The myotoxicity of bupivacaine, a 31P n.m.r. investigation.

Phosphorus nuclear magnetic resonance (n.m.r.) spectroscopy is a recently introduced method for the non-invasive study of muscle biochemistry. It was shown in the rat that an intramuscular injection of the drug resulted in degeneration that was reflected spectroscopically in a progressive decrease in the intracellular concentrations of phosphocreatine and adenosine triphosphate without a corresponding rise in that of inorganic phosphate. Furthermore, ATP was depleted in the presence of significant levels of phosphocreatine. As regeneration occurred spectra returned to normal and this was complete by day 10. No such spectroscopic effects were demonstrated in man following the use of bupivacaine in an intravenous regional anaesthetic. It is suggested that further studies in man are required before this drug can be administered intramuscularly with confidence.