TETRACYCLINE HYDROCHLORIDE
Clinical safety rating: avoid
Positive evidence of fetus risks but benefits may outweigh risks in some cases
Inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing aminoacyl-tRNA from binding to the mRNA-ribosome complex.
| Metabolism | Not extensively metabolized; primarily excreted unchanged in urine and bile. |
| Excretion | Renal (60% unchanged via glomerular filtration), biliary (40% as active drug and metabolites, with enterohepatic recirculation; fecal elimination of unabsorbed drug). |
| Half-life | 6-11 hours (prolonged to 57-120 hours in severe renal impairment; reduced in hepatic dysfunction; clinically relevant for dosing interval adjustments). |
| Protein binding | 20-67% (primarily albumin; variable due to chelation with divalent cations). |
| Volume of Distribution | 1.3-1.8 L/kg (large distribution indicates extensive tissue penetration; accumulates in liver, kidney, bone, and teeth). |
| Bioavailability | Oral: 75-80% (reduced by 50-80% with concurrent dairy, antacids, or iron; food may decrease absorption by 50%). |
| Onset of Action | Oral: 1-2 hours (therapeutic serum levels); IV: immediate (peak serum levels within 15-30 minutes); Topical: hours to days (clinical effect). |
| Duration of Action | 12-24 hours (serum levels above MIC for susceptible organisms; may be prolonged in renal impairment; typical dosing every 6-12 hours). |
| Molecular Weight | 480.9 |
250-500 mg orally every 6 hours; or 500 mg to 1 g intravenously every 12 hours. Maximum oral dose: 4 g/day.
| Dosage form | CAPSULE |
| Renal impairment | For GFR 50-90 mL/min: no adjustment. For GFR 10-50 mL/min: administer every 12-24 hours. For GFR <10 mL/min: administer every 24 hours or avoid use. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce dose by 50%. Child-Pugh C: avoid use due to hepatotoxicity. |
| Pediatric use | Children >8 years: 6.25-12.5 mg/kg orally every 6 hours; or 10-20 mg/kg intravenously every 12 hours. Not recommended in children <8 years. |
| Geriatric use | No specific dose adjustment, but monitor renal function; consider lower doses due to age-related renal decline. Avoid in patients with hepatic impairment. |
| 1st trimester | Avoid use; associated with fetal skeletal malformations and congenital cataracts; also may cause maternal hepatotoxicity. |
| 2nd trimester | Avoid use; associated with fetal bone and tooth discoloration; also may cause maternal hepatotoxicity. |
| 3rd trimester | Avoid use; causes permanent yellow-gray-brown discoloration of deciduous teeth and enamel hypoplasia; also may inhibit fetal bone growth and cause maternal hepatotoxicity. |
Clinical note
Antacids and calcium supplements decrease absorption Can cause photosensitivity and tooth discoloration in children.
| Placental transfer | Tetracycline crosses the placenta by passive diffusion; cord blood levels reach approximately 50-60% of maternal serum levels. |
| Breastfeeding | Tetracycline is excreted into breast milk in small amounts; theoretical risk of dental staining and bone growth inhibition in nursing infants. American Academy of Pediatrics considers tetracycline compatible with breastfeeding for short-term use, but alternative agents are preferred. |
■ FDA Black Box Warning
Use during tooth development (last half of pregnancy, infancy, and childhood to the age of 8 years) may cause permanent discoloration of the teeth (yellow-gray-brown) and enamel hypoplasia. Avoid in pregnancy and in children under 8 years unless no alternative therapy.
| Common Effects | acne |
| Serious Effects |
Hypersensitivity to tetracyclinesSevere hepatic impairmentPregnancy (especially second and third trimesters)Lactation (relative, but caution)Concurrent use with oral retinoids (e.g., isotretinoin) due to increased risk of pseudotumor cerebri
| Precautions | Photosensitivity: exaggerated sunburn reaction may occur; avoid prolonged sun exposure., Use may result in overgrowth of nonsusceptible organisms, including fungi; if superinfection occurs, discontinue and institute appropriate therapy., Hepatotoxicity: reported rarely; caution in patients with hepatic impairment., Renal impairment: may increase serum half-life and require dose adjustment., Pseudotumor cerebri (benign intracranial hypertension): reported in adults; usually resolves after discontinuation. |
Loading safety data…
| Lactation Rating | L2 (Safer; limited data suggest no increased risk in nursing infants) |
| Teratogenic Risk | Use contraindicated in pregnancy. Tetracycline crosses the placenta. First trimester: No clear evidence of teratogenicity, but risk cannot be excluded; animal studies show skeletal abnormalities. Second and third trimesters: Causes permanent discoloration of deciduous teeth (yellow-gray-brown) due to incorporation into dental enamel; also inhibits fetal skeletal growth and causes hypoplasia of enamel. Risk of maternal hepatotoxicity with IV use in pregnancy. |
| Fetal Monitoring | If inadvertent exposure during pregnancy, monitor fetal growth and dental development. No specific monitoring required for lactation; observe infant for rash, diarrhea, or oral thrush. Hepatic and renal function monitoring recommended in mother if high doses or prolonged therapy. |
| Fertility Effects | No conclusive evidence of impaired fertility in humans. Animal studies show altered spermatogenesis at high doses. Reversible reduction in sperm motility reported in some studies. |
| Food/Dietary | Avoid dairy products (milk, yogurt, cheese), calcium-fortified foods, iron-rich foods, and high-acid foods within 2 hours of tetracycline. Separate administration from calcium, magnesium, zinc, and iron supplements by at least 2 hours. Do not take with antacids or bismuth subsalicylate. |
| Clinical Pearls | Avoid in children <8 years and pregnant/breastfeeding women due to permanent tooth discoloration and bone growth inhibition. Administer on an empty stomach 1 hour before or 2 hours after meals. Avoid concurrent dairy, antacids, iron, calcium, magnesium, zinc, or bismuth subsalicylate. Use with caution in renal impairment due to anti-anabolic effects. Monitor for photosensitivity, pseudotumor cerebri, and superinfection. Outdated drug can cause Fanconi syndrome. |
| Patient Advice | Take tetracycline on an empty stomach at least 1 hour before or 2 hours after meals. · Do not take with dairy products, antacids, iron supplements, or multivitamins. · Avoid prolonged sun exposure and use sunscreen to prevent photosensitivity. · Finish the entire course even if you feel better; do not skip doses. · Report severe headache, vision changes, or watery diarrhea immediately. · Do not use after expiration date as it may cause kidney damage. · Use birth control as tetracycline may reduce effectiveness of oral contraceptives. |