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Fatal combined intoxication with new antidepressants. Human cases and an experimental study of postmortem moclobemide redistribution
Forensic Science International 100 (1999) 109–116
Fatal combined intoxication with new antidepressants. Human cases and an experimental study of postmortem moclobemide redistribution a, b a Sidsel Rogde *, Thor Hilberg , Brita Teige a
Institute of Forensic Medicine, University of Oslo, Oslo, Norway b National Institute of Forensic Toxicology, Oslo, Norway Received 1 October 1998; accepted 19 October 1998
Abstract Three cases are presented in which death was caused by suicidal intoxication with moclobemide in combination with a selective serotonin reuptake inhibitor. Both antidepressant drug types are considered to be relatively safe with regard to lethal overdose. However, the combination may cause the serotonin syndrome, a condition with a high mortality rate. In one of the cases, there was clinical information consistent with the serotonin syndrome, in the two other cases, there was no information of the clinical course. Postmortem redistribution of the selective monoamine oxidase inhibitor moclobemide was investigated in a rat model. Postmortem concentrations in blood from the vena cava and the heart were found to be in good accordance with antemortem concentrations. Postmortem concentrations in vitreous humour and various tissues were also measured. The apparent volume of distribution was calculated to be 0.9560.10 l / kg, which is in the same range as that reported in man. 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Moclobemide; MAO-A inhibitor; Selective serotonin reuptake inhibitor; SSRI; Postmortem redistribution; Serotonin syndrome; Intoxication; Suicide
1. Introduction It is well known that persons suffering from depression are at increased risk of taking their own lives [1], and that intoxication by prescription drugs is a widely used suicide *Corresponding author. Rettsmedisinsk institutt, Rikshospitalet, N-0027 Oslo, Norway. Tel.: 147-22-86-8663; fax: 147-22-20-95-83. E-mail address: [email protected] (S. Rogde) 0379-0738 / 99 / $ – see front matter 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S0379-0738( 98 )00184-4
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method [2]. Tricyclic antidepressants (TCAs), especially amitriptyline and doxepin, have been widely used for this purpose in our country [3]. Concomitant with the introduction of a new generation of antidepressants, the number of deaths caused by TCA intoxication has decreased [4], and the new antidepressants seem to be far safer with regard to intoxication [5]. However, the combination of a selective monoamine oxidase (MAO-A) inhibitor with a selective serotonin reuptake inhibitor (SSRI) may cause the serotonin syndrome, even in therapeutic use [6] and, thus, lethal intoxications by such combinations can be expected. Forensic pathologists and toxicologists are well aware that postmortem concentrations may be difficult to interpret and even impossible to compare with concentrations in the living due to postmortem redistribution [7]. While this phenomenon has been studied concerning the SSRIs, information on moclobemide, the one drug that is seen in all three cases described here, is more sparse. We therefore found it worthwhile to investigate postmortem redistribution of this drug in a rat model.
2. Human cases
2.1. Case 1 A 51-year-old female, who was very warm and sweating profusely, was found unconscious in her home. There was an empty package of Aurorix (moclobemide) in her house. Many other drugs were also found, including Fevarin (fluvoxamine, SSRI). On admission to hospital, she had severe cardiac arrhythmia and unmeasurable arterial blood pressure. Serum was screened for paracetamol, ethanol, lithium and salicylic acid — with negative results. She received assisted respiration and intensive care. However, she gradually developed multiple organ failure and died four days later. A medicolegal autopsy was performed. Evidence of hypoxic brain damage was found. There was also an incipient bronchopneumonia and widespread centrilobular necrosis of the liver. Postmortem femoral blood concentrations were: moclobemide 20 mmol / l, fluvoxamine 1.7 mmol / l. The concentrations were considered high, especially when taking into consideration that death occurred more than four days after ingestion. Analyses were also performed on an antemortem blood sample that was taken three days after admission to hospital (31 h prior to death). The concentrations then were 60 mmol / l moclobemide and 0.6 mmol / l fluvoxamine. The cause of death was assumed to be intoxication with a combination of the MAO-A inhibitor and the SSRI. The hypoxic brain damage, the bronchopneumonia and the liver necrosis were considered to have been caused by the toxic effect exerted by the combined ingestion of the two drugs. The clinical picture was considered to be consistent with the serotonin syndrome.
2.2. Case 2 A 27-year-old female was found dead in her bed. There was a suicide note in her vicinity. Beside her bed were empty packages of Aurorix (moclobemide), Fevarin
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(fluvoxamine), Imovane (zopiclone, a hypnotic drug) and Somadril Comp (a muscle relaxant consisting of carisoprodol and paracetamol). A medicolegal autopsy was performed. No signs of injury or disease were found. The toxicological analyses of femoral blood revealed 50 mmol / l moclobemide, 6 mmol / l fluvoxamine, both regarded as high concentrations, 125 mmol / l paracetamol, 34 mmol / l carisoprodol and 64 mmol / l meprobamate (a metabolite of carisoprodol). The three latter concentrations are somewhat above those normally observed with therapeutic dosing. The zopiclone concentration was 0.46 mmol / l, which is above the level seen after therapeutic use [8]. The maximum zopiclone intake was 75 mg, as judged from the empty Imovane package found at the scene. Death was considered to be caused by intoxication, primarily by a combination of moclobemide and fluvoxamine.
