Due to polypharmacy and the rising popularity of so-called alternative medicines (SCAM), oncology patients are particularly at risk of drug-drug interactions (DDI) or herb-drug interactions (HDI). The aims of this study were to assess DDI and HDI in outpatients taking oral anticancer drugs.
All prescribed and non-prescribed medications, including SCAMs, were prospectively collected by hospital pharmacists during a structured interview with the patient. DDI and HDI were analyzed using four interaction software programs: Thériaque®, Drugs.com®, Hédrine, and Memorial Sloan Kettering Cancer Center (MSKCC) database. All detected interactions were characterized by severity, risk, and action mechanism. The need for pharmaceutical intervention to modify drug use was determined on a case-by-case basis.
A total of 294 patients were included, with a mean age of 67 years [55-79]. The median number of chronic drugs per patient was 8 [1-29] and 55% of patients used at least one SCAM. At least 1 interaction was found for 267 patients (90.8%): 263 (89.4%) with DDI, 68 (23.1%) with HDI, and 64 (21.7%) with both DDI and HDI. Only 13% of the DDI were found in Thériaque® and Drugs.com® databases, and 125 (2.5%) were reported with a similar level of risk on both databases. 104 HDI were identified with only 9.5% of the interactions found in both databases. 103 pharmaceutical interventions were performed, involving 61 patients (20.7%).
The authors concluded that potentially clinically relevant drug interactions were frequently identified in this study, showing that several databases and structured screening are required to detect more interactions and optimize medication safety.
These data imply that DDIs are more frequent than HDIs. This does, however, not tell us which are more important. One crucial difference between DDIs and HDIs is that the former are usually known to the oncology team who should thus be able to prevent them or deal with them appropriately; in contrast, HDIs are often not known to the oncology team because many patients fail to disclose the fact that they take herbal remedies. Some forget, some do not think of herbals as medicine, others may be worried about their physician’s reaction.
It follows that firstly, conventional healthcare practitioners should always ask about the usage of herbal remedies, and secondly, they need to be informed about which herbal remedy might interact with which drug. The first can easily be implemented into routine history-taking; the second is more problematic, not least because our knowledge about HDIs is still woefully incomplete. In view of this, it might often be wise to tell patients to stop taking herbal remedies while they are on prescription drugs.