The aim of this study is to investigate histopathologically the time course of the myotoxic effects of different concentrations of bupivacaine and levobupivacaine after a single intramuscular injection in adult albino rats.Materials and methods
Eighty male adult albino rats were allocated to five different groups of 16 rats each (n=16). The first two groups (B.100 and B.200) received intramuscular injections with 100 and 200 μl of 0.5% bupivacaine, respectively, into the right tibialis anterior muscle. The second two groups (L.100 and L.200) received intramuscular injections with 100 and 200 μl of 0.5% levobupivacaine in the same place. The fifth group (CS) received a 100 μl intramuscular injection of 0.9% isotonic saline. Four rats from each group were killed after 2, 4, 10 and 20 days. Samples were examined blindly under a light microscope for evidence of myotoxicity and analysed statistically.Results
Muscle damage in B.100, B.200, L.100 and L.200 groups was similar qualitatively. In samples taken 2 days after injection, the muscle damage and inflammatory cells’ infiltration had started. Muscle damage and inflammatory cells’ infiltration reached their maximum on day 4 in all the treated groups in comparison with the control saline group. However, muscle damage was more marked in the B.100 and B.200 groups than the L.100 and L.200 groups. Progressive replacement of the damaged muscle fibres with connective tissue was detected on days 2 and 4 after injection. Muscle samples taken 10 and 20 days after bupivacaine and levobupivacaine injection showed persistence of the muscle fibre damage, with their massive replacement with connective tissue fibres.Conclusion
A single intramuscular injection of different concentrations of bupivacaine and levobupivacaine showed time-dependent and dose-dependent myotoxic effects on the skeletal muscle fibres. However, levobupivacaine was found to be qualitatively less myotoxic than bupivacaine. In all of the treated groups, the damaged muscle fibres failed to regenerate and had been replaced progressively with connective tissue fibres.