Formulary
Doxycycline: Uses, Dosing, Side Effects and Indian Brand Names
Doxycycline is the most versatile tetracycline, first-line for rickettsial infections, chlamydia, and brucellosis, with the unique advantage of no renal dose adjustment and minimal food interference among tetracyclines.
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Doxycycline: Uses, Dosing, Side Effects and Indian Brand Names
Doxycycline is the most versatile tetracycline, first-line for rickettsial infections, chlamydia, and brucellosis, with the unique advantage of no renal dose adjustment and minimal food interference among tetracyclines.
NEET PG High-Yield: 30S ribosomal subunit inhibition (same as aminoglycosides -- but different sites). Bacteriostatic. Drug of choice for Rickettsia (scrub typhus is a favourite Indian exam topic). Teeth staining in children <8 years. No dose adjustment in renal failure (unique among tetracyclines -- GI excretion). Photosensitivity. Chelation with divalent cations (less than tetracycline). Oesophageal ulceration -- take upright with water. Contraindicated in pregnancy (Category D). Do not combine with isotretinoin (pseudotumour cerebri).
Clinical overview
Doxycycline is the most widely prescribed tetracycline and one of the most versatile antibiotics in clinical practice, with broad-spectrum activity against Gram-positive and Gram-negative bacteria, atypical organisms (Mycoplasma, Chlamydia, Rickettsia), spirochaetes, and even some protozoa (Plasmodium falciparum). It is the drug of choice for rickettsial infections (Indian tick typhus, scrub typhus -- both endemic in India), Chlamydia trachomatis (genital), Brucella (with streptomycin or rifampicin), cholera, and Lyme disease. In Indian practice, scrub typhus is a critical indication -- empiric doxycycline for undifferentiated acute febrile illness in endemic areas has saved many lives. Doxycycline has two major advantages over older tetracyclines: it is NOT significantly chelated by calcium in food (though it should still be taken with water, not milk), and it does NOT require dose adjustment in renal impairment because it is excreted primarily through the GI tract (faecal elimination) and is the safest tetracycline in renal failure. The class-wide contraindication in children under 8 years relates to permanent staining of developing teeth and inhibition of bone growth, though the WHO now considers short courses of doxycycline acceptable in children for rickettsial infections when alternatives are lacking. Photosensitivity is the most common adverse effect, and patients must be advised about sun protection. Doxycycline also has anti-inflammatory properties used in sub-antimicrobial doses for acne vulgaris and rosacea.
Pharmacological class
Doxycycline belongs to the Tetracycline Antibiotics (Second-Generation Tetracycline) class. Binds reversibly to the 30S ribosomal subunit, specifically the 16S rRNA acceptor (A) site, preventing aminoacyl-tRNA from binding and blocking the addition of amino acids to the growing peptide chain. This inhibits bacterial protein synthesis. Doxycycline is bacteriostatic at usual concentrations. Unlike first-generation tetracyclines, doxycycline is more lipophilic, allowing better tissue penetration.
Indian brand names and formulations
Available as: Doxt (Dr. Reddy's), Doxy-1 (Cipla), Microdox (Micro Labs), Tetradox (various).
Capsules: 100 mg. Tablets: 100 mg (regular, dispersible). Modified-release capsules: 40 mg (sub-antimicrobial dose for acne -- Oracea equivalent). IV infusion: 100 mg vial (limited use). Gel: 10% (for periodontal disease).
Regulatory status
Doxycycline is classified under Schedule H in India under the Drugs and Cosmetics Act, 1940. Prescription-only. Listed on NLEM. Available at Jan Aushadhi centres.
Indications
- Rickettsial infections (scrub typhus, Indian tick typhus -- drug of choice)
- Genital Chlamydia trachomatis (7-day course, alternative to azithromycin single dose)
- Community-acquired pneumonia (covers atypical pathogens)
- Brucellosis (with streptomycin or rifampicin for 6 weeks)
- Cholera (adjunct to rehydration)
- Lyme disease (early)
- Acne vulgaris (sub-antimicrobial dose: 40 mg MR daily)
- Malaria prophylaxis (P. falciparum areas)
- Pelvic inflammatory disease (with ceftriaxone + metronidazole)
- MRSA skin infections (community-acquired, susceptible strains)
Dosing
Adults: 100 mg twice daily on day 1 (loading dose), then 100 mg once or twice daily depending on indication. Scrub typhus: 100 mg twice daily for 7 days. Chlamydia: 100 mg twice daily for 7 days. Acne (sub-antimicrobial): 40 mg MR once daily. Malaria prophylaxis: 100 mg daily (start 1-2 days before, continue 4 weeks after). No dose adjustment in renal impairment.
