Сульфаниламиды

Описание

The antibacterial properties of the sulfonamides were discovered in the mid-1930s following an incorrect hypothesis but after observing the results carefully and drawing correct conclusions. Prontosil rubrum, a red dye, was one of a series of dyes examined by Gerhard Domagk of Bayer of Germany in the belief that it might be taken up selectively by certain pathogenic bacteria and not by human cells, in a manner analogous to the way in which the Gram stain works, and, therefore, serve as a selective poison to kill these cells. The dye, indeed, proved to be active in vivo against streptococcal infections in mice. Curiously, it was not active in vitro.

Использование

Sulfanilamide drugs do not currently have a clear classification. However, they are grouped as systemic (absorptive action), and local. They are subdivided into short-lasting (sulfacytine, sulfadiazin, sulfamerazine, sulfametazine, sulfametizole, sulfisoxazole); moderate-lasting (sulfamethoxazole, sulfapyridine); and long-lasting (sulfamethoxypiridazine, sulfamter), which, however, are no longer used as independent drugs because of extremely rare, yet nonetheless occurring, hypersensitivity reactions. Drugs for local use include those for ophthalmological use (sulfacetamide, sulfozoxazol); vaginal use (sulfabenzamide, sulfacetamide, sulfathiazole, sulfizoxazol); and external use (maphenid, silver sulfadiazine). Finally, this group includes sulfasalazine and phthalylsulfathiazole, a drug that acts in the lumen of the intestines, but which is poorly absorbed from the gastrointestinal tract.

Антимикробная активность

Sulfonamides exhibit broad-spectrum activity against common Gram-positive and Gram-negative pathogens, although the potency against many bacteria within the spectrum is modest by present standards. Meningococci are generally much more susceptible than gonococci. Other organisms commonly susceptible include Bordetella pertussis, Yersinia pestis, Actinomyces spp., Nocardia spp., Bacillus anthracis, Corynebacterium diphtheriae, Legionella pneumophila, Brucella spp. and several important causes of sexually transmitted diseases (Chlamydia trachomatis, Haemophilus ducreyi and Calymmatobacterium granulomatis). Activity against anaerobes is generally poor. Pseudomonas aeruginosa is usually resistant, as are Leptospira, Treponema and Borrelia spp., rickettsiae, Coxiella burnetii and mycoplasmas. Mycobacteria are resistant, although the related sulfone, dapsone, exhibits good activity against M. leprae and para-aminosalicylic acid, which is structurally similar, was formerly widely used in tuberculosis. Sulfonamides act synergistically with certain diaminopyrimidines against many bacteria and some protozoa, including plasmodia and Toxoplasma gondii.
In-vitro tests are markedly influenced by the composition of the culture medium and the size of the inoculum. The different derivatives vary somewhat in antibacterial activity . Among those that are still fairly widely available as antibacterial agents, sulfadimidine shows comparatively low activity, whereas sulfadiazine, sulfisoxazole (sulphafurazole) and sulfamethoxazole, the sulfonamide commonly combined with trimethoprim , are relatively more active.

Приобретенная устойчивость

Resistance is now widespread and there is complete crossresistance among sulfonamides. Plasmid-mediated resistance in all enterobacteria is common. Resistance is found in 25–40% of strains of Escherichia coli and other enterobacteria infecting the urinary tract. Many strains of meningococci and H. ducreyi are now resistant.

Фармацевтические приложения

The original sulphonamide, sulphanilamide, is the active principle of Prontosil, which holds a special place in medicine as the first agent to exhibit broad-spectrum activity against systemic bacterial disease . Within a few years of the introduction of Prontosil, numerous sulfonamide derivatives were synthesized. Advances included increased antibacterial potency, decreased toxicity, and the introduction of compounds with special properties such as high or low solubility and prolonged duration of action. Most have since been discarded, as safer and more active antibacterial agents have overtaken them, but a few are still in use for particular purposes, often in combination with diaminopyrimidines . Some survive in topical preparations, often in multi-ingredient formulations. Discussion here is limited to the most important sulfonamides that are still widely available; a short description is included of some of the many other compounds that are of more restricted availability.

Механизм действия

The sulfonamides are bacteriostatic when administered to humans in achievable doses. They inhibit the enzyme dihydropteroate synthase, an important enzyme needed for the biosynthesis of folic acid derivatives and, ultimately, the thymidine required for DNA. They do this by competing at the active site with p-aminobenzoic acid (PABA), a normal structural component of folic acid derivatives.

Клиническое использование

Sulfonamides were formerly much used, alone or in combination with trimethoprim, for the treatment of urinary tract infection, but are no longer recommended because of potential adverse reactions. Use in the treatment of respiratory infections is now confined to a few special problems, notably nocardiasis (and also for cerebral nocardiasis) and, in combination with trimethoprim, in the prevention and treatment of Pneumocystis jirovecii pneumonia. The value of sulfonamides in the prophylaxis and treatment of meningococcal infection is now greatly reduced by bacterial resistance. Sulfonamides are sometimes used for chlamydial infections and chancroid but are unreliable. Some formulations are used topically in eye infections and bacterial vaginosis. Combined preparations with pyrimethamine are used in the treatment of drug-resistant malaria and for toxoplasmosis.