Tetracyclines · Anti-infectives
Doxycycline
Vibramycin® · Doxycin®(brand names vary by market)
Broad, oral, kidney-independent, and it must not be taken lying down.
Also: tablet, oral liquid, injection
Mechanism
Binds the 30S ribosomal subunit and blocks aminoacyl-tRNA docking. Excellent intracellular penetration, which is why it reaches the organisms that live inside cells.
Indications
- Atypical and community-acquired pneumonia
- Tick-borne illness including Lyme and rickettsial disease
- Chlamydia
- Acne and rosacea
- Community-acquired MRSA skin infection
- Malaria prophylaxis
Formulations
Dosing concepts
Renal impairment
Non-renally cleared, so no dose adjustment is needed. That makes it unusually useful in kidney disease, where most broad oral options require adjustment.
Administration
Taken with a full glass of water, sitting or standing, and not immediately before lying down.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~95%
- Half-life
- 18 to 22 h
- Elimination
- mixed: Largely non-renal, with intestinal excretion; safe in renal impairment
- Protein binding
- ~90%
Adverse effects
- PhotosensitivitycommonGenuinely severe sunburn on modest exposure; a summer prescription needs explicit advice.
- Pill oesophagitiscommonPainful, avoidable, and entirely about how the tablet is taken.
- Nauseacommon
- Tooth discolouration in children under 8serious
- Intracranial hypertensionseriousRare; headache with visual change warrants stopping.
Contraindications & precautions
Contraindications
- Pregnancy
- Children under 8, except for serious rickettsial illness where benefit outweighs risk
Precautions
- Sun exposure
- Concurrent iron, calcium, magnesium or antacids
- Oesophageal disorders
Interactions
- Ciprofloxacin (and all fluoroquinolones, tetracyclines) + Calcium, magnesium, aluminum, iron, zinc. Antacids, dairy, supplementscautionSub-therapeutic antibiotic levels: treatment failure that looks like resistance.
- Broad-spectrum antibiotics (any) + WarfarinmonitorModest INR rise, additive with any CYP effect of the specific agent.
Monitoring
Clinical response
Efficacy
Sun exposure advice given
The commonest avoidable harm with this drug
Counselling points
- Take it with a full glass of water and stay upright for at least 30 minutes.
- Use high-factor sunscreen and cover up: this medicine makes you burn much more easily.
- Keep it four hours away from indigestion remedies, iron and calcium supplements.
- It can be taken with food if it upsets your stomach, though absorption is slightly reduced.
Clinical pearls
- It needs no renal adjustment, which repeatedly makes it the right answer in an older patient with chronic kidney disease and a chest infection.
- The cation chelation trap is the same as with the fluoroquinolones: a patient taking their antibiotic with a glass of milk or their calcium tablet is taking very little antibiotic at all.
References & review
- Doxycycline product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.