Polymyxin B

# Polymyxin b ## Overview - **Classification**: Polymyxin antibiotic, polypeptide antibiotic. - **Mechanism**: Cationic detergent action on bacterial cell membranes. Binds to LPS, disrupts outer membrane integrity, leading to leakage of intracellular contents and cell death. Effective against Gram-negative bacteria. ## Primary Indications 1. **Systemic Infections**: Multidrug-resistant (MDR) Gram-negative infections (e.g., *Pseudomonas aeruginosa*, *Acinetobacter baumannii*, *Klebsiella pneumoniae*) when other options are ineffective. 2. **Topical Infections**: Ophthalmic, otic, and skin infections caused by susceptible Gram-negative organisms. 3. **Meningitis/Ventricular Infections**: Intrathecal administration for MDR Gram-negative CNS infections. ## Adult Dosing ### Standard Dosing **Systemic (IV) for Serious Infections** (e.g., VAP, HAP, cUTI, bloodstream infections) - **Loading Dose**: **2.5 mg/kg** (25,000 units/kg) IV. - **Maintenance Dose**: **1.25 to 1.5 mg/kg** (12,500 to 15,000 units/kg) IV. - **Frequency**: Every 12 hours (after loading dose). - **Route**: Intravenous infusion over 60 minutes. - **Maximum Daily Dose**: **2.5 mg/kg/day** (25,000 units/kg/day) or **200 mg/day** (2,000,000 units/day). - **Special Considerations**: Dose based on Ideal Body Weight (IBW) for patients up to 130% IBW. Use Adjusted Body Weight (AdjBW) for obese patients (>130% IBW). **Intrathecal (Meningitis/Ventricular Infections)** - **Dose**: **50,000 units**. - **Frequency**: Once daily. - **Route**: Intrathecal or intraventricular injection. **Ophthalmic Solution/Ointment (External Ocular Infections)** - **Solution**: 1-2 drops into affected eye(s). - **Frequency**: 4-6 times daily. - **Ointment**: Small amount into conjunctival sac. - **Frequency**: 3-4 times daily. **Otic Solution (External Ear Infections)** - **Dose**: 3-4 drops into affected ear. - **Frequency**: 3-4 times daily. ### Dose Adjustments - **Renal Impairment**: Requires significant dose reduction. - CrCl 20-50 mL/min: Reduce maintenance dose by 50% (e.g., **0.625-0.75 mg/kg** IV every 12 hours). - CrCl < 20 mL/min: Reduce maintenance dose further or prolong interval. Expert consultation is recommended. - **Hepatic Impairment**: No specific dose adjustments provided; use with caution. - **Elderly Patients**: Consider age-related decline in renal function; dose adjust based on CrCl. ## Pediatric Dosing ### Neonates (0-28 days) **Systemic (IV) for Serious Infections** - **Dose**: Loading dose **2.5 mg/kg** (25,000 units/kg) IV, followed by. - **Frequency**: Maintenance dose of **1.25 to 1.5 mg/kg** (12,500 to 15,000 units/kg) IV every 12 hours. - **Route**: Intravenous infusion over 60 minutes. - **Maximum**: Not to exceed adult max of **2.5 mg/kg/day** (25,000 units/kg/day). - **Special Notes**: High risk of nephrotoxicity. Closely monitor renal function. Dosing based on IBW. ### Infants (1-12 months) **Systemic (IV) for Serious Infections** - **Dose**: Loading dose **2.5 mg/kg** (25,000 units/kg) IV, followed by. - **Frequency**: Maintenance dose of **1.25 to 1.5 mg/kg** (12,500 to 15,000 units/kg) IV every 12 hours. - **Route**: Intravenous infusion over 60 minutes. - **Maximum**: Not to exceed adult max of **2.5 mg/kg/day** (25,000 units/kg/day). ### Children (1-12 years) **Systemic (IV) for Serious Infections** - **Dose**: Loading dose **2.5 mg/kg** (25,000 units/kg) IV, followed by. - **Frequency**: Maintenance dose of **1.25 to 1.5 mg/kg** (12,500 to 15,000 units/kg) IV every 12 hours. - **Route**: Intravenous infusion over 60 minutes. - **Maximum**: Not to exceed adult max of **2.5 mg/kg/day** (25,000 units/kg/day). **Intrathecal (Meningitis/Ventricular Infections)** - **Dose**: **50,000 units**. - **Frequency**: Once daily. - **Special Notes**: Used for Gram-negative meningitis when other options fail. ### Adolescents (13-18 years) - **Dose**: Follow adult systemic dosing recommendations. - **Maximum**: Follow adult maximum daily doses. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to polymyxin B. - **Relative**: Concomitant use with other nephrotoxic or neurotoxic drugs (high risk of additive toxicity). ### Common Adverse Effects - **Very Common (>10%)**: - **Nephrotoxicity**: Acute tubular necrosis, proteinuria, hematuria, azotemia. - **Neurotoxicity**: Paresthesias (facial, peripheral), dizziness, vertigo, blurred vision, ataxia, drowsiness. - **Common (1-10%)**: - Headache, fever, urticaria, rash. - Local injection site reactions (pain, thrombophlebitis). - **Serious but Rare**: - **Neuromuscular blockade**: Can lead to respiratory paralysis, especially with rapid IV infusion, renal impairment, or pre-existing neuromuscular disorders. - Anaphylaxis. ### Key Drug Interactions - **Neuromuscular Blockers (e.g., rocuronium, succinylcholine)**: Potentiates neuromuscular blockade, increasing risk of respiratory depression/paralysis. Avoid concurrent use or monitor closely. - **Nephrotoxic Drugs (e.g., aminoglycosides, amphotericin B, NSAIDs, vancomycin)**: Significantly increases risk of nephrotoxicity. Avoid concurrent use if possible; if unavoidable, monitor renal function very closely. - **Ototoxic Drugs (e.g., loop diuretics, aminoglycosides)**: Potential for increased ototoxicity. ## Monitoring & Follow-up - **Before Treatment**: - Baseline renal function (SCr, BUN, CrCl). - Electrolytes (Na, K, Mg, Ca). - Urinalysis. - **During Treatment**: - **Renal function**: Daily or every other day initially, then 2-3 times/week (SCr, BUN, CrCl, urine output). - **Neurological assessment**: Monitor for paresthesias, dizziness, ataxia, signs of neuromuscular blockade. - **Electrolytes**: Regularly. - **Clinical Signs**: Watch for decreased urine output, peripheral numbness/tingling, muscle weakness, visual disturbances. ## Clinical Pearls - 💡 **Last-resort agent**: Reserved for severe, multidrug-resistant Gram-negative infections due to high toxicity profile. - 💡 **Nephrotoxicity**: Dose-dependent and often reversible if detected early. Aggressive hydration may help mitigate risk. - 💡 **Infusion Rate**: Infuse IV doses slowly over **60 minutes** to minimize acute neurotoxicity and injection site reactions. - 💡 **Combination therapy**: Often used with other antibiotics (e.g., rifampin, meropenem) for synergistic effects and to reduce resistance. - 💡 **Patient Counseling**: Educate patients on potential side effects like tingling, numbness, and advise them to report these immediately. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.