GUANABENZ ACETATE

antihypertensive

Guanabenz acetate, [(2,6-dichlorobenzylidene)amino]guanidine monoacetate (Wytensin), is acentral 2-adrenergic agonist that reduces the release of norepinephrinefrom the neuron when stimulated. The effect ofthe drug results in decreased sympathetic tone in the heart,kidneys, and peripheral blood vessels. The drug does not produceorthostatic hypotension.

α 2 -adrenergic agonist and IGRS (imidazoline I 2 binding site) selective ligand.

The oral bioavailability of guanabenz is 70 to 80%. Following an oral dose, the hypotensive effect of guanabenz begins within 1 hour, peaks within 2 to 7 hours, and is diminished within 6 to 8 hours. It has an elimination half-life averaging 4 to 14 hours. The blood pressure response can persist for at least 12 hours. Following IV dosing, guanabenz is distributed into the CNS, with brain concentrations 3 to 70 times higher than concurrent plasma concentrations. Guanabenz is approximately 90% bound to plasma proteins. In patients with hepatic or renal impairment, its elimination half-life may be prolonged.
Guanabenz is metabolized principally by hydroxylation to its inactive metabolite, 4-hydroxyguanabenz, which is eliminated in the urine as its glucuronide (major) and sulfate conjugates. Guanabenz and its inactive metabolites are excreted principally in urine, with approximately 70 to 80% of its oral dose excreted in urine within 24 hours and approximately 10–30% in feces via enterohepatic cycling. Approximately 40% of an oral dose of guanabenz is excreted in urine as 4-hydroxyguanabenz and its glucuronide, and less than 5% is excreted unchanged. The remainder is excreted as unidentified metabolites and their conjugates.

Overall, the therapeutic applications for guanabenz are similar to those of clonidine and other α2-adrenergic agonists. One advantage for guanabenz is its once-a-day dosing schedule. Guanabenz has been used in diabetic patients with hypertension without adverse effect on the control of or therapy for diabetes, and it has been effective in hypertensive patients with chronic obstructive pulmonary disease, including asthma, chronic bronchitis, or emphysema. Guanabenz has been used alone or in combination with naltrexone in the management of opiate withdrawal in patients physically dependent on opiates and undergoing detoxification. Guanabenz also has been used as an analgesic in a limited number of patients with chronic pain

Overall, the frequency of adverse effects produced by guanabenz is similar to that produced by clonidine and the other α2-adrenergic agonists, but the incidence is lower. As with the other centrally active sympatholytics (e.g., clonidine), abrupt withdrawal of guanabenz may result in rebound hypertension, but the withdrawal syndrome symptoms appear to be less severe.