Specimen types , Stomach contents
Stomach (or gastric) contents are valuable for two primary reasons. After overdosage, drug concentrations in the stomach may be quite high, even after the majority of the drug has passed into the small intestine. Analysis of the stomach contents is uncomplicated by metabolism, so drugs that are metabolised extensively in the body may be detected unchanged. Similarly, drugs that may be difficult to detect in the blood because of extensive distribution in the body might be detected readily in the stomach. In some cases, where death occurred relatively shortly after drug ingestion, it may be possible to see remains of tablets or capsules. If these are sufficiently intact, it may be possible to search them against drug identification databases such as TICTAC (TicTac Communications Ltd.) or, if this is not possible, to analyse a sample of the tablet or capsule to identify the drug. The disadvantage of stomach contents is its composition, which varies from a thin watery fluid to a semi solid, depending on the amount and type of food present. The interpretative value of stomach contents lies in confirming the consumption of an oral overdose. If the total amount of drug detected in the stomach contents is significantly greater than the prescribed dose, the possibility of drug abuse or an overdose should be considered. There are, however, two important caveats. Firstly, stomach contents are rarely homogeneous, and therefore it is difficult to measure accurately the representative concentration of drug in the volume of stomach contents received, unless the contents are homogenised. Most chromatographic assays are based on volumes as small as 1 mL or less, and the potential for sampling errors is consequently great. The second reason why the accurate estimation of a dose in the gastric contents is difficult is that the total stomach contents are often not sent to the laboratory, only a portion being subsampled at autopsy and submitted. Results should therefore be reported as the amount of drug present in the volume or mass of stomach contents received. Specimen collection guidelines should encourage pathologists to submit the complete stomach contents rather than an aliquot. There are two misconceptions regarding interpretation of drug concentrations in the stomach. Firstly, the concentration (as distinct from the amount) of a substance in the stomach contents is virtually meaningless by itself. Shortly after a therapeutic dose, the concentration of a drug in the stomach may be very high, even if the total amount is not. Secondly, the absence of a large amount of residual drug in the stomach does not necessarily rule out an oral overdose. It may take several hours to die from a drug overdose, during which most or all of the drug could have passed from the stomach to the small intestine, or even have been largely absorbed. On the other hand, consumption of an oral overdose of medicine can result in a formation of a medicine ‘mass’ or bezoar in the stomach, which may take several hours or even a day or more to dissipate. High concentrations of some drugs can delay gastric emptying. It must therefore be accepted that gastric drug concentrations should never be interpreted on the same basis as those for blood. The detection of a drug or metabolite in the stomach contents does not necessarily mean that the drug was taken orally. Gastric juice is constantly being secreted into the stomach, which in turn is formed from extracellular fluid; this may contain significant amounts of basic drugs and metabolites circulating in the blood. It is also important to bear in mind that gastric juice may have been contaminated with bile from retching or vomiting. In overdose patients administered oral charcoal, large amounts of charcoal in the stomach lead to an underestimation of the total amount of drug present. A review of the record of any antemortem clinical treatment should highlight this possibility.
