OBJECT DRUGS

Central Alpha-adrenergic Agonists:

• Clonidine (Catapres, etc.)
• Guanabenz (Wytensin)
• Guanfacine (Tenex, etc.)

PRECIPITANT DRUGS

• Yohimbine

Comment:

Yohimbine acts through inhibition of alpha-2 adrenergic receptors, while central alpha-adrenergic agonists stimulate those same receptors. As a result of this pharmacologic antagonism, it is likely that yohimbine will inhibit the antihypertensive effect of clonidine, guanabenz, and guanfacine.

Class 2: Use Only if Benefit Felt to Outweigh Risk

• Use Alternative: If yohimbine is being used as an "herbal Viagra' in a patient on clonidine, guanabenz, or guanfacine, it would be prudent to use an alternative drug for erectile dysfunction, such as phosphodiesterase inhibitors: sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra). Unlike yohimbine, phosphodiesterase inhibitors may increase the antihypertensive effect of clonidine, guanabenz, or guanfacine. Monitor blood pressure.
• Monitor:If yohimbine is used with clonidine, guanabenz, or guanfacine, monitor blood pressure for evidence of reduced antihypertensive effect.