Coadministration of omeprazole (20 mg once daily) and darunavir/ritonavir (at a dose lower than recommended or with a different dosing regimen) had no effect on darunavir AUC, Cmax and Cmin. Darunavir coadministered with low dose ritonavir can be coadministered with proton pump inhibitors without dose adjustments.
Prezista Summary of Product Characteristics, Janssen-Cilag Ltd, June 2012.

The interaction between darunavir/ritonavir and omeprazole was evaluated in clinical studies and no dose adjustment is needed for either drug. Coadministration of omeprazole (20 mg once daily) and darunavir/ritonavir (400/100 mg twice daily) was studied in 16 subjects. There was no significant change in darunavir exposure (Cmax, AUC and Cmin increased by 2%, 4% and 8% respectively).
Prezista Prescribing Information, Tibotec Inc, June 2012.

The effect of darunavir/ritonavir (600/100 mg twice daily) on the activity of CYP2C9, 2D6 and 2C19 was investigated in 12 HIV- subjects using single doses of a probe cocktail containing warfarin (10 mg with vitamin K, CYP2C9), dextromethorphan (30 mg, CYP2D6) and omeprazole (40 mg, CYP2C19). The AUC ratio of omeprazole to 5-OH omeprazole decreased by 31%, suggesting induction of CYP2C19.
Cocktail study to investigate the in-vivo drug interaction potential of darunavir co-administered with low-dose ritonavir on cytochrome P450 enzymes 2D6, 2C9 and 2C19. Sekar V, Spinosa-Guzman S, Meyvisch P, et al. 9th International Workshop on Clinical Pharmacology of HIV Therapy, New Orleans, April 2008.

The effect of ranitidine (150 mg twice daily) and omeprazole (20 mg once daily) on the plasma pharmacokinetics of a non-licensed dose of darunavir/ritonavir (400/100 mg twice daily) was investigated in 12 HIV-negative volunteers. Treatment was given for 4 days with an additional morning dose on day 5, and regimens were separated by a washout period of 7 days. Compared with darunavir/ritonavir alone, no significant changes in darunavir pharmacokinetic parameters were observed during coadministration with either ranitidine or omeprazole. No dose adjustments are required when darunavir/ritonavir is coadministered with omeprazole or ranitidine.
Pharmacokinetic interaction between darunavir boosted with ritonavir and omeprazole or ranitidine in human immunodeficiency virus-negative healthy volunteers. Sekar VJ, Lefebvre E, De Paepe E, et al. Antimicrob Agents Chemother, 2007, 51(3): 958-961.