How frequently are contraindicated or warned against combinations of drugs prescribed to patients receiving long-term opioid therapy for chroic pain?

Purpose To analyse the proportion of patients treated with an opioid for chronic pain who were prescribed concomitant medications that are warned against or contraindicated in the German summary of product characteristics to determine if warnings on drug–drug interactions (DDIs) are observed. Methods This retrospective analysis used longitudinal aggregated patient data from the Intercontinental Marketing Services Disease Analyzer in Germany. Patients with two or more prescriptions of morphine, hydromorphone, oxycodone or tramadol from 1 January 2006 to 31 December 2008 were included; drugs prescribed within 30 days of an opioid prescription were identified as concomitant medications. The frequency of concomitant treatment with drugs warned against or contraindicated in the German opioid summary of product characteristics was determined. Concomitant treatment with drugs metabolised by CYP3A4 inhibitors and inducers and CYP2D6 inhibitors was also considered. Results The Intercontinental Marketing Services database contained 13 405 eligible patients; 72% had concomitant diseases which may increase the risk for DDIs (hypertension, diabetes mellitus, renal failure, renal glomerular disease or renal tubulointerstitial disease). Very few patients received concomitant prescriptions of an opioid with a contraindicated drug. Many patients were prescribed opioids concomitantly with drugs with potential for harmful safety-related DDIs or DDIs that alter the effectiveness of one or more of the opioids. A large proportion of all concomitant prescriptions with potential for DDIs were given to at-risk patients aged 65 years and older. Conclusions Many patients that received an opioid for chronic pain were prescribed concomitant medications with the potential for safetyrelated DDIs or interactions that would alter the effectiveness of the opioid.