Inhibition of CYP2C19 may block the activation of clopidogrel, which could reduce its effects.Almost all benzodiazepines are metabolised by the CYP3A4 and CYP2D6 pathways, and inhibition of these enzymes results in a higher area under the curve (i.e., the total effect over time of a given dose). Other examples of drugs dependent on CYP3A4 for their metabolism are escitalopram, warfarin, oxycodone, tramadol, and oxymorphone. The concentrations of these drugs may increase if they are used concomitantly with omeprazole.Omeprazole is also a competitive inhibitor of p-glycoprotein, as are other PPIs.Drugs that depend on an acidic stomach environment (such as ketoconazole or atazanavir) may be poorly absorbed, whereas acid-labile antibiotics (such as erythromycin which is a very strong CYP3A4 inhibitor) may be absorbed to a greater extent than normal due to the more alkaline environment of the stomach.St. Johns wort (Hypericum perforatum) and Gingko biloba significantly reduce plasma concentrations of omeprazole through induction of CYP3A4 and CYP2C19.Proton-pump inhibitors like omeprazole have been found to increase the plasma concentrations of methotrexate. Pharmacology
Omeprazole irreversibly blocks the enzyme system on parietal cells that is needed for the secretion of gastric acid. It is a specific H+/K+ATPase inhibitor. This is the enzyme needed for the final step in the secretion of gastric acid. Mechanism of action
Omeprazole is a selective and irreversible proton pump inhibitor. It suppresses stomach acid secretion by specific inhibition of the H+/K+-ATPase system found at the secretory surface of gastric parietal cells.
Pregnancy and breastfeeding
The safety of using omeprazole has not been established in pregnant or breastfeeding women. Epidemiological data do not show an increased risk of major birth defects after maternal use of omeprazole during pregnancy.No clinical trials have deeply evaluated the potential consequences of the use of omeprazole in breastfeeding. However, the pharmacokinetics of the omeprazole molecule strongly suggest the safety of omeprazole use during breastfeeding:

Omeprazole has a high plasma protein binding rate (95%), indicating that a little amount of drug is transferred to the milk duct during breast milk formation. Omeprazole needs to be administered in an enteric-coated formulation due to its rapid degradation in the acidic conditions of the stomach. This suggests that most of the free molecules ingested by the infant are likely degraded before being absorbed.Omeprazole at normal doses is likely safe during breastfeeding. Interactions
Important drug interactions are rare. However, the most significant major drug interaction concern is the decreased activation of clopidogrel when taken together with omeprazole. Although still controversial, this may increase the risk of stroke or heart attack in people taking clopidogrel to prevent these events. This interaction is possible because omeprazole is an inhibitor of the enzymes CYP2C19 and CYP3A4. Clopidogrel is an inactive prodrug that partially depends on CYP2C19 for conversion to its active form.