2.3. Case 3 A 22-year-old female was found dead in her bed. Empty packages of Aurorix (moclobemide) and Seroxat (paroxetine, SSRI) were found in her home. A medicolegal autopsy was performed. On her left wrist were found four shallow sharp lesions from which there was no significant haemorrhage. In the brain stem, inflammatory changes, located around the nucleus of the trigeminal nerve, were observed. These changes were not considered to have been of importance for death. Toxicological analyses of postmortem femoral blood revealed 31 mmol / l moclobemide and 2.2 mmol / l paroxetine, which are high concentrations. Ethyl alcohol was found at a concentration of 0.4 g / l. Death was considered to be due to intoxication with moclobemide and paroxetine.
3. Animal studies
3.1. Materials and methods Male Wistar rats with a body weight of 258–278 g were fasted overnight and fed 50 mg of moclobemide as grounded Aurorix tablets (Roche, Switzerland) in 2 ml of water by a gastric tube. Ninety minutes after dosing, the rats were anaesthetised with a subcutaneous injection of fluanisone, fentanyl and midazolam (5, 0.1 and 2.5 mg per kg rat, respectively). A blood sample (¯500 ml) was drawn from the heart and transferred to a silanized glass tube containing 25 ml of a 67% (w / v) potassium fluoride solution. The rats were then sacrificed with CO 2 and were left at room temperature for 2 h, when autopsy was performed. Postmortem heart blood samples (¯500 ml) were drawn after having clamped the inferior vena cava just above the diaphragm. Blood from the inferior vena cava (|500 ml) was sampled after clamping just superior to the renal veins. The following tissue samples were also collected: vitreous humour from both eyes, tissue from the upper lobe of the right and left lungs, the heart, one sample from the right part of the median liver lobe and another from the left caudate liver lobe lying next to the stomach, lower pole of right kidney, thigh muscle and forebrain. In addition, the stomach and the proximal 50 cm of the small intestine were dissected out. The carcasses
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were minced in a manual meat mincer twice and 5 g were sampled for further homogenisation, as for the other tissues.
3.2. Extraction, chromatography and analytical procedures Tissue samples were homogenised with an Ultra-Turrax T5 homogeniser (IKA, Janke & Kunkel, Germany) in water to a final concentration of 0.2 g tissue / ml homogenate. Moclobemide concentrations in blood and vitreous humour samples were determined from a calibration curve prepared from blood, while tissue concentrations were determined from a calibration curve prepared from liver tissue. All samples were kept at 2208C until analysis, when 100 ml of an aqueous solution of the internal standard, methadone, and 300 ml of 1 M Tris (pH 10.7) were added. The mixture was extracted on ice for 10 min with 400 ml of butylacetate, and centrifuged for 10 min at 740 g. The organic phase was transferred to 100 ml autosampler vials. The gas chromatograph was HP 5890, and the column was a polar 15 m30.32 mm DB 1701, 0.32 mm film thickness (J&W Scientific, USA). The injection volume was 5 ml (split mode, 1:10) and a nitrogen–phosphorous detector was employed. The injector temperature was 2508C, and the detector temperature was 3008C. The temperature program started at 1508C for 1 min and increased by 208C per min to 2508C, with a hold time of 0.5 min, with further increments of 58C per min to 2808C, with a hold time of 10 min. The carrier gas used was helium, with a flow rate of 1.5 ml / min, and make up gas to a total of 30 ml / min. Recovery in blood exceeded 73% at concentrations of 1 and 10 mmol / l and in liver tissue exceeded 78% at concentrations of 5 and 50 mmol / kg. The calibration ranges were from 1 to 300 mmol / l in blood and liver tissue, and there was linearity within these ranges (R 2 .0.99). The coefficient of variation (CV) of within-run precision was better than 6.0%. Results are presented as mean6standard error of the mean (s.e.m.) in mmol / l or mmol / kg. The apparent volume of distribution was calculated as the concentration of drug in carcass homogenate divided by antemortem heart blood drug concentration.
4. Results The moclobemide concentrations found in antemortem heart blood (Table 1) were above the therapeutic concentration ranges seen in humans [9]. Accordingly, the rats were observed to be slightly sedated. The postmortem-to-antemortem heart blood drug concentration ratio was 1.260.1 and there was no significant difference between the antemortem and postmortem blood drug concentrations. The tissue-to-antemortem blood drug concentration ratios are outlined in Table 1. There were no significant differences between the drug concentrations in the right and left lungs or between the liver lobes.
5. Discussion In order to interpret the postmortem moclobemide concentrations in our case reports, we found it worthwhile to study moclobemide redistribution experimentally.
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Table 1 Concentration of moclobemide in blood and tissues from six rats, expressed as mean values6standard error of the mean (mmol / l or mmol / kg) Mean6s.e.m. Antemortem heart blood concentration Postmortem heart blood concentration Postmortem vena cava blood concentration Vitreous humour–antemortem blood drug concentration ratio Lung–antemortem blood drug concentration ratio Myocardium–antemortem blood drug concentration ratio Liver–antemortem blood drug concentration ratio Kidney–antemortem blood drug concentration ratio Muscle–antemortem blood drug concentration ratio Brain–antemortem blood drug concentration ratio Apparent volume of distribution
46.166.5 52.866.8 57.468.2 0.560.0 2.060.2 1.560.1 4.460.8 4.160.2 0.960.1 1.760.1 0.9560.10
Conversion factor: 0.27 mmol / l5mg / l. The tissue concentrations are expressed as tissue-to-antemortem heart blood drug concentration ratios. The apparent volume of distribution is in l / kg.
