An antiviral drug that was found to have antiparkinsonism properties by chance is which of the following?

• A. Isocarboxazid
• B. Entacapone
• C. Amantadine
• D. Rasagiline

Answer: (C)

A drug that started as an antiviral can surprise by helping motor symptoms in Parkinson’s, showing how altering brain neurotransmission can benefit movement even if the drug wasn’t designed for it.

Amantadine fits this description. It was developed to treat influenza A, but clinicians noticed it could improve Parkinsonian symptoms such as rigidity and bradykinesia, and it can also help reduce dyskinesias caused by L-DOPA. Its actions in the brain are thought to involve promoting dopamine release and activity, plus blocking NMDA receptors, which may dampen excitatory signals that contribute to abnormal movements. While its exact mechanism isn’t fully pinpointed, these effects explain why it helps PD symptoms and why it’s the antiviral with antiparkinsonian properties discovered by chance.

The other options don’t share this serendipitous antivirals-to-Parkinson’s link. Isocarboxazid is an antidepressant MAO inhibitor, not antiviral. Entacapone is a COMT inhibitor used to boost L-DOPA’s effect. Rasagiline is an MAO-B inhibitor used in PD management but also not discovered as an antiviral.