Doxycycline is a broad-spectrum, second-generation, long-acting tetracycline-class antibiotic. It is a semi-synthetic derivative of oxytetracycline. It is bacteriostatic and exerts its effect by inhibiting protein synthesis in susceptible bacteria. It is widely used in India for a variety of bacterial infections, including respiratory, genitourinary, and skin/soft tissue infections, as well as for prophylaxis of malaria and treatment of rickettsial diseases.
Adult: 100 mg orally every 12 hours on the first day, followed by 100 mg once daily or 50 mg every 12 hours. For severe infections (e.g., chronic UTI), 100 mg every 12 hours may be continued. For malaria prophylaxis: 100 mg once daily, starting 1-2 days before travel, during travel, and for 4 weeks after leaving the endemic area.
Note: Take with a full glass of water while sitting or standing upright to prevent esophageal irritation and ulceration. Can be taken with food or milk to reduce GI upset, but avoid concurrent intake of dairy products, antacids, calcium, magnesium, aluminum, iron, or zinc supplements, bismuth subsalicylate, or multivitamins containing these cations. Maintain at least a 2-3 hour gap. Complete the full prescribed course.
Doxycycline binds reversibly to the 30S ribosomal subunit of susceptible bacteria, preventing the binding of aminoacyl-tRNA to the acceptor site (A-site) on the mRNA-ribosome complex. This inhibits the addition of new amino acids to the growing peptide chain, thereby inhibiting protein synthesis and exerting a bacteriostatic effect.
Pregnancy: Pregnancy Category D. Contraindicated. Tetracyclines cross the placenta and can cause permanent discoloration of the fetus's deciduous teeth (yellow-gray-brown) and possibly inhibit bone growth. Risk is greatest during the second and third trimesters.
Driving: May cause dizziness, lightheadedness, or blurred vision (especially with intracranial hypertension). Patients should be cautioned about driving or operating machinery if they experience these effects.
| Antacids (Aluminum, Calcium, Magnesium) | Markedly decreased absorption of doxycycline due to chelation. | Major |
| Iron supplements (Ferrous sulfate) | Decreased absorption of both drugs. | Major |
| Warfarin | Doxycycline may potentiate anticoagulant effect, increasing INR and risk of bleeding. | Moderate |
| Oral Contraceptives (Estrogen-containing) | Possible reduced efficacy of contraceptives, leading to breakthrough bleeding or pregnancy. Use backup method. | Moderate |
| Penicillins (e.g., Amoxicillin) | Bacteriostatic effect of doxycycline may interfere with bactericidal action of penicillins. Avoid concurrent use. | Moderate |
| Isotretinoin | Increased risk of intracranial hypertension (pseudotumor cerebri). Avoid concomitant use. | Major |
| Methoxyflurane | Concurrent use with tetracyclines can cause fatal nephrotoxicity. | Major |
| Barbiturates, Carbamazepine, Phenytoin | May increase the metabolism of doxycycline, reducing its serum levels. | Moderate |
Same composition (Doxycycline (100mg)), different brands: