TETRACHEL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TETRACHEL (TETRACHEL).
Tetracycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing the attachment of aminoacyl-tRNA to the mRNA-ribosome complex.
| Metabolism | Tetracycline is primarily metabolized in the liver via glucuronidation and undergoes enterohepatic circulation. Minor metabolism may involve microsomal enzymes. |
| Excretion | Renal 60% (glomerular filtration), fecal 40% (biliary excretion of active drug and metabolites). |
| Half-life | 6-11 hours (prolonged in renal impairment; up to 57 hours in anuria). |
| Protein binding | 65% (primarily albumin). |
| Volume of Distribution | 1.3 L/kg (extensive tissue penetration, including bone and teeth). |
| Bioavailability | Oral: 77-96% (decreased by food, dairy, antacids). |
| Onset of Action | Oral: 1 hour; IV: immediate; Topical: 2-3 days. |
| Duration of Action | Oral: 12 hours; IV: 12 hours; Topical: up to 12 hours after application. |
| Molecular Weight | 444.44 |
500 mg orally once daily for 28 days; for severe infections, 500 mg twice daily for 14 days.
| Dosage form | CAPSULE |
| Renal impairment | CrCl >50 mL/min: no adjustment. CrCl 30-50 mL/min: 250 mg once daily. CrCl <30 mL/min: 125 mg once daily. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: 250 mg once daily. Child-Pugh C: 125 mg once daily. |
| Pediatric use | Children ≥8 years: 5 mg/kg orally once daily (max 500 mg) for 28 days. |
| Geriatric use | Initiate at low end of dosing range; monitor renal function and adjust dose based on CrCl. |
| 1st trimester | Avoid: tetracycline is classified as FDA pregnancy category D. It crosses the placenta and can cause fetal harm, including skeletal development abnormalities and permanent tooth discoloration (yellow-gray-brown). Use only if no safer alternative is available for serious maternal infection. |
| 2nd trimester | Avoid in second and third trimesters due to risk of permanent tooth discoloration (dentin and enamel hypoplasia) and inhibition of bone growth in the fetus. Tetracycline forms a calcium-tetracycline orthophosphate complex in bone and teeth, leading to discoloration and structural defects. |
| 3rd trimester | Contraindicated after the fourth month of pregnancy. Exposure during the latter half of pregnancy causes permanent yellow-gray-brown discoloration of deciduous teeth if taken after 4 months gestation, and permanent teeth are also affected. Risk of enamel hypoplasia and bone growth retardation. |
Clinical note
Comprehensive clinical and safety monograph for TETRACHEL (TETRACHEL).
| Placental transfer | Tetracycline readily crosses the placenta. Studies demonstrate transfer to fetal serum and tissues, achieving fetal plasma concentrations approximately 50-60% of maternal levels. Accumulation in fetal bone and teeth due to chelation with calcium is well established. |
■ FDA Black Box Warning
Tetracycline can cause fetal harm when administered to a pregnant woman. Use during tooth development (last half of pregnancy, infancy, and children up to 8 years) may cause permanent discoloration of teeth (yellow-gray-brown). It should not be used in this age group unless other drugs are not likely to be effective or are contraindicated.
| Serious Effects |
Hypersensitivity to tetracyclinesPregnancy (second and third trimester)Lactation (relative, but avoid if alternatives exist)Renal impairment (especially with preserved hepatic function) due to risk of hepatotoxicity and increased azotemiaHepatic impairment (increased risk of hepatotoxicity)Concomitant use with methoxyflurane (risk of nephrotoxicity)
| Precautions | Photosensitivity: exaggerated sunburn reaction; avoid direct sunlight and UV light., Hepatotoxicity: may cause liver damage, especially in patients with renal impairment or receiving high doses., Renal impairment: accumulation may occur; dosage adjustment required., Superinfection: use of tetracycline may result in overgrowth of non-susceptible organisms, including fungi., Pseudomembranous colitis: Clostridium difficile-associated diarrhea has been reported., Intracranial hypertension: bulging fontanelles in infants and benign intracranial hypertension in adults., Tissue irritation: avoid extravasation; thrombophlebitis risk with IV administration. |
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| Breastfeeding | Tetracycline is excreted into breast milk in low concentrations. Use caution due to potential for serious adverse reactions in nursing infants, including tooth discoloration and inhibition of bone growth if absorbed. The American Academy of Pediatrics considers tetracycline compatible with breastfeeding, but alternatives are preferred when possible. Consider temporary cessation of breastfeeding if maternal tetracycline therapy is prolonged or at high doses. |
| Lactation Rating | L2 (Probably Compatible) - Based on limited human data, small amounts are excreted into breast milk, and absorption by the infant is limited due to binding with milk calcium. However, theoretical risk of bone and tooth effects exists with prolonged exposure. |
| Teratogenic Risk | Tetracyclines, including Tetrachel, are classified as FDA Pregnancy Category D. They can cause fetal harm when administered to a pregnant woman. Use during the second and third trimesters (weeks 13 to 40) is associated with permanent discoloration of teeth (yellow-gray-brown) and enamel hypoplasia in the child. Additionally, there is a risk of retarded skeletal growth and potentially reversible inhibition of bone growth. Use during the first trimester is generally discouraged unless no alternative therapy is available, as there may be a small risk of teratogenicity (e.g., neural tube defects, cardiovascular malformations) based on some observational studies, though evidence is conflicting. |
| Fetal Monitoring | Pregnant women receiving tetracycline should have baseline and periodic liver function tests (LFTs) and renal function tests (serum creatinine, BUN) due to risk of hepatotoxicity and nephrotoxicity in the mother. In prolonged therapy, monitor for signs of superinfection and C. difficile diarrhea. Fetal monitoring includes ultrasound assessment for skeletal abnormalities if used in the second/third trimester, and postpartum dental examination of the infant for enamel hypoplasia and tooth discoloration. |
| Fertility Effects | Tetracycline has been shown to impair fertility in animal studies; effects on human fertility are not well-established. It may reduce sperm motility and concentration in men, and in women, it may cause reversible inhibition of spermatogenesis or ovarian function. Clinical significance is considered low with short-term use, but prolonged therapy may warrant fertility counseling. |
| Food/Dietary | Avoid dairy products, calcium-fortified foods, and antacids containing calcium, magnesium, or aluminum, as they reduce absorption. Iron supplements, bismuth subsalicylate, and zinc also chelate tetracyclines. Take tetracycline 1 hour before or 2 hours after meals. Avoid alcohol (hepatotoxicity risk). |
| Clinical Pearls | Tetracyclines are bacteriostatic antibiotics that inhibit protein synthesis. Avoid in children under 8 years and pregnant/breastfeeding women due to bone and tooth discoloration. Administer on an empty stomach (1 hour before or 2 hours after meals) with a full glass of water to prevent esophagitis. Do not take with dairy, antacids, or iron supplements as they chelate and reduce absorption. Photosensitivity risk: advise sun avoidance and sunscreen use. |
| Patient Advice | Take this medication on an empty stomach with a full glass of water. · Avoid dairy products, antacids, and iron supplements within 2 hours of taking this drug. · Use sunscreen and protective clothing to prevent severe sunburn. · Complete the full course of therapy even if you feel better. · Report any signs of allergic reaction, severe headache, or vision changes immediately. |