Polymyxin adverse effects

During treatment with any of the polymyxins, neurotoxicity can occur in up to 7% of patients with normal renal function. Circumoral paresthesia, vasomotor instability, ataxia, dizziness, convulsions of varying severity, and apnea have been reported. Of 31 patients with cystic fibrosis 21 had one or more adverse effects attributed to colistin (14). The most common reactions involved reversible neurological effects, including oral and perioral paresthesia (n = 16), headache (n = 5), and lower limb weakness (n = 5). All of these effects, although bothersome, were benign and reversible. There was no relation between the occurrence of any colistin-associated adverse effect and plasma colistin concentration or colistin pharmacokinetics. 

Polymyxin B is effective against many gramnegative bacteria, including E. coli, Klebsiella, and Salmonella. Systemic administration of this drug, however, is often associated with extreme nephrotoxicity. Hence, this agent is used primarily for the treatment of local, superficial infections of the skin, eyes, and mucous membranes. When applied topically for these conditions, adverse reactions are relatively rare. Polymyxin B is often combined with other antibiotics such as bacitracin and neomycin in commercial topical preparations. 

Bacitracin is bactericidal for most gram-positive organisms, especially Staphylococcus and Streptococcus species. It is particularly useful when combined with polymyxin B in an ophthalmic ointment. Bacitracin-polymyxin B ointment (Polysporin) provides broad-spectrum antibacterial activity for patients who require nighttime therapy or who are not comfortable with eyedrops. Bacitracin-polymyxin B ointment is particularly effective in the pediatric population because of the high incidence of Streptococcus infection.The usual dose frequency is three to four times daily.Although adverse events are rare, hypersensitivity reactions can occur. Additionally, bacitracin can sometimes be uncomfortable. 

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