Tetracyclines

• The drug binds reversibly to the 30S subunit of the bacterial ribosome.
• tetracyclines are effective against gram-positive and gram-negative bacteria.
• The suffix "-cycline" is commonly used to indicate tetracycline.
• doxycycline is the preferred tetracycline for parenteral administration.
• minocycline is available intravenously
• Doxycycline + minocycline are absorbed on oral administration
• Tetracyclines are effective against

  • gram + bacilli: B, anthracis
  • gram - rods: V. cholera, Y. pestis
  • anaerobic organisms: clostridium
  • spirochetes: borrelia, leptospira
  • mycoplasma
  • chlamydia
  • richettsia
• The tetracyclines concentrate in the liver, kidney, spleen, and skin, and they bind to tissues undergoing calcification.
• all tetracyclines enter the cerebrospinal fluid (CSF), but levels are insufficient for therapeutic efficacy.
• All the tetracyclines concentrate in the liver and are excreted in bile + breast milk.
• Side effects of tetracyclines include

  • gastric discomfort
  • discoloration and hypoplasia of the teeth of growing children
  • hepatotoxicity
  • phototoxicity
  • vestibular problems: dizziness, nausea, vomiting
  • pseudotumor cerebri: intracranial hypertension
  • superinfections (candida)
• Tetracycline contraindications include

  • renal impairment
  • azotemia
  • pregnancy
  • breastfeeding
  • dairy
• 1st generation tetracyclines required more doses than newer generations.
• Tetracyclines are divided according to their duration of action.

  • Short-acting (tetracycline)- t1/2 = 8 hours
  • Long-acting (doxycycline + minocycline) - t1/2 = > 16 hours