Tetracycline antibiotic Pregnancy: Pregnancy Category D (US) - teratogenic. Pregnant women with renal disease may be more prone to tetracycline-associated liver failure.

Tetracycline

Tetracycline is a broad-spectrum tetracycline-class antibacterial used for infections such as acne, respiratory and genital chlamydial infections, and other susceptible organisms.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 1 gram daily, given as 500 mg twice a day or 250 mg four times a day

Route: Oral

Frequency: Twice daily or four times daily

Max: Up to 500 mg four times a day for severe infections or infections not responding to smaller doses

US labelling (tetracycline hydrochloride). Take with adequate fluid to reduce oesophageal irritation/ulceration; absorption impaired by antacids (aluminium, calcium, magnesium), iron, zinc, sodium bicarbonate, food and some dairy. Indication-specific regimens: streptococcal infections - continue 10 days; brucellosis - 500 mg four times daily for 3 weeks with streptomycin; syphilis (penicillin-allergic) - early (under 1 year) 500 mg four times daily for 15 days, over 1 year (except neurosyphilis) 500 mg four times daily for 30 days; gonorrhoea - 500 mg four times daily for 7 days; uncomplicated Chlamydia trachomatis urethral/endocervical/rectal - 500 mg four times daily for at least 7 days; moderate-to-severe acne - initial 1 g daily in divided doses, then reduce gradually to maintenance 125 mg to 500 mg daily.

Paediatric dose

Route: oral

Frequency: daily total divided in four equal doses

For paediatric patients above eight years of age (US labelling): usual daily dose 10 mg/lb to 20 mg/lb (25 mg/kg to 50 mg/kg) body weight divided in four equal doses. Range stated, so no single per-kg value. Tetracyclines can cause permanent tooth discoloration and enamel hypoplasia during tooth development - avoid in children under 8 years; verify against a children's formulary.

Dose adjustments

Renal

In renal impairment, decrease total dosage by reducing individual doses and/or extending the interval between doses.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to any of the tetracyclines

Side effects

Gastrointestinal: anorexia, nausea, epigastric distress, vomiting, diarrhoea, glossitis
Oesophagitis and oesophageal ulceration (especially with capsules taken before lying down)
Permanent tooth discoloration and enamel hypoplasia during tooth development
Skin: photosensitivity, fixed drug eruption, maculopapular and erythematous rashes
Hepatotoxicity and liver failure (notably in renal impairment); hypersensitivity reactions

Interactions

Avoid concurrent use with penicillin or other bactericidal antibacterials (bacteriostatic drugs may interfere with bactericidal action)
May depress plasma prothrombin activity - patients on anticoagulants may need reduced anticoagulant dose
Absorption impaired by antacids containing aluminium, calcium or magnesium, and by iron, zinc or sodium bicarbonate
May render oral contraceptives less effective

Clinical monograph

How it works

It binds reversibly to the 30S ribosomal subunit and prevents aminoacyl-tRNA binding to the ribosome, inhibiting bacterial protein synthesis with a bacteriostatic effect.

Prescribing in practice

It is contraindicated in pregnancy, breastfeeding and young children because it is deposited in growing bone and teeth, causing permanent discolouration and enamel hypoplasia.
Absorption is markedly reduced by milk, antacids and iron or other multivalent cations, which should be separated from dosing.
It can cause photosensitivity, so patients should avoid excessive sun exposure during treatment.

Monitoring

Monitor renal and hepatic function with prolonged or high-burden therapy, particularly in those with pre-existing impairment.

Counselling the patient

Take it on an empty stomach with water and avoid milk, antacids and iron around the dose.
Use sun protection as your skin may burn more easily.
It must not be used in pregnancy or in young children.

Evidence & guidelines

The class effect on bone and dental development underpins long-standing contraindications in pregnancy and early childhood reflected in UK prescribing references.

Reference: NICE; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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