Journal of Analytical Toxicology, Vol. 24, October 2000
Lamotrigine Distribution in Two Postmortem Cases*
Barry Levine*, Rebecca A. lufer, and John E. Smialek
Office of the Chief Medical Examiner, State of Maryland, 111 Penn Street, Baltimore, Maryland 21201
I Abstract
[
Lamotrigine (Lamictal | is a new anticonvulsant drug recently
approved for use in the United States. Although a therapeutic range
for lamotrigine has not been definitively established, a range of
between 2 and 14 mg/L has been reported. Two cases are presented
in which lamotrigine was identified in cases investigated by the
Office of the Chief Medical Examiner, State of Maryland.
tamotrigine was identified by gas chromatography-nitrogenphosphorus detection following an alkaline extraction. A DB-5
column provided analytical separation; no derivatization was
required. Confirmation was achieved by full scan electron ionization
gas chromatography-mass spectrometry. In Case 1, primidone
(11 rag/t) and phenobarbital (5.5 mg/L) were found in the heart
blood in addition to lamotrigine (8.3 rag/L); in Case 2, no drugs
other than lamotrigine (52 rag/L) were detected in the heart blood.
The peripheral blood concentration in Case 2 was 54 mg/L. The liver
lamotrigine concentrations in the two cases were 41 and 220 mg/kg.
The medical examiner ruled that the cause of death in Case 1 was
seizure disorder and the manner of death was natural. In Case 2, the
medical examiner ruled that the cause of death was lamotrigine
intoxication and the manner of death was undetermined.
Introduction
Lamotrigine, 3,5-diamino-6-(2,3-dichlorophenyl)- l,2,4-triazine (BW430C, Lamictal), is a new anticonvulsant drug recently approved for use in the United States. It is structurally
unrelated to classical anticonvulsant drugs such as phenobarbital, phenytoin, and carbamazepine (Figure 1). Lamotrigine
was initially approved in the United States as add-on therapy for
adults with partial seizures alone or with secondarily generalized
seizures. Good efficacy has also been demonstrated for patients
with absence, atypical absence, myoclonic, and atonic seizures.
The drug is also effective in treating patients with Lennox-Gastaut syndrome. Lamotrigine has been used successfully to treat
seizures in children (1). The mechanism of action of lamotrigine is related to a reduction in the release of glutamate and
aspartate caused by a blockade of presynaptic voltage-sensitive
" Presentedat the 29th annual Society of ForensicToxicologists meeting, San Juan,
Puerto Rico, October 1999.
t Author ~owhom correspondence should be addressed.
sodium channels, leading to a reduction in neuronal firing. At
higher concentrations, lamotrigine acts on calcium channels,
causing a stabilization of neuronal membranes (2)
The dosage of lamotrigine is between 50 and 400 mg per
day. The starting dose is 25 to 50 mg daily with increases every
1 to 2 weeks by 50 mg per day increments. A maintenance
dose for adults is between 200 and 400 mg per day, with adjustments based on co-administered drugs (1). Lamotrigine is
well absorbed after oral administration with minimal first pass
effect; the bioavailability is 98%. The peak plasma concentration
occurs 2-3 h after a single dose (3). The pharmacokinetics of
lamotrigine conforms to a one-compartment model with first
order kinetics (4). Lamotrigine is well distributed throughout
the body. The volume of distribution is 1.2L/kg. The drug is approximately 55% plasma protein bound. For patients not on
hepatic enzyme inducing or inhibiting drugs, the elimination
half-life is about 24 h (3,4). The half-life can be shortened to
about 15 h for patients also taking carbamazepine, phenobarbital, phenytoin, or primidone. The half-life can be lengthened
to 60 h for patients taking valproic acid (5).
Lamotrigine is extensively metabolized to glucuronide conjugates. The major urinary metabolite is the 2-N-glucuronide;
other minor metabolites include the 5-N-glucuronide and the
2-N-methyl compound. Approximately 8% of the dose is excreted unchanged, and 63% is excreted as a glucuronide in
CI
CI
N
NZNH2
CgH7Cl2Ns
Exact mass: 255.0
Mol. wt.: 256.1
C, 42.21; H, 2.76; CI, 27.69; N, 27.35
Figure 1. Structureof lamotrigine.
Reproduction (photocopying) of editorial content of this journal is prohibited without publisher's permission.
635
Journal of Analytical Toxicology,Vol. 24, October 2000
the urine (3). During an overdose, the metabolism does not appear to be saturable (1).
The utility of therapeutic drug monitoring has not been
firmly established. Initial work suggested a therapeutic range of
1-4 mg/L (1). However, an approximate therapeutic range of
2-14 mg/L has also been used more recently (6). Additionally,
a tentative trough therapeutic concentration of 2-3 mg/L has
been used (5)
The following paper reports two cases where lamotrigine was
identified in cases investigated by the Office of the Chief Medical Examiner, State of Maryland.
a Hewlett-Packard 7673A automatic sampler. The column used
was a cross-linked HP-5 fused-silica capillary column (25 m x
0.32-ram i.d., 0.17-]Jm film thickness). Helium was the carrier
gas flowing at 1 mL/min. The oven temperature began at 100~
for 1 min, increased at 30~
to 200~ increased at
10~
to 260~ and increased at 20~
to 300~
holding for 8 min. Splitless injection mode was used.
Drug confirmation was performed using a Hewlett-Packard
5890 series 2 GC equipped with a 5972 mass selective detector.
Similar chromatographic conditions to those listed were used.
The mass spectrometer (MS) was operated in the scan electron
impact mode.
Case Histories
Results
Case 1
A 36-year-old white female was found by her son face down on
the bedroom floor. The previous evening, the victim had a witnessed seizure. Relevant past medical history included a seizure
disorder since the age of six. External examination was not
noteworthy except for evidence of therapy. The internal organ
examination was unremarkable. The brain was normal macroscopically.
