Clinically-relevant chemotherapy interactions with complementary and alternative medicines in patients with cancer

Complementary and alternative medicines (CAMs), in particular herbal medicines, are commonly used by cancer patients in conjunction with chemotherapy treatment for their anticancer properties and supportive care. However, the effects of many of these herbs are not well-documented due to limited studies done on them. Severe herb-drug interactions (HDIs) have been recorded in some cases, and failure to recognize these harmful HDIs can lead to dire consequences in cancer patients. This study discusses clinically-relevant interactions between anticancer drugs (ACDs) and herbs classified into 7 categories: cancer treatment and prevention, immune-system-related, alopecia, nausea and vomiting, peripheral neuropathy and pain, inflammation, and fatigue. Some promising patents which contain these herbs and thus may manifest these interactions are also presented in this article. Pharmacokinetic interactions involved mainly induction or inhibition of the cytochrome P450 isozymes and p-glycoprotein, while pharmacodynamic interactions were related to increased risks of central nervous system-related effects, hepatotoxicity and bleeding, among others. Clinicians should be vigilant when treating cancer patients who take CAMs with concurrent chemotherapy since they face a high risk of HDIs. These HDIs can be minimized or avoided by selecting herb-drug pairs which are less likely to interact. Furthermore, close monitoring of pharmacological effects and plasma drug levels should be carried out to avoid toxicity and ensure adequate chemotherapeutic coverage in patients with cancer.