The present rat model has previously been documented to exhibit postmortem drug redistribution properties in a comparable manner to those described in man [10–12]. The insignificant drug concentration changes found in this study imply that there should be little or no potential for postmortem drug redistribution with this substance. The apparent volume of distribution calculated is in the same region as that found in man [13]. The relatively low value found is a further indication that there is little potential for drug release from parenchymal tissues back to the blood. These observations are very much in contrast to tricyclic antidepressants like amitriptyline and nortriptyline that have large apparent volumes of distribution, high tissue-to-blood concentration ratios and a profound potential for postmortem drug level increases, particularly in heart blood. The present study implies that one can assume the concentration of moclobemide found in postmortem blood samples to be reasonably representative of the concentration at the time of death, thus, it may be concluded that the moclobemide concentrations in all three cases were well above the therapeutic level [9]. The concentration of several drugs in vitreous humour has previously been reported to be closely related to the unbound fraction in the blood. The results in the present study indicate that this is also the case for moclobemide in rats (Table 1), assuming that the degree of protein binding is in the same order of magnitude as in man [9]. Note, however, that postmortem release of both digoxin [14] and amitriptyline [15] into vitreous humour has been reported, so, depending on the postmortem interval, the drug concentration in this tissue may be substantially higher than antemortem. Unlike older monoamine oxidase inhibitors, moclobemide is a reversible and selective inhibitor of the MAO-A isozyme, and is found to have antidepressant properties. Recommended dosage is 300 to 600 mg divided into two or three daily doses. The bioavailability is 44–69% at therapeutic doses initially, but increases with chronic use to more than 80% [9]. The volume of distribution is 0.8–1.3 l / kg [9,13] and protein binding in plasma is about 50%. The half-life is 1–2 h, and is not affected by age or
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renal function, but may be prolonged by hepatic disorders. The plasma concentrations seen after therapeutic doses range from 0.4 to 3.4 mg / l (1.4 to 12 mmol / l) [9]. Postmortem peripheral blood concentrations associated with assumed therapeutic use have been observed in the range of 0.2 to 2.1 mg / l (0.6 to 6.5 mmol / l), while concentrations in cases with lethal intoxications (where other substances were also involved) were 1.9 to 21 mg / l (5.8 to 64.5 mmol / l) [16]. Two moclobemide fatalities have been reported from France [17]. In these cases, the blood concentrations of moclobemide were 15.5 and 13.8 mg / ml (57.4 and 51.1 mmol / l, respectively). Only the former was described as a single drug intoxication. Camaris and Little [18] have reported a moclobemide fatality with a blood concentration of 137 mg / l (507.4 mmol / l). The site for blood sampling was not indicated in their study. The serotonin syndrome is described in a review article by Sternbach [19]. The syndrome is most commonly the result of the interaction between serotoninergic agents and irreversible monoamine oxidase inhibitors. The most frequent clinical features are changes in mental status, restlessness, myoclonus, hyperreflexia, diaphoresis, shivering and tremor. Originally it was thought only to occur in relationship with irreversible non-selective monoamine oxidase inhibitors in combination with serotonin reuptake inhibitors or with tryptophan. Moclobemide is an inhibitor of monoamine oxidase, but contrary to the old generation of these drugs, this drug has a reversible effect on the enzyme and is considered safe with regard to interactions. There are, however, isolated reports of such interactions. Spigseth et al. [6] described this syndrome in a patient who had just changed the antidepressive treatment to moclobemide from clomipramine, a tricyclic antidepressant with a significant ability to inhibit serotonin reuptake. The authors recommend serotonin reuptake inhibitors to be discontinued for some time before starting moclobemide treatment, depending on the half-life of the various serotonin reuptake inhibitors. Case reports of lethal interactions in overdoses have been reported by several authors [20–24]. In two of these reports [21,22], it is stated that a combination of drugs may have been used ‘in order to get high’. Iwersen and Schmoldt [25] reported three suicide attempts with moclobemide, one of which was a combination of moclobemide and clomipramine. There were no signs of serotonin syndrome. All three cases described from our institutes are suicidal overdoses. In one of the cases, there was clinical evidence that might be consistent with the serotonin syndrome, while this may only be hypothesised in the other two cases as a possible mechanism of death. In Case 1, the fluvoxamine concentration was almost three-fold higher in postmortem blood than in the antemortem sample. We believe that this difference is due to postmortem redistribution. In Case 2, a fluvoxamine concentration of 6 mmol / l was found. It is possible that postmortem redistribution had taken place. Fluvoxamine is used in daily doses of 50 to 300 mg, has a half-life of about 15 h and an apparent volume of distribution of more than 5 l / kg [26]. Serum concentrations observed after therapeutic doses are in the region of 0.05 to 0.25 mg / l (0.16 to 0.8 mmol / l) [27]. Plasma protein binding is about 80%. The drug may inhibit cytochrome P (CYP) 1A2 and, to a lesser extent, CYP 2D6, causing impaired elimination of other drugs [27]. Lethal intoxication with fluvoxamine has been associated with postmortem peripheral blood concentrations of 3.4 to 10.7 mg / l (10.7–33.6 mmol / l) [16], while lethal intoxication together with
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other substances has been reported with concentrations of 1.2 to 8.1 mg / l (3.8 to 25.4 mmol / l). Postmortem concentrations of 0.2 to 0.7 mg / l (0.6 to 2.2 mmol / l) have been associated with assumed therapeutic use [16]. In Case 3, a paroxetine concentration of 2.2 mmol / l was found. Paroxetine is used in daily doses of 20 to 50 mg, has a half-life of 10 to 16 h and an apparent volume of distribution of 17 l / kg [26], which is in the same order of magnitude as for tricyclic antidepressants. Serum concentrations after therapeutic doses are in the region between 0.01 and 0.15 mg / l (0.03 to 0.46 mmol / l) [28], and plasma protein binding is 95%. These figures indicate relatively high concentrations in tissue compared to blood. Accordingly, there is probably a potential for postmortem redistribution of these drugs [12]. Lethal intoxications with paroxetine together with other substances have been reported to occur with blood concentrations of 0.7 to 4.6 mg / l (2.1 to 14 mmol / l) [16]. Postmortem peripheral blood concentrations in cases where paroxetine was assumed to be used therapeutically were 0.09 to 0.5 mg / l (0.3 to 1.5 mmol / l) [16]. The relatively higher postmortem blood concentrations of fluvoxamine and paroxetine compared with the serum concentrations in the therapeutic situation also indicate a tendency for postmortem redistribution. Paracetamol [29] and zopiclone [30] (both observed in Case 3) have previously been reported not to be subject to postmortem redistribution. Meprobamate has a low volume of distribution at 0.7 l / kg [31] and carisoprodol probably also has a relatively low value. Hence, the postmortem concentrations found for these substances should be reasonably representative for the antemortem values. The number of deaths due to suicidal intoxications with antidepressants has declined after the introduction of the new generation of safer antidepressants [4]. However, the sales statistics show that an increasing number of persons now receive antidepressive drug treatment. It is therefore important to realise that the ‘safe’ drugs may also represent a potential means of suicide, especially when two such drugs are given in combination. In order to monitor the potential dangers of new drugs, it is important that medicolegal autopsies combined with thorough toxicological analyses are performed in cases in which intoxication is suspected.
References [1] M. Monk, Epidemiology of suicide, Epidemiol. Rev. 9 (1987) 51–69. [2] S. Rogde, H.P. Hougen, K. Poulsen, Suicides in two Scandinavian capitals — A comparative study, Forensic Sci. Int. 80 (1996) 211–219. [3] B. Teige, Fatal drug and alcohol intoxications outside hospital, Tidsskr. Nor. Lœgeforen. 105 (1985) 1857–1859. [4] B. Teige, Man tar hva man har–om medikamentdødsfall hos ikke-narkomane (On drug deaths in non-addicts). (In Norwegian) Proceedings XIIIth Nordic Congress in Forensic Medicine, 1997, pp. 55–63. [5] B.M. Power, P. Hackett, L.J. Dusci, K.F. Ilett, Antidepressant toxicity and the need for identification and concentration monitoring in overdose, Clin. Pharmacokinet. 29 (1995) 154–171. [6] O. Spigseth, T. Mjorndal, O. Lovheim, Serotonin syndrome caused by a moclobemide–clomipramine interaction, Br. Med. J. 306 (1993) 248.
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[7] D. Pounder, G.R. Jones, Post-mortem redistribution — a toxicological nightmare, Forensic Sci. Int. 45 (1990) 253–263. [8] C. Fernandez, C. Martin, F. Gimenez, R. Farinotti, Clinical pharmacokinetics of zopiclone, Clin. Pharmacokinet. 29 (1995) 431–441. [9] B. Fulton, P. Benfleld, Moclobemide. An update of its pharmacological properties and therapeutic use, Drugs 52 (1996) 450–474. [10] T. Hilberg, A. Bugge, K.M. Beylich, J. Ingum, A. Bjørneboe, J. Mørland, An animal model of postmortem amitriptyline redistribution, J. Forensic Sci. 38 (1993) 81–90. [11] T. Hilberg, J. Mørland, A. Bjørneboe, Postmortem release of amitriptyline from the lungs; a mechanism of postmortem drug redistribution, Forensic Sci. Int. 64 (1994) 47–55. ˚ Ripel, L. Slørdal, A. Bjørneboe, J. Mørland, The extent of postmortem drug redistribution [12] T. Hilberg, A. in a rat model. Submitted, 1998. [13] J. Raaflaub, P. Haefelfinger, K.H. Trautmann, Single-dose pharmacokinetics of the MAO-inhibitor moclobemide in man, Arzneimittelforschung 34 (1984) 80–82. [14] P.F. Binnion, G. Frazer, [ 3 H]Digoxin in the optic tract in digoxin intoxication, J. Cardiovasc. Pharmacol. 2 (1980) 699–706. ˚ Ripel, A.J. Smith, L. Slordal, J. Mørland, A. Bjørneboe, Postmortem amitriptyline [15] T. Hilberg, A. pharmacokinetics in pigs after oral and intravenous routes of administration, J. Forensic Sci. 43 (1998) 380–387. [16] H. Druid, P. Holmgren, A compilation of fatal and control concentrations of drugs in postmortem femoral blood, J. Forensic Sci. 42 (1997) 79–87. ´ [17] Y. Gaillard, G. Pepin, Moclobemide fatalities: report of two cases and analytical determinations by GC–MS and HPLC–PDA after solid-phase extraction, Forensic Sci. Int. 87 (1997) 239–248. [18] C. Camaris, D. Little, A fatality due to moclobemide, J. Forensic Sci. 42 (1997) 954–955. [19] H. Sternbach, The serotonin syndrome, Am. J. Psychiatry 148 (1991) 705–713. [20] P.J. Neuvonen, S. Pohjola-Sintonen, E. Vuori, Five fatal cases of serotonin syndrome after moclobemide– citalopram or moclobemide–clomipramine overdoses, Lancet 342 (1993) 1419. [21] A.F. Hemandes, M.N. Montero, A. Pla, E. Villaneuva, Fatal moclobemide overdose or death caused by serotonin syndrome?, J. Forensic Sci. 40 (1995) 128–130. [22] N. Keltner, C.P. Harris, Serotonin syndrome: a case of fatal SSRI / MAOI interaction, Perspect. Psychiatr. Care 30 (1994) 26–31. [23] B.M. Power, M. Pinder, L.P. Hackett, K.F. Ilett, Fatal serotonin syndrome following a combined overdose of moclobemide, clomipramine and fluoxetine, Anaesth. Intens. Care 23 (1995) 499–502. [24] M.J. Kuisma, Fatal serotonin syndrome with trismus, Ann. Emerg. Med. 26 (1995) 108. [25] S. Iwersen, A. Schmoldt, Three suicide attempts with moclobemide, Clin. Toxicol. 34 (1996) 223–225. [26] J. van Harten, Clinical pharmacokinetics of selective serotonin reuptake inhibitors, Clin. Pharmacokinet. 24 (1993) 203–220. [27] E. Perucca, G. Gatti, E. Spina, Clinical pharmacokinetics of fluvoxamine, Clin. Pharmacokinet. 27 (1994) 175–190. [28] C.M. Kaye, R.E. Haddock, P.F. Langley, G. Mellows, T.C. Tasker, B.D. Zussman, W.H. Greb, A review of the metabolism and pharmacokinetics of paroxetine in man, Acta Psychiatr. Scand. Suppl. 350 (1989) 60–75. [29] K. Yonemitsu, D.J. Pounder, Postmortem toxico-kinetics of co-proxamol, Int. J. Leg. Med. 104 (1992) 347–353. [30] D.J. Pounder, J.I. Davies, Zopiclone poisoning: tissue distribution and potential for postmortem diffusion, Forensic Sci. Int. 65 (1994) 177–183. [31] R.C. Baselt, R.H. Cravey, Disposition of Toxic Drugs and Chemicals in Man, fourth ed. Chemical Toxicology Institute, Foster City, CA, 1995.
Fatal combined intoxication with new antidepressants. Human cases and an experimental study of postmortem moclobemide redistribution a, b a Sidsel Rogde *, Thor Hilberg , Brita Teige a
Institute of Forensic Medicine, University of Oslo, Oslo, Norway b National Institute of Forensic Toxicology, Oslo, Norway Received 1 October 1998; accepted 19 October 1998
Abstract Three cases are presented in which death was caused by suicidal intoxication with moclobemide in combination with a selective serotonin reuptake inhibitor. Both antidepressant drug types are considered to be relatively safe with regard to lethal overdose. However, the combination may cause the serotonin syndrome, a condition with a high mortality rate. In one of the cases, there was clinical information consistent with the serotonin syndrome, in the two other cases, there was no information of the clinical course. Postmortem redistribution of the selective monoamine oxidase inhibitor moclobemide was investigated in a rat model. Postmortem concentrations in blood from the vena cava and the heart were found to be in good accordance with antemortem concentrations. Postmortem concentrations in vitreous humour and various tissues were also measured. The apparent volume of distribution was calculated to be 0.9560.10 l / kg, which is in the same range as that reported in man. 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Moclobemide; MAO-A inhibitor; Selective serotonin reuptake inhibitor; SSRI; Postmortem redistribution; Serotonin syndrome; Intoxication; Suicide
1. Introduction It is well known that persons suffering from depression are at increased risk of taking their own lives [1], and that intoxication by prescription drugs is a widely used suicide *Corresponding author. Rettsmedisinsk institutt, Rikshospitalet, N-0027 Oslo, Norway. Tel.: 147-22-86-8663; fax: 147-22-20-95-83. E-mail address: [email protected] (S. Rogde) 0379-0738 / 99 / $ – see front matter 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S0379-0738( 98 )00184-4
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method [2]. Tricyclic antidepressants (TCAs), especially amitriptyline and doxepin, have been widely used for this purpose in our country [3]. Concomitant with the introduction of a new generation of antidepressants, the number of deaths caused by TCA intoxication has decreased [4], and the new antidepressants seem to be far safer with regard to intoxication [5]. However, the combination of a selective monoamine oxidase (MAO-A) inhibitor with a selective serotonin reuptake inhibitor (SSRI) may cause the serotonin syndrome, even in therapeutic use [6] and, thus, lethal intoxications by such combinations can be expected. Forensic pathologists and toxicologists are well aware that postmortem concentrations may be difficult to interpret and even impossible to compare with concentrations in the living due to postmortem redistribution [7]. While this phenomenon has been studied concerning the SSRIs, information on moclobemide, the one drug that is seen in all three cases described here, is more sparse. We therefore found it worthwhile to investigate postmortem redistribution of this drug in a rat model.
2. Human cases
2.1. Case 1 A 51-year-old female, who was very warm and sweating profusely, was found unconscious in her home. There was an empty package of Aurorix (moclobemide) in her house. Many other drugs were also found, including Fevarin (fluvoxamine, SSRI). On admission to hospital, she had severe cardiac arrhythmia and unmeasurable arterial blood pressure. Serum was screened for paracetamol, ethanol, lithium and salicylic acid — with negative results. She received assisted respiration and intensive care. However, she gradually developed multiple organ failure and died four days later. A medicolegal autopsy was performed. Evidence of hypoxic brain damage was found. There was also an incipient bronchopneumonia and widespread centrilobular necrosis of the liver. Postmortem femoral blood concentrations were: moclobemide 20 mmol / l, fluvoxamine 1.7 mmol / l. The concentrations were considered high, especially when taking into consideration that death occurred more than four days after ingestion. Analyses were also performed on an antemortem blood sample that was taken three days after admission to hospital (31 h prior to death). The concentrations then were 60 mmol / l moclobemide and 0.6 mmol / l fluvoxamine. The cause of death was assumed to be intoxication with a combination of the MAO-A inhibitor and the SSRI. The hypoxic brain damage, the bronchopneumonia and the liver necrosis were considered to have been caused by the toxic effect exerted by the combined ingestion of the two drugs. The clinical picture was considered to be consistent with the serotonin syndrome.
2.2. Case 2 A 27-year-old female was found dead in her bed. There was a suicide note in her vicinity. Beside her bed were empty packages of Aurorix (moclobemide), Fevarin
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(fluvoxamine), Imovane (zopiclone, a hypnotic drug) and Somadril Comp (a muscle relaxant consisting of carisoprodol and paracetamol). A medicolegal autopsy was performed. No signs of injury or disease were found. The toxicological analyses of femoral blood revealed 50 mmol / l moclobemide, 6 mmol / l fluvoxamine, both regarded as high concentrations, 125 mmol / l paracetamol, 34 mmol / l carisoprodol and 64 mmol / l meprobamate (a metabolite of carisoprodol). The three latter concentrations are somewhat above those normally observed with therapeutic dosing. The zopiclone concentration was 0.46 mmol / l, which is above the level seen after therapeutic use [8]. The maximum zopiclone intake was 75 mg, as judged from the empty Imovane package found at the scene. Death was considered to be caused by intoxication, primarily by a combination of moclobemide and fluvoxamine.
2.3. Case 3 A 22-year-old female was found dead in her bed. Empty packages of Aurorix (moclobemide) and Seroxat (paroxetine, SSRI) were found in her home. A medicolegal autopsy was performed. On her left wrist were found four shallow sharp lesions from which there was no significant haemorrhage. In the brain stem, inflammatory changes, located around the nucleus of the trigeminal nerve, were observed. These changes were not considered to have been of importance for death. Toxicological analyses of postmortem femoral blood revealed 31 mmol / l moclobemide and 2.2 mmol / l paroxetine, which are high concentrations. Ethyl alcohol was found at a concentration of 0.4 g / l. Death was considered to be due to intoxication with moclobemide and paroxetine.
3. Animal studies
3.1. Materials and methods Male Wistar rats with a body weight of 258–278 g were fasted overnight and fed 50 mg of moclobemide as grounded Aurorix tablets (Roche, Switzerland) in 2 ml of water by a gastric tube. Ninety minutes after dosing, the rats were anaesthetised with a subcutaneous injection of fluanisone, fentanyl and midazolam (5, 0.1 and 2.5 mg per kg rat, respectively). A blood sample (¯500 ml) was drawn from the heart and transferred to a silanized glass tube containing 25 ml of a 67% (w / v) potassium fluoride solution. The rats were then sacrificed with CO 2 and were left at room temperature for 2 h, when autopsy was performed. Postmortem heart blood samples (¯500 ml) were drawn after having clamped the inferior vena cava just above the diaphragm. Blood from the inferior vena cava (|500 ml) was sampled after clamping just superior to the renal veins. The following tissue samples were also collected: vitreous humour from both eyes, tissue from the upper lobe of the right and left lungs, the heart, one sample from the right part of the median liver lobe and another from the left caudate liver lobe lying next to the stomach, lower pole of right kidney, thigh muscle and forebrain. In addition, the stomach and the proximal 50 cm of the small intestine were dissected out. The carcasses
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were minced in a manual meat mincer twice and 5 g were sampled for further homogenisation, as for the other tissues.
3.2. Extraction, chromatography and analytical procedures Tissue samples were homogenised with an Ultra-Turrax T5 homogeniser (IKA, Janke & Kunkel, Germany) in water to a final concentration of 0.2 g tissue / ml homogenate. Moclobemide concentrations in blood and vitreous humour samples were determined from a calibration curve prepared from blood, while tissue concentrations were determined from a calibration curve prepared from liver tissue. All samples were kept at 2208C until analysis, when 100 ml of an aqueous solution of the internal standard, methadone, and 300 ml of 1 M Tris (pH 10.7) were added. The mixture was extracted on ice for 10 min with 400 ml of butylacetate, and centrifuged for 10 min at 740 g. The organic phase was transferred to 100 ml autosampler vials. The gas chromatograph was HP 5890, and the column was a polar 15 m30.32 mm DB 1701, 0.32 mm film thickness (J&W Scientific, USA). The injection volume was 5 ml (split mode, 1:10) and a nitrogen–phosphorous detector was employed. The injector temperature was 2508C, and the detector temperature was 3008C. The temperature program started at 1508C for 1 min and increased by 208C per min to 2508C, with a hold time of 0.5 min, with further increments of 58C per min to 2808C, with a hold time of 10 min. The carrier gas used was helium, with a flow rate of 1.5 ml / min, and make up gas to a total of 30 ml / min. Recovery in blood exceeded 73% at concentrations of 1 and 10 mmol / l and in liver tissue exceeded 78% at concentrations of 5 and 50 mmol / kg. The calibration ranges were from 1 to 300 mmol / l in blood and liver tissue, and there was linearity within these ranges (R 2 .0.99). The coefficient of variation (CV) of within-run precision was better than 6.0%. Results are presented as mean6standard error of the mean (s.e.m.) in mmol / l or mmol / kg. The apparent volume of distribution was calculated as the concentration of drug in carcass homogenate divided by antemortem heart blood drug concentration.
4. Results The moclobemide concentrations found in antemortem heart blood (Table 1) were above the therapeutic concentration ranges seen in humans [9]. Accordingly, the rats were observed to be slightly sedated. The postmortem-to-antemortem heart blood drug concentration ratio was 1.260.1 and there was no significant difference between the antemortem and postmortem blood drug concentrations. The tissue-to-antemortem blood drug concentration ratios are outlined in Table 1. There were no significant differences between the drug concentrations in the right and left lungs or between the liver lobes.
5. Discussion In order to interpret the postmortem moclobemide concentrations in our case reports, we found it worthwhile to study moclobemide redistribution experimentally.
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Table 1 Concentration of moclobemide in blood and tissues from six rats, expressed as mean values6standard error of the mean (mmol / l or mmol / kg) Mean6s.e.m. Antemortem heart blood concentration Postmortem heart blood concentration Postmortem vena cava blood concentration Vitreous humour–antemortem blood drug concentration ratio Lung–antemortem blood drug concentration ratio Myocardium–antemortem blood drug concentration ratio Liver–antemortem blood drug concentration ratio Kidney–antemortem blood drug concentration ratio Muscle–antemortem blood drug concentration ratio Brain–antemortem blood drug concentration ratio Apparent volume of distribution
46.166.5 52.866.8 57.468.2 0.560.0 2.060.2 1.560.1 4.460.8 4.160.2 0.960.1 1.760.1 0.9560.10
Conversion factor: 0.27 mmol / l5mg / l. The tissue concentrations are expressed as tissue-to-antemortem heart blood drug concentration ratios. The apparent volume of distribution is in l / kg.
The present rat model has previously been documented to exhibit postmortem drug redistribution properties in a comparable manner to those described in man [10–12]. The insignificant drug concentration changes found in this study imply that there should be little or no potential for postmortem drug redistribution with this substance. The apparent volume of distribution calculated is in the same region as that found in man [13]. The relatively low value found is a further indication that there is little potential for drug release from parenchymal tissues back to the blood. These observations are very much in contrast to tricyclic antidepressants like amitriptyline and nortriptyline that have large apparent volumes of distribution, high tissue-to-blood concentration ratios and a profound potential for postmortem drug level increases, particularly in heart blood. The present study implies that one can assume the concentration of moclobemide found in postmortem blood samples to be reasonably representative of the concentration at the time of death, thus, it may be concluded that the moclobemide concentrations in all three cases were well above the therapeutic level [9]. The concentration of several drugs in vitreous humour has previously been reported to be closely related to the unbound fraction in the blood. The results in the present study indicate that this is also the case for moclobemide in rats (Table 1), assuming that the degree of protein binding is in the same order of magnitude as in man [9]. Note, however, that postmortem release of both digoxin [14] and amitriptyline [15] into vitreous humour has been reported, so, depending on the postmortem interval, the drug concentration in this tissue may be substantially higher than antemortem. Unlike older monoamine oxidase inhibitors, moclobemide is a reversible and selective inhibitor of the MAO-A isozyme, and is found to have antidepressant properties. Recommended dosage is 300 to 600 mg divided into two or three daily doses. The bioavailability is 44–69% at therapeutic doses initially, but increases with chronic use to more than 80% [9]. The volume of distribution is 0.8–1.3 l / kg [9,13] and protein binding in plasma is about 50%. The half-life is 1–2 h, and is not affected by age or
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renal function, but may be prolonged by hepatic disorders. The plasma concentrations seen after therapeutic doses range from 0.4 to 3.4 mg / l (1.4 to 12 mmol / l) [9]. Postmortem peripheral blood concentrations associated with assumed therapeutic use have been observed in the range of 0.2 to 2.1 mg / l (0.6 to 6.5 mmol / l), while concentrations in cases with lethal intoxications (where other substances were also involved) were 1.9 to 21 mg / l (5.8 to 64.5 mmol / l) [16]. Two moclobemide fatalities have been reported from France [17]. In these cases, the blood concentrations of moclobemide were 15.5 and 13.8 mg / ml (57.4 and 51.1 mmol / l, respectively). Only the former was described as a single drug intoxication. Camaris and Little [18] have reported a moclobemide fatality with a blood concentration of 137 mg / l (507.4 mmol / l). The site for blood sampling was not indicated in their study. The serotonin syndrome is described in a review article by Sternbach [19]. The syndrome is most commonly the result of the interaction between serotoninergic agents and irreversible monoamine oxidase inhibitors. The most frequent clinical features are changes in mental status, restlessness, myoclonus, hyperreflexia, diaphoresis, shivering and tremor. Originally it was thought only to occur in relationship with irreversible non-selective monoamine oxidase inhibitors in combination with serotonin reuptake inhibitors or with tryptophan. Moclobemide is an inhibitor of monoamine oxidase, but contrary to the old generation of these drugs, this drug has a reversible effect on the enzyme and is considered safe with regard to interactions. There are, however, isolated reports of such interactions. Spigseth et al. [6] described this syndrome in a patient who had just changed the antidepressive treatment to moclobemide from clomipramine, a tricyclic antidepressant with a significant ability to inhibit serotonin reuptake. The authors recommend serotonin reuptake inhibitors to be discontinued for some time before starting moclobemide treatment, depending on the half-life of the various serotonin reuptake inhibitors. Case reports of lethal interactions in overdoses have been reported by several authors [20–24]. In two of these reports [21,22], it is stated that a combination of drugs may have been used ‘in order to get high’. Iwersen and Schmoldt [25] reported three suicide attempts with moclobemide, one of which was a combination of moclobemide and clomipramine. There were no signs of serotonin syndrome. All three cases described from our institutes are suicidal overdoses. In one of the cases, there was clinical evidence that might be consistent with the serotonin syndrome, while this may only be hypothesised in the other two cases as a possible mechanism of death. In Case 1, the fluvoxamine concentration was almost three-fold higher in postmortem blood than in the antemortem sample. We believe that this difference is due to postmortem redistribution. In Case 2, a fluvoxamine concentration of 6 mmol / l was found. It is possible that postmortem redistribution had taken place. Fluvoxamine is used in daily doses of 50 to 300 mg, has a half-life of about 15 h and an apparent volume of distribution of more than 5 l / kg [26]. Serum concentrations observed after therapeutic doses are in the region of 0.05 to 0.25 mg / l (0.16 to 0.8 mmol / l) [27]. Plasma protein binding is about 80%. The drug may inhibit cytochrome P (CYP) 1A2 and, to a lesser extent, CYP 2D6, causing impaired elimination of other drugs [27]. Lethal intoxication with fluvoxamine has been associated with postmortem peripheral blood concentrations of 3.4 to 10.7 mg / l (10.7–33.6 mmol / l) [16], while lethal intoxication together with
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other substances has been reported with concentrations of 1.2 to 8.1 mg / l (3.8 to 25.4 mmol / l). Postmortem concentrations of 0.2 to 0.7 mg / l (0.6 to 2.2 mmol / l) have been associated with assumed therapeutic use [16]. In Case 3, a paroxetine concentration of 2.2 mmol / l was found. Paroxetine is used in daily doses of 20 to 50 mg, has a half-life of 10 to 16 h and an apparent volume of distribution of 17 l / kg [26], which is in the same order of magnitude as for tricyclic antidepressants. Serum concentrations after therapeutic doses are in the region between 0.01 and 0.15 mg / l (0.03 to 0.46 mmol / l) [28], and plasma protein binding is 95%. These figures indicate relatively high concentrations in tissue compared to blood. Accordingly, there is probably a potential for postmortem redistribution of these drugs [12]. Lethal intoxications with paroxetine together with other substances have been reported to occur with blood concentrations of 0.7 to 4.6 mg / l (2.1 to 14 mmol / l) [16]. Postmortem peripheral blood concentrations in cases where paroxetine was assumed to be used therapeutically were 0.09 to 0.5 mg / l (0.3 to 1.5 mmol / l) [16]. The relatively higher postmortem blood concentrations of fluvoxamine and paroxetine compared with the serum concentrations in the therapeutic situation also indicate a tendency for postmortem redistribution. Paracetamol [29] and zopiclone [30] (both observed in Case 3) have previously been reported not to be subject to postmortem redistribution. Meprobamate has a low volume of distribution at 0.7 l / kg [31] and carisoprodol probably also has a relatively low value. Hence, the postmortem concentrations found for these substances should be reasonably representative for the antemortem values. The number of deaths due to suicidal intoxications with antidepressants has declined after the introduction of the new generation of safer antidepressants [4]. However, the sales statistics show that an increasing number of persons now receive antidepressive drug treatment. It is therefore important to realise that the ‘safe’ drugs may also represent a potential means of suicide, especially when two such drugs are given in combination. In order to monitor the potential dangers of new drugs, it is important that medicolegal autopsies combined with thorough toxicological analyses are performed in cases in which intoxication is suspected.
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