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. |
| Molecular Weight | 444.44 |
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 | Contraindicated due to risk of fetal harm; tetracyclines cross placenta and may cause skeletal abnormalities and discoloration of deciduous teeth. |
| 2nd trimester | Contraindicated; risk of fetal bone and tooth effects, including enamel hypoplasia and permanent tooth discoloration. |
| 3rd trimester | Contraindicated; fetal exposure may lead to dental staining and bone growth retardation. |
Clinical note
Comprehensive clinical and safety monograph for TETRACYN (TETRACYN).
| Placental transfer | Crosses placenta readily; achieves fetal serum concentrations 60-70% of maternal levels. |
| Breastfeeding | Tetracyn is excreted into breast milk in low concentrations; however, potential for dental staining and bone development effects in nursing infants exists. Use only if benefits outweigh risks; consider alternative agents. |
■ 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 |
PregnancyChildren under 8 years of age (due to dental staining and bone growth retardation)Hypersensitivity to tetracyclinesSevere hepatic impairment
| 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. |
| Food/Dietary | Avoid dairy products (milk, cheese, yogurt) and calcium-fortified foods within 2 hours of dose. Avoid iron-rich foods or supplements simultaneously. Separate antacids, bismuth subsalicylate, and magnesium-containing laxatives by 2 hours. |
Loading safety data…
| Lactation Rating | L4 (Possibly Hazardous) |
| 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. |
| 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. |
| Clinical Pearls | Avoid during pregnancy (2nd and 3rd trimester) and in children under 8 years due to teeth discoloration and bone growth inhibition. Use with caution in renal impairment; adjust dose. Can cause photosensitivity; avoid excessive sun exposure. Monitor for superinfection with prolonged use. Not effective against Group A streptococcal infections. |
| Patient Advice | Take on an empty stomach 1 hour before or 2 hours after meals with a full glass of water. · Avoid dairy products, antacids, iron, and calcium supplements within 2 hours of taking this medication. · Complete the full course even if you feel better; skipping doses can lead to resistance. · Report any severe diarrhea, vaginal itching, or skin rash to your doctor immediately. · Wear sunscreen and protective clothing to avoid sunburn; limit sun exposure. |