Phellodendron

Statins metabolized by CYP3A4 (simvastatin, atorvastatin, lovastatin) have increased plasma concentrations when co-administered with berberine, raising risk of myopathy and rhabdomyolysis. Berberine itself has lipid-lowering effects that can produce additive LDL reduction.

Consider pravastatin or rosuvastatin (minimal CYP3A4 metabolism) if Phellodendron is used. Monitor CK and for muscle pain if co-administering CYP3A4 statins.

Berberine (primary alkaloid in Phellodendron) 0.2 g three times daily increased cyclosporine A blood trough concentrations by up to 88.9% in renal transplant recipients through CYP3A4 inhibition in gut and liver plus P-glycoprotein inhibition. Elevated cyclosporine levels cause nephrotoxicity, hypertension, and neurotoxicity.

Avoid in transplant recipients or patients on cyclosporine for autoimmune indications. If used, monitor cyclosporine trough levels weekly and watch for nephrotoxicity.

Repeated oral berberine (300 mg TID × 14 days) in healthy volunteers decreased CYP2D6 activity as measured by a 9-fold increase in 0-8 h urinary dextromethorphan/dextrorphan ratio, demonstrating potent CYP2D6 inhibition in vivo.

Avoid combination especially at antitussive doses >60 mg/day. Elevated dextromethorphan can cause serotonin syndrome, dissociative effects. Consider alternative antitussive.

Losartan is a prodrug requiring CYP2C9-mediated conversion to its active metabolite E-3174. Berberine 300 mg TID in healthy volunteers doubled the losartan/E-3174 urinary ratio indicating CYP2C9 inhibition and reduced formation of the active antihypertensive metabolite.

Monitor blood pressure response to losartan. Consider alternative ARB not reliant on CYP2C9 activation (valsartan, irbesartan) if Phellodendron/berberine is required.

Berberine inhibits CYP3A4 in human liver microsomes (IC50 ~400 μM) and in vivo, increasing midazolam AUC. Elevated midazolam levels prolong sedation, amnesia, and risk of respiratory depression.

Stop Phellodendron at least 1 week before procedures using midazolam sedation. For inpatient sedation, use reduced midazolam doses and enhanced respiratory monitoring.

Berberine activates AMPK and improves insulin sensitivity, producing clinically meaningful glucose lowering comparable to metformin in type 2 diabetes. Combined with metformin, additive hepatic glucose suppression and hypoglycemia risk is documented; pharmacokinetic interaction may additionally increase metformin exposure.

Monitor fasting glucose weekly when initiating. Metformin dose reduction of 500 mg may be needed. Counsel on hypoglycemia symptoms.

Digoxin is a P-glycoprotein substrate; berberine inhibits intestinal P-gp efflux (demonstrated in rat everted-sac, Ussing chamber, and Caco-2 models), potentially increasing digoxin absorption and plasma levels. Given digoxin's narrow therapeutic index, this creates arrhythmia and toxicity risk.

Avoid combination. If unavoidable, check digoxin trough levels within 7 days and watch for nausea, visual halos, or arrhythmia.

Warfarin's more active S-enantiomer is metabolized by CYP2C9. Berberine's CYP2C9 inhibition (demonstrated via losartan clearance) predicts reduced warfarin clearance and elevated INR. Additionally, berberine has mild antiplatelet effects in vitro.

Check INR 3-5 days after starting Phellodendron and weekly for the first month. Warn patients about bleeding signs. Reduce warfarin dose by 10-20% preemptively in patients with labile INR.