Caffeine impairs intramuscular energy balance in patients susceptible to malignant hyperthermia.

Malignant hyperthermia (MH) is a metabolic myopathy with an abnormal release of calcium by the sarcoplasmic reticulum (SR), triggered by volatile anesthetics and succinylcholine. Similarly, caffeine enhances Ca²⁺release by the SR in vitro. In a prospective, randomized study, high-energy phosphates were studied by intramuscular 31-phosphorus magnetic resonance spectroscopy (³¹P-MRS) in 10 MH-susceptible (MHS) and 7 MH-nonsusceptible (MHN) subjects before and after injection of 0.5 ml caffeine (20 mM). Intramuscular energy balance, measured by the ratios of P_i/PCr and P_i/γ-ATP, did not differ between MHS and MHN patients before and after intramuscular caffeine injection. However, within each group, P_i/PCr and P_i/γ-ATP increased significantly only in the MHS group. Intramuscular caffeine injection seemed to impair the metabolic balance in MHS individuals. This may reflect a local calcium overload leading to consumption of high-energy phosphates and increase of inorganic phosphate. Intramuscular stimulation by caffeine and ³¹P-MRS may provide a valuable tool to investigate MH-related metabolic disturbances. Muscle Nerve 28: 353–358, 2003 [ABSTRACT FROM AUTHOR]