Levodopa Guanethidine

Drugs that may be affected by tricyclic compounds include anticholinergics, carbamazepine, clonidine, dicumarol, grepafloxacin, guanethidine, levodopa, quinolones, sparfloxacin, and sympathomimetics. 

Clinically important, potentially hazardous interactions with guanethidine, levodopa, metodopramide, piperazine... 

May decrease the effects of amphetamines, levodopa, dopamine agonists, cionidine, guanethidine, adrenaiine... 

Clinically important, potentially hazardous interactions with alcohol, amiodarone, anticholinergics, antihistamines, barbituates, cisapride, dofetilide, doxazosin, erythromycin, guanethidine, hydralazine, levodopa, lithium, methyldopa, metoclopramide, moxifloxacin, piperazine, quinidine, sibutramine, sotalol, thiazide diuretics, thioridazine... 

When two patients taking guanethidine were given levodopa it was possible to reduce the guanethidine dosage in one and to stop adjunctive diuretics in the other. 

A brief report describes a patient taking guanethidine and a diuretic who, when given levodopa (dose not stated), required a reduction in his daily dose of guanethidine, from 60 to 20 mg. Another patient similarly treated was able to discontinue the diuretic. The suggested reason is that the hypotensive adverse effects of the levodopa are additive with the effects of the guanethidine. Direct information seems to be limited to this report but it would be wise to confirm that excessive hypotension does not develop if levodopa is added to treatment with guanethidine. 

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