Schisandra

Schisandra extracts potently inhibit CYP3A4/5 and P-glycoprotein via multiple dibenzocyclooctadiene lignans: schisantherin A and schisandrin A/B exhibit time-dependent (mechanism-based) CYP3A4 inhibition; gomisin C irreversibly inactivates CYP3A4 more potently than ketoconazole (IC50 0.059 µM). In a rigorous clinical pharmacokinetic study of 12 healthy male volunteers, Schisandra sphenanthera extract (SchE) treatment for 13 days produced mean AUC increases of 164.2% (95% CI: 70.1-258.4%), Cmax increases of 227.1% (95% CI: 155.8-298.4%), and 49% reduction in tacrolimus clearance. The 90% CI for the AUC ratio was 187.3-341.2%. CYP3A5 genotype strongly influences the magnitude of interaction: CYP3A5 non-expressers experience greater relative increases.

Schisandra is contraindicated in patients receiving tacrolimus without intensive therapeutic drug monitoring. If co-administration occurs (occasionally intentional in Chinese transplant medicine to reduce tacrolimus costs), tacrolimus trough levels must be monitored every 2-3 days with dose adjustment as needed. Transplant pharmacists and physicians must specifically screen patients for Schisandra/Wu Wei Zi/Wuzhi capsule use. Any change in Schisandra supplementation can cause dangerous fluctuations in tacrolimus exposure.

Schisandra sphenanthera extract (SchE) inhibits intestinal and hepatic CYP3A4/5 via potent lignan-mediated inhibition. In a clinical pharmacokinetic study of 12 healthy male volunteers, SchE (3 capsules twice daily for 7 days) increased oral midazolam AUC by 119.4% (95% CI: 83.9-155.0%), AUMC by 183.4%, and Cmax by 85.6% (all P<0.01 or P<0.05). The mechanism involves reduced first-pass intestinal and hepatic CYP3A4-mediated metabolism and possible P-gp inhibition, markedly increasing benzodiazepine bioavailability. In human liver microsomes, gomisin A, C, and G inhibit CYP3A4 with IC50 values of 1.86, 0.059, and 0.19 µM respectively.

Avoid co-administering Schisandra with CYP3A4-metabolized sedating benzodiazepines. If unavoidable, initiate benzodiazepine at the lowest effective dose with close monitoring for excessive sedation, respiratory depression, and prolonged hypnotic effects. Apply equal caution to other CYP3A4-metabolized sedatives including alprazolam, triazolam, and buspirone. In operative settings, anesthesiologists should be informed of concurrent Schisandra use.

Schisandra lignans (schisandrin B and gomisin A) are documented inhibitors of both CYP3A4 and P-glycoprotein, which are the two primary determinants of cyclosporine bioavailability and clearance. Inhibition of both pathways synergistically increases cyclosporine oral bioavailability and reduces systemic clearance, potentially producing supratherapeutic cyclosporine concentrations. Cyclosporine has a narrow therapeutic index, and elevated levels cause nephrotoxicity, neurotoxicity, and hypertension. In vitro, gomisin C is a stronger CYP3A4 inhibitor than ketoconazole, suggesting potent clinical interaction potential with cyclosporine.

Monitor cyclosporine whole-blood trough concentrations closely if Schisandra is co-administered. Cyclosporine dose reduction may be required (potentially significant). Assess renal function (serum creatinine, eGFR), blood pressure, and other cyclosporine-related adverse effects regularly. Transplant patients must not self-initiate Schisandra or Wu Wei Zi products without informing their transplant physician and pharmacist.

Schisandra chinensis activates the pregnane X receptor (PXR) via key constituents including schisandrol A/B, schisandrin, and selected gomisin H analogues. PXR activation induces expression of CYP3A4, CYP2C9, and MDR2/MRP2 (drug efflux transporter). A rat pharmacokinetic study showed Wu Wei Zi extract increased warfarin clearance by inducing CYP-mediated warfarin metabolism, resulting in reduced plasma warfarin exposure and potentially sub-therapeutic anticoagulation. Note: At lower doses or with specific formulations, schisandra lignans may also inhibit CYP2C9, complicating directional prediction; the net effect in humans is not confirmed clinically.

Monitor INR closely when initiating, changing dose, or discontinuing Schisandra in patients on warfarin. Sub-therapeutic anticoagulation (falling INR) may require warfarin dose increases to maintain target INR. Conversely, discontinuation of Schisandra may cause INR to rise. Advise patients to keep warfarin prescriber informed of any herbal supplement use and to report changes in bleeding pattern or thrombotic symptoms.

