Pharmacology: Pharmacokinetics: Irbesartan is rapidly absorbed from the gastrointestinal tract with an oral bioavailability of 60% to 80%. Peak plasma concentrations of Irbesartan occur 1.5 to 2 hours after an oral dose. Irbesartan is about 96% bound to plasma proteins. It undergoes some metabolism in the liver, primarily by the cytochrome P450 isoenzyme CYP2C9, to inactive metabolites. It is excreted as unchanged drug and metabolites in the bile and in urine; about 2% as unchanged drug. The terminal elimination half-life is about 11 to 15 hours. Hydrochlorothiazide is fairly rapidly absorbed from the gastrointestinal tract. It is reported to have bioavailability of about 65 to 75%. It has been estimated to have plasma half-life of between about 5 and 15 hours and appears to be preferentially bound to red blood cells. It is excreted mainly unchanged in the urine. Hydrochlorothiazide crosses the placental barrier and distributed into breast milk.