[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Tetracyclines](https://durgical.com/en/pharmacology/classes/tetracyclines/) › Tetracycline

[Pharmacology](https://durgical.com/en/pharmacology/) · [Tetracyclines](https://durgical.com/en/pharmacology/classes/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](https://durgical.com/en/pharmacology/classes/tetracyclines/)
- Target: Bacterial ribosome, 30S subunit (16S rRNA, A site)
- ATC code: J01AA07
- WHO Model List of Essential Medicines

◆**Bacterial ribosome, 30S subunit (16S rRNA, A site)**Tetracycline

ⓘ 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](https://www.rcsb.org/structure/5J5B) · Drag to rotate · pinch to zoom

## 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.

- Absorbed by mouth or applied to the eye
- Binds the 30S ribosomal subunit
- Aminoacyl-tRNA cannot enter the A site
- 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 →](https://durgical.com/en/conditions/conjunctivitis/)
- Syphilis in people allergic to penicillin [Syphilis →](https://durgical.com/en/conditions/syphilis/)
- Adjunctive treatment of severe acne

## Adverse effects

### Common

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

### Serious (rare, important)

- Permanent tooth discoloration and slower bone growth in children and late pregnancy
- Intracranial hypertension
- Oesophageal ulcer

## 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.

## Memory aid

«Tetra hates milk»: calcium grabs it in the gut and in the teeth.

## 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)](https://durgical.app/estudiar/?add=/en/pharmacology/tetracycline/)

## Related drugs

- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Minocycline](https://durgical.com/en/pharmacology/minocycline/)
- [Demeclocycline](https://durgical.com/en/pharmacology/demeclocycline/)

## Related conditions

- [Conjunctivitis](https://durgical.com/en/conditions/conjunctivitis/)
- [Syphilis](https://durgical.com/en/conditions/syphilis/)

[← Back to the class: Tetracyclines](https://durgical.com/en/pharmacology/classes/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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=00acf413-c5d2-4a54-9d0d-56266cbc9edc) (DailyMed (U.S. National Library of Medicine), 2026); [Tetracycline: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682098.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/?query=tetracycline) (World Health Organization, 2025); [Structure of the WT E coli ribosome bound to tetracycline](https://www.rcsb.org/structure/5J5B) (RCSB Protein Data Bank, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/tetracycline/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/tetracycline/