1986–91 : There were 46 drug-related deaths identified in this 6-year period, of which 10 cases were attributed to medication errors and 36 attributed to ADRs.
RESULTS
1986–91
There
were 46 drug-related deaths identified in this 6-year period, of which 10 cases
were attributed to medication errors and 36 attributed to ADRs. Non-steroidal
anti-inflammatory drugs (NSAIDs) were the most common drug class to be
associated with death, accounting for 14/46 (30%) of the cases.
1992–2000
A
further 40 cases of drug-related deaths were identi-fied from January 1992 to June
2000. There were 24 cases of clear-cut ADRs, 3 cases that were because of
medication error alone and 13 cases where there were elements of both. Once
more, NSAIDs accounted for the greatest number of cases, being associated with
14/40 (35%) of all cases. Warfarin was responsible for seven deaths, three
because of error, and heparin for two, one because of error.
2001–05
Hand
searching of all the determinations of the Coro-ner’s inquests from November
2001 to June 2005 identified 43 cases of death due to adverse drug events of
3366 inquests. Thirty-six deaths were a result of an ADR, and seven were
directly related to either a medical error or both a medical error and an ADR.
One death because of an ADR was compounded by a diagnostic error.
Warfarin
accounted for the greatest number of adverse events, with 11/43 (26%) of the
deaths, in contrast to the previous two series, where the majority of adverse
drug events were related to NSAIDs.
The
details of the eight cases in which error played some part are as follows.
Case 1: A 14-year-old boy
who was taking fluoxe-tine 20 mg daily and diazepam 3 mg twice daily was
admitted for detoxification to a specialist centre for the treatment of drug
and alcohol addiction. The patient was prescribed 20 mg of methadone and 50 mg
of thioridazine, and the dose of diazepam was increased to 10 mg twice daily
upon admission. Thirty-six hours after admission, the patient was found in bed
blue and not breathing. Cardio-pulmonary resuscitation was unsuccessful. The
pathologist considered the death to be because of the inhalation of gastric
contents and asphyxia secondary to potentially toxic blood concen-tration of
methadone, in the presence of significant therapeutic concentrations of
diazepam and thiori-dazine and high therapeutic concentrations of fluoxe-tine.
Comment: No analysis for
drugs of abuse was taken upon
admission to the centre, so the treating doctors did not know whether the
patient was actually abus-ing heroin or other drugs. Methadone is an extremely
dangerous drug, which is absorbed only slowly after oral administration, so
that maximum blood concen-trations, and hence maximum respiratory depression,
can occur many hours after ingestion. Pharmacody-namic interactions with other
respiratory sedatives, including diazepam, are to be expected.
Case 2: A 58-year-old man
with a grade 1 sub-arachnoid haemorrhage underwent carotid angiogra-phy. Staff
failed to recognise that no contrast medium (a clear, colourless liquid) had
been loaded into the syringe, and therefore a bolus of air, instead of
contrast, was injected into the right carotid artery. The patient died in spite
of appropriate emergency treatment of air embolism.
Comment: A rare example of
an ADR because of the (unobserved)
absence of drug.
Case 3: A 31-year-old woman
with suspected tuberculosis was
injected with 100 000 units of tuberculin purified protein derivative (PPD)
intra-dermally, a 1000-fold overdose. She became unwell with increased
temperature and rigors, developed pulmonary fibrosis and died. The junior
doctor who had administered the drug had used the appropri-ate dosage for the
multiple puncture Heaf test and assumed the single injection was simply an
alternative means of delivering the tuberculin PPD when a Heaf gun was not
available.
Comment: Errors of this
type are predictable when there are
two formulations of the same product that differ enormously in concentration.
Case 4: A 64-year-old man
who was taking diclofenac for chronic
joint pain underwent arthro-plasty of the left hip and insertion of a spacer.
During the operation, he developed atrial fibrillation and was treated with
warfarin; postoperatively, his heart rhythm returned to normal. Six days later
he passed large amounts of melaena and was presumed to have had acute
gastrointestinal bleeding. Intravenous vitamin K was given because his
international normalised ratio (INR) was increased. (The INR is a measure of
blood clotting where 1.3 or less is normal, and the therapeutic target is
usually 2.5.) He had a cardiac arrest and died in spite of resuscitation.
Comment: This case
highlights the risks of prescrib-ing warfarin with diclofenac, especially if
the INR is not carefully monitored.
Case 5: An 80-year-old
woman with long history of heart
trouble and osteoarthritis was admitted to hospital suffering from urinary
retention. She had episodes consistent with transient ischaemic attacks. There
was no history of peptic ulcer. Her warfarin (1 mg daily) was continued, and 1
month after admis-sion, she was started on aspirin, 75 mg daily. A chest radiograph
showed right basal consolidation due to pneumonia, which was treated with
amoxicillin and clarithromycin. Her condition deteriorated, and she suffered
from severe rectal bleeding. The INR was 5.7. She died shortly afterwards.
Comment: The risk of
gastrointestinal haemor-rhage is doubled by low-dose aspirin, and so
combination of warfarin and low-dose aspirin is potentially hazardous. As
clarithromycin can inhibit the metabolism of warfarin and increase INR, and as
the risk of bleeding rises steeply as INR increases, this patient was at risk
from two potentially lethal adverse drug interactions simultaneously.
Case 6: A 72-year-old
woman who took warfarin 1 mg daily
was admitted to hospital complaining of right-sided weakness and slurred speech
after falling out of bed. She had become jaundiced a few days before the
admission, and when visited by her general practitioner (GP), her INR had not
been checked or warfarin treatment stopped. Her INR on admission was 5.5, and a
computerised tomography (CT) scan showed an acute haemorrhage in the left
parietal white matter. She was prescribed 10 mg of intravenous vita-min K to
reverse the effects of warfarin, but this was not administered until 7 h later.
She suddenly became deeply unconscious and subsequently died.
Comment: Liver impairment
during warfarin treat-ment is especially dangerous, because it can have the
dual effect of increasing the concentration and effect of warfarin, which is no
longer effectively metabolised, and reducing the production of vitamin
K–dependent clotting factors, which are synthesised in the liver.
Case 7: A 69-year-old
woman with past history of hypertension,
gout and arthritis presented to the acci-dent and emergency department with
sudden onset of shortness of breath and dizziness. She was prescribed
enoxaparin 130 mg daily subcutaneously. Two days after admission, it was noted
by staff that she had not been given two previous doses of enoxaparin. She was
given a single dose but suffered a cardiac arrest caused by a pulmonary embolus
later that after-noon, and resuscitation was unsuccessful. The Coro-ner’s
verdict was: ‘Died from a naturally occurring pulmonary embolism following the
failure to admin-ister 2 doses of a prescribed medication’.
Comment: This case
illustrates the danger of omit-ting potentially life-saving treatment.
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