, peripheral edema, or orthostatic hypotension. Psychiatric symptoms including depression, anxiety, and hallucinations may occur, particularly in elderly patients. Abrupt discontinuation may precipitate parkinsonian crisis or neuroleptic malignant syndrome. Perform periodic ophthalmologic examinations due to potential corneal edema. Exercise caution in patients with eczema or other exfoliative skin conditions. Pregnancy Category C: Use only if potential benefit justifies potential risk to fetus.
Contraindications
Hypersensitivity to amantadine or any component of the formulation. Severe renal impairment (CrCl <15 mL/min) without appropriate dosage adjustment. History of angle-closure glaucoma. Concurrent use with live attenuated influenza vaccine. Patients with uncontrolled psychosis or severe psychoneurosis not controlled by chemotherapy.
Possible side effect
Common adverse reactions include nausea (5-10%), dizziness (5-7%), insomnia (5-10%), and dry mouth (5-10%). Less frequently observed effects include livedo reticularis (1-5%), peripheral edema (1-3%), orthostatic hypotension (2-5%), and visual disturbances (1-3%). Neuropsychiatric effects may include anxiety, depression, confusion, and hallucinations, particularly in elderly patients. Rare but serious adverse events include suicidal ideation, neuroleptic malignant syndrome, and congestive heart failure.
Drug interaction
Concomitant use with anticholinergic agents may enhance anticholinergic effects. Co-administration with CNS stimulants may increase nervousness, anxiety, and insomnia. May potentiate effects of alcohol and other CNS depressants. Thiazide diuretics may decrease renal clearance of amantadine. QT-prolonging agents may have additive effects on cardiac repolarization. Avoid concurrent use with memantine due to similar mechanism of action.
Missed dose
If a dose is missed, take it as soon as remembered unless it is nearly time for the next dose. Do not double the dose to make up for a missed administration. For twice-daily regimens, if missed for more than 4 hours, wait until the next scheduled dose. Maintain regular dosing schedule to ensure consistent therapeutic levels, particularly for antiviral prophylaxis.
Overdose
Symptoms may include severe nausea, vomiting, agitation, hallucinations, cardiac arrhythmias, and seizures. Management includes gastric lavage if presented within 1 hour of ingestion, activated charcoal, and supportive care. Acidification of urine may enhance elimination. Hemodialysis may be effective due to the drug’s relatively low molecular weight and partial protein binding. Monitor cardiac function and neurological status closely. Specific antidote is not available.
Storage
Store at controlled room temperature 20-25°C (68-77°F). Protect from light and moisture. Keep container tightly closed. Dispense in original container with child-resistant closure. Do not freeze. Keep out of reach of children and pets. Do not use beyond expiration date printed on packaging.
Disclaimer
This information is provided for educational purposes only and does not constitute medical advice. Healthcare professionals should consult full prescribing information before administration. Patients should be instructed to take Symmetrel only as prescribed by their physician. Individual response to therapy may vary based on multiple factors including age, renal function, and concomitant medications. Regular monitoring and appropriate dose adjustments are essential for safe and effective use.
Reviews
Clinical studies demonstrate 70-90% efficacy in influenza A prophylaxis when initiated prior to or within 48 hours of exposure. Parkinson’s disease studies show significant improvement in Unified Parkinson’s Disease Rating Scale scores, with particular benefit for bradykinesia and rigidity. Multiple sclerosis fatigue studies indicate moderate improvement in fatigue scales compared to placebo. Long-term use requires careful monitoring due to potential side effect profile. Overall, Symmetrel remains a valuable therapeutic option when used appropriately within its indications and with proper patient selection.