Interactions : אינטראקציות

4.5     Interaction with other medicinal products and other forms of interaction
Effects of omeprazole on the pharmacokinetics of other active substances Active substances with pH dependent absorption

The decreased intragastric acidity during treatment with omeprazole might increase or decrease the absorption of active substances with a gastric pH dependent absorption.
Nelfinavir, Atazanavir
The plasma levels of Nelfinavir and Atazanavir are decreased in case of co-administration with omeprazole.
Concomitant administration of omeprazole with Nelfinavir is contraindicated (see section 4.3).
Co-administration of omeprazole (40 mg once daily) reduced mean Nelfinavir exposure by ca. 40% and the mean exposure of the pharmacologically active metabolite M8 was reduced by ca. 75-90%.
The interaction may also involve CYP2C19 inhibition.
Concomitant administration of omeprazole with Atazanavir is not recommended (see section 4.4).
Concomitant administration of omeprazole (40 mg once daily) and Atazanavir 300 mg/Ritonavir 100 mg to healthy volunteers resulted in a 75% decrease of the Atazanavir exposure. Increasing the Atazanavir dose to 400 mg did not compensate for the impact of omeprazole on Atazanavir exposure. The co-administration of omeprazole (20 mg once daily) with Atazanavir         400 mg/ritonavir 100 mg to healthy volunteers resulted in a decrease of approximately 30% in the
Atazanavir exposure as compared to Atazanavir 300 mg/ritonavir 100 mg once daily.
Digoxin

Concomitant treatment with omeprazole (20 mg daily) and Digoxin in healthy subjects increased the bioavailability of Digoxin by 10%. Digoxin toxicity has been rarely reported. However caution should be exercised when omeprazole is given at high doses in elderly patients. Therapeutic drug monitoring of Digoxin should be then be reinforced.
Clopidogrel

Results from studies in healthy subjects have shown a pharmacokinetic (PK)/pharmacodynamic (PD) interaction between Clopidogrel (300 mg loading dose/75 mg daily maintenance dose) and omeprazole (80 mg p.o. daily) resulting in a decreased exposure to the active metabolite of clopidogrel by an average of 46% and a decreased maximum inhibition of (ADP induced) platelet aggregation by an average of 16%.
Inconsistent data on the clinical implications of a PK/PD interaction of omeprazole in terms of major cardiovascular events have been reported from both observational and clinical studies. As a precaution, concomitant use of omeprazole and Clopidogrel should be discouraged (see section         4.4).

Other active substances

The absorption of Posaconazole, Erlotinib, Ketoconazole and Itraconazole is significantly reduced and thus clinical efficacy may be impaired. For Posaconazole and Erlotinib concomitant use should be avoided.

Active substances metabolised by CYP2C19

Omeprazole is a moderate inhibitor of CYP2C19, the major omeprazole metabolising enzyme.
Thus, the metabolism of concomitant active substances also metabolised by CYP2C19, may be decreased and the systemic exposure to these substances increased. Examples of such drugs are R- warfarin and other vitamin K antagonists, cilostazol, diazepam and phenytoin.

Cilostazol

Omeprazole, given in doses of 40 mg to healthy subjects in a cross-over study, increased Cmax and AUC for Cilostazol by 18% and 26% respectively, and one of its active metabolites by 29% and 69% respectively.

Phenytoin

Monitoring Phenytoin plasma concentration is recommended during the first two weeks after initiating omeprazole treatment and, if a Phenytoin dose adjustment is made, monitoring and a further dose adjustment should occur upon ending omeprazole treatment.

Unknown mechanism

Saquinavir
Concomitant administration of omeprazole with Saquinavir/Ritonavir resulted in increased plasma levels up to approximately 70% for Saquinavir associated with good tolerability in HIV-infected patients.

Tacrolimus

Concomitant administration of omeprazole has been reported to increase the serum levels of Tacrolimus. A reinforced monitoring of Tacrolimus concentrations as well as renal function (creatinine clearance) should be performed, and dosage of Tacrolimus adjusted if needed.

Methotrexate

When given together with proton-pump inhibitors, Methotrexate levels have been reported to increase in some patients. In high-dose Methotrexate administration a temporary withdrawal of omeprazole may need to be considered.

Effects of other active substances on the pharmacokinetics of omeprazole Inhibitors of CYP2C19 and/or CYP3A4

Since omeprazole is metabolised by CYP2C19 and CYP3A4, active substances known to inhibit CYP2C19 or CYP3A4 (such as clarithromycin and voriconazole) may lead to increased omeprazole serum levels by decreasing omeprazole’s rate of metabolism. Concomitant Voriconazole treatment resulted in more than doubling of the omeprazole exposure. As high doses of omeprazole have been well-tolerated adjustment of the omeprazole dose is not generally required. However, dose adjustment should be considered in patients with severe hepatic impairment and if long-term treatment is indicated.
Inducers of CYP2C19 and/or CYP3A4

Active substances known to induce CYP2C19 or CYP3A4 or both (such as Rifampicin and St John’s wort) may lead to decreased omeprazole serum levels by increasing omeprazole’s rate of metabolism.