Black Pepper

Piperine reduces first-pass metabolism of propranolol (a high-extraction CYP2D6/CYP1A2 substrate), producing an earlier tmax and higher Cmax and AUC. In a crossover study, piperine 20 mg/day for 7 days significantly increased propranolol bioavailability in healthy volunteers.

Monitor blood pressure and heart rate when patients on propranolol consume piperine-standardized supplements. Dose reduction of propranolol may be required.

Piperine inhibits CYP1A2 (the main theophylline-metabolizing enzyme), producing higher Cmax, longer elimination half-life, and greater AUC in healthy volunteers given 20 mg piperine daily for 7 days with a 150 mg theophylline dose.

Theophylline has a narrow therapeutic index. Avoid piperine-containing supplements or monitor theophylline levels closely if co-administered; watch for nausea, tachycardia, arrhythmia, or seizures that signal toxicity.

Piperine inhibits both intestinal P-glycoprotein (IC50 74.1 microM in Caco-2 cells) and CYP3A4 (Ki 44-77 microM), which together account for most of cyclosporine's first-pass elimination. Co-administration is predicted to raise cyclosporine plasma levels.

Transplant and autoimmune patients on cyclosporine should avoid piperine-standardized supplements. If dietary black pepper is heavy, monitor cyclosporine trough levels and creatinine; consider 10-15% dose reduction.

Piperine is a selective non-competitive inhibitor of CYP3A4 (IC50 5.5 microM, Ki 5.4 microM) and a mechanism-based inactivator. Pretreatment with piperine 15 mg/day for 3 days in 20 healthy volunteers reduced midazolam clearance and prolonged its half-life.

Expect prolonged sedation and enhanced amnestic effects. Reduce midazolam dose or avoid piperine-containing supplements before procedural sedation or anxiolytic use.

Piperine inhibits intestinal P-glycoprotein, the main efflux transporter for fexofenadine. In 12 healthy subjects, piperine 20 mg/day for 10 days increased fexofenadine AUC by 68% without significantly changing half-life.

Clinically modest; monitor for exaggerated antihistaminic effect (drowsiness, dry mouth). Consider lower fexofenadine dose if using piperine-standardized products chronically.

Piperine inhibits CYP2C9 and CYP3A4 (the principal enzymes metabolizing S- and R-warfarin) and displaces warfarin from plasma protein binding sites. Animal studies show altered warfarin pharmacokinetics and anticoagulation when co-administered.

Advise patients on warfarin to avoid piperine-standardized supplements. If heavy dietary black pepper or piperine exposure is expected, monitor INR more frequently and anticipate dose adjustment.

Piperine inhibits P-glycoprotein-mediated efflux and CYP3A4, increasing rifampin absorption. In tuberculosis patients, piperine co-administration has been used to boost rifampin blood levels (the basis of fixed-dose 'bioenhanced' formulations).

Intentional combination can lower required rifampin dose but may also increase hepatotoxicity risk. Monitor LFTs and treat piperine dose as a deliberate pharmacokinetic modifier, not incidental.

Piperine inhibits CYP2C9 (the primary enzyme metabolizing phenytoin) and intestinal P-glycoprotein, increasing phenytoin absorption and plasma concentrations. In healthy volunteers and epilepsy patients, piperine 20 mg/day modestly increased phenytoin plasma concentrations and AUC.

Monitor phenytoin serum levels and signs of toxicity (nystagmus, ataxia, sedation) when patients consume piperine-containing supplements or heavy black pepper intake. Anticipate potential need for dose reduction.

Piperine is a mechanism-based inhibitor of CYP3A4, the primary enzyme metabolizing carbamazepine. In 12 healthy subjects, piperine 20 mg/day for 10 days increased carbamazepine AUC by 48% after a single 200 mg dose.

Advise patients on carbamazepine to avoid piperine-standardized supplements (e.g., BioPerine) and limit large dietary black pepper intake. Monitor carbamazepine levels and watch for neurotoxicity (diplopia, ataxia, sedation) if co-administered.

Piperine inhibits CYP2C9, the primary enzyme metabolizing diclofenac. In 12 healthy subjects, piperine 20 mg/day for 10 days increased diclofenac AUC by 68% and prolonged its half-life by 34%.

Counsel patients using piperine-containing supplements or large amounts of black pepper with chronic NSAID therapy to monitor for GI bleeding, renal impairment, and other NSAID toxicities. Consider alternative analgesic or reduce NSAID dose.