Detection of deacetylmetipranolol arising from storage of standard solution of metipranolol

Abstract

Metipranolol is a beta-blocker in the WADA list of substances prohibited in particular sports. It is converted to deacetylmetipranolol by the first pass metabolism and the parent compound is not excreted. A standard methanolic solution of metipranolol can be converted to deacetylmetipranolol during prolonged storage at -20°C. Spiking blank urine with this aged standard can lead to misinterpretation of the form of metipranolol in a suspected urine sample since the normal GC-MS screening procedure for derivatized beta-blockers cannot separate this metabolite from the parent compound. A specific Ge-temperature program is required. However a LC-MS/MS method can separate metipranolol and its metabolite.