British Journal of British Journal of Pharmacology (2018) 175 532–543 532 BJP Pharmacology RESEARCH PAPER Opioid-induced inhibition of the human 5-HT and noradrenaline transporters in vitro: link to clinical reports of serotonin syndrome Correspondence Professor Matthias E. Liechti, Division of Clinical Pharmacology and Toxicology, University Hospital Basel, Schanzenstrasse 55, Basel, CH-4056, Basel, Switzerland. E-mail:
[email protected] Received 21 June 2017; Revised 3 November 2017; Accepted 8 November 2017 Anna Rickli1, Evangelia Liakoni2, Marius C Hoener3 and Matthias E Liechti1 1Clinical Pharmacology and Toxicology, Department of Biomedicine, Department of Internal Medicine, University Hospital Basel, University of Basel, Basel, Switzerland, 2Clinical Pharmacology and Toxicology, Department of General Internal Medicine, Inselspital, Bern University Hospital, Univer- sity of Bern, Bern, Switzerland, and 3Neuroscience Research, pRED, Roche Innovation Center Basel, F.Hoffmann-La Roche Ltd, Basel, Switzerland BACKGROUND AND PURPOSE Opioids may inhibit the 5-HT transporter (SERT) and the noradrenaline transporter (NET). NET inhibition may contribute to an- algesia, and SERT inhibition or interactions with 5-HT receptors may cause serotonergic toxicity. However, the effects of different opioids on the human SERT, NET and 5-HT receptors have not been sufficiently studied. EXPERIMENTAL APPROACH We determined the potencies of different opioids to inhibit the SERT and NET in vitro using human transporter-transfected fi HEK293 cells. We also tested binding af nities at 5-HT1A,5-HT2A and 5-HT2C receptors. Additionally, we assessed clinical cases of the serotonin syndrome associated with each opioid reported by PubMed and a World Health Organization database. KEY RESULTS Dextromethorphan, l(R)-methadone, racemic methadone, pethidine, tramadol and tapentadol inhibited the SERT at or close to observed drug plasma or estimated brain concentrations in patients.