Amanatadine (Symmetrel) is a unique medication for influenza that's also used as a Parkinson's aid.

Amantadine is a weak dopamine agonist and interestingly also displays some antagonist properties at N-methyl-D-aspartate receptors, (i.e. it has some anti-excitotoxin properties similar to Memantine). Accordingly, Amantadine has been used as an anti-Parkinson agent and is therefore used in the management of parkinsonism, (mainly in early disease when symptoms are mild) to help improve bradykinesia, rigidity, and tremors.

But interestingly Amantadine is also an antiviral that inhibits replication of the influenza type-A virus and activity has been reported against other viruses. It is used prophylactically against infection with influenza type-A virus and to ameliorate symptoms when given during the early stages of the infection. Amantadine has been used in the battle against bird-flu and SARS. (If you would like to see how this product and others have been used in the treatment of biological agents, please click here).

Amantadine has also been used in the management of herpes.

Dosage:
In Parkinson's the treatment is usually started with 100 mg. daily, increasing to 100 mg. twice daily after a week or more. Doses of up to 400 mg daily have occasionally been used, but this dose should not be exceeded. The lowest effective dose should be used in patients over 65 years of age because of the potential for reduced renal clearance in this age group. Withdrawal of Amantadine treatment for parkinsonism should be gradual to avoid exacerbating the condition; the manufacturers suggest decreasing the dose by half at weekly intervals.

The dose of Amantadine for the treatment of influenza A is 100 mg. twice daily usually given daily for about 5 days. For the prophylaxis of influenza-A a single 100 mg. dose is given daily for as long as protection from infection is required, which may be for up to 6-weeks. If Amantadine is being given with an influenza vaccination, then it is usually only given for up to 3-weeks after vaccination.

A daily dose of less than 100 mg. or 100 mg. given at intervals greater than one day has been recommended for patients over 65 years of age.

For herpes zoster the treatment with 100 mg. twice daily may be given for 14-days; if pain persists often the treatment is continued for a further 14-days.

Side effects:
Amantadine may enhance the adverse effects of antimuscarinics and the dose of these drugs should be reduced when used with Amantadine. If combined with the classic Parkinson's drug Sinemet, then the adverse effects of L-dopa may be exacerbated. It is also recommend that Amantadine should be used with caution if combined with drugs with CNS stimulant properties, particularly those that may enhance dopamine. Furthermore, the rate of excretion of Amantadine may be reduced by drugs that raise urinary pH.