Tetracyclines

These are broad spectrum antibiotics. The majority were discovered in the 1950's at which time they had a wider spectrum of activity than most other antibiotics.¹ They were active against:

• Gram positive and Gram negative bacteria
• Rickettsia
• Spirochaetes
• Lymphogranuloma venereum and some large viruses

Due to increasing bacterial resistance they are now no longer used against staphylococcus, streptococcus or pneumococcus. Minocycline has the widest antibacterial spectrum, as it is also active against neisseria meningitidis.
Their mechanism of action is by inhibiting essential reactions for vital processes within bacterial cells. e.g. protein synthesis. They can also alter the cytoplasmic membrane, allowing nucleotides and other essential compounds to leak out of the cell. They do not kill bacteria, but inhibit them. Their absorption is affected by dairy products and advice labels usually direct patients to avoid taking milk with the tablets.

• Tetracycline
• Doxycycline
• Minocycline
• Oxytetracycline

They are available as topical, oral or intravenous medication.

Where possible treatment should be indicated by sensitivity from a cultured specimen. If empirical treatment is required, your local primary care trust will have produced a formulary with recommended treatments based onknowledge of local prevalent pathogens and resistance.

Tetracyclines bind to calcium and are deposited in growing bones and teeth, causing brown discolouration. This can occur from the fourth month in-utero until 12 years of age. They also cause dental hypoplasia. They should not be given to:

• Pregnant women
• Children under 12 years - except in prophylaxis of anthrax, as above.
• Breast feeding mothers - is found in breast milk.

It should also be withheld from patients with kidney disease, as it can worsen renal failure.

• GI effects- nausea, vomiting and diarrhoea. Occasional antibiotic related colitis.
• Sore mouth, dysphagia and oesophagitis
• Increased photosensitivity