Doxycycline

Mechanism of Action

• Member of the tetracycline family of antibiotics.  Act by inhibiting bacterial protein synthesis.  Mainly useful in treating intracellular bacterial pathogens e.g. Chlamydia, Mycoplasma; but can also be useful at treating H influenzae and Strep pneumoniae
  • Used in treating pneumonia (particularly in older patients)
• Long acting (half life 18-22 hours), oral tetracycline

Pharmacology

• Circulates mainly protein bound (90%)
• Metabolised mainly by the liver and excreted in the bile/urine

Contraindications

• Pregnancy, SLE, Myaesthenia gravis, porphyria

Side effects

• Photophobia- avoid sun beds/overexposure to sun; use protection
• Stomach upset/indigestion/abdominal pain
• Diarrhoea
• Headache
• Thrush
• Throat irritation (take with a large glass of water; sitting upright/standing)
• NB Take doxycycline eithe 1 hour before or 2 hours after eating or taking any antacids, iron tablets, (basically medications containing metal compounds)
• Can also cause liver toxicity; benign intracranial hypertension