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). |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Antacids and calcium supplements decrease absorption Can cause photosensitivity and tooth discoloration in children.
| Breastfeeding | Tetracycline is excreted into breast milk; M/P ratio not established but concentration approx 0.5-1.0 mcg/mL. Potential for serious adverse reactions in nursing infants (e.g., permanent tooth discoloration, bone growth inhibition, photosensitivity). The American Academy of Pediatrics considers it compatible but alternative agents preferred. Avoid prolonged use; use only if clearly needed. |
| 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. |
■ 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 tetracyclines","Pregnancy (last half) and breastfeeding","Children under 8 years of age (risk of permanent tooth discoloration)"]
| 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."] |
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| 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. |