Doxycycline
Doxycycline is an oral and parenteral tetracycline antibiotic used in adults and adolescents for skin, respiratory, sexually transmitted, tick-borne and selected travel-related infections, with broad activity and convenient once or twice-daily dosing.
- Chemical formula
- C22H24N2O8
- CAS number
- 564-25-0
- ATC code
- J01AA02
- Molecular weight
- 444.43 g/mol
- Drug class
- Tetracycline antibiotic
- Also known as
- GS-3065, Doxiciclina
What is it?
Doxycycline is a semi-synthetic tetracycline introduced in the 1960s. It is supplied as oral tablets, capsules, oral suspension and parenteral solution. Doxycycline is dispensed only on prescription and is part of the World Health Organization List of Essential Medicines. The molecule has broader tissue penetration and a longer half-life than older tetracyclines, supporting once or twice-daily dosing in most indications.
Mechanism of action
Doxycycline reversibly binds the 30S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis by preventing the binding of aminoacyl-tRNA to the ribosomal A site. It is generally bacteriostatic. The spectrum covers many Gram-positive and Gram-negative bacteria, including atypical respiratory pathogens, Chlamydia trachomatis, Borrelia burgdorferi (Lyme disease), Rickettsia species and several other intracellular and tick-borne organisms. Resistance through ribosomal protection and efflux pumps has emerged in some regions.
Pharmacokinetics
Doxycycline is well absorbed orally, with bioavailability above 90% — significantly better than older tetracyclines. Plasma protein binding is approximately 90%. The drug is partially metabolised and excreted in faeces and urine, with a terminal half-life of approximately 16 to 22 hours, supporting once or twice-daily dosing. Co-administration with antacids, calcium, iron and dairy products can substantially reduce absorption through chelation of the molecule.
Indications
Doxycycline is approved in adults and adolescents for the treatment of acne, rosacea, respiratory tract infections, atypical pneumonia, sexually transmitted infections including non-gonococcal urethritis, Lyme disease, rickettsioses, anthrax exposure and selected travel-related infections. It is also used as malaria prophylaxis in selected regions. According to clinical guidelines, choice of antibiotic depends on the suspected organism and local resistance.
Safety profile
Common adverse effects include gastrointestinal symptoms, photosensitivity, oesophageal irritation if not taken with adequate water and upright posture, and vaginal candidiasis. Tetracyclines including doxycycline are associated with permanent yellow-grey-brown discoloration of teeth and reduced bone growth when given to children under 8 years and during the second half of pregnancy. According to the prescribing information, these populations are contraindicated unless the benefit clearly outweighs the risk.
Products containing this ingredient
Frequently asked questions
Why must doxycycline be taken with plenty of water? ▾
Doxycycline can cause oesophageal irritation, ulceration and rarely perforation if it lodges in the oesophagus before dissolving. The prescribing information recommends taking the tablet with a full glass of water and remaining upright for at least 30 minutes after the dose. Taking the medication well before bedtime and avoiding lying down immediately after a dose reduces this risk substantially.
Why is doxycycline avoided in children and pregnancy? ▾
Tetracyclines, including doxycycline, can cause permanent yellow-grey-brown discoloration of developing teeth and reduce bone growth when administered to children under 8 years or during the second half of pregnancy. According to the prescribing information, these populations are contraindicated except when the benefit clearly outweighs the risk and no suitable alternative is available, such as severe rickettsioses.
Does doxycycline cause photosensitivity? ▾
Yes. Doxycycline can cause an exaggerated sunburn-like reaction on areas of the skin exposed to sunlight or ultraviolet light, in some patients within hours of sun exposure. According to the prescribing information, patients should use sun protection, wear protective clothing and avoid prolonged sun exposure or sunbeds during treatment, with discontinuation if a phototoxic reaction develops.
Can doxycycline be taken with milk or supplements? ▾
Calcium in dairy products, as well as iron, magnesium, aluminium and zinc-containing supplements or antacids, can chelate doxycycline and substantially reduce absorption. According to the prescribing information, doxycycline should be separated from these products by at least two to three hours. The medication can be taken with food to reduce gastrointestinal upset, although this also slightly reduces bioavailability.
What are the main contraindications for doxycycline? ▾
Doxycycline is contraindicated in known hypersensitivity to tetracyclines, in children under 8 years and during the second half of pregnancy and breastfeeding (with rare exceptions). Caution is required in severe hepatic impairment, in patients with photosensitivity disorders and in concomitant retinoid therapy due to the risk of intracranial hypertension. According to the prescribing information, the medical history must be reviewed by a clinician before any prescription.
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