Diagnostic data in clinical toxicology--should we use a Bayesian approach?

Advances pertaining to the pharmacology and interactions of irreversible nonselective monoamine oxidase inhibitors

Recent advances clarifying the pharmacology and interactions of irreversible nonselective monoamine oxidase inhibitors that have not been considered in depth lately are discussed. These new data elucidate aspects of enzyme inhibition and pharmacokinetic interactions involving amine oxidases, cytochrome P450 enzymes, aminotransferases (transaminases), and decarboxylases (carboxy-lyases) and the effects of tyramine. Phenelzine and tranylcypromine remain widely available, and many publications have data relevant to this review. Their effect on CYP 450 enzymes is less than many newer drugs. Tranylcypromine only inhibits CYP 450 2A6 (selectively and potently). Phenelzine has no reported interactions, but, like isoniazid, weakly and irreversibly inhibits CYP 450 2C19 and 3A4 in vitro. It might possibly be implicated in interactions (as isoniazid is). Phenelzine has some clinically relevant inhibitory effects on amine oxidases, aminotransferases, and decarboxylases, and it lowers pyridoxal phosphate levels. It commonly causes pyridoxal deficiency, weight gain, sedation, and sexual dysfunction, but only rarely causes hepatic damage and failure, or neurotoxicity. The adverse effects and difficulties with monoamine oxidase inhibitors are less than previously believed or estimated, including a lower risk of hypertension, because the tyramine content in foods is now lower. Potent norepinephrine reuptake inhibitors have a strong protective effect against tyramine-induced hypertension. The newly discovered trace amine-associated receptors probably mediate the pressor response. The therapeutic potential of tranylcypromine and L-dopa in depression and Parkinson disease is worthy of reassessment. Monoamine oxidase inhibitors are not used to an extent proportionate with their benefits; medical texts and doctors' knowledge require a major update to reflect the evidence of recent advances.

A risk assessment based approach to the management of acute poisoning

Early assessment and management of poisoning constitutes a core emergency medicine competency. Medical and psychiatric emergencies coexist; the acute poisoning is a dynamic medical illness that represents an acute exacerbation of a chronic underlying psychosocial disorder. The emergency physician must use an approach that ensures early decisions address potentially time critical interventions, while allowing management to be tailored to the individual patient's needs in that particular medical setting. This article outlines a rationale approach to the management of the poisoned patient that emphasises the importance of early risk assessment. Ideally, this approach should be used in the setting of a health system designed to optimise the medical and psychosocial care of the poisoned patient.

A review of serotonin toxicity data: implications for the mechanisms of antidepressant drug action

Data now exist from which an accurate definition for serotonin toxicity (ST), or serotonin syndrome, has been developed; this has also lead to precise, validated decision rules for diagnosis. The spectrum concept formulates ST as a continuum of serotonergic effects, mediated by the degree of elevation of intrasynaptic serotonin. This progresses from side effects through to toxicity; the concept emphasizes that it is a form of poisoning, not an idiosyncratic reaction. Observations of the degree of ST precipitated by overdoses of different classes of drugs can elucidate mechanisms and potency of drug actions. There is now sufficient pharmacological data on some drugs to enable a prediction of which ones will be at risk of precipitating ST, either by themselves or in combinations with other drugs. This indicates that some antidepressant drugs, presently thought to have serotonergic effects in animals, do not exhibit such effects in humans. Mirtazapine is unable to precipitate serotonin toxicity in overdose or to cause serotonin toxicity when mixed with monoamine oxidase inhibitors, and moclobemide is unable to precipitate serotonin toxicity in overdose. Tricyclic antidepressants (other than clomipramine and imipramine) do not precipitate serotonin toxicity and might not elevate serotonin or have a dual action, as has been assumed.

Comparison of the fatal toxicity index of zopiclone with benzodiazepines

BACKGROUND

Zopiclone is a hypnosedative structurally unrelated to the benzodiazepines but operating at the same receptor complex. Although zopiclone has been used in clinical practice for many years, relatively little is known of its relative toxicity in comparison with other hypnosedatives.

METHOD

Deaths, where hypnosedatives were implicated, in New Zealand (NZ) in 2001 were identified from a chemical injury database. Prescription and aggregate defined daily dose (DDD) data forNZ in 2001 were obtained from a national prescribing database. Rates of death per prescription and DDD, and relative rates between individual hypnosedatives and benzodiazepines, and their respective 95% CI were calculated.

RESULTS

Of the 200 poisoning deaths in NZ for 2001, 39 involved hypnosedatives, and zopiclone was involved in 12. Hypnosedatives were the sole agents in only one death and were the primary agents in eight deaths. Zopiclone was the sixth most commonly involved agent in poisoning deaths in NZ in 2001. The relative rate of death per prescription (95% CI) and DDD (95% CI) of zopiclone compared with benzodiazepines were 1.04 (0.49-2.05) and 0.59 (0.28-1.16), respectively. The relative rates of death per DDD (95% CI) for alprazolam and chlormethiazole compared with the other sedatives/anxiolytics were 6.2 (1.6-17.0) and 20.9 (2.5-79.8) respectively.

CONCLUSIONS

The fatal toxicity for zopiclone was not significantly different from that for benzodiazepines as a group when adjusted for usage, whereas alprazolam and chlormethiazole had greater toxicity. Hypnosedatives are contributory factors rather than primary substances in poisoning deaths.

Changes in Fatalities Due to Overdose of Anxiolytic and Sedative Drugs in the UK (1983???1999)

OBJECTIVE

To establish the frequency with which anxiolytic and sedative drugs result in fatal poisonings and to examine longitudinal changes in poisoning deaths.

METHOD

The number of fatal poisonings between 1983 and 1999 in England, Scotland and Wales due to a single anxiolytic or sedative drug was obtained from the Department of Health in the UK. This was divided by the number of prescriptions for these drugs in England and Scotland to derive a fatal toxicity index (FTI) of deaths per million prescriptions.

RESULTS

Chloral hydrate, clomethiazole, barbiturates, and related sedatives had much higher FTIs than benzodiazepines, buspirone, zolpidem and zopiclone. There has been a substantial reduction in the annual number of deaths from sedative drug poisoning between 1983 and 1999. This has been due to a sustained reduction in prescriptions for high toxicity drugs and more recently a major reduction in temazepam deaths that coincided with the withdrawal of gelatin capsule formulations.

CONCLUSION

Deaths would be expected to be further reduced if there were reduced prescriptions of high toxicity drugs--and the continuing need for short-acting barbiturates, clomethiazole and chloral hydrate should be questioned.