Minocycline pharmacokinetics

Pharmacokinetics. Most tetracyclines are only partially absorbed from the alimentary tract, enough remaining in the intestine to alter the flora and cause diarrhoea. They are distributed throughout the body and cross the placenta. Tetracyclines in general are excreted mainly unchanged in the urine and should be avoided when renal function is severely impaired. Exceptionally, doxycycline and minocycline are eliminated by nonrenal routes and are preferred for patients with impaired renal function. 

B. Pharmacokinetics Oral absorption is variable, especially for the older drugs, and may be impaired by foods and multivalent cations (calcium, iron, aluminum). Tetracyclines have a wide tissue distribution and cross the placental barrier. All of the tetracyclines undergo entero-hepatic cycling. Doxycycline is excreted mainly in feces the other drugs are eliminated primarily in the urine. The half-lives of doxycycline and minocycline are longer than those of other tetracyclines. 

The pharmacokinetics of tetracycline (4-hour AUC and peak level) were not significantly different between 7 healthy women taking a combined oral contraceptive (ethinylestradiol/norethisterone) and 4 healthy women not taking any medication. For reports of facial pigmentation due to minocycline and ethinylestradiol, see Tetracyclines Minocycline + Ethinylestradiol , p.350. 

Information seems to be limited. There are two isolated eases of increased theophylline levels with minocycline and tetracycline, but controlled studies have not shown any significant changes in overall theophylline pharmacokinetics. It has been suggested that a clinically important interaction may possibly only occur in a few patients. Further study is needed. There seems to be no evidence of adverse interactions with any of the other tetracyclines. However, note that acute infections per se can alter theophylline pharmacokinetics. 

K. Nagpal, S.K. Singh, and D.N. Mishra, Formulation, optimization, in vivo pharmacokinetic, behavioral and biochemical estimations of minocycline loaded chitosan nanoparticles for enhanced brain uptake, Chem. Pharm. Bull, 61 (3), 258-272, 2013. 

These differ little in antibadetial activity and are distinguished by their pharmacokinetic behaviour. Minocycline (Rj=N(CH3)2, R2=H, R3=0H, R4=H) shows a broader spedmm of antibacterial activity. The tetracydines ad by blocking the binding of aminoacyl tRNA to the A site on the ribosome. The tetracydines subsequently inhibit protein synthesis at the small rihosomal suhunits of both the 70S (prokaryote) and SOS (eukaryote) tihosome. However, an active transport system for the tetracydines in bacteria means effective concentrations are achieved in the bacterial cdls but not in mammalian cdls. The tetracyclines are presented as capsules and tablets for oral use. 

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