Dan Shen

Danshen inhibits CYP2C9-mediated warfarin hydroxylation (tanshinones inhibit both in vitro and in vivo), reduces warfarin protein binding to albumin (danshensu displaces warfarin), and exerts pharmacodynamic anticoagulant effects via antithrombin III-like activity, platelet aggregation inhibition, and promotion of fibrinolytic activity. Combined effect dramatically increases warfarin AUC and prothrombin time. Case reports of gross overanticoagulation and life-threatening bleeding are documented.

Danshen is CONTRAINDICATED in patients taking warfarin. Multiple case reports describe fatal and near-fatal bleeding complications. If a patient has been self-medicating with danshen, check INR immediately and hold warfarin until stable. If concurrent use is unavoidable (highly discouraged), reduce warfarin dose by 30-50% and monitor INR every 3-7 days.

Danshen inhibits platelet aggregation and promotes fibrinolytic activity. Combined with antiplatelet drugs, there is additive inhibition of platelet function via multiple pathways: Danshensu inhibits thromboxane synthesis, tanshinones reduce platelet activation, and clopidogrel blocks P2Y12 receptors. Clinical studies show significant pharmacodynamic herb-drug interactions in human subjects.

Avoid concurrent use of danshen with antiplatelet agents, particularly when combined (e.g., dual antiplatelet therapy). If used together, closely monitor for bleeding signs. Patients should avoid this combination especially before surgery or dental procedures. Discontinue danshen at least 2 weeks before elective procedures.

Danshen components interfere with fluorescence polarization immunoassay (FPIA) digoxin measurements, causing falsely elevated digoxin readings in vitro. In vivo, danshen may also affect P-glycoprotein transport of digoxin. This creates diagnostic confusion and potential dosing errors for patients monitored by digoxin assay.

Use MEIA (microparticle enzyme immunoassay) or mass spectrometry-based digoxin assays (not FPIA) in patients using danshen, or measure free digoxin concentration. Clinicians should be alerted that standard digoxin assays can yield false positives with danshen. Adjust clinical monitoring accordingly.

Tanshinones in danshen inhibit CYP3A4 in vitro, and single-dose danshen extract modestly inhibits CYP3A4 activity in healthy volunteers (midazolam pharmacokinetic study). Multiple-dose administration paradoxically may induce CYP3A4. This biphasic effect creates complexity in predicting interactions with sensitive CYP3A4 substrates.

Monitor CYP3A4-sensitive drug levels (cyclosporine, tacrolimus, simvastatin) closely when danshen use begins or is stopped. Be aware that single doses may inhibit while chronic use may induce CYP3A4. Transplant patients should avoid danshen entirely due to unpredictable immunosuppressant level changes.

Danshen has documented antihypertensive effects via vasorelaxation (tanshinones), inhibition of angiotensin-converting enzyme activity, and antioxidant protection of vascular endothelium (increased eNOS expression). Additive blood pressure lowering with conventional antihypertensives may cause symptomatic hypotension.

Monitor blood pressure closely when initiating or stopping danshen in hypertensive patients. The combination has been studied in Taiwanese patients (Fufang Danshen add-on) with modest BP-lowering results. Dose adjustment of antihypertensive drugs may be required.

Tanshinones from Salvia miltiorrhiza inhibit CYP1A2 in vitro. CYP1A2 substrates like theophylline (narrow therapeutic index), clozapine, and olanzapine may exhibit elevated plasma levels with concurrent danshen use, increasing risk of theophylline toxicity (arrhythmia, seizures) or clozapine toxicity (agranulocytosis, seizures).

Monitor theophylline serum levels closely when danshen is used concurrently. For clozapine, monitor for toxicity signs and consider dose reduction. This is a particularly important consideration in patients with epilepsy or heart conditions on theophylline therapy.