Tetracyclines
- Doxycycline
- Oxytetracycline
- Minocycline
- Both Gram negative and Gram Positive bacteria but Pseudomonas aeruginosa and Proteus spp. are intrinsically resistant
- Treatment of choice for a number of specific conditions including those caused by Chlamydia, rickesttsia, brucella and Borrelia burgdorferi
- Action against Haemophilus Influenzae
- Microbiologically there is little distinction between the tetracyclines
- Pregnant and Breast-feeding
- Children under 12 years
- In patients with myasthenia gravis as muscle weakness may be increased
- Tetracyclines may exacerbate the symptoms of Systemic Lupus Erythematosus
- Hepatic impairment
- Renal impairment
Tetracyclines are bacteriostatic, broad spectrum antibiotics that inhibit bacterial protein synthesis. Competition with the tRNA anticodon binding of the mRNA codon A site, preventing codon / anticodon recognition in the 30S segment of the bacterial ribosome. Tetracycline binding is reversible. Selectivity is largely through active uptake into prokaryotic cells of the tetracyclines.
- Doxycycline - Oral
- Oxytetracycline - Oral
- Tetracyclines are generally safe but can deposit in bones and teeth causing brown discolouration of growing teeth, so should be avoided in pregnant women and children
- Nausea and vomiting, diarrhoea, dysphagia and oesophageal irritation
- Other rare side effects include hepatotoxicity, pancreatitis, photosensitivity and hypersensitivity reactions
- Benign intra-cranial hypertension is recognised. If headache or visual disturbance occurs, should be withdrawn
- Nephrotoxicity is seen, but not with doxycycline
- Tetracyclines possibly enhance the anticoagulant effect of warfarin
- Tetracyclines metabolism may be increased by P450 inducers
- Ciclosporin plasma concentration may be increased if prescribed with doxycycline
- Possible increased risk of benign intracranial hypertension when tetracyclines are given with retinoids
- Tetracycline efficacy is reduced by antacids and oral iron replacement therapy
Patients should be advised to complete the prescribed course of antibiotic therapy. It is important that patients take tetracyclines with plenty of water, 30 minutes before food and particularly not at the same time as milk, antacids or calcium supplements.
Due to tetracyclines’ ability to cause photosensitivity, all patients taking a tetracycline should be warned to protect their skin from sunlight (even on bright but cloudy days). They should also avoid sunbed use.
Tetracyclines chelate metal ions and absorption is decreased in the presence of milk (calcium).
Tetracyclines are widely distributed through the body and are excreted by the kidneys.
