Ethionamide

Ethionamide (2-ethyl-4-thiocarbamoylpyridine or 2-ethylisothio-nicotinamide) is an active antituberculosis drug. Recently the sulphoxide of ethionamide has been shown to behave similarly . The structure of ethionamide shows similarities to other antituberculosis compounds, notably the thiosemicarbazones and isonicotinic hydrazide. Unlike these drugs the metabolism of thioamides has not been investigated although the behaviour of the -CSNH, group in thioureas and thiosemicarbazones is to some extent understood. Thiorea and thiosemicarbazide (released from thiosemicarbazones) appear to be stable. Mono-N-substituted thioureas are highly toxic to rats, probably due to release of hydrogen sulphide, whereas N, N’-diarylthioureas are less so. On the basis of toxicity thioamides would be labile, being converted into the corresponding amide with the associated production of hydrogen sulphide.

Infections caused by Mycobacterium avium-intracellulare complex (MAl) and by drug-resistant Mycobacterium tuberculosis are increasingly common in the United States, fueled in large part by the spread of the acquired immunodeficiency syndrome (AIDS). As a result, second-line antimycobacterial agents such as ethionamide (ETA) are being used much more frequently. In vitro, ETA is active against most mycobacteria, including M. tuberculosis and MAl, thus displaying a broad range of potential clinical application." It is relegated to second-line status primarily because oral administration frequently results in gastrointestinal intolerance." Because many patients cannot tolerate the tablets, we evaluated the pharmacokinetics and relative bioavailability of ETA suppositories compared to the tablets.