Polymyxin B

Mechanism :

It is an antibiotic active against most gram-negative bacteria except Proteus, Serratia and Neisseria species. It is used typically in the treatment of skin infections, external ear infections, and conjunctivitis. It is also used orally in the treatment of diarrhea as it is not absorbed orally.

Indication :

Multidrug-resistant gram-negative bacterial infections, severe bacterial meningitis.
Ophthalmic infection caused by sensitive strains of Pseudomonas aeruginosa.

Contraindications :

Concurrent neurotoxic agent use.

Concurrent nephrotoxic agent use.

Dosing :

Severe bacterial infections:

Infants: 40,000 units/kg/day IV divided every 12 hourly (Max: 45,000 units/kg/day) OR 40,000 units/kg/day IM divided every 6 hourly.

Children: 15,000-25,000 units/kg/day IV divided every 12 hourly (Max: 25,000 units/kg/day IV) OR 25,000-30,000 units/kg/day IM divided every 12 hourly.

Bacterial meningitis:

<2 years: 25,000 units intrathecal once a day for >2 weeks after negative CSF cultures.

>2 years: 50,000 units intrathecal once a day for >2 weeks after negative CSF cultures.

Ophthalmic infection caused by sensitive strains of Pseudomonas aeruginosa:

1 to 3 drops (0.1% to 0.25% solution) to the affected eye every 1 hour, increasing the interval as response indicates. Maximum total systemic and ophthalmic dose is 25,000 units/kg/day.

Local treatment of cystitis:

>2 years: 200,000 to 400,000 units (20 to 40 mg)/day as a continuous bladder irrigation. Administration rate is adjusted to patient’s urine output.

Adverse Effect :

Nephrotoxicity, ototoxicity, neurological disturbances etc.

Interaction :

Neuromuscular blocking agents, Anaesthetic, Aminoglycoside, Colistin, Sodium citrate.

Hepatic Dose :

No dose adjustment recommended.