Polymyxin B-Associated Muscle Injury: A Case Report.

BACKGROUND: Colistin is a last-line antibiotic used to treat multidrug-resistant Acinetobacter baumannii. The most common adverse effects are nephrotoxicity and neurotoxicity. In contrast, there are extremely rare reports of muscle injury induced by polymyxin B, which is related to colistin in its mechanism of action. CASE PRESENTATION: We report the case of a 63-year-old woman who received polymyxin B (intravenous plus inhalation) combined with tigecycline and vancomycin for pulmonary infection caused by extensive drug resistant Acinetobacter baumannii and bloodstream infection caused by Bacillus cereus following cerebral embolism surgery. During the course of treatment, infection markers gradually improved. However, serum creatine kinase (CK), myoglobin (MB), and serum creatinine (SCr) levels progressively increased. Considering the temporal association between polymyxin B administration and the elevation of serum biomarkers, as well as the causality assessment using the Naranjo scale and WHO-Uppsala Monitoring Centre (WHO-UMC) criteria, polymyxin B-associated muscle injury was suspected. After discontinuation of polymyxin B and initiation of supportive management, laboratory abnormalities gradually resolved, and infection was effectively controlled. CONCLUSION: Polymyxin B may cause muscle injury presenting with marked MB elevation, a rare but serious adverse reaction. Clinicians should closely monitor CK, MB, and renal function, especially in critically ill patients receiving combination therapy. Early recognition and timely intervention are essential for managing this potential adverse reaction.