Background: Postmortem redistribution (PMR) is the changes that occur in drug
concentrations after death. Lidocaine is the most popular local anesthetic used worldwide
and midazolam is a widely used pre-anesthetic anxiolytic and sedative. Aim of the
Work: This work was performed to study potential early phase postmortem
redistribution of lidocaine and midazolam, as well as, the influence of storage
temperature on it in adult albino rats. This was done by measuring their concentrations in
blood (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 blood
ratio (L/P) was performed. Materials and Methods: This study was carried out on 36
adult 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), and
sacrificed 30 minutes later. This group was subdivided into three equal groups; AM
control (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), and
sacrificed 30 minutes later. This group was subdivided into three equal groups; AM
control (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 in
both tissues and blood samples as compared to those of corresponding AM control
groups. Markers of PMR revealed early phase PMR of lidocaine by L/P ratios > 20 at 21
ºC. 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 interfered
with PMR assessment. Midazolam revealed minimal early phase postmortem
redistribution as demonstrated by C/P ratios just above 1 at 4 ºC. L/P ratio was a more
reliable marker for PMR than C/P ratio. Conclusion: Lidocaine was highly liable to
undergo 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 postmortem
degradation and had minimal early phase PMR as demonstrated by C/P ratios just above
1 at 4 ºC. Recommendation: it is recommended to increase forensic toxicologists'
awareness about PMR of lidocaine and midazolam, and their influence on the
interpretation of PM toxicological analysis.