EARLY PHASE POSTMORTEM REDISTRIBUTION OF LIDOCAINE AND MIDAZOLAM IN ADULT ALBINO RATS

Abstract

Background: Postmortem redistribution (PMR) is the changes that occur in drugconcentrations after death. Lidocaine is the most popular local anesthetic used worldwideand midazolam is a widely used pre-anesthetic anxiolytic and sedative. Aim of theWork: This work was performed to study potential early phase postmortemredistribution of lidocaine and midazolam, as well as, the influence of storagetemperature on it in adult albino rats. This was done by measuring their concentrations inblood (cardiac blood and external iliac vein blood) and tissues (heart, lungs and liver).Calculation of cardiac blood to peripheral blood ratio (C/P) and Liver to peripheral bloodratio (L/P) was performed. Materials and Methods: This study was carried out on 36adult male albino rats which divided into two main groups (18 rats each). Group I(Lidocaine): Rats received a single SC injection of 2% lidocaine HCL (67 mg/kg), andsacrificed 30 minutes later. This group was subdivided into three equal groups; AMcontrol (L-AM), 15 minutes PM at 4oC (L-PM4) and 15 minutes PM at 21oC (L-PM21).Group II (Midazolam): Rats received single IV injection of midazolam (75 mg/kg), andsacrificed 30 minutes later. This group was subdivided into three equal groups; AMcontrol (M-AM), 15 minutes PM at 4oC (M-PM4), 15 minutes PM at 21oC (M-PM21).Results: There were significant changes in lidocaine and midazolam concentrations inboth tissues and blood samples as compared to those of corresponding AM controlgroups. Markers of PMR revealed early phase PMR of lidocaine by L/P ratios > 20 at 21oC. Storage temperature at 4oC arrested lidocaine PMR as recorded by both C/P ratios <1 and L/P ratios < 5. Midazolam was prone to postmortem degradation that interferedwith PMR assessment. Midazolam revealed minimal early phase postmortemredistribution as demonstrated by C/P ratios just above 1 at 4 oC. L/P ratio was a morereliable marker for PMR than C/P ratio. Conclusion: Lidocaine was highly liable toundergo early phase PMR as demonstrated by L/P ratios above 20 at 21 oC. However,storage at 4oC retarded lidocaine PMR. Midazolam was subjected to postmortemdegradation and had minimal early phase PMR as demonstrated by C/P ratios just above1 at 4 oC. Recommendation: it is recommended to increase forensic toxicologists'awareness about PMR of lidocaine and midazolam, and their influence on theinterpretation of PM toxicological analysis.