Guanethidine interaction with other drugs

Interactions with other drugs may complicate guanethidine therapy. Sympathomimetic agents, at doses available in over-the-counter cold preparations, can produce hypertension in patients taking guanethidine. Similarly, guanethidine can produce hypertensive crisis by... 

Interactions of sympathomimetics with other vasoactive drugs are complex. Some drugs block the reuptake mechanism for noradrenaline in adrenergic nerve terminals and potentiate the pressor effects of noradrenaline e.g. cocaine, tricyclic antidepressants or highly noradrenaline-selective reuptake inhibitors such as roboxetine. Others deplete or destroy the intracellular stores within adrenergic nerve terminals (e.g. reserpine and guanethidine) and thus block the action of indirect S5unpathomimetics. 

Tricyclic drug interactions (Table 30-3) include additive depression of the CNS with other central depressants, including ethanol, barbiturates, benzodiazepines, and opioids. Tricyclics may also cause reversal of the antih)pertensive action of guanethidine by blocking its transport into sympathetic nerve endings. Less commonly, tricyclics may interfere with the antihypertensive actions of methylnorepinephrine (the active metabolite of methyl-dopa) and clonidine. 

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