Background and importance Cancer pain management is a recurrent topic in many oncology pharmacies. Drug to drug interactions with patients’ current drugs, together with other parameters, is routinely assessed by pharmacists to obtain maximum efficacy with tolerable side effects.

Aim and objectives The aim was to evaluate drug-to-drug potential interactions with analgesics for mild to moderate pain in patients receiving oral cancer treatment.

Material and methods This was a retrospective observational study. All cancer patients treated with oral antineoplastic drugs at an oncology pharmacy unit were included in the analysis. The study period was from January to December 2019. Analgesics for mild pain (acetaminophen, NSAIDs) and mild to moderate pain (weak opioids) were included, according to ESMO Clinical Practice Guidelines for the management of cancer pain in adult patients (Fallon et al, 2018). For each patient, drug-to-drug interactions for 17 analgesics were evaluated using the Lexicomp database. Risk was rated as A (no interaction), B (no action needed), C (monitor therapy), D (modify regimen) or X (avoid combination).

Results 541 patients, receiving 46 different drugs for cancer treatment, were seen by an oncology pharmacist. All had their potential drug-to-drug interactions checked to assess available options for analgesia. Most patients (88%) had a potential clinically significant interaction between treatment and at least one of the analgesics studied.

78% of patients had at least one analgesic contraindicated due to potential interactions. In all of these patients, the contraindicated drug was metamizole (dipyrone), as it increases the myelosuppressive effect of the oncology drug. A few patients (0.9%) also had a weak opioid contraindicated as it enhances the depressive effect in the CNS. In 19% of patients, it was necessary to modify treatment, and in 20% an appropriate monitoring plan was recommended.

Conclusion and relevance Most cancer patients receiving anticancer oral drugs could have clinically relevant potential drug-to-drug interactions with drugs used for analgesia for mild and mild–moderate cancer pain. Oncology pharmacists should be aware of this and routinely check for potential interactions with anticancer treatment and analgesics, as part of their pharmaceutical care protocols, to define options for cancer pain control.

References and/or acknowledgements None

Conflict of interest No conflict of interest