Doxycycline

Class: Tetracycline
Mech.: Active uptake into bacteria →inhib protein synth by binding to 30S ribosome. Bacteriostatic

Absorption: Good oral absorption. Impaired by divalent cations. IM painful. IV may cause thrombophlebitis. Never intrathecal.
Distribution: Good CSF. Conc. in liver → enterohepatic circ. Penetrates most tissues and fluids. Crosses placenta.
Metab.:
Excretion, t_: bile; doesn’t require renal excretion
Toxicity/S.E.s: GI — burning, discomfort, nausea, vomitiing; superinfection — due to broad spectrum, candida albicans (1°), staph enterocolitis, pseudomemb. colitis; hepatotoxicity (esp. in pregnancy); renal toxicity; Fanconi synd.; perm. brown discoloration of teeth; slowing of bone growth; phototoxicity (more than others); thrombophlebitis; hematopoetic changes; rare hypersens. rxns.


Utility: gram - cocci, gram - bacilli, acid fast bacilli, chlamydiae, mycoplasma, rickettsia, spirochetes. No effect on viruses or fungi. Also used for acne, prophylaxis for Travelers’ diarrhea.
Special Features: Broad spectrum. Decreased effect of oral contraceptives.