Source: Υπουργείο Υγείας (CY) Revision Year: 2014 Publisher: MEDOCHEMIE LTD, 1-10 Constantinoupoleos street, 3011 Limassol, Cyprus
Pharmacotherapeutic group: tetracycline
ATC code: J01AA07
Tetracycline hydrochloride is a broad spectrum bacteriostatic antibiotic. It is taken up into sensitive bacterial cells by an active transport mechanism and binds reversibly to the 30S sub-unit of the bacterial ribosome. This prevents the binding of aminoacyl transfer RNA resulting in inhibition of protein synthesis and thus cell growth.
The following Gram positive organisms are usually sensitive to tetracycline: Staphylococcus aureus (some strains), Staphylococcus sp. (coagulase negative), Strep. pneumoniae, Strep. pyogenes, some Strep. agalactiae (group B) and some viridans streptococci. The enterococci are resistant. Other sensitive bacteria include strains of Actinomyces israelii, Bacillus anthracis, Erysipelothrix rhusiopathiae, Listeria monocytogenes, Clostridium sp., Propionibacterium acnes.
The following Gram negative organisms are usually sensitive: N. meningtidis, N. gonorrhoea, Acinetobacter sp., Moraxella (Branhamella) catarrhalis, Bordetella pertussis, Brucella sp., Calymmatobacterium granulomatis, Campylobacter sp., Eikenella corrodens, Francisella tularensis, Haemophilus influenzae, Haemophilus ducreyi (some strains), Legionella, Pasteurella multocida, Streptobacillus moniliformis, Aeromonas hydrophila, Plesiomonas shigelloides, Vibrio cholerae, Vibrio parahaemolyticus. Among the Enterbacteriaceae resistant strains are common, although Salmonella sp., Shigella sp. and Yersinia sp. are usually susceptible. Proteus sp., Providencia sp and Pseudomonas aeruginosa are not susceptible. Some species formerly classed as pseudomonas are susceptible, including Burkholderia mallei, Burkholderia pseudomallei and Stenotrophomonas (Xanthomonas) maltophilia.
Other organisms that are usually sensitive to tetracycline include Helicobacter pylori, Chlamydia sp., Rickettsia sp., Coxiella sp., Borrelia burgdorferi, Leptospira sp., Treponema sp., Mycoplasma pneumoniae and Ureaplasma urealyticum.
Organisms with minimum inhibitory concentrations (MIC) up to 4g/ml are considered sensitive, those with an MIC between 4g/ml and 12.5g/ml are considered moderately sensitive.
Resistance to tetracycline is usually plasmid mediated and transferable. With the widespread use of tetracycline resistant strains of the majority of sensitive species have now been reported. The main increases in resistance have occurred among the Enterobacteriaceae, staphylococci and streptococci.
Tetracycline is incompletely absorbed following oral administration, approximately 75% is absorbed. Absorption is reduced in the presence of food, dairy products and divalent and trivalent metal ions. Administration of 500mg every six hours should produce steady state concentrations of 4μg/ml – 5μg/ml. peak plasma concentrations occur after 1-3 hours, protein binding is 25% to 65%. Elimination half life is 8 – 10 hours and is prolonged in renal impairment. There is good distribution into tissues and body fluids with the exception of the cerebrospinal fluid. Bile concentrations exceed blood plasma levels, bronchial secretion levels are about 10% plasma levels. Tetracycline crosses the placental barrier and is excreted in milk.
Approximately 60% of a dose is excreted as unchanged drug in the urine and concentrations of 300g/ml can be achieved, and a significant route of excretion is via the bile to the faeces. Some enterohepatic reabsorption occurs and complete elimination is slow.
There was evidence of mutagenicity at tetracycline hydrochloride concentrations of 10 and 60µg/ml, respectively, in two in vitro mammalian cell assay system.
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