Drug interactions and duplicate prescriptions among ambulatory cancer patients.

The pharmacotherapeutic treatment of patients with cancer is generally associated with multiple side-effects. Drug interactions and duplicate prescriptions between anti-cancer drugs or interactions with medication to treat comorbidity can reinforce or intensify side-effects.
The aim of the present study is to gain more insight into the prevalence of drug interactions and duplicate prescriptions among patients being treated in the outpatient day care departments for oncology and hematological illnesses. This will be the first study into the prevalence of drug interactions with OTC-drugs in cancer patients.

The pharmacotherapeutic treatment of patients with cancer is generally associated with multiple side-effects. The cause of the side-effects is usually due to the toxicity of the drugs themselves. In addition, drug interactions can intensify side-effects. In general, interactions are the cause of approximately 20-30% of all drug side-effects, of which 70% needs clinical attention and 1-2% is even life-threatening [1]. Cancer patients are particularly susceptible to drug interactions [2]. In addition to chemotherapy, cancer patients often use co-medication to treat cancer related pain and venous thrombosis or to reduce the side-effects of the anti-cancer drugs. Interactions with drugs used to treat comorbidities can also occur.

Before or during administration of cytotoxic drugs.

The patients are asked to complete a short questionnaire followed by an interview. The questionnaire contains questions about the demographic characteristics (available online as appendix). A list of the medication used to treat comorbidities for a period of six months prior to the study is requested from the patients’ community pharmacy and this is discussed in the interview with the patient. During this interview the patient is also asked about the comorbidity and the use of OTC drugs. Data about the use of anti-cancer drugs, diagnose, aim of treatment (palliative/adjuvant), treatment start date and cancer-related co-medication is gathered by medical chart review and, if necessary, in an interview with the prescribing doctor. The most recent renal function (creatinine) value and liver function parameters (ASAT, ALAT and ã-GT) is obtained from the laboratory database of the hospital.