Investigation of Post-Mortem Redistribution Using In Vitro Models

In unexplained death cases it is important to be able to determine the role (if any) of the drugs detected may have played in the death. However, drug concentrations can change between the time of death and the time of the analysis of the post-mortem sample, thus the concentration of the drug detected needs to be interpreted with caution. Post-mortem redistribution (PMR) is a process that involves the passive movement of drugs after death that can lead to changes in post-mortem drug concentrations at certain sites after death. In addition, other factors that could account for post-mortem changes include the environment in which an individual is found, as certain environments could accelerate decomposition, also the circumstances surrounding the death and the length of time between the death and recovery of the body. Certain organs including lungs, liver, and heart are depots of drugs for PMR as they can have higher concentrations than surrounding sites. The bladder has traditionally not been considered a possible depot for PMR. However one study, a case report, published in Japan discussing an individual that had a PMI of nine days with higher concentrations of diphenhydramine and dihydrocodeine in the femoral vein compared to the cardiac blood, has suggested that it may be. There have been no further studies to elucidate any possible role of the bladder in the PMR process.

The aim of this thesis was to determine if the bladder is a potential site for PMR and to develop methodology to allow further study. The investigation included the influence of temperature, pH, porcine bladder degradation, and solution volume on diffusion from the bladder using in vitro diffusion through porcine bladder sections, whole porcine bladders and finally in vivo diffusion from the bladder in rat models over nine days.

This thesis looked at three methods to investigate the possible diffusion of drugs from the bladder. 1) porcine bladder sections; 2) whole porcine bladders and 3) whole rats.

The initial method used Franz Cells to determine the diffusion of rhodamine B, amitriptyline and amitriptyline’s metabolite nortriptyline across the porcine bladder wall. Acceptor chamber solutions were 20 mM pH 7.4 phosphate buffer (PBS) and 20 mM pH 5 ammonium acetate (AA). Donor solutions, dependent on experiment, contained 100 mg/L rhodamine B or amitriptyline and nortriptyline in the respective solutions. Sampling was over five days. Parameters included temperature (37 °C, 20 °C, and 5 °C), pH (7.4, 5), intra-variability of porcine bladder diffusion and tissue degradation. Quantitation methods of rhodamine B (UV, Agilent, Cary 60), amitriptyline, and nortriptyline (HPLC, Dionex Ultimate 3000) were validated according to SWGTOX guidelines.

The femoral vein has been stated as the best site for sampling post-mortem blood and interpretation due to the isolation from the main viscera. However, due to the above case report suggesting redistribution from the bladder this is a possible factor that could affect this sampling site. The porcine bladder sections and whole porcine bladders were analysed to determine how much drug would diffuse through the tissue over the first 100 hrs after death, which is the initial steps in determining the likelihood of drugs diffusing from the bladder to the femoral vein. Whole porcine bladder studies used the validated UV method for rhodamine B. Experimental temperature was 20 °C. Full and half-filled porcine bladders contained rhodamine B (100 or 200 mg/L) dissolved in pH 7.4 PBS and pH 5 AA. Triplicate analysis performed using the UV spectrophotometer at 554 nm. The in-vivo study involved catheterizing a rat and inserting silver nitrate into the bladder then securing it for Computed Tomography (CT) analysis over nine days.

There was increased diffusion of all three drugs at physiological temperature (37°C) with a peak rhodamine B concentration of 3.46 ± 2.72 mg/L (intra-bladder, pH 5), 6.69 mg/L and 6.69 ± 4.76 mg/L for amitriptyline and nortriptyline respectively (pH 7.4). The other parameters including solution pH and tissue degradation showed no significant difference for drugs diffusing through the bladder over 5 days. Concentration and volume was not a factor for rhodamine B diffusing through the whole porcine bladder tissue. There was an increase in drug diffusion over the five days with a peak concentration of 3.5 ± 1.02 mg/L (pH 7.4). The rat bladder was intact for two days, and then between 2-6 days, an opening was observed with leakage of solution. However, after day 7 this solution was not observed on the CT image. The CT data show that it is a good technique for the detection of diffusion of ions from the bladder, but would need to be further developed to look at the diffusion of larger molecular weight organic molecules.

Based on this work, methods for investigating the diffusion of drugs across the bladder have been developed and validated. The use of μCT shows promise for the further visualization of PMR to investigate not only diffusion from the bladder but also diffusion from other drug depots in the body. However, based on this work it is unlikely that the bladder is a significant source of PMR to the femoral vein, at least in PMI of less than 100 hours after death.