Polymyxin

# Polymyxin ## Overview - **Classification**: Polymyxin antibiotic. - **Mechanism**: Cationic detergent disrupting bacterial outer membrane integrity, leading to cell death. Binds to lipopolysaccharide (LPS) in Gram-negative bacteria. ## Primary Indications 1. **Multi-drug Resistant (MDR) Gram-negative infections**: Especially *Pseudomonas aeruginosa*, *Acinetobacter baumannii*, *Klebsiella pneumoniae*. Often used as a last-line agent. 2. **Urinary Tract Infections (UTIs)**: Due to susceptible MDR Gram-negative organisms. 3. **Meningitis**: (Off-label for IV, intraventricular use for specific cases). ## Adult Dosing ### Standard Dosing **Multi-drug Resistant Gram-Negative Infections (Intravenous)** - **Loading Dose**: **20,000 to 25,000 units/kg** (max **2,000,000 units**) - **Frequency**: Single dose - **Route**: IV infusion over 60 minutes - **Maintenance Dose**: **12,500 to 15,000 units/kg/day** - **Frequency**: Divided **every 12 hours (q12h)** - **Route**: IV infusion over 60 minutes - **Maximum Dose**: **2,500,000 units/day** ### Dose Adjustments - **Renal Impairment**: - CrCl 20-50 mL/min: **75%** of daily dose. - CrCl <20 mL/min: **50%** of daily dose. - Hemodialysis: Administer after dialysis. (e.g., 15,000 units/kg loading, then 7,500-10,000 units/kg **q48-72h**). - **Hepatic Impairment**: No specific dose adjustments needed. - **Elderly Patients**: Adjust dose based on renal function, often reduced CrCl. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose**: **20,000 to 30,000 units/kg/day** - **Frequency**: Divided **q12h** - **Maximum**: **2,500,000 units/day** - **Special Notes**: Use with extreme caution. Renal function is immature; monitor closely. ### Infants (1-12 months) - **Dose**: **25,000 to 30,000 units/kg/day** - **Frequency**: Divided **q12h** - **Maximum**: **2,500,000 units/day** ### Children (1-12 years) - **Dose**: **25,000 to 30,000 units/kg/day** - **Frequency**: Divided **q12h** - **Maximum**: **2,500,000 units/day** ### Adolescents (13-18 years) - **Dose**: Approach adult dosing, typically **20,000 to 25,000 units/kg/day** - **Frequency**: Divided **q12h** - **Maximum**: **2,500,000 units/day** ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to polymyxins. - **Absolute**: Concomitant use with other highly nephrotoxic or neurotoxic drugs unless absolutely necessary. - **Relative**: Myasthenia gravis (risk of respiratory depression). ### Common Adverse Effects - **Very Common (>10%)**: **Nephrotoxicity** (acute tubular necrosis), **Neurotoxicity** (paresthesia, dizziness, weakness, ataxia, blurry vision). - **Common (1-10%)**: Fever, rash, facial flushing, pruritus, urticaria, GI upset. - **Serious but Rare**: Respiratory paralysis (especially with neuromuscular blockers), *Clostridioides difficile* infection (CDI). ### Key Drug Interactions - **Nephrotoxic drugs**: **Aminoglycosides** (gentamicin), **amphotericin B**, **NSAIDs**, **cyclosporine**, **vancomycin**, **cisplatin**, **loop diuretics**. Increased risk of **nephrotoxicity**. Avoid or monitor renal function intensely. - **Neuromuscular blocking agents**: Enhanced neuromuscular blockade, leading to potential **respiratory depression/paralysis**. Monitor for muscle weakness. - **Myasthenia Gravis medications**: May exacerbate muscle weakness. ## Monitoring & Follow-up - **Before Treatment**: Baseline renal function (SCr, BUN, CrCl), urine output, neurological exam. - **During Treatment**: - **Renal function**: Daily SCr, BUN, urine output. CrCl 2-3 times/week. - **Neurological**: Monitor for paresthesia, dizziness, weakness, ataxia. - **Fluid status**: Maintain adequate hydration. - **Clinical Signs**: Decreased urine output, rising SCr, tingling/numbness, muscle weakness, confusion. ## Clinical Pearls - 💡 **Tip 1**: Polymyxin B is a **last-line agent** for MDR Gram-negative infections due to its significant nephro- and neurotoxicity. - 💡 **Tip 2**: A **loading dose** is crucial for achieving rapid therapeutic concentrations, especially in critically ill patients. - 💡 **Tip 3**: **Careful renal function monitoring** and appropriate dose adjustments are paramount to minimize toxicity. - 💡 **Tip 4**: Maintain **adequate hydration** to help reduce the risk of nephrotoxicity. - 💡 **Tip 5**: For IV administration, infuse slowly over at least **60 minutes** to reduce infusion-related reactions. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.