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Pharmacology · Tetracyclines

Tetracycline !

The parent drug of its class. On the WHO list as an eye ointment for conjunctivitis; by mouth it is used for acne and as a penicillin alternative.

Updated 2026-11-01

  • Class: Tetracyclines
  • Target: Bacterial ribosome, 30S subunit (16S rRNA, A site)
  • ATC code: J01AA07
  • WHO Model List of Essential Medicines

The figure shows tetracycline bound to the Escherichia coli 70S ribosome.

Target in 3D: Bacterial ribosome, 30S subunit (16S rRNA, A site). PDB structure 5J5B (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Tetracycline binds the 16S rRNA of the 30S subunit and stops aminoacyl-tRNA from occupying the A site. Protein synthesis stops and the bacteria cannot multiply. Bacteria resist it with efflux pumps and ribosomal protection proteins.

  1. Absorbed by mouth or applied to the eye
  2. Binds the 30S ribosomal subunit
  3. Aminoacyl-tRNA cannot enter the A site
  4. Bacterial growth stops

Pharmacokinetics

Absorption
Oral absorption is reduced by food, dairy products, antacids and iron.
Elimination
Urine and faeces.

Indications

  • Bacterial conjunctivitis and other eye infections (eye ointment on the WHO list) Conjunctivitis →
  • Syphilis in people allergic to penicillin Syphilis →
  • Adjunctive treatment of severe acne

Adverse effects

Common

  • Nausea, diarrhoea and abdominal discomfort
  • Photosensitivity
  • Yeast infections

Contraindications

  • Allergy to any tetracycline
  • Second half of pregnancy and children up to 8 years (systemic use)

Key interactions

Antacids, calcium, magnesium, iron, dairy products
Bind tetracycline and prevent absorption.
Oral contraceptives
May be less effective.
Warfarin
Anticoagulant effect may increase.

What is monitored

  • Response of the infection
  • Serology after syphilis treatment

Administration and safety

  • Oral doses are taken with a full glass of water, apart from food, dairy products and minerals
  • Eye ointment: a thin ribbon into the lower eyelid, without touching the eye with the tube

Nursing care

  • Teach to separate doses from milk, antacids and iron
  • Teach sun protection
  • Advise an extra contraceptive method if needed

Pregnancy and breastfeeding

Avoided in the second half of pregnancy because it stains the baby's teeth and affects bone growth.

Test yourself

Think of the answer, then tap the question to see it.

Why is oral tetracycline taken away from dairy products?

Calcium chelates it and prevents its absorption.

Which tetracycline form is on the WHO list?

Tetracycline eye ointment.

Which hormonal medicine may be weakened by tetracycline?

Oral contraceptives.

Add to my cards (3)

← Back to the class: Tetracyclines

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - TETRACYCLINE HYDROCHLORIDE capsule (DailyMed (U.S. National Library of Medicine), 2026); Tetracycline: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025); Structure of the WT E coli ribosome bound to tetracycline (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.