2.5 to 5 mg/kg/day of colistin base IV or IM in 2 to 4 divided doses, depending on severity of infection.

Reference:

1. Product Information: Coly-Mycin(R) M Parenteral intramuscular injection, intravenous injection, colistimethate intramuscular injection, intravenous injection. JHP Pharmaceuticals, LLC (per FDA), Rochester, MI, Jan, 2013.
2. Nakwan N, Usaha S, Chokephaibulkit K et al: Pharmacokinetics of colistin following a single dose of intravenous colistimethate sodium in critically ill neonates. Pediatr Infect Dis J Nov, 2016; 35(11): 1211-1214.