Guanethidine Epinephrine

Tricyclic antidepressants potentiate the pressor effects of directly acting sympathomimetic amines, such as adrenaline (epinephrine) or noradrenaline (norepinephrine), to cause hypertension. Small amounts of these, such as may be present in local anaesthetic solutions, can be dangerous. Tricyclic antidepressants will inhibit the antihypertensive effects of the older anti hypertensive drugs, such as adrenergic neurone-blocking agents, e.g. guanethidine, a-methyl-DOPA, and clonidine. 

Guanethidine possesses high af nity for the axolemmal and vesicular amine transporters. It is stored instead of NE, but is unable to mimic functions of the latter. In addition, it stabilizes the axonal membrane, thereby impeding the propagation of impulses into the sympathetic nerve terminals. Storage and release of epinephrine from the adrenal medulla are not affected, owing to the absence of a reuptake process. The drug does not cross the blood-brain barrier. 

Clinically important, potentially hazardous interactions with amprenavir, clonidine, ephedra, epinephrine, eucalyptus, guanethidine, iobenguane, isocarboxazid, linezolid, MAO inhibitors, paroxetine, phenelzine, quinolones, sparfloxacin, St John s wort, tranylcypromine... 

Indications Psychosis, manic-depressive disorders Category Antipsychotic, phenothiazine Muscarinic antagonist Half-life initial 2 hours terminal 30 hours Clinically important, potentially hazardous interactions with alcohol, antihistamines, arsenic, chlorpheniramine, dofetilide, epinephrine, evening primrose, guanethidine, mivacurium, quinolones, sparfloxacin... 

Clinically important, potentially hazardous interactions with alcohol, amiodarone, beta-blockers, cimetidine, donidine, digoxin, diltiazem, disopyramide, ephedrine, epinephrine, ergot alkaloids, guanethidine, halothane, isoprenaline, lidocaine, noradrenaline, NSAIDs, phenylephrine, quinidine, reserpine, verapamil... 

Cyclobenzaprine Decongestants (topical and systemic) Dextromethorphan Dopamine Ephedrine Epinephrine Guanethidine... 

The mydriasis due to phenylephrine given as a 10% eye drop solution was prolonged for up to 10 hours in a patient taking guanethidine for hypertension. This enhanced mydriatic response has been described in another study using guanethidine eye drops with adrenaline (epinephrine), phenylephrine or methoxamine eye drops. ... 

Mitchell JR, Cavanaugh JH, Arias L, Oates JA. Guanethidine and related agents. III. Antagonism ly drugs which inhibit the no epinephrine pump in maa J Clin Invest( 970) 49,159 1604. 

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