Contraindications
- Children under 8 years (permanent teeth staining -- yellow-brown discolouration; inhibition of bone growth)
- Pregnancy (all trimesters -- dental staining of foetus, hepatotoxicity in mother, inhibition of foetal skeletal development)
- Lactation (excreted in breast milk, affects infant teeth and bones)
- Severe hepatic impairment
Adverse effects
- Photosensitivity (phototoxic reaction -- advise sun protection; most common with doxycycline among tetracyclines)
- GI disturbances (nausea, vomiting, diarrhoea -- take with food and plenty of water; do NOT lie down for 30 min after taking -- oesophageal ulceration risk)
- Oesophageal ulceration (if capsule lodges in oesophagus -- take upright with a full glass of water)
- Teeth staining in children (permanent, yellow-brown; dose and duration dependent)
- Vaginal candidiasis (disruption of normal flora)
- Benign intracranial hypertension (pseudotumour cerebri -- rare, may present with headache and papilloedema)
Drug interactions
- Antacids, iron, calcium supplements, dairy: chelation reduces absorption (though less than with older tetracyclines); separate by 2-3 hours
- Warfarin: doxycycline may increase INR by displacing warfarin from albumin and reducing gut flora vitamin K synthesis
- Oral contraceptives: may reduce efficacy (gut flora disruption); advise additional contraception
- Methotrexate: may increase methotrexate levels
- Isotretinoin: both cause benign intracranial hypertension -- do NOT combine
- Penicillins: theoretical antagonism (bacteriostatic tetracycline may interfere with bactericidal penicillin action -- though clinical significance is debated)
Pregnancy and lactation
Contraindicated in all trimesters. Category D. Causes permanent discolouration of foetal teeth (second and third trimester exposure), inhibition of bone growth, and rarely maternal hepatotoxicity (especially IV use in pregnancy). Use azithromycin or amoxicillin as alternatives.
Exam-style clinical scenario
A 28-year-old agricultural worker in South India presents with high fever for 5 days, headache, an eschar on the ankle, and regional lymphadenopathy. What is the likely diagnosis and treatment? Scrub typhus (Orientia tsutsugamushi, transmitted by Leptotrombidium mite) -- doxycycline 100 mg twice daily for 7 days. The eschar is pathognomonic.
Cost in India
Rs 30-60 for a strip of 10 capsules (100 mg). Available at Jan Aushadhi centres at subsidised rates.
Clinical governance
Author: MedNext Editorial Team. Clinical reviewer: Awaiting clinical review. Jurisdiction: India (Drugs and Cosmetics Act, 1940). Sources: CIMS India, Indian Pharmacopoeia. Publication state: Awaiting clinical review. Correction: Report errors at support@mednext.academy.
Frequently Asked Questions
Why can doxycycline be taken with food while other tetracyclines cannot?
Older tetracyclines (tetracycline HCl) are heavily chelated by calcium, iron, and other divalent cations in food, reducing absorption by 50-80%. Doxycycline's more lipophilic structure means it is absorbed primarily by passive diffusion rather than through cation-dependent transport, so food (including dairy) has much less effect on its absorption. However, dairy and antacids still reduce it somewhat, so separating by 2 hours is still advisable.
Why is doxycycline safe in renal failure?
Doxycycline is unique among tetracyclines because it is excreted primarily through the GI tract (chelated by bile salts and intestinal contents) rather than through the kidneys. Other tetracyclines accumulate in renal failure and can worsen azotaemia by inhibiting protein synthesis and increasing BUN from amino acid catabolism. Doxycycline does not accumulate and is the only tetracycline considered safe in renal impairment.
Why is scrub typhus so important for Indian medical students?
Scrub typhus (Orientia tsutsugamushi) is endemic in the 'tsutsugamushi triangle' that includes much of South and Southeast Asia. India reports thousands of cases annually, particularly from South India, Northeast India, and Himachal Pradesh. It causes undifferentiated febrile illness, and delayed diagnosis leads to complications including ARDS, meningoencephalitis, and multi-organ failure. Doxycycline must be started empirically in endemic areas; waiting for confirmation can be fatal.
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