Drug Interaction Between Rabeprazole and Oxybutynin
There is no clinically significant drug interaction between rabeprazole and oxybutynin, and these medications can be safely co-administered without dose adjustment. 1, 2
Mechanism and Evidence
Pharmacokinetic Compatibility
Rabeprazole undergoes almost complete, mainly non-enzymatic metabolism with minimal involvement of CYP3A4 and CYP2C19, and renal elimination of metabolites 2
Rabeprazole demonstrates minimal effect on other drug metabolism in vivo studies, with no noteworthy impact on medications metabolized through cytochrome P450 pathways 2
Extended-release oxybutynin bioavailability is not substantially altered by proton pump inhibitors, as demonstrated in controlled studies where omeprazole (a PPI with higher interaction potential than rabeprazole) showed AUC ratios for oxybutynin and its active metabolite N-desethyloxybutynin falling within the 80-125% bioequivalence range 1
Comparative PPI Interaction Profiles
Rabeprazole has a lower potential for drug interactions compared to omeprazole, which has high affinity for CYP2C19 and moderate affinity for CYP3A4 3
Among proton pump inhibitors, pantoprazole and rabeprazole demonstrate the lowest propensity for clinically relevant drug interactions, particularly compared to omeprazole and esomeprazole 4, 5, 3
Clinical Application
Prescribing Considerations
No dose adjustment is required for either medication when rabeprazole and oxybutynin are co-administered 1, 2
Standard dosing can be maintained: rabeprazole 20 mg daily for acid-related disorders and oxybutynin per indication (typically 5-15 mg daily for immediate-release or 5-30 mg daily for extended-release formulations) 4, 6, 7
Monitoring Requirements
Routine monitoring beyond standard clinical assessment is not necessary for this drug combination 1, 2
Monitor for anticholinergic side effects of oxybutynin (dry mouth, constipation, urinary retention) as these are medication-specific rather than interaction-related 4
Avoid oxybutynin in patients with narrow-angle glaucoma or impaired gastric emptying, as these are contraindications to anticholinergic therapy regardless of PPI co-administration 4
Important Caveats
The slight increase in digoxin concentrations with rabeprazole (due to P-glycoprotein interaction) is not relevant to oxybutynin, which is not a P-glycoprotein substrate 2
Gastric pH elevation from rabeprazole does not affect oxybutynin absorption from extended-release formulations, as confirmed by bioequivalence studies 1