Stability of drugs of forensic interest in post mortem blood
The stability study of drugs of forensic interest in human post-mortem blood is an important forensic study, because in some cases, a requirement for the laboratory to undertake a full drug screening is after a few months of storage due to a need for new evidence. Therefore, it is necessary and important to know if drugs are stable over a period of time under different conditions to enable a solid interpretation to be made from any results. Some studies have been published on the stability of drugs at different temperatures but none had covered the whole set of drugs that has been studied in this thesis. The periods of study that have been covered by other studies varied from a few days to a maximum of 70 weeks, but again not all drugs have been covered. The drugs studies in this thesis are two sets of drugs, benzodiazepines and tricyclic antidepressants, their stability being determined over twelve months and at three different temperatures 25,5 and -20°C. In this thesis, blood was 'spiked' with eight drugs, Diazepam, Temazepam, Triazolam, Desmethyldiazepam, Amitriptyline, Nortriptyline, Imipramine and Chlorpromazine. The samples were stored with blanks at different temperatures for different storage times. Each month a number of samples were removed from storage and analysed to test the effect of storage time and temperature on drug concentration. Different solid phase and liquid-liquid extraction methods were tested for the determination of benzodiazepines. Liquid-liquid extraction methods for - 2 - the determination of Diazepam, Temazepam, desmethyldiazepam and Triazolam proved after study to be tedious and time-consuming. A method based on solid phase extraction was used to determine the four benzodiazepine drugs. The extraction method gave good recoveries and was highly efficient. The method of analysis used for the determination of stability of benzodiazepine drugs was the high performance liquid chromatography (HPLC) method. Tricyclic antidepressant drugs are the other drugs studied for their stability in blood. Different solid phase extraction methods were used for the determination of drugs in post-mortem blood but gave poor recoveries. The best method of extraction used was a liquid-liquid extraction method which yielded high recoveries and proved to be quick. The method of analysis used for the determination of tricyclic antidepressants for the purpose of stability of the study was gas chromatography (GC). At a recognised toxic level for each drug under study a reasonable amount of the drug was found to be detectable after one year at storage regardless of the storage temperature or media. The decrease rate of each drug concentration with time at the three storage conditions (25, 5 and -200e) was obtained.