TERRAMYCIN-POLYMYXIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TERRAMYCIN-POLYMYXIN (TERRAMYCIN-POLYMYXIN).
Terramycin (oxytetracycline) inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing aminoacyl-tRNA attachment. Polymyxin disrupts bacterial cell membrane permeability by binding to lipopolysaccharides, leading to cell death.
| Metabolism | Oxytetracycline is primarily excreted unchanged in urine; minimal hepatic metabolism. Polymyxin is not metabolized hepatically; primarily renally excreted. |
| Excretion | Renal (terramycin: ~70% unchanged in urine; polymyxin B: ~60% unchanged in urine), biliary/fecal (terramycin: ~20-30% in feces; polymyxin B: ~40% fecal elimination) |
| Half-life | Terramycin: 6-10 hours (prolonged in renal impairment); polymyxin B: 6-7 hours (prolonged in renal impairment); clinical context: dosing interval adjustment required for renal dysfunction |
| Protein binding | Terramycin: ~25-35% bound to plasma proteins (mainly albumin); polymyxin B: ~80-90% bound to plasma proteins (albumin, α-1-acid glycoprotein) |
| Volume of Distribution | Terramycin: 1.3-1.8 L/kg (distributes widely, including pleural fluid, ascites, bile); polymyxin B: 0.3-0.5 L/kg (limited distribution, primarily extracellular) |
| Bioavailability | Terramycin: oral ~60-80% (food decreases absorption), IM ~70-80%; polymyxin B: not absorbed orally (0.1-0.3%), IM ~100%, IV 100% |
| Onset of Action | Topical: immediate local antimicrobial effect; ophthalmic: within 30 minutes; systemic (IM/IV): 1-2 hours for therapeutic plasma concentrations |
| Duration of Action | Topical: 6-12 hours depending on formulation; systemic: 8-12 hours (terramycin), 8-12 hours (polymyxin B); clinical note: combination provides broad coverage for 8-hour dosing interval |
| Molecular Weight | Terramycin (oxytetracycline): 460.43 Da; Polymyxin B: 1303.48 Da. Combined product: not applicable (mixture). |
Adults: 1-2 drops into affected eye(s) every 4 hours, or 1/2-1 inch ribbon of ointment into conjunctival sac 3-4 times daily. For dermatological use: apply sparingly to affected area 2-3 times daily.
| Dosage form | TABLET |
| Renal impairment | Terramycin-Polymyxin (oxytetracycline/polymyxin B) is primarily used topically; systemic absorption is minimal. No specific GFR-based dose adjustments required for topical use. For rare systemic use, oxytetracycline requires adjustment if GFR <50 mL/min: prolong dosing interval to every 12-24 hours. Polymyxin B: adjust if GFR <30 mL/min, reduce dose by 50% or increase interval to 12-24 hours. |
| Liver impairment | No specific Child-Pugh based adjustments required for topical use. For systemic oxytetracycline, use with caution in severe hepatic impairment; consider dose reduction or alternative therapy. Polymyxin B is not hepatically metabolized; no adjustment needed. |
| Pediatric use | Children ≥2 years: same as adult dosing for ophthalmic and topical use. For infants <2 years: use only if clearly needed; no specific weight-based dosing established for topical forms. |
| Geriatric use | No specific dose adjustments needed for topical ophthalmic or dermatologic use. Use caution with systemic administration due to potential renal impairment; monitor renal function and adjust accordingly. |
| 1st trimester | Avoid; potential for fetal nephrotoxicity and ototoxicity, especially with oxytetracycline which can cause skeletal development delay and discoloration of teeth. |
| 2nd trimester | Avoid; risk of nephrotoxicity, ototoxicity, and effects on fetal bone and teeth development. |
| 3rd trimester | Avoid; can cause permanent discoloration of teeth (brown-yellow) and potential inhibition of bone growth. |
Clinical note
Comprehensive clinical and safety monograph for TERRAMYCIN-POLYMYXIN (TERRAMYCIN-POLYMYXIN).
| Placental transfer | Oxytetracycline crosses the placenta; polymyxin likely crosses to a lesser extent. Fetal serum levels may reach 50-60% of maternal levels. |
| Breastfeeding | Polymyxin is not absorbed orally, but oxytetracycline is excreted into breast milk in low concentrations. Theoretical risk of dental staining and bone growth suppression in nursing infants. Use only if benefit outweighs risk. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to oxytetracycline, polymyxin, or any componentPatients with myasthenia gravis (due to polymyxin neuromuscular blockade risk)Children under 8 years (risk of permanent tooth discoloration)
| Precautions | Prolonged use may result in overgrowth of nonsusceptible organisms including fungi., Photosensitivity reactions may occur with oxytetracycline., Renal impairment may require dose adjustment for polymyxin., Avoid use in children under 8 years due to tooth discoloration., Caution in patients with myasthenia gravis due to potential neuromuscular blockade from polymyxin. |
| Food/Dietary | Avoid dairy products (milk, cheese, yogurt), antacids, and iron-fortified foods within 2-3 hours of administration. Calcium, magnesium, aluminum, and zinc can chelate tetracyclines, reducing absorption. Do not take with mineral supplements or laxatives containing magnesium. |
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| Lactation Rating | L3 - Limited Data (moderately safe) |
| Teratogenic Risk | Terramycin (oxytetracycline) is a tetracycline antibiotic that crosses the placenta. Tetracyclines are associated with fetal risk, including permanent tooth discoloration and enamel hypoplasia when used during the second and third trimesters. They may also cause skeletal growth retardation and are contraindicated after the first trimester. Polymyxin B sulfate has limited data; animal studies show no teratogenicity but fetal harm cannot be ruled out. Avoid use during pregnancy unless no safer alternative. |
| Fetal Monitoring | Monitor maternal renal and hepatic function. Assess for signs of superinfection and hypersensitivity. Fetal monitoring for growth and development if used during pregnancy; avoid prolonged use. Baseline and periodic liver function tests recommended with oxytetracycline. |
| Fertility Effects | No specific data on fertility effects in humans. Animal studies with tetracyclines have shown transient impairment of spermatogenesis and reduced fertility at high doses; polymyxin B has no known effects. Reversible upon discontinuation. |
| Clinical Pearls | Terramycin (oxytetracycline) is primarily bacteriostatic, while polymyxin is bactericidal. Monitor renal function in patients receiving polymyxin due to risk of nephrotoxicity. Avoid use in children under 8 years due to tooth discoloration and bone growth inhibition. Caution in patients with myasthenia gravis or porphyria. |
| Patient Advice | Take on an empty stomach (1 hour before or 2 hours after meals) unless gastrointestinal upset occurs. · Avoid dairy products, antacids, iron supplements, and calcium-rich foods within 2-3 hours of dosing. · Do not take with magnesium-containing laxatives or bismuth subsalicylate. · Complete the full course of therapy even if symptoms improve. · Report any signs of superinfection (e.g., oral thrush, vaginal discharge) or persistent diarrhea. · Use sunscreen and protective clothing; may cause photosensitivity. · Not for use in pregnant women or children under 8 years. · Store at room temperature, away from light and moisture. · Do not share medication with others. |