Symmetrel: Effective Antiviral and Parkinson's Disease Treatment
| Product dosage: 100mg | |||
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Synonyms | |||
Symmetrel (amantadine hydrochloride) is a well-established antiviral and antiparkinsonian agent with a unique dual mechanism of action. This medication has demonstrated clinical efficacy for over five decades in managing influenza A virus infections and symptoms of Parkinson’s disease. As a dopamine agonist and NMDA receptor antagonist, Symmetrel offers a distinctive therapeutic profile that sets it apart from other agents in its class. Its proven safety record and predictable pharmacokinetics make it a valuable option in neurological and infectious disease therapeutics.
Features
- Contains amantadine hydrochloride as the active pharmaceutical ingredient
- Available in 100mg capsule and syrup formulations (50mg/5mL)
- Rapid oral absorption with peak plasma concentrations within 2-4 hours
- Extensive tissue distribution including central nervous system penetration
- Renal elimination with elimination half-life of approximately 12-15 hours
- Stable at room temperature with long shelf life
Benefits
- Provides effective prophylaxis against influenza A virus strains
- Reduces duration and severity of influenza symptoms when administered early
- Improves Parkinson’s disease symptoms including rigidity, bradykinesia, and tremor
- Decreases drug-induced extrapyramidal symptoms in psychiatric patients
- Offers convenient once or twice daily dosing regimen
- Demonstrates favorable safety profile with minimal drug interactions
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 commonly prescribed for the treatment of Parkinson’s disease, particularly for managing early-stage symptoms and reducing levodopa-induced dyskinesias. The medication is also utilized off-label for managing fatigue in multiple sclerosis patients and addressing drug-induced extrapyramidal symptoms in psychiatric patients receiving neuroleptic medications.
Dosage and direction
For influenza prophylaxis in adults: 200mg once daily or 100mg twice daily. For influenza treatment: 200mg once 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. Maximum recommended dose is 400mg daily in divided doses. For patients with renal impairment (creatinine clearance 30-50 mL/min): 200mg first day followed by 100mg daily. For severe renal impairment (creatinine clearance 15-29 mL/min): 200mg first day followed by 100mg every other day. Administration with food may reduce gastrointestinal upset.
Precautions
Patients should be monitored for signs of congestive heart failure, peripheral edema, and orthostatic hypotension. Use with caution in patients with history of seizures, as amantadine may lower seizure threshold. Psychiatric symptoms including depression, anxiety, and hallucinations may occur, particularly in elderly patients. Abrupt discontinuation may lead to parkinsonian crisis or neuroleptic malignant syndrome. Patients should avoid alcohol consumption during therapy. Caution advised when operating machinery or driving until response to medication is established.
Contraindications
Hypersensitivity to amantadine or any component of the formulation. Severe renal impairment (creatinine clearance <15 mL/min). History of angle-closure glaucoma. Concurrent use of live attenuated influenza vaccine. Patients with uncontrolled hypertension or severe cardiovascular disease. Pregnancy unless potential benefit justifies potential risk to fetus. Breastfeeding mothers due to secretion in human milk.
Possible side effect
Common adverse effects include nausea (5-10%), dizziness (5-10%), insomnia (5-10%), and dry mouth (5-10%). Less frequently reported effects include orthostatic hypotension (2-5%), peripheral edema (2-5%), livedo reticularis (1-5%), and blurred vision (1-3%). Neuropsychiatric effects including anxiety, depression, and hallucinations occur in approximately 1-5% of patients. Rare but serious adverse effects include suicidal ideation, seizures, and neuroleptic malignant syndrome upon abrupt withdrawal.
Drug interaction
Concomitant use with anticholinergic agents may increase anticholinergic side effects. May potentiate CNS stimulant effects of dexamphetamine and methylphenidate. Co-administration with thioridazine may increase risk of Parkinson’s-like symptoms. Quinidine and quinine may reduce renal clearance of amantadine. May enhance effects of levodopa and dopamine agonists. Alcohol may increase risk of CNS side effects. Urinary acidifiers such as ascorbic acid may increase renal excretion.
Missed dose
If a dose is missed, take it as soon as remembered unless it is nearly time for the next scheduled dose. Do not double the dose to make up for a missed dose. For twice-daily dosing regimen, if missed for more than 4 hours, skip the missed dose and resume regular schedule. Maintain consistent dosing intervals to ensure stable plasma concentrations. Contact healthcare provider if multiple doses are missed consecutively.
Overdose
Symptoms of overdose may include agitation, hallucinations, cardiac arrhythmias, hypertension or hypotension, hyperthermia, and urinary retention. Severe overdose may lead to convulsions, coma, and respiratory depression. Treatment is supportive and symptomatic. Gastric lavage may be considered if presented within 1-2 hours of ingestion. Activated charcoal may be administered. Acidification of urine may enhance elimination. Hemodialysis may be effective due to low molecular weight and minimal protein binding. Monitor cardiac function and electrolyte status closely.
Storage
Store at controlled room temperature (20-25°C or 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. Properly dispose of unused medication through take-back programs or according to local regulations.
Disclaimer
This information is provided for educational purposes only and does not constitute medical advice. Individual response to medication may vary. Healthcare professionals should consult official prescribing information before administering Symmetrel. Patients should not make changes to their medication regimen without consulting their healthcare provider. The full prescribing information contains complete details regarding indications, contraindications, warnings, and precautions.
Reviews
Clinical studies demonstrate Symmetrel’s efficacy in reducing influenza A symptoms by 50-60% when initiated within 48 hours of symptom onset. In Parkinson’s disease trials, approximately 60-70% of patients show significant improvement in motor symptoms. Long-term safety data from post-marketing surveillance confirms the generally favorable risk-benefit profile. Elderly patients may experience increased sensitivity to CNS effects. Patient satisfaction surveys indicate good tolerability with appropriate dose titration.