How the dose is calculated
Doxycycline is dosed in mg/kg/day. Standard treatment dosing is divided every 12 hours; malaria chemoprophylaxis uses a lower once-daily dose. Tetracyclines can stain developing teeth, so use is generally avoided under age 8 except for specific indications with no safer alternative (e.g. severe rickettsial or vector-borne disease) — confirm current age-specific guidance before prescribing.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| Standard infection | 4 mg/kg/day | every 12h (2×/day) | 200 mg/day |
| Malaria chemoprophylaxis | 2 mg/kg once daily (adult: 100 mg) | once daily | 100 mg/day |
| Chlamydia trachomatis | 100 mg BD (use Standard option above) | × 7 days | 200 mg/day |
| Lymphogranuloma venereum (LGV) | 100 mg BD | × 3 weeks | 200 mg/day |
| Granuloma inguinale / donovanosis | 100 mg BD | × 3 weeks | 200 mg/day |
| Syphilis, early (primary, secondary, latent <1 yr) | 100 mg BD | × 15 days | 200 mg/day |
| Syphilis, late (>1 yr) | 100 mg BD | × 30 days | 200 mg/day |
| Chancroid (H. ducreyi) | 100 mg BD | × 7 days | 200 mg/day |
Doxycycline is generally avoided in children under 8 years because of the risk of permanent tooth discoloration, except when treating specific infections (e.g. severe rickettsial disease, leptospirosis, anthrax exposure) where no safer alternative exists — recent guidance suggests short courses carry lower risk than previously believed, but this remains a specialist decision, not a routine one.
The five sexually-transmitted-infection indications above (chlamydia trachomatis, LGV, granuloma inguinale/donovanosis, and both stages of syphilis) all use the same 100 mg twice-daily adult dose already produced by the "Standard" option above once weight reaches the adult cap — they're listed separately here because the correct course length differs by indication, which the calculator doesn't need to know to get the per-dose mg right. Doxycycline for syphilis is an alternative regimen, generally reserved for penicillin allergy — benzathine penicillin G remains first-line.
Clinical use
- Doxycycline is the treatment of choice for many rickettsial diseases (e.g. Rocky Mountain spotted fever, scrub typhus) even in young children, since delayed treatment carries far greater risk than the tooth-staining concern.
- Also used for malaria chemoprophylaxis in travellers to chloroquine-resistant areas, leptospirosis, and as an alternative for atypical respiratory pathogens.
- For malaria chemoprophylaxis specifically, doxycycline is contraindicated in pregnancy and in children under 8 years — an alternative agent must be used instead in both groups.
- A single flat adult dose of 100 mg twice daily, just for different durations, covers several sexually transmitted infections — chlamydia trachomatis and chancroid (7 days), lymphogranuloma venereum and granuloma inguinale/donovanosis (3 weeks), and syphilis (15 days early, 30 days late) — always confirm the course length for the specific diagnosis rather than assuming a fixed duration.
- Should be taken with a full glass of water and the patient should remain upright for 30 minutes afterward, to reduce the risk of oesophageal irritation/ulceration.
- Photosensitivity is common — advise sun protection during treatment.
Frequently asked questions
Is doxycycline safe for young children?
It's generally avoided under age 8 because of a risk of permanent tooth discoloration, but it is still used at any age for specific severe infections (like rickettsial disease) where no safer alternative exists and delayed treatment is more dangerous than the tooth-staining risk.
What is doxycycline used for in malaria prevention?
It's one of the standard chemoprophylaxis options for travellers to areas with chloroquine-resistant P. falciparum, dosed at 100 mg once daily, starting 1–2 days before travel, continued throughout the stay, and continued for 4 weeks after leaving the risk area. It must not be used for this purpose in pregnancy or in children under 8 years — use an alternative agent instead.
What is the doxycycline dose for chlamydia trachomatis?
100 mg twice daily for 7 days — the same dose the "Standard" option above already produces once weight reaches the adult cap.
What is the doxycycline dose for syphilis?
100 mg twice daily for 15 days for early syphilis (primary, secondary, or latent <1 year), or for 30 days for late syphilis (>1 year) — used as an alternative regimen, generally when benzathine penicillin G (the first-line treatment) can't be used, such as in penicillin allergy.
What is the doxycycline dose for lymphogranuloma venereum (LGV) or donovanosis?
100 mg twice daily for 3 weeks for both lymphogranuloma venereum and granuloma inguinale (donovanosis) — a longer course than most other doxycycline indications on this page.
Why should doxycycline be taken with a full glass of water?
Doxycycline capsules/tablets can irritate or ulcerate the oesophagus if they don't pass through quickly — a full glass of water and staying upright afterward reduces this risk.
Does doxycycline make skin more sensitive to sun?
Yes — photosensitivity is a recognised side effect, so sun protection (sunscreen, protective clothing) is recommended during treatment.
References
- American Academy of Pediatrics. Update on Doxycycline Use in Children of All Ages. Pediatrics. 2015.
- Centers for Disease Control and Prevention. Yellow Book — Malaria Chemoprophylaxis.
- British National Formulary for Children (BNFc) — Doxycycline.
- Tripathi KD. Essentials of Medical Pharmacology, 8th edition — pages 813, 875.