Doxycycline !

The most used tetracycline: for rickettsial fevers, chlamydia, leptospirosis, cholera and malaria prevention. Taken upright with water, away from minerals.

Updated 2026-11-01

Class: Tetracyclines
Target: Bacterial ribosome, 30S subunit (16S rRNA, A site)
ATC code: J01AA02
WHO Model List of Essential Medicines

Bacterial ribosome, 30S subunit (16S rRNA, A site)Doxycycline

The figure shows doxycycline bound to the 30S ribosomal subunit of Escherichia coli.

Target in 3D: Bacterial ribosome, 30S subunit (16S rRNA, A site). PDB structure 9SX2 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Doxycycline binds the 16S rRNA of the 30S subunit and blocks aminoacyl-tRNA from entering the A site, so the protein chain cannot grow. It is mainly bacteriostatic and reaches intracellular bacteria such as Rickettsia and Chlamydia.

Absorbed almost completely by mouth
Enters the bacterium and binds the 30S subunit
Aminoacyl-tRNA cannot reach the A site
Protein synthesis and growth stop

Pharmacokinetics

Absorption: About 90% absorbed by mouth; food changes it little, but calcium, magnesium, aluminium and iron reduce it.
Distribution: Wide, including intracellular sites.
Elimination: Urine and faeces; it can be used in kidney failure without dose change.
Half-life: About 18–22 hours, similar in severe kidney failure.

Indications

Chlamydia trachomatis infection (WHO first choice), including lymphogranuloma venereum Chlamydia infection →
Leptospirosis and rickettsial fevers (spotted fever, typhus, Q fever) Leptospirosis →
Prevention of Plasmodium falciparum malaria in travellers Malaria →
Community-acquired pneumonia (WHO second choice) Community-acquired pneumonia →
Syphilis when penicillin cannot be used Syphilis →
Cholera (WHO first choice) and anthrax after exposure

Adverse effects

Common

Nausea and stomach upset
Photosensitivity (exaggerated sunburn)
Oesophageal irritation or ulcer if swallowed without water
Vaginal yeast infection

Contraindications

Allergy to any tetracycline
Second half of pregnancy and children up to 8 years, except severe disease (e.g. spotted fever, anthrax) without alternatives

Key interactions

Antacids, calcium, magnesium, iron, bismuth: Chelate doxycycline and lower absorption; doses are spaced.
Warfarin: Tetracyclines can increase its effect.
Carbamazepine, phenytoin, barbiturates, rifampicin: Shorten doxycycline's half-life.
Isotretinoin: Both can raise intracranial pressure; combined use is avoided.

What is monitored

Headache or visual change (intracranial hypertension)
Skin after sun exposure
INR on warfarin

Administration and safety

Swallow with a full glass of water and stay upright for a while; not at bedtime
Separate from antacids, minerals and iron
The IV form is protected from light and infused slowly

Nursing care

Teach sun protection
Teach to report painful swallowing, severe headache or blurred vision
Ask about pregnancy and the child's age
For malaria prevention, explain that it is continued after leaving the risk area as prescribed

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 doxycycline swallowed with plenty of water while upright?

A capsule or tablet that stays in the oesophagus causes irritation and ulcers.

Which antimalarial use does doxycycline have?

Prevention of Plasmodium falciparum malaria in travellers.

Does doxycycline need a dose change in kidney failure?

No; its half-life stays similar, because it is also cleared in the faeces.

Which minerals cut doxycycline absorption?

Calcium, magnesium, aluminium and iron.

Add to my cards (4)

← 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 - DOXYCYCLINE HYCLATE capsule (DailyMed (U.S. National Library of Medicine), 2026); Doxycycline: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025); 30S Doxycycline Bound E. coli Ribosome (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.