Toxicological detection of pholcodine and its metabolites in urine and hair using radio immunoassay, fluorescence polarisation immunoassay, enzyme immunoassay, and gas chromatography-mass spectrometry.

Abstract

Pholcodine (3-O-(2'-morpholinoethyl)-morphine) is used in many countries as an antitussive without analgesic or addictive properties. It is of forensic relevance that pholcodine interferes with opiate immunoassays. In this paper a gas chromatographic-mass spectrometric (GC-MS) procedure for the precise and sensitive detection of pholcodine and its metabolites in urine and hair, after acid hydrolysis, extraction and acetylation, is presented. Furthermore, detection of pholcodine using radio immunoassay (RIA), fluorescence polarisation immunoassay (FPIA) and enzyme immunoassay (EIA) for opiates is described. Using GC-MS, unmodified pholcodine could be detected in urine samples 4-7 weeks after ingestion of a single therapeutic dose of 50mg of pholcodine, the desmorpholinohydroxy metabolite for 1-2 weeks and the other metabolites (nor-, nordesmorpholinohydroxy-, hydroxy-, oxo- and noroxo-pholcodine) only during the first few hours. Morphine could also be detected in urine samples for the first few days. It was however mainly formed artificially during acid hydrolysis and only in trace amounts by metabolism. All the immunoassays tested gave positive results in urine samples during the first week taking the cut-off values recommended by the manufacturer into consideration. If values between the cut-off and the detection limit were taken into consideration, RIA and FPIA gave positive results for 2-4 weeks and EIA up to 2 weeks. Pholcodine could also be detected by RIA and GC-MS in samples of head hair clipped 10 weeks after ingestion of 50mg and in daily shaved samples of beard hair over a period of three weeks after ingestion of three doses of 60mg. It can be concluded that the widely used immunoassays for opiates show positive results in urine and hair samples for a long time after ingestion of the non-opioid pholcodine and that these results can be confirmed by the GC-MS procedure described in this paper.