TETREX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TETREX (TETREX).
Tetracycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing aminoacyl-tRNA from binding to the A site.
| Metabolism | Primarily excreted unchanged in urine; minimal hepatic metabolism. |
| Excretion | Renal: 60% unchanged; biliary/fecal: 40% (mainly as glucuronide conjugates). |
| Half-life | Terminal elimination half-life: 6-11 hours (mean 8 hours); prolonged in renal impairment (up to 20 hours). |
| Protein binding | 90-95% bound to serum proteins (mainly albumin). |
| Volume of Distribution | Vd: 1.3-1.6 L/kg; indicates extensive tissue penetration. |
| Bioavailability | Oral: 75-85% (food reduces by 20%). |
| Onset of Action | Oral: 30-60 minutes; intravenous: immediate (minutes). |
| Duration of Action | 12-24 hours (bacteriostatic levels maintained with twice-daily dosing). |
| Molecular Weight | 444.44 |
250-500 mg orally every 6 hours or 500 mg to 1 g intravenously every 6-12 hours, not to exceed 4 g/day.
| Dosage form | CAPSULE |
| Renal impairment | GFR 10-50: 250-500 mg every 12-24 hours; GFR <10: 250-500 mg every 24 hours. |
| Liver impairment | Child-Pugh A: No adjustment; Child-Pugh B: Reduce dose by 50%; Child-Pugh C: Avoid use. |
| Pediatric use | 25-50 mg/kg/day orally in divided doses every 6 hours; for severe infections, up to 100 mg/kg/day divided every 6 hours. Intravenously: 20-40 mg/kg/day divided every 6-12 hours. |
| Geriatric use | Reduce dose by 50% or extend interval to every 12 hours due to decreased renal function. |
| 1st trimester | Avoid use in first trimester due to risk of fetal toxicity, including teratogenic effects such as skeletal and neural tube defects. |
| 2nd trimester | Avoid use in second trimester; may cause maternal hepatotoxicity and fetal harm including growth retardation. |
| 3rd trimester | Avoid use in third trimester; risk of renal toxicity and other adverse effects in the neonate. |
Clinical note
Comprehensive clinical and safety monograph for TETREX (TETREX).
| Placental transfer | Crosses the placenta readily; achieves fetal concentrations approximately 50% of maternal levels. |
| Breastfeeding | Contraindicated during breastfeeding due to potential for serious adverse effects in the nursing infant, including bone and tooth development disturbances and hypersensitivity reactions. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to tetracycline antibioticsPregnancy (all trimesters)BreastfeedingSevere hepatic impairmentSevere renal impairment
| Precautions | Photosensitivity, Tooth discoloration in children <8 years, Superinfection with prolonged use, Hepatotoxicity in high doses, Renal impairment requires dose adjustment |
| Food/Dietary | Avoid dairy products (milk, cheese, yogurt) within 2 hours of dosing as calcium chelates tetracycline, reducing absorption. Also avoid calcium-fortified juices and calcium supplements. Food in general (especially high-calcium foods) may decrease absorption; take on empty stomach. Alcohol: no direct interaction but may exacerbate hepatotoxicity; limit use. |
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| Lactation Rating |
| L5 - Contraindicated |
| Teratogenic Risk | TETREX (tetracycline) is contraindicated in pregnancy. First trimester: Associated with fetal skeletal development abnormalities and potential for neural tube defects. Second and third trimesters: Causes permanent tooth discoloration (yellow-gray-brown) and enamel hypoplasia; also inhibits fetal bone growth. Use only for life-threatening conditions (e.g., anthrax) with no alternative. |
| Fetal Monitoring | If inadvertently used in pregnancy, monitor fetal growth via ultrasound and assess neonatal teeth and bone development at birth. Maternal monitoring: hepatic function, renal function, and signs of pseudotumor cerebri. |
| Fertility Effects | TETREX may impair fertility in both sexes. In males, it can reduce sperm count and motility. In females, it may interfere with ovulation and cause reversible infertility. Effects are dose-dependent and typically resolve after discontinuation. |
| Clinical Pearls | TETREX (tetracycline) is bacteriostatic against intracellular bacteria; avoid use in children <8 years and pregnant/nursing women due to permanent tooth discoloration and bone growth inhibition. Contraindicated in hepatic impairment; monitor liver function tests. Photosensitivity common: advise strict sun avoidance and sunscreen. Do not use past expiration due to nephrotoxic degradation products. Administer on empty stomach (1h before or 2h after meals) with full glass of water; avoid dairy, antacids, iron, calcium, magnesium, and zinc within 2 hours. May reduce efficacy of oral contraceptives; recommend additional contraception. Potentiates warfarin: monitor INR. |
| Patient Advice | Take this medication on an empty stomach, at least 1 hour before or 2 hours after meals, with a full glass of water. · Avoid dairy products, antacids, iron supplements, and multivitamins containing calcium, magnesium, or zinc within 2 hours of taking this drug. · Do not use expired tetracycline as it can cause kidney damage. · Use sunscreen and protective clothing; avoid prolonged sun exposure as this drug increases sun sensitivity. · Notify your doctor if you experience severe headache, vision changes, or yellowing of the skin or eyes. · This medication may reduce the effectiveness of birth control pills; use an additional non-hormonal contraceptive method. · Complete the full course of treatment even if you feel better to prevent resistance. · Keep out of reach of children; store at room temperature away from light and moisture. |