Tetracyclines

Tetracyclines are broad-spectrum bacteriostatic antibiotika. It used to be widely used in pediatrics, but only until it was found to damage tooth enamel and growth cartilage.

Antimicrobial spectrum

 * Broad spectrum, G + and G−, mycoplasmas, chlamydia , spirochetes , some protozoa (amoebae).
 * Many strains are resistant (many G + cocci, G− aerobic rods), resistance is cross-linked.
 * Does not affect Pseudomonas spp., Proteus spp. and Serratia spp.

Mechanism of action

 * Inhibition of proteosynthesis, reversible binding to the 30S subunit of the ribosome.

Pharmacokinetics

 * It is preferred after administration, better on an empty stomach.
 * They form inactive chelates with Ca 2+, Fe 2+ , Mg 2+ , Al 3+ ions , which limit absorption - do not administer simultaneously with antacids , do not drink with milk.
 * Tissue penetration very good.
 * They penetrate the placenta, high risk of fetal damage.
 * They are widely distributed - in addition to the CNS, they penetrate mainly into bones and teeth, into milk (they cannot be given during pregnancy and lactation).
 * They are concentrated in the liver, subject to enterohepatic circulation, excreted in the bile , and doxycycline is excreted in the faeces, otherwise by the kidneys.

Pharmacodynamics

 * Bacteriostaticity does not depend on concentration but on exposure time.
 * Their postantibiotic effect is insignificant.

Side effects

 * There are many side effects, which affects the possibility of their use.
 * Bone deposition and interference with tooth enamel, tooth enamel damage, tooth discoloration , phototoxicity, GIT problems ( nausea , vomiting , diarrhea ), suppression of the natural flora in the GIT (may result in blood clotting disorders due to vitamin K deficiency , superinfection), fatty liver degeneration.

Contraindication

 * Pregnant and lactating women, children up to 8 years.

Main indications

 * Chlamydial infections, ehrlichemia infections , rickettsiae , brucellosis infections , mycoplasmas.
 * Infections in dentistry.
 * Bacterial involvement of the bile, urinary and genital tracts.
 * Some anthropozoonoses.
 * Acne vulgaris.

Interaction

 * Do not combine with beta-lactams.
 * Increases the effect of PAD, immunosuppressants and digoxin.

Representatives
1st generation : tetracycline, oxytetracycline, rolitetracycline for im or iv administration.

2nd generation : doxycycline and minocycline.

3rd generation : thiacycline - does not have cross-resistance.

Today, only doxycycline and minocycline are used in practice.

Doxycycline

 * Very lipophilic.
 * It is administered parenterally, its absorption is less affected than with other tetracyclines.
 * It has a long half-life (16 hours) - dosing of 12 or 24 hours.
 * Dosage - first day 2 × 100 mg, next days 100 mg every 24 hours.

Minocycline

 * Specific indication - acne.

Source
BENEŠ, Jiří. Studijní materiály [online]. [cit. 2010]. .