L'hydrate de chloral, l'un des plus anciens hypnotiques de synthèse, reste plutôt par tradition encore utilisé en psychiatrie. Son effet sédatif en prémédication lors d'examens spécialisés ou en dentisterie chez l'enfant, et en réanimation néonatale a suscité un regain d'intérêt. L'hydrate de chloral avait une réputation de produit d'usage facile et sûr, ceci malgré de nombreuses publications sur ses effets secondaires datant d'une centaine d'années. Une récente évaluation a remis en cause le ratio bénéfice/risque réel lié à son utilisation. Plus particulièrement, la suspicion sur un pouvoir mutagène et cancérigène a entraîné de fortes restrictions de son utilisation chez l'enfant et son retrait dans la composition de certains produits à visée d'analgésie externe. Après un rappel de la pharmacologie, des indications, des effets secondaires et des contre-indications, nous discuterons de l'indication psychiatrique actuelle de cette molécule.

Synthesised by Justin Liebig in 1832 chloral hydrate is one of the oldest synthetic agents. Since 1869 it has been in use for hypnotic or sedative purposes. Chloral hydrate was used a lot from the end of the 19th century to the middle of the 20th century. Since then chloral hydrate has been less frequently in use as a hypnotic. In the 1990's, the principal use of chloral hydrate in pediatrics was the sedation of children for minor surgery during dental or diagnostic procedures. In general practice, it is an analgesia found in topical preparations. It was known as safe and easy to use. Now it is shown to be potentially dangerous (risk of death in case of intoxication) and there is doubt about genotoxicity and carcinogenecity. The pharmacological property was known in 1948 when Butler discovered the principal active metabolite, trichloroethanol. The gastro-intestinal tract rapidly absorbs chloral hydrate after oral or rectal use. The sedative and hypnotic effects appear in 20 to 60 minutes. The main metabolites [trichloroethanol (TCE) and trichloroacetic acid (TCA)] are formed by hepatocytes and erythrocytes. The half-life of chloral hydrate is short (a few minutes), the half lives of the metabolics are longer, 8 to 12 hours for TCE and 67 hours for TCA. The affinity for lipids is high. It is eliminated principally by the kidneys. Its mechanism of action is unknown. It is a depressor of the SNC, and the sedation is attributed to chloral hydrate and the hypnotic effect to TCE. The interactions appear with : alcohol, anticoagulants, amitriptyline and furosemide. The use of flumazenil (a gaba antagonist), in case of intoxication, indicates a possible action of GABA. The posology is usually between 0.5 to 2 g per day. Chloral hydrate is taken during meals to prevent gastric irritation. The main side effects are digestive, cardiologic (risk of rhythm disorder), dermatologic, neuropsychiatric (withdrawn, delusions, hallucination, dependence) and ophthalmologic. Death occurs after absorption of doses of around 10 g of hydrate chloral, some cases were reported with 5 g. The use of hydrate chloral is contra-indicated in cases of gastric ulcers, hepatic insufficiency, porphyry, respiratory insufficiency, association with anticoagulants and hyper sensibility. Nowadays should we be using chloral hydrate in cases of insomnia in adult and older people ? A recent preclinical working group of the French Agency for evaluation of medicinal products reassessed the benefit/risk ratio of chloral hydrate. Many references are found about genotoxicity and carcinogenicity in recent literature. In France, since the end of 2000, chloral hydrate has been withdrawn from many medications for external use in dermatology and in stomatology. Chloral hydrate can be used as a pediatric sedative only once in a lifetime. The psychiatric indication for insomnia is no longer justified and especially in older people.