Symmetrel is the drug which has developed as an antiviral drug for prophylaxis of influenza A₂. It also possesses the ability to benefit Parkinson’s disease, herpes zoster, and drug-induced extrapyramidal reactions.
It is a weak dopamine agonist and causes rapid onset of action. It alters dopamine release and reuptake. As an antiviral drug, it inhibits replication of influenza type-A virus. About 2/3rd patients derive more benefit. However, tolerance develops over months and the efficacy is gradually lost.
Amantadine promotes presynaptic synthesis and release of DA in the brain and has anticholinergic property. These were believed to explain all its beneficial effect in parkinsonism.
Amantadine can be used in milder cases, or in short courses to supplement levodopa for advanced cases. In the later situation, it serves to suppress motor fluctuations and abnormal movements.
Fixed dose of 100 mg BD is commonly used. The effect of a single dose lasts 8-12 hrs.
If you are about to start using Symmetrel, speak with your doctor about what you need to know. Chemically, it is a unique tricyclic amine to any nucleic acid precursor, but inhibits replication of influenza A virus (a myxovirus).
The antiviral activity of Symmetrel is strain specific; influenza B is not affected. Moreover, H5N1 (avian influenza/bird flu) and H1N1 (swine flu) strains of influenza A are resistant in most areas.
It appears to act at an early step (possibly uncoating ) as well as at a late step (viral assembly) in viral replication. A protein designated ‘M2’ which acts as an ion channel has been identified as one of its targets of action.
Resistance to Symmetrel develops by mutation causing amino acid substitutions in the M2 protein. Symmetrel is well absorbed orally and excreted unchanged in urine over 2-3 days.
3 Proper Usage
To use Symmetrel properly, you must follow all instructions given by your doctor. The dose of this medicine will vary according to patient’s condition or requirements.
You should follow the doctor's directions and advice. Symmetrel is the drug which is used is to treat a variety of health disorders such as:
Prophylaxis of influenza A₂: during an epidemic or seasonal influenza, especially in high-risk patients amantadine is used as a prophylactic medicine.
Influenza season and epidemics generally last ~ 2 months, and only this period needs to be covered by prophylaxis.
Only when the epidemic causing strain of virus is known to be sensitive to amantadine, prophylactic use should be considered. For seasonal prophylaxis success rate is variable, but often substantial.
Symmetrel does not interfere with antibody response to influenza vaccine; both may be given together. If the vaccine is given, amantadine should be used up to 3 weeks.
Treatment of influenza (A₂) illness: a modest therapeutic effect (reduction in fever, congestion, cough and quicker recovery) occurs if the drug is given immediately after the symptoms appear. 100mg/day is advised for 5 days.
Parkinsonism: the usual dose is 100mg/day up to 100mg twice daily for 1 week or more. The maximum therapeutic dose is 400mg/day.
Herpes zoster: 100mg twice daily for 14 days, may continue for another 14 days if pain persists.
Always try to take your medicine in time. If you miss any dose of this medicine, you should take it as soon as possible. But when it is time for your next dose, then skip the missed dose and go back to your regular dosing schedule.
You should store the medicine in a closed container at room temperature away from heat, moisture, and direct light. All kinds of medicines should be kept out of the reach of children. Outdated medicine must be disposed of by an appropriate way.
4 Precautions to Take
In using Symmetrel, you must be careful and take some precautions as advised by your doctor. It is better to remain ready to face any undesired effects after taking any drug. Some important measures should be taken if you feel any discomfort after administration of such medicines.
Firstly, you have to stop using this drug and then consult with your physician immediately because of excessive undesirable effects. You should take this medicine exactly as directed by your doctor.
Never try to increase either the frequency of drug administration or the dosage of the drug. Excessive use of drugs beyond maximum therapeutic dose makes an individual more prone to infections.
Patients with cardiovascular or liver disease impaired kidney function, recurrent eczema contradicts the use of amantadine. Additionally, it is contraindicated in epilepsy and another CNS disease; gastric ulcer and pregnancy.
Ankle edema has been reported in some individuals due to vasoconstrictions. Although these side effects are not serious, but may require medical attention sometimes.
Livedo reticularis (bluish discolouration) and edema of ankles are the characteristic side-effects which occur due to postcapillary vasoconstriction. Side effects are accentuated when it is combined with anticholinergics.
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