The usefulness of systematic toxicological screening in poisoned patients has not been established. In several reports, the concordance between the drug(s) suspected clinically and the drugs detected by toxicological screens ranged from 26 to 96 per cent and was dependent on the physician, the age of the patient, and the drug ingested (LheureuxeLal 1995). The results rarely contributed to the management of the patient. Toxicology screens give qualitative or semiquantitative results for drugs which are frequently involved in poisonings, but they do not usually include toxins which induce severe poisoning and for which analysis is essential for the prognosis or the treatment (e.g. theophylline, digoxin, lithium, carbon monoxide, methanol, ethylene glycol, etc.) ( Jaeger etal 1994; Lh§UÍ§UX..§L.§.L 1995).
In practice, four different situations may be observed.
1. Poisoning is definite, the toxin(s) is known according to the history, and the symptoms are related to the toxin(s) and dose. A toxicological analysis is not absolutely necessary if it has no prognostic, therapeutic, or medicolegal implications.
2. Poisoning is definite and the toxin(s) is known, but the symptoms are not related to the suspected toxin(s) or to the dose. A toxicological analysis is indicated in order to detect other toxins which may have been ingested.
3. Poisoning is suspected because of symptomatology (toxic symptoms or syndromes), but the toxin(s) is unknown. Only a toxicological analysis can confirm or refute poisoning.
4. Poisoning must be excluded by toxicological analysis in patients presenting with disturbances of the central nervous system (trauma, brain death, elderly patients), cardiovascular symptoms, or convulsions.
According to the history and the symptoms, the analysis should be directed towards specific drugs or groups of drugs.
Biomedical abnormalities may provide diagnostic clues for toxins which are not usually included in routine screens. They reflect the toxic effects and are sometimes more useful than the measurement of plasma drug concentrations in the management of the patient (Jaeger. etal 1991; Lbeuieux.et.al 1995). Some examples of disturbances suggesting specific poisonings are given in Table.!.
Table 1 Examples of clinical findings in specific poisonings
Therapeutic tests, such as naloxone in opiate and flumazenil in benzodiazepine poisoning, may also confirm the diagnosis ( Jaeger,,eLa( 1991).
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