Tetracycline is a broad-spectrum, bacteriostatic antibiotic belonging to the tetracycline class. It inhibits protein synthesis by binding to the 30S ribosomal subunit, preventing aminoacyl-tRNA attachment. It is effective against a wide range of Gram-positive and Gram-negative bacteria, spirochetes, mycoplasmas, chlamydiae, and rickettsiae. In the Indian context, it is a critical, cost-effective antibiotic for managing various bacterial infections, though its use is declining due to resistance and the availability of newer tetracyclines.
Adult: 500 mg orally every 6 hours. For severe infections, initial dose may be 500 mg every 6 hours, reduced to 250 mg every 6 hours or 500 mg every 12 hours based on response. For acne: 500 mg twice daily, tapering as condition improves.
Note: Take on an empty stomach, at least 1 hour before or 2 hours after meals. Take with a full glass of water (at least 200 mL) while standing or sitting upright to prevent esophageal irritation and ulceration. Do NOT take with dairy products, antacids, calcium, iron, magnesium, zinc supplements, or bismuth subsalicylate. Maintain at least a 2-3 hour gap.
Tetracycline reversibly binds to the 30S subunit of the bacterial ribosome at a position that blocks the binding of aminoacyl-tRNA to the acceptor site on the mRNA-ribosome complex. This inhibition prevents the addition of new amino acids to the growing peptide chain, thereby halting protein synthesis.
Pregnancy: CONTRANDICATED (Pregnancy Category D). Tetracycline crosses the placenta and can cause permanent yellow-gray-brown discoloration of deciduous teeth, enamel hypoplasia, and inhibition of fetal skeletal growth (reversible). Risk is greatest during the second and third trimesters.
Driving: Generally safe. However, dizziness or visual disturbances (pseudotumor cerebri) have been reported rarely. Patients experiencing these effects should not drive or operate machinery.
| Antacids (Aluminum, Magnesium, Calcium) | Markedly decreased tetracycline absorption due to chelation. | Major |
| Iron Supplements/Salts | Markedly decreased absorption of both agents. | Major |
| Warfarin | Increased anticoagulant effect; risk of bleeding. | Major |
| Oral Contraceptives (Estrogen-containing) | Possible decreased contraceptive efficacy; risk of breakthrough bleeding. | Moderate |
| Methoxyflurane | Increased risk of fatal nephrotoxicity. | Contraindicated |
| Retinoids (Isotretinoin, Acitretin) | Additive risk of pseudotumor cerebri. | Major |
| Digoxin | Increased digoxin bioavailability, risk of toxicity. | Moderate |
| Penicillins (e.g., Amoxicillin) | Antagonistic antibacterial effect; avoid concurrent use. | Moderate |
Same composition (Tetracycline (500mg)), different brands: