One may think of the human body as a static entity after death, it is clearly not so. Although in the living we routinely rely on pharmacokinetics to interpret blood drug concentrations, post-mortem redistribution (PMR) makes this difficult. The complexity of PMR lead Pounder to describe PMR as a toxicological nightmare (1;2). When measuring drug concentrations after death, it is important to consider the phenomenon of PMR. The properties of drugs (medication) after death change considerably. Postmortem drug concentrations may not be a true reflection of antemortem concentrations and as a result, incorrect conclusions could be drawn about the cause of death. Collection and analysis of not only peripheral blood, but also other fluids/tissues is usually important in postmortem work.  Various factors such as the site of collection, time elapsed since death also influences the result obtained and subsequent interpretation of postmortem drug concentration (Table 1).

Curry and Sunshine in 1960 were amongst the first to show that there was a difference in peripheral (femoral) blood barbiturate concentration and liver concentrations with liver being higher (3). Initially much attention was paid to barbiturates and this was followed by digoxin and tricyclic antidepressants (TCA). Holt and Benstead found postmortem blood concentrations of digoxin in femoral vein, neck veins and right ventricle were significantly different (4). Femoral blood was the lowest. TCAs, the most studied drugs, post mortem liver concentrations were found to be much higher than blood in TCA and non-TCA related drugs (5). Since the advent of drugs of abuse, a number of abused drugs including cocaine and methamphetamines have recently received attention.

To understand post mortem changes we first need to understand what happens to the cell structure and integrity of its contents upon death. Aerobic respiration, synthesis of enzymatic and structural proteins, and, preservation of the genetic apparatus of the cell are key to the integrity of the cell membrane. Figure 1 shows the mechanisms that take place upon cell injury. Sequences of events depend on the organ involved. Brain neurons show irreversible damage within three to five minutes, myocardium in about 30 to 40 minutes and liver between one to two hours after ischemia.

There are number of pharmacokinetic properties of the drug that affect its postmortem distribution characteristics. Some of these are: volume of distribution, lipophilicity and pKa of the drug in question.  The apparent volume of distribution (Vd), a significant factor in PMR, is a parameter relating the concentration of a drug in the plasma to the total amount of the drug in the body. It is assumed that the drug is uniformly distributed to reach the concentration that is actually measured in plasma. Vd is the total amount of the drug in body divided by the plasma concentration and is expressed in liters per kilogram of body weight. Drugs that have a Vd of greater the 3 L/kg are more likely to have PMR characteristics. Many drugs are sequestered in muscle and adipose tissues, thus body composition is an important factor also. Age, gender, and diseases are the other variables that influence Vd. Drugs that are bound to plasma proteins and are not bound to tissue components have a lower Vd, example ethanol; whereas drugs that are sequestered in muscle and adipose tissue and other intracellular components have a large apparent Vd.  Table 2 lists a few drugs with their respective Vd.

Many of the highly lipophilic drugs are concentrated in the adipose tissue by simple physical dissolution depending on the concentration gradient and pH on both sides of the membrane.  Water-soluble molecules, such as ethanol, diffuse across the lipid membranes through proteic pores because of osmotic and oncotic gradient.  Weak acids and bases are transported by active transport that requires energy in the form of ATP and/or a carrier to transport the drug across the membrane. All this stops upon death. Some of the lipophilic drugs have a very wide distribution in tissues due to cellular uptake and accumulation. This most likely happens due to binding to membrane phospholipids and accumulation in acidic compartments.

Lipophilic and organic basic drugs typically concentrate in solid organs such as liver, lungs and myocardium. Thus organs such as esophagus, stomach, lungs and liver, which are proximal to the major blood vessels and heart, are more likely to play an important role in PMR. Upon cell death the aqueous cell contents become progressively acidic (Figure 1).  Organic bases, depending on their pKa, are gradually ionized and dissolve in the aqueous medium. Once lysis occurs passive diffusion takes over and they are readily released into plasma. This is a significant contributor to PMR.  Lipophilicity influences PMR in a number of anatomical sites such as the stomach, lungs, cardiac muscle, cardiac blood or liver, but does not appear to influence sites such as the brain or the vitreous humor.

Robertson and Drummer showed that putrefaction can lead to bioconversion of various benzodiazepines by enteric bacteria commonly found after death (6;7). The rate of conversion is reduced at 4°C when compared with 22°C to 37°C demonstrating the need to keep cadavers at cool temperatures. These bacteria are known to cross the gastrointestinal wall and enter blood and lymph vessels and then transmigrate through the body within a few hours postmortem. In the presence of glucidic substrates, such as glucose or ribose, bacteria can produce ethanol (8). Since glucose is the primary substrate of postmortem ethanol production, tissues (liver, skeletal muscles, lungs, and myocardium) with high glucose storage capacity are the greatest source of ethanol production. Urine is a poor medium for microbial ethanol production unless the deceased was diabetic.

Movement of body by various individuals (police, health care workers, family etc) can have a significant impact as a few hours after death blood starts to settle (hypostasis) in the lower part of an organ or the body. Hypostasis occurs by sedimentation of blood and plasma to the lower part of the corpse. Postmortem blood sediments and clots unevenly. This is brought about by blood clotting followed by lysis. Clots trap red blood cells so sampling this can influence the concentration of drugs that are bound to the erythrocytes and therefore unevenly distributed between red cells and plasma e.g. tacrolumus. Movement of blood within the vessels also occurs shortly after death and can be part of the explanation of PMR. 

