Opioid/barbiturate Human Toxicity

David A.Joyce djoyce at receptor.pharm.uwa.edu.au
Sun Nov 3 19:59:06 EST 1996

Dear Colleagues,
I wonder if there is any subscriber who has data relevant to this
issue in forensic toxicology. We have recently had involvement in a
case where a woman has died after ingestion of an overdose of
oxycodone (blood level 0.9mg/L), together with the intravenous
administration of an anaesthetic dose of thiopentone (as part of an
alleged "suicide pact", in which the person who is believed to have
administered the thiopentone survived). She must have lived for some
hours after the thiopentone, because levels in blood were quite low
(1.2mg/L, plus some pentabarbitone). Liver level was 9mg/kg. The blood
oxycodone level was within the range associated with death where other
drugs have been present (though only relatively low concentrations of
minor tranquillisers, in some of these cases), but below any level
which has been reported in oxycodone-only deaths (of which there are
only a few reports).
Opinion on the role of thiopentone ranges from confidence that it
contributed (because the respiratory depression which lead to death
was due to all potential respiratory depressants present, though some
may have been much more influential than others, and because
experience with barbiturate/opioid fatalities implies that the mixture
is very respiratory depressant) to confidence that it has made no
contribution whatsoever (because this blood concentration of
thiopentone is generally seen in patients who have had anaesthetics
(thiopentone alone) at a stage when they awake again, and because old
studies of respiratory depression imply that thiopentone, in any
anaesthetic concentration, causes negligable respiratory depression).
Do any of you have any experience or data which may shed some light on
this dispute? There has already been great argument on the data as
summarised above, so we really don't need off-the-cuff opinions. What
we need now is advice from someone who has met similar situations
before or knows of data which closely bears on the issue.
I would be keen to hear soon from anyone who can offer informal
David Joyce MD,
Clinical Pharmacologist

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