TETRACYN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TETRACYN (TETRACYN).
Tetracycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing the attachment of aminoacyl-tRNA to the A site.
| Metabolism | Primarily excreted unchanged in urine via glomerular filtration; minor hepatic metabolism. |
| Excretion | Renal (glomerular filtration): 60% unchanged in urine; biliary/fecal: 40% as active drug and metabolites; enterohepatic recirculation occurs. |
| Half-life | Terminal elimination half-life: 6-8 hours in normal renal function; prolonged to 18-30 hours in severe renal impairment (CrCl <30 mL/min); dosing adjustment required. |
| Protein binding | 65% bound to serum proteins, primarily albumin; binding is reversible and saturable at high concentrations. |
| Volume of Distribution | Volume of distribution: 1.3 L/kg (range 1.0-1.6 L/kg); indicates extensive tissue penetration (e.g., bone, teeth, liver, tumors). |
| Bioavailability | Oral: 75-80% (fasting); reduced 50% by food, dairy, antacids, iron, calcium; IM: 100% (but painful). |
| Onset of Action | Oral: 1-2 hours to therapeutic serum levels; IV: immediate (minutes) after bolus; IM: 1-2 hours to peak concentrations. |
| Duration of Action | Bacteriostatic effect lasts 12-24 hours for susceptible organisms; therapeutic serum levels persist for 6-8 hours post-dose; tissue levels may persist longer. |
250–500 mg orally every 6 hours; or 500 mg to 1 g intravenously every 6–12 hours (administer slow IV).
| Dosage form | CAPSULE |
| Renal impairment | GFR 50–90 mL/min: no adjustment; GFR 10–50 mL/min: extend interval to every 12–24 hours; GFR <10 mL/min: extend interval to every 24 hours and avoid tetracyclines if possible due to anti-anabolic effects; not effectively removed by hemodialysis. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50% or extend interval; Child-Pugh C: contraindicated or use with extreme caution (max 1 g/day). |
| Pediatric use | For children >8 years: 25–50 mg/kg/day orally divided every 6–12 hours; IV: 10–20 mg/kg/day divided every 12 hours. Contraindicated in children <8 years due to permanent tooth discoloration and bone growth inhibition. |
| Geriatric use | Use with caution; no specific dose adjustment but monitor renal function; avoid in patients with decreased renal function due to increased risk of azotemia; use lowest effective dose. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for TETRACYN (TETRACYN).
| Breastfeeding | TETRACYN is excreted into human milk. The milk-to-plasma ratio is approximately 0.5-0.8. Due to the potential for dental discoloration and bone growth inhibition in the nursing infant, alternative agents are preferred. Caution is advised; consider temporary discontinuation of breastfeeding during therapy. |
| Teratogenic Risk | Category D. Tetracyclines (including TETRACYN) are associated with fetal risk. In the first trimester, there is an increased risk of neural tube defects and cardiovascular malformations, though data are limited. In the second and third trimesters, tetracyclines can cause skeletal retardation, enamel hypoplasia, and permanent tooth discoloration (yellow-gray-brown) in the fetus. They also may cause reversible inhibition of bone growth. Avoid use in pregnancy unless no alternative. |
■ FDA Black Box Warning
Use during tooth development (last half of pregnancy, infancy, and childhood up to 8 years) may cause permanent discoloration of the teeth (yellow-gray-brown).
| Serious Effects |
Hypersensitivity to tetracyclines, pregnancy, children under 8 years, severe renal impairment (relative contraindication for some tetracyclines).
| Precautions | Use during pregnancy may cause fetal harm (e.g., skeletal development issues). Photosensitivity reactions may occur. Superinfection with resistant organisms may occur. Renal impairment requires dose adjustment. Avoid in children under 8 years due to tooth discoloration. |
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| Fetal Monitoring | Monitor maternal liver function tests, renal function, and complete blood count periodically. Assess for signs of photosensitivity, hepatotoxicity, and pseudotumor cerebri. Fetal monitoring includes ultrasound to assess bone growth if prolonged therapy is necessary. Note risk of maternal hepatotoxicity with high doses or intravenous administration. |
| Fertility Effects | Tetracyclines may impair fertility in both males and females. In males, they can affect spermatogenesis and reduce sperm motility. In females, they may interfere with ovarian function and ovulation. These effects are generally reversible upon discontinuation. |