Sampling sites: It is important in postmortem analysis to compare concentrations in blood from several sites, even when reference values are available. Blood must be taken at the central (cardiac) and peripheral sites. Cardiac blood samples are collected from right and left chambers separately. Femoral blood is less affected by time delay as compared to central blood and is the specimen of choice (9). Other tissues such as liver, lungs, skeletal muscle and vitreous humor have been used for drug analysis. Of these, vitreous humor that is isolated is less susceptible to PMR. It contains no micro-organisms or glucose and is protected from putrefaction. It is therefore the sample of choice to differentiate exogenous ethanol from endogenous ethanol production from putrefaction. Premortem blood ethanol concentration can be estimated from vitreous humour, unfortunately, concentrations of other drugs may not be accurately estimated from vitreous humor.  Animal studies have shown that vitreous humor concentrations of cocaine and other drugs were significantly higher when collected 8 hours after death (10). Flanagan and  co-workers provide guidelines for sample collection, labeling, transport and storage for specimen taken during postmortem examination (11).

Cook and co-workers reviewed coroners’ cases from October 1990 to July 1997 and found six cases where both antemortem and postmortem blood levels were available (12). They compared ratios of antemortem levels with postmortem levels from central (cardiac-blood) to peripheral (femoral blood). They found that the drugs that have a high PMR also have a high postmortem to antemortem ratio. They caution on interpreting antemortem drug concentrations and amount ingested from postmortem measurements.

Recently Reis (2007) and co-workers reviewed 95% of the autopsies performed in Sweden where femoral blood was available. For 15 different antidepressants they provide both therapeutic and postmortem blood levels. Having reviewed a total of 8591 cases they state  “We would like to point out that, because no exact cut-off limits for fatal levels can be defined, common sense, a thorough review of all medico-legal findings, and circumstances cannot be replaced by a blood drug concentration”(13).

Recommended reviews for further information
Pelissier-Alicot AL, Gaulier JM, Champsaur P, Marquet P. Mechanisms underlying postmortem redistribution of drugs: a review. J Anal Toxicol 2003; 27(8):533-544.
Yarema MC, Becker CE. Key concepts in postmortem drug redistribution. Clin Toxicol 2005; 43(4):235-241.
Drummer,O.H.; Gerostamoulos,J. Postmortem drug analysis: analytical and toxicological aspects. Ther Drug Monit. 24(2):199-209, 2002
Drummer,O.H. Post-mortem toxicology. Forensic Sci Int. 165(2-3):199-203, 2007

Previously published in CSCC News, vol. 50, no. 2 April 2008.

Figure 1

Table 1: Factors to consider when interpreting post-mortem results

Table 2: Some selected examples of drugs with their volume of distribution (15)

Reference List

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(2) Pounder DJ, Jones GR. Post-mortem drug redistribution - a toxicological nightmare. Forensic Sci Int 1990; 45(3):253-263.
(3) Curry A, Sunshine I. The liver:blood ratio in cases of barbiturate poisoning. Toxicol Appl Pharmacol 1960; 2:602-606.
(4) Holt D, Benstead J. Postmortem assay of digoxin by radioimmunoassay. J Clin Pathol 1975; 28:483-486.
(5) Apple F, Brandt C. Liver and blood postmortem tricyclic antidepressant concentrations. Am J Clin Pathol 1988; 89(6):794-796.
(6) Robertson MD, Drummer OH. Stability of nitrobenzodiazepines in postmortem blood. Journal of Forensic Sciences 43(1):5-8, 1998.
(7) Robertson MD, Drummer OH. Postmortem distribution and redistribution of nitrobenzodiazepines in man. J Forensic Sci 1998; 43(1):9-13.
(8) Corry JE. A review. Possible sources of ethanol ante- and post-mortem: its relationship to the biochemistry and microbiology of decomposition. Journal of Applied Bacteriology 1978; 44(1):1-56.
(9) Pelissier-Alicot AL, Gaulier JM, Champsaur P, Marquet P. Mechanisms underlying postmortem redistribution of drugs: a review. J Anal Toxicol 2003; 27(8):533-544.
(10) McKinney PE, Phillips S, Gomez HF, Brent J, MacIntyre M, Watson WA. Vitreous humor cocaine and metabolite concentrations: do postmortem specimens reflect blood levels at the time of death? J Forensic Sci 1995; 40(1):102-107.
(11) Flanagan RJ, Connally G, Evans JM. Analytical toxicology: guidelines for sample collection postmortem. Toxicological Reviews 24(1):63-71, 2005.
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(13) Reis M, Aamo T, Ahlner J, Druid H. Reference concentrations of antidepressants. A compilation of postmortem and therapeutic levels. Journal of Analytical Toxicology 31(5):254-64, 2007.
(14) Yarema MC, Becker CE. Key concepts in postmortem drug redistribution. Clin Toxicol 2005; 43(4):235-241.
(15) Baselt RC. Disposition of Toxic Drugs and Chemicals. Seventh Edition ed. Foster City, California: Biomedical Publications, 2004.