Zomep Mechanism of Action

Pharmacology: Pharmacokinetics: Omeprazole is rapidly but variably absorbed after oral doses. Absorption is not significantly affected by food. Omeprazole is acid-labile and the pharmacokinetics of the various formulations developed to improve oral bioavailability may vary. The absorption of omeprazole also appears to be dose- dependent, increasing the dosage above 40 mg has been reported to increase the plasma concentration in a non-linear fashion because of saturable first-pass hepatic metabolism. In addition, bioavailability is higher after long-term use. Bioavailability of omeprazole may be increased in elderly patients, in some ethnic groups such as Chinese, and in patients with hepatic impairment, but is not markedly affected in patients with renal impairment. On absorption, omeprazole is almost completely metabolized in the liver, primarily by the cytochrome P450 isoenzyme CYP2C19 to form hydroxy omeprazole, and to a small extent by CYP3A4 to form Omeprazole sulfone. The metabolites are inactive and are excreted mostly in the urine and to a lesser extent in bile. The elimination half-life from plasma is reported to be about 0.5 to 3 hours. Omeprazole is about 95% bound to plasma proteins.
Metabolism: The major enzyme involved in omeprazole metabolism is cytochrome P450 isoenzyme CYP2C19. This enzyme is polymorphically expressed and individuals who are deficient in the enzyme are poor metabolizers of Omeprazole. This occurs in about 3% of Caucasians and 15% of Chinese, Japanese and Koreans. These individuals have markedly higher plasma concentrations of Omeprazole and they may require dosage adjustment. Some Omeprazole is metabolized by CYP3A4 and some by CYP206 to form desmethylomeprazole.