Stability of analytes in biosamples - an important issue in clinical and forensic toxicology?

Knowledge of the stability of drugs in biological samples is important for the interpretation of toxicological findings. This paper reviews data on the stability of drugs in blood, plasma, or serum. Since such data have already been reviewed for classic drugs of abuse, the focus here is on newer drugs of abuse and on therapeutic drugs. Key information about the conditions of the stability experiments will be provided and the following drugs or drug classes are covered: amphetamines, amphetamine-derived, piperazine-derived, and phenethylamine-derived designer drugs, antidepressants, neuroleptics, anti-HIV drugs, antiepileptics, cardiovascular drugs, and others. In addition, aspects of stability experiments and their evaluations are discussed. The data presented show that the majority of drugs are stable in blood, plasma, or serum samples under the conditions usually encountered in a clinical or forensic toxicology laboratory. Instability usually only occurs for drugs carrying ester moieties, sulfur atoms, or other easily oxidized or reduced structures. Nevertheless, clinical or forensic specimens should always be stored at least in the refrigerator and preferably at -20 degrees C or lower to avoid any degradation. Finally, results obtained from biosamples that have been stored at room temperature for a longer time should be interpreted with great care and partial degradation should always be considered.