Guanfacine pharmacodynamic properties

Elimination of clonidine is 65% by renal excretion and 35% by liver metabolism, while guanfacine and its metabolites are excreted primarily in the urine, with approximately 50% as unchanged drug. These differences in elimination may account for differences in the pharmacodynamic properties of the two drugs. The behavioral effects of clonidine last only 3 to 6... 

Sorkin, E.M. and Heel, R.C. (1986) Guanfacine a review of the pharmacodynamic and pharmacikinetic properties, and therapeutic efficacy in the treatment of hypertension. Drugs 31 301—336. 

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