Megabac 4.5 IM/IV Injection

✔️ Mechanism of Action

Megabac (Colistimethate Sodium) is a polycationic surface-active agent that disrupts the bacterial outer membrane, increasing permeability and leading to cell death. It binds to lipopolysaccharides and phospholipids, displacing stabilizing ions and ultimately causing bacterial lysis. It may also precipitate cytoplasmic components inside the bacterial cell.

✔️ Dosage & Administration

🔹 Adults

Maintenance dose: 9 MIU/day divided into 2–3 doses

Critically ill patients: Loading dose of 9 MIU is recommended

🔹 Renal Impairment Dosage Adjustments

CrCl <50–30 ml/min: 5.5–7.5 MIU/day

CrCl <30–10 ml/min: 4.5–5.5 MIU/day

CrCl <10 ml/min: 3.5 MIU/day

Hemodialysis patients:

Non-HD days: 2.25 MIU/day

HD days: 3 MIU/day (post-dialysis)

🔹 Pediatric Dosage

≤40 kg: 75,000–150,000 IU/kg/day in 3 divided doses

40 kg (e.g., children with cystic fibrosis): higher doses may be required (>150,000 IU/kg/day)

Dose should be based on lean body weight

✔️ Administration Guidelines

💧 Intravenous Injection (Bolus or Infusion)

Reconstitute the vial with 5 mL of water for injection

For infusion: dilute in 50–100 mL 0.9% sodium chloride

Infuse over 30–60 minutes

💉 IM Injection

Reconstitute with 2 mL of water for injection

Administer into a large muscle mass

💧 Continuous Infusion Option

First, inject half the dose over 3–5 minutes

Add the second half to an appropriate IV solution and infuse over the next 22–23 hours

Use only with compatible diluents: 0.9% NaCl, 5% Dextrose variants, or Lactated Ringer’s

📌 Use reconstituted solution within 24 hours; do not mix with other drugs in the same IV line.

✔️ Adverse Effects

• GI upset, rash, itching
• Tingling in the extremities, dizziness, and vertigo
• Fever, headache, elevated BUN or creatinine

Serious:

• Nephrotoxicity
• Respiratory distress or apnea
• Neuromuscular blockade (rare but potentially fatal)

✔️ Reconstitution Guidelines

IM: Reconstitute with 2 mL of water for injection

IV bolus: Reconstitute with 5 mL of water for injection

IV infusion: Dilute reconstituted vial in 50–100 mL 0.9% NaCl

🕒 Use reconstituted solution within 24 hours; store at 2°C–8°C; do not freeze

✔️ Overdose Effects

Symptoms may include:

• Neurological signs: lethargy, confusion, ataxia, paresthesia
• Respiratory muscle paralysis → apnea or death
• Acute renal failure
• Treatment: Immediate drug discontinuation and supportive care

✔️ Contraindications

Hypersensitivity to colistimethate sodium or any formulation component

✔️ Pregnancy & Lactation

Pregnancy Category C: Use only if benefits outweigh fetal risks

Unknown if excreted in human milk – caution in breastfeeding

✔️ Precautions & Warnings

• Renal monitoring is essential – Megabac is nephrotoxic at high or prolonged doses
• Caution in neonates, infants, and hepatic impairment
• Risk of neurotoxicity (e.g., dizziness, tingling, slurred speech), especially in overdose or impaired renal function
• Avoid concurrent use with aminoglycosides, neuromuscular blockers, and sodium cephalothin

✔️ Storage Conditions

• Before reconstitution: Store below 30°C
• After reconstitution: Store at 2–8°C and use within 24 hours
• Keep out of reach of children