Tetracyclines

• Chlamydia (non-pregnant)
• Acne (non-pregnant)
• Rickettsial disease, Lyme (pregnancy: only if life-threatening)

Bind 30S ribosomal subunit → block aminoacyl-tRNA → inhibit protein synthesis.

• Deposits in fetal teeth and bones — yellow-brown staining
• Photosensitivity
• Take upright with water — oesophageal ulceration

Doxycycline (non-pregnant)

100 mg BD × 7 days

• AbsolutePregnancy >18 weeks (fetal teeth/bone)
• AbsoluteChildren <8 years
• CautionHepatic impairment

• GI upset
• Photosensitivity
• Oesophageal ulceration if taken supine
• Idiopathic intracranial hypertension

• • After 18 weeks: permanent yellow-brown tooth discolouration, enamel hypoplasia, transient inhibition of long-bone growth
• • Before 15 weeks: azithromycin generally preferred for chlamydia

• Iron, calcium, antacids, dairy

  Caution

  Chelation — separate 2–4 h

• Retinoids

  Avoid

  Raised ICP

• Warfarin

  Caution

  ↑ INR

• 💡 Use azithromycin 1 g single dose for chlamydia in pregnancy (BASHH)
• 💡 Doxycycline preferred outside pregnancy for most STIs