Introduction: This survey aims to identify herb-chemotherapeutic drug combinations in a defined group of cancer patients and to explore possible clinical consequences of these combinations.
Methods: Herb-chemotherapeutic drug combinations were identified among adult cancer patients, and clinical consequences of the combinations were explored by literature searches in medical databases on possible mutual effects on similar cytochrome P-450 metabolising enzymes (CYPs) and/or the P-glycoprotein (P-gp) transporter.
Results: Among 42 cancer patients using herbal remedies concurrently with chemotherapy, 136 two-agent herb-drug combinations were registered and 47 different potential herb-drug interactions were identified on the level of CYP metabolism and P-gp transport in vitro. Garlic, ginger, green tea and noni juice were the herbal remedies most frequently used in such combinations. For 48 % of the herbal remedies identified no literature data exist on their interaction potentials. Clinical studies were available for four herbal remedies only. Minor clinical potential for CYP interactions in humans was indicated for green tea and Echinacea. P-gp interactions were only investigated for garlic, which showed a significant interaction potential both in vivo and in vitro.
Conclusion: The large number of in vitro potential herb-drug interactions identified urge for more clinical pharmacokinetic interaction studies in humans.