Dong Quai

Pharmacodynamic interaction: dong quai contains coumarin derivatives (ferulic acid, osthole) that inhibit platelet aggregation and have antithrombin activity. Animal studies show dong quai significantly increases prothrombin time (PT) without affecting warfarin plasma concentrations, confirming a pharmacodynamic rather than pharmacokinetic mechanism. A well-documented case report describes a patient on stable warfarin 5 mg/day who developed INR of 4.05 and 4.90 after adding dong quai 565 mg 1-2x daily; INR normalised after discontinuation.

Concurrent use of dong quai with warfarin should be avoided. If a patient insists on using dong quai, INR should be monitored weekly initially and with any dose change. Educate the patient on signs of bleeding (unexplained bruising, blood in urine/stool, prolonged bleeding).

Ferulic acid in dong quai inhibits TXA2/PGI2 synthesis and thromboxane B2 formation, reducing platelet aggregation through prostaglandin pathways. Osthole similarly inhibits platelet aggregation. Additive antiplatelet effect with aspirin (COX inhibition) or clopidogrel (ADP receptor blockade) increases haemorrhage risk.

Avoid combining dong quai with antiplatelet medications. If combination is unavoidable (e.g., patient uses dong quai for menstrual symptoms while on aspirin), monitor closely for signs of abnormal bleeding. Discontinue dong quai at least 2 weeks prior to surgery.

Dong quai has been traditionally promoted for its phytoestrogenic properties. However, a randomised, double-blind, placebo-controlled trial found that dong quai used alone did not produce significant estrogenic effects on the endometrium or vaginal cell maturation in postmenopausal women. Despite this, its coumarin constituents could theoretically modulate estrogenic activity. Theoretical interaction with exogenous estrogen therapy remains unvalidated clinically.

Inform patients using HRT or combined oral contraceptives about the theoretical interaction with dong quai. While clinical significance appears low, combination is not recommended in the absence of compelling benefit. Monitor for unexpected hormonal effects.

Dong quai root contains furanocoumarins (bergapten/5-methoxypsoralen, psoralen, imperatorin) which are potent photosensitisers that absorb UVA radiation and cause phototoxic reactions. When combined with other photosensitising drugs (e.g., tetracyclines, fluoroquinolones, thiazides, amiodarone), the risk of severe phototoxic skin reactions (sunburn, blistering, hyperpigmentation) is substantially increased.

Advise patients taking photosensitising medications to avoid dong quai. If dong quai is used, counsel on sun avoidance, use of broad-spectrum sunscreen, and protective clothing. Photosensitive patients (lighter skin types) are at greatest risk.

Ferulic acid in dong quai has been shown to modulate serotonergic neurotransmission (inhibiting platelet serotonin release and influencing 5-HT activity). Theoretical risk of additive serotonergic effects when combined with SSRIs/SNRIs. Additionally, dong quai coumarin constituents may weakly inhibit CYP1A2 and CYP2C9 in vitro, potentially altering metabolism of some antidepressants.

No documented clinical cases of serotonin syndrome with dong quai + SSRIs. Monitor for symptoms of serotonin excess (agitation, tremor, hyperthermia, diaphoresis) if combination is used. Combination is not recommended in vulnerable patients.

Dong Quai coumarins (osthole, angelicone) exert antiplatelet and mild anticoagulant effects. NSAIDs independently inhibit COX-1-mediated thromboxane A2 synthesis, reducing platelet aggregation. Co-administration produces additive antiplatelet and anticoagulant activity plus compounded gastrointestinal mucosal risk.

Caution when combining Dong Quai with NSAIDs. Monitor for abnormal bleeding (unusual bruising, blood in stools or urine, prolonged wound bleeding). Advise patients to disclose herbal use to prescribers managing pain or inflammation. Consider paracetamol as a safer alternative when possible.

Dong Quai root contains furanocoumarins (psoralen, bergapten, imperatorin) which are potent photosensitizing agents that intercalate DNA upon UVA activation. Co-administration with exogenous photosensitizers such as aminolevulinic acid creates additive photosensitization, dramatically increasing risk of phototoxic injury.

Avoid concurrent use. Discontinue Dong Quai at least 2 weeks before photodynamic therapy or aminolevulinic acid administration. Counsel patients to avoid prolonged sun or UV exposure while taking Dong Quai, particularly in combination with any photosensitizing medications (tetracyclines, fluoroquinolones, thiazides).

Human hepatocyte ex vivo studies showed Dong Quai is a CYP450 inducer (CYP2C9, CYP2C8, CYP2D6, CYP3A4), which could reduce plasma levels of CYP-metabolised chemotherapy agents. Furthermore, growth inhibition assays in 8 human cancer cell lines showed Dong Quai had overall antagonistic cytotoxic interactions with standard chemotherapy agents.

Advise against Dong Quai use during active chemotherapy. The herb may reduce antitumour drug efficacy via CYP induction and may antagonise cytotoxic activity in cancer cells. Oncologists should be informed of any herbal supplement use before and during cancer treatment.

Dong Quai exhibits estrogenic activity via phytoestrogenic constituents and ferulic acid-mediated ER binding. This may directly antagonise the anti-estrogenic mechanism of tamoxifen in oestrogen receptor-positive (ER+) breast cancer treatment, potentially reducing therapeutic efficacy and stimulating tumour growth.

Contraindicated in patients on tamoxifen for ER+ breast cancer. The estrogenic properties of Dong Quai are mechanistically incompatible with tamoxifen therapy. Patients should be explicitly counselled against use. Screen for Dong Quai use in all women on hormonal cancer therapies.

Dong Quai polysaccharides and ferulic acid have demonstrated hypoglycemic activity in animal models, including improved insulin sensitivity and glucose uptake. Concurrent use with antidiabetic agents may produce additive blood-glucose lowering, though clinical evidence in humans is limited and the effect magnitude is uncertain.

Monitor blood glucose more frequently when initiating or discontinuing Dong Quai in patients on antidiabetic medication. Be alert for signs of hypoglycemia (dizziness, diaphoresis, tremor, confusion). Clinical significance at standard doses is considered low, but caution is warranted at higher doses.