Which of the following drugs decreases the effect of levodopa-

Ans. is 'c' i.e., Vit. B complex Interactions of levodopa Pyridoxine abolishes the therapeutic effect by enhancing peripheral decarboxylation of levodpa. Less levodpoa is thus available to cross BBB, to be conveed into dopamine in dopaminergic neurones in CNS Phenothiazines, butyrophenones, and metoclopramide reverse therapeutic effect by blocking DA receptors. The antidopaminergic domperidone blocks levodopa induced nausea and vomiting without abolishing its antiparkinsonian effect, because domperidone does not cross the blood brain barrier. Reserpine abolishes levodopa action by preventing entry of DA into synaptic vesicles. Nonselective MAO inhibitors: prevent degradation of peripherally synthesized DA and NA hypeensive crisis may occur. Atropine and other anticholinergic drugs have additive antiparkinsonion action, but retard its absorption more time is available for peripheral degradation Efficacy of levodopa may be reduced. Note : Pyridoxine is a component of vit B complex.