DrugFriday: Doxycycline


Doxycycline is an antibiotic belonging to the Tetracycline group of antibiotics

Mechanism of Action:

Doxycycline curbs bacterial growth by inhibiting RNA dependent protein synthesis in the bacteria.


The main site of metabolism of Doxycycline is liver. Oral absorption of the drug is almost complete and 90% of the drug remains protein bound.

Elimination of the drug is both through urine and stools.

Indications and Dosage:

Dosage is usually 200 mg/ day given in 2 divided doses, most commonly orally due to good absorption. Intravenous route may be used when oral administration is not possible.


  • Bacterial infections like Cholera, Brucellosis, Plague, Relapsing fever etc
  • Gram negative infections like E.Coli, Shigella, Klebsiella etc
  • Atypical pneumonia by organisms like Chlamydia, Mycoplasma
  • STDs such as Chlamydia, Gonorrhea,   Syphilis
  • Malaria
  • Ocular chlamydial infection
  • Bartonella infective endocarditis in combination with Gentamycin and Ceftriaxone

Adverse effects:

  • Diarrhea, enterocolitis, esophageal ulcers, dysphagia
  • Hepatotoxicity
  • Hemolytic anemia
  • Thrombocytopenia
  • Urticaria

Use in pregnancy:

Category D (to be used only in life threatening emergency in absence of alternatives)

Use in lactation:

Enters breast-milk, hence not recommended


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