COLY-MYCIN S
Clinical safety rating: caution
Comprehensive clinical and safety monograph for COLY-MYCIN S (COLY-MYCIN S).
Colistin is a polymyxin antibiotic that binds to lipopolysaccharides in the outer membrane of Gram-negative bacteria, disrupting the membrane and causing cell death.
| Metabolism | Colistin is primarily metabolized via hydrolysis to a lesser extent; hepatic CYP450 enzymes are not significantly involved in its metabolism. |
| Excretion | Renal: ~70-80% unchanged via glomerular filtration; biliary/fecal: ~15-20% as active drug and metabolites. |
| Half-life | Terminal elimination half-life: 2-4 hours in normal renal function; prolonged in renal impairment (up to 24-48 hours in anuria). |
| Protein binding | Colistin: ~50% bound to albumin; colistimethate sodium: <10% bound. |
| Volume of Distribution | Colistimethate: 0.3-0.6 L/kg; colistin: 0.5-1.0 L/kg (indicating distribution primarily into extracellular fluid). |
| Bioavailability | IM: ~60-70% of colistimethate is systemically absorbed; Oral: negligible (<1%); Topical: minimal systemic absorption (<0.1%). |
| Onset of Action | IM: 1-2 hours; IV: within 30-60 minutes; Topical: variable, within 24-48 hours for local effects. |
| Duration of Action | IM/IV: 6-8 hours with colistimethate; colistin base has longer duration (12-24 hours). Topical: depends on formulation, typically 12-24 hours. |
2.5 mg/kg/dose IV every 12 hours for 7-14 days (based on colistin base activity).
| Dosage form | SUSPENSION |
| Renal impairment | CrCl 50-80 mL/min: 2.5 mg/kg IV every 24 hours; CrCl 30-49 mL/min: 2.5 mg/kg IV every 36 hours; CrCl 10-29 mL/min: 2.5 mg/kg IV every 48 hours; CrCl <10 mL/min: 2.5 mg/kg IV every 72 hours. |
| Liver impairment | No specific dose adjustment recommended; use with caution in severe hepatic impairment. |
| Pediatric use | Children ≥1 year: 2.5 mg/kg/dose IV every 12 hours based on colistin base activity; maximum 5 mg/kg/day. |
| Geriatric use | Dose based on renal function; monitor renal function closely due to age-related decline in CrCl. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for COLY-MYCIN S (COLY-MYCIN S).
| Breastfeeding | Colistimethate is excreted into human milk in low concentrations (M/P ratio not established). Limited data suggest negligible risk to infant; however, monitor for diarrhea or allergic reaction. Use caution in nursing mothers. |
| Teratogenic Risk | FDA Pregnancy Category C. Colistimethate (active component) crosses placenta. First trimester: No adequate human data; teratogenic in animal studies (cleft palate, skeletal abnormalities). Second/third trimester: Potential for fetal nephrotoxicity and ototoxicity due to colistin accumulation; reserve for serious infections when no alternative. |
■ FDA Black Box Warning
Nephrotoxicity and neurotoxicity: Colistin can cause acute kidney injury and neuromuscular blockade leading to respiratory arrest. Use with caution in patients with renal impairment and monitor renal function closely.
| Serious Effects |
["Hypersensitivity to colistin or any component of the formulation","Due to lack of safety data, contraindicated in patients with myasthenia gravis or other neuromuscular diseases where neuromuscular blockade could be exacerbated."]
| Precautions | ["Monitor renal function closely during therapy; dose adjustment required in renal impairment.","Neurotoxicity may manifest as paresthesias, dizziness, slurred speech, vertigo, and neuromuscular blockade; use caution with concomitant neurotoxic agents.","Clostridium difficile-associated diarrhea has been reported.","Respiratory arrest has occurred, especially with rapid intravenous infusion or in patients with neuromuscular disorders."] |
| Food/Dietary | No significant food interactions. May be taken with or without food. Maintain adequate hydration. |
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| Fetal Monitoring | Monitor maternal renal function (serum creatinine, BUN, urine output) and electrolyte levels (especially sodium and potassium). Assess for signs of nephrotoxicity or neurotoxicity (paresthesias, dizziness). In fetus, consider periodic ultrasound if prolonged therapy. |
| Fertility Effects | Animal studies show no impairment of fertility. No human data on fertility effects. |
| Clinical Pearls | Colistimethate sodium is a prodrug of colistin, a polymyxin antibiotic. It is reserved for multidrug-resistant Gram-negative infections. Nephrotoxicity and neurotoxicity are dose-limiting; monitor renal function closely. Inhalational use may cause bronchospasm; pretreat with bronchodilator. Dose adjustment required in renal impairment based on calculated CrCl. Avoid concurrent use with other nephrotoxic agents. Neuromuscular blockade possible; use caution with neuromuscular disease or concomitant neuromuscular blockers. |
| Patient Advice | Take this medication exactly as prescribed; do not skip doses. · If using the oral suspension, shake well before each use. · Report any signs of kidney problems: decreased urination, swelling, or fatigue. · Report numbness, tingling, or muscle weakness immediately. · If using the inhaled form, use a bronchodilator first if prescribed. · Drink plenty of fluids unless advised otherwise by your doctor. · Do not stop taking this medicine without consulting your doctor. |