Rhabdomyolysis induced by long term consumption of caffeine and diphenhydramine without physical exercise chronic caffeine and DPH rhabdomyolysis

Abstract

Caffeine and diphenhydramine are widely consumed components of over-the-counter medications and energy drinks, and numerous cases of intoxication and rhabdomyolysis following acute overdose have been reported. However, muscle injury associated with chronic ingestion without an identifiable precipitating factor is extremely rare. We report a case of a man in his twenties with long-term habitual use of caffeine-containing energy drinks and diphenhydramine who developed severe rhabdomyolysis without strenuous physical activity or trauma. On admission, creatine kinase was markedly elevated, and magnetic resonance imaging demonstrated myositis-like changes in the affected muscles. Measured serum concentrations of caffeine （3.75 μg/mL） and diphenhydramine （0.15 μg/mL） were substantially lower than toxic levels. Supportive therapy and discontinuation of both agents resulted in rapid clinical and biochemical improvement; however, low-level persistence of serum drug concentrations during the clinical course suggested delayed elimination and possible tissue accumulation. This case highlights that chronic exposure to commonly used substances may result in clinically significant muscle injury that cannot be fully assessed by serum concentrations alone. Careful medication and dietary history taking, including over-the-counter drugs and energy drinks, is essential when evaluating unexplained muscle symptoms, even in young patients.