A 77-year-old female participant with a history of HIV infection, diabetes, osteoporosis, hypertension, and depression presented to the physician with gastro-esophageal reflux disease (GERD) symptoms. Her current medication regimen consisted of the following:
• abacavir-lamivudine (Epzicom) 600mg/300mg PO QD
• atazanavir (Reyataz) 300mg PO QD
• carvedilol 6.25mg PO BID
• chlorthalidone 12.5 mg PO QD
• lisinopril 40mg PO QD
• metformin 500mg PO BID
• ritonavir (Norvir) 100mg PO QD
For the newly diagnosed GERD, the physician e-prescribed omeprazole (Prilosec) 40mg daily for 8 weeks (then dose to be tapered to 20mg) and ranitidine (Zantac) 150mg QHS. In performing the prospective drug regimen review, the CareKinesis clinical pharmacist identified a potentially significant drug-drug interaction. Both proton pump inhibitors (PPIs – omeprazole) and H2-antagonists (ranitidine) reduce the bioavailability of atazanavir by as much as 90% due to pH increases, which may result in HIV treatment failure. Thus, if used concomitantly with atazanavir, omeprazole dose is not recommended to exceed 20mg daily.
CLINICAL PHARMACIST RECOMMENDATION
The clinical pharmacist alerted the physician of this potentially significant drug-drug interaction and offered to assist with counseling the participant regarding the safest non-pharmacologic options for treating GERD. By implementing lifestyle modifications, the participant’s heartburn symptoms may be alleviated or even avoided altogether. If lifestyle modifications were not possible or were ineffective, the clinical pharmacist recommended that the physician consider a trial of calcium carbonate (Tums), and cautioned that the calcium carbonate must be administered 1 hour before or 2 hours after atazanavir in order to minimize the risk of drug-drug interaction.
After weighing the benefits and risks, the physician decided to trial the ranitidine therapy. To avoid the potentially significant drug-drug interaction, the clinical pharmacist recommended that the participant take the ranitidine at either the same time as the atazanavir dose or 10 hours after the atazanavir dose, as per manufacturer prescribing information.
The physician accepted the recommendation, and the participant was counseled to separate the dosing 10 hours apart: atazanavir dosed in the morning and ranitidine dosed at bedtime. Viral loads will be continually re-assessed due to concern with potential HIV treatment failure.