Case 2
A 48-year-old white female with a history of depression was
found unresponsive by her mother. The decedent had two prior
suicide attempts with drugs. Risperidal | and Lamictal were
found at the scene. Externally, there was no evidence of injury
or therapy. Internally, there was mild fatty change in the liver
and pulmonary congestion and edema. There were no other significant findings.
Specimens from each case were tested for volatiles, therapeutic, and abused drugs. This included volatile testing
for methanol, ethanol, acetone, and isopropanol by headspace
GC; acid/neutral drug testing by GC-NPD; alkaline drug testing
by GC-NPD; morphine by radioimmunoassay; and acetaminophen, ethchlorvynol, and salicylate by color test. No
ethanol or other volatile substances were detected in either
case. Table I lists the drugs identified and quantitated in the
heart blood of each case. Each drug was identified by GC-NPD
and confirmed by full-scan GC-MS. No risperidone was detected in Case 2. Table II provides the distribution of lamotrigine in all of the specimens received with each case.
Discussion
One characteristic that distinguishes lamotrigine from many
other anticonvulsant drugs is that it is extractable under
Experimental
tamotrigine extraction
To a 5 mL standard, fluid, or tissue homogenate were added
2 mL 0.1N sodium hydroxide, 100 mL of 100 mg/L ethylmorphine (internal standard solution), and 20 mL n-butyl chloride.
After mechanical rotation and centrifugation, the n-butyl chloride layer was separated and extracted with 3 mL 1N sulfuric
acid. The acid layer was removed, alkalinized with 0.5 mL ammonium hydroxide, and extracted with 5 mL methylene chloride. The methylene chloride was transferred to a conical
centrifuge tube and evaporated to dryness at 40~ The residue
was reconstituted in 0.1 mL isopropanol and transferred to an
autosampler vial for gas chromatographic (GC) analysis. Quantitation was based on the area ratio of analyte to the internal
standard in comparison to four fortified standards at concentrations ranging from 0.5 to 8.0 mg/L. Appropriate dilution of
specimens with distilled water was performed to ensure quantitation within the limits of the standard curve.
Instrumentation
Lamotrigine analysis was performed on a Hewlett-Packard
5890 GC with a nitrogen-phosphorus detector (GC-NPD) and
636
Table I. Toxicologic Findings in the Heart Blood of the
Presented Cases
Case no.
Drugs identified
1
Lamotrigine
Phenobarbital
Primidone
Lamotrigine
2
Concentration
(mg/L)
8.3
5.5
11
52
Table II. Distribution of/amotrigine in the Presented
Cases
Specimen
Bile (mg/L)
Blood (heart)(mg/L)
Blood (peripheral)(mg/L)
Kidney (mg/kg)
Liver (mg/kg)
Urine (rag/L)
Concentration
Case 1
Case 2
6.8
8.3
not tested
25
41
not tested
92
52
54
110
220
37
Journal of Analytical Toxicology, Vol. 24, October 2000
]
m
2
~
i I
I?
.
.
.
.
.
.
.
.
.
.
.
.
.
i
. . . .
I
. . . .
I
. . . .
I
. . . .
I
. . . .
In/z
Figure 2. Mass spectrumof lamotrigine.
alkaline conditions. In fact, lamotrigine was first identified in
this laboratory on the basic drug extraction part of the comprehensive drug testing procedure. On a DB-5 column, lamotrigine elutes around diazepam and hydrocodone; no derivatization was required for acceptable chromatography. The
lowest calibrator prepared for these cases was 0.5 mg/L, and this
served as the limit of quantitation for the assay. Sensitivity was
not a problem. Alternatively, an electron capture detector could
be used because the molecule has two chlorine atoms. Therefore, much lower level detection could be achieved if necessary.
The upper limit of linearity was 8.0 mg/L.
The mass spectrum of lamotrigine has a base peak ofm/z 185.
There is a prominent ion at m/z 255, the molecular ion. In
addition, there are significant ions at m/z 123 and 157. Figure
2 shows the full scan electron ionization spectrum for lamotrigine.
The blood lamotrigine concentration in the first case, 8.3
rag/L, is consistent with therapeutic use of the drug. A therapeutic range for lamotrigine has not been definitively established, but a range of between 2 and 14 mg/L has been reported
(6). The blood iamotrigine concentration in the second case, 52
mg/L is over three times the reported therapeutic range. In one
study, the median concentration associated with toxic effects
from lamotrigine use was 16.0 mg/L, with a range of 7.9 to 19.4
mg/L (7). In eight postmortem cases involving lamotrigine,
Pricone et al. (8) found blood concentrations ranging from 0.9
to 39 mg/L. Only one death was attributed to drug intoxication,
and there was a combination of carbamazepine, lamotrigine,
i
paroxetine, and thioridazine.
No unique tissue distribution pattern for
lamotrigine was observed from these cases.
This is consistent with the reported volume of
distribution that suggests distribution
throughout the body. The heart blood and peripheral blood concentrations were similar in
the one case where both were analyzed. The
liver-to-blood ratios were similar in the therapeutic case and in the intoxication case (4.9
and 4.2, respectively). Pricone et al. (8) found
liver-to-blood ratios ranging from 3.2 to 18.8
in seven postmortem cases.
Based on the history and autopsy and toxicology findings, the medical examiner ruled
that the cause of death in the first case was
seizure disorder and the manner of death was
natural. In the second case, the medical examiner ruled that the cause of death was lamotrigine intoxication and the manner of death was
undetermined.
. . . .
I
. . . .
I
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Manuscript received March 27, 2000;
revision received May 23, 2000.
637