Schisandra lignans, particularly schisandrin B and gomisin A, are documented inhibitors of P-glycoprotein (P-gp/ABCB1) efflux transporter. In a clinical pharmacokinetic study of 12 healthy male volunteers, Schisandra chinensis extract (300 mg twice daily for 14 days) significantly increased talinolol (a P-gp probe substrate) AUC by 47%, Cmax by 51%, and t1/2 by 7% compared to talinolol alone, via P-gp inhibition. This interaction predicts increased oral bioavailability and systemic exposure for any drug that is a P-gp substrate, including digoxin, fexofenadine, and the direct oral anticoagulant dabigatran.

Monitor serum levels and clinical effects of P-gp substrates with narrow therapeutic indices when co-administered with Schisandra. For digoxin, monitor for toxicity signs (bradycardia, visual disturbances, nausea, fatigue) and check digoxin levels. For dabigatran, monitor for bleeding. Patients receiving Schisandra and digoxin simultaneously may require digoxin dose adjustment. Apply similar caution to other P-gp substrates.

Simvastatin and atorvastatin undergo extensive first-pass CYP3A4-mediated metabolism. Schisandra sphenanthera extract (Wuzhi capsule) has documented inhibitory effects on the bioavailability of simvastatin and atorvastatin in pre-clinical models, significantly increasing statin AUC and plasma concentrations. Elevated statin concentrations increase the risk of statin-associated myopathy, rhabdomyolysis, and hepatotoxicity. In contrast, rosuvastatin, which is minimally metabolized by CYP3A4 and eliminated primarily by biliary excretion, was not significantly affected by Schisandra co-administration in rat studies, making it a safer statin alternative.

In patients on simvastatin or atorvastatin who are taking Schisandra supplements, monitor for statin myopathy symptoms (muscle pain, weakness, dark urine suggestive of myoglobinuria) and measure creatine kinase if symptoms develop. Consider switching to rosuvastatin or pravastatin (less CYP3A4-dependent) as safer alternatives when Schisandra cannot be discontinued. Advise patients not to exceed maximum approved simvastatin doses (40 mg) and to report muscle symptoms promptly.

Schisandra lignans (gomisin B, C, G) are potent CYP3A4 inhibitors with gomisin C demonstrating mechanism-based irreversible inactivation of CYP3A4 stronger than ketoconazole itself (IC50 <0.059 microM). Co-administration with azole antifungals that are also CYP3A4 substrates increases their plasma concentrations. Additionally, P-glycoprotein inhibition by schisandra further elevates systemic exposure of azoles.

Avoid concurrent use of Schisandra with azole antifungals; if necessary, reduce azole dose and monitor for increased antifungal adverse effects (hepatotoxicity, QT prolongation). Therapeutic drug monitoring of itraconazole levels is advisable.

Schisandra extract significantly increases paclitaxel oral bioavailability by 2-3 fold via combined CYP3A4 and CYP2C8 inhibition and P-glycoprotein inhibition in preclinical models. Schisandrol B increases paclitaxel AUC by inhibiting both intestinal CYP3A4 and P-gp. This dramatically elevates paclitaxel plasma levels, increasing its toxicity risk (neutropenia, peripheral neuropathy, cardiotoxicity).

Contraindicated to combine Schisandra with paclitaxel or other narrow therapeutic index chemotherapy drugs. Inform oncologist of any Schisandra use before initiating cancer chemotherapy. This interaction is potentially life-threatening.

All HIV protease inhibitors and many NNRTIs are CYP3A4 substrates and P-gp substrates. Schisandra potent inhibition of both CYP3A4 and P-glycoprotein can dramatically increase plasma levels of antiretrovirals (e.g., lopinavir, ritonavir). Elevated ritonavir and lopinavir levels risk cardiac toxicity, hepatotoxicity, and QT prolongation. Some evidence also suggests potential interactions with NNRTI drug levels.

Avoid concurrent use of Schisandra with antiretroviral therapy. Inform HIV physicians of any Schisandra supplement use; this interaction may require complete discontinuation of Schisandra to avoid life-threatening drug toxicity. Monitor viral load and CD4 count if unavoidable.

Schisandra chinensis extract significantly inhibits rat hepatic CYP3A, CYP2D2, and CYP1A2 in vivo. Sertraline is listed as a known CYP3A4 and P-gp substrate influenced by Schisandra extract in published pharmacokinetic models. Increased plasma concentrations of CYP3A4-metabolized antipsychotics and antidepressants may increase risk of QT prolongation and sedative toxicity.

Monitor psychiatric drug plasma levels and adverse effects when combining Schisandra with antidepressants or antipsychotics metabolized by CYP3A4. Reduce antipsychotic dose cautiously if co-administration is necessary and monitor ECG for QTc prolongation.