In my practice, I most often see amantadine used for dyskinesia and motor symptoms associated with Parkinson’s. It can also be used for medication-induced Parkinsonism. In general, amantadine is not a first-line agent for treating movement disorders, but I think it is a good medication to remember some important clinical pearls that could show up in real life or on your board exam.
Renal Elimination
Renal function tends to decline over time as patients age. Amantadine is eliminated by the kidneys to a significant extent. It is very important to monitor for adverse effects and toxicity if you notice a decline in renal function. Dose adjustments are required with this medication, and that is an important nugget to remember.
Dopamine Enhancement/Agonist Action
Amantadine is associated with increasing the action of dopamine and having agonist-type action. Because of this mechanism, psychiatric changes can happen. Hallucinations, behavioral changes, insomnia, and other psychiatric adverse effects are possible and should be monitored for. This is more likely at higher dosages, in those who are older or have poor renal function. This is similar to other dopamine agonists and Sinemet.
Livedo Reticularis
One really unique adverse effect to know about amantadine is livedo reticularis. If you ever have a board exam question about this adverse effect, it’s a good bet that amantadine may be associated with this. It is a skin condition of the vessels causing purple/red/blue patches. It is mostly on the trunk but can extend to the lower limbs. It is associated with patients who have Parkinson’s disease. It is reversible if the medication is discontinued. It can generally just be monitored and is associated with chronic therapy.
Withdrawal Risks
Abrupt withdrawal or reducing the dose too quickly can cause a withdrawal effect that can mimic signs and symptoms of NMS. This can be very serious so a discussion about adherence is critical when patients are taking moderate/high dosages for long periods of time.
Orthostasis
One last adverse effect I would pay attention to is low blood pressure. The elderly and those at risk for falls are particularly concerning. Many of these patients are already taking blood pressure-lowering medications so adding amantadine to the medication regimen can enhance this effect.
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