Box 3 Colistin and polymyxin B

Colistin

Drug class: Cell membrane-altering antibiotic

Usual dose: 1.7 mg/kg (IV) every 8 h (1 mg = 12,500 U)*

Pharmacokinetic parameters

• Bioavailability: Not applicable

• Serum half-life (normal/end-stage renal disease): 3.5/48-72 h

• Volume of distribution (Vd): 15.8 L/kg Primary mode of elimination: Renal Comments

Colistin has less nephrotoxic potential than was previously thought. Particularly useful for multidrug-resistant P aeruginosa and Acinetobacter spp. For P aeruginosa or Acinetobacter meningitis, also give amikacin 10-40 mg (IT) q 24 h, or colistin 10 mg (IT) q 24 h. IT colistin dose: 10 mg (IT) q 24 h.

Cerebrospinal fluid penetration: 25% Polymyxin B

Drug class: Cell membrane-altering antibiotic

Usual dose: 1-1.25 mg/kg (IV) q 12 h (1 mg = 10,000 U)*

Pharmacokinetic parameters

• Bioavailability: Not applicable

• Serum half-life (normal/end-stage renal disease): 6/48 h

• Volume of distribution (Vd): No data Primary mode of elimination: Renal Comments

Inhibits cytokine/endotoxin release from gram-negative bacilli. IT polymyxin B dose = 5 mg (50,000 U) q 24 h x 3d,then q 48 h x 2 wk. Dissolve 50 mg (500,000 U) into 10 mL for IT administration. Cerebrospinal fluid penetration: <10%

Colistin and polymyxin B Traditional uses

• Gram-negative bacillary infections Increased/New uses

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