ABSTRACT
Levodopa, a dopamine precursor, crosses the blood–brain barrier. Thus, it is able to help to correct the akinesia associated with Parkinson’s disease by forming dopamine at nigro-striatal dopaminergic sites. Unfortunately, the peripheral decarboxylation of levodopa necessitates the use of levodopa dosages that are much higher than is otherwise necessary. Combining carbidopa, a peripheral decarboxylase inhibitor, and levodopa in a fixed-ratio formulation allows for a significant reduction in the required dosage of levodopa and, consequently, a significant reduction in both the incidence and severity of levodopa-associated adverse drug reactions. Fixed-ratio combination levodopa and carbidopa pharmacotherapy has been associated with postural (orthostatic) hypotension. Therefore, concurrent pharmacotherapy with antihypertensives may require blood pressure monitoring and a possible reduction of the dosage of the antihypertensive. The signs and symptoms of fixed-ratio combination levodopa and carbidopa overdosage include abnormal involuntary movements such as choreiform and dystonic movements.
