Tetracyclines biliary excretion

Two tetracyclines have sufficiently distinctive features to warrant separate mention. Doxycycline, with its longer half-hfe and lack of nephrotoxicity, is a popular choice for patients with preexisting renal disease or those who are at risk for developing renal insufficiency. The lack of nephrotoxicity is related mainly to biliary excretion, which is the primary route of doxycycline elimination. Doxycycline is the preferred parenteral tetracycline Doxycycline is a potential first-hne agent in the prophylaxis of anthrax after exposure. Doxycycline is the treatment of choice for the primary stage of Lyme disease in adults and children older than 8 years. 

Chlortetracycline has, in many respects, a pharmacological profile similar to that of oxytetracycline. Similarly to other tetracyclines, the main excretory routes are through the urinary system, biliary system, and intestine. Its higher biliary excretion rate makes chlortetracycline a better choice than oxytetracycline for liver infections. 

The tetracyclines, apart from doxycycline and minocycline, are slowly eliminated by renal excretion (glomerular filtration). Their slow elimination can be attributed to enterohepatic circulation whereby drug excreted by the liver in bile is reabsorbed from the intestine. The half-life of oxytetracycline differs widely between animal species goat (3.4 h), cattle (4.0 h), sheep (5.2 h), dog (6.0 h), pig (6.0 h), donkey (6.5 h), horse (9.6 h), and red-necked wallaby (.Macropus rufogriseus) (11.4 h). Doxycycline, unlike other tetracyclines, is eliminated by biliary excretion and diffusion into the intestine. The half-life of doxycycline is relatively short in dogs (7.0 h) and cats (4.6 h) compared with human beings (16 h). The half-life of doxycycline in chickens (4.8 h) is shorter than in turkeys (10 h) (Santos et al, 1996). Minocycline is mainly eliminated by hepatic metabolism. 

Decreased intracellular accumulation is a mechanism of bacterial resistance Elimination is predominantly via biliary excretion The patient should discontinue the tetracycline if she becomes pregnant Vaginal candidiasis may occur during treatment... 

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