page57
Antidepressants
Tricyclic and related antidepressants
Tricyclic
and related antidepressants cause dry mouth,
coma of
varying degree, hypotension, hypothermia, hyperreflex-
ia,
extensor plantar responses,
convulsions,
respiratory
failure,
cardiac conduction defects,
and arrhythmias.
Dilated pupils and urinary retention also occur.
Metab-
olic acidosis may complicate severe poisoning; delirium
with confusion, agitation, and visual and auditory hallu-
cinations are common during recovery.
Assessment
in hospital
is strongly advised in case of
poisoning by
tricyclic and related antidepressants
but
symptomatic treatment
can be given before transfer.
Supportive measures
to ensure a clear
airway and
adequate ventilation during transfer
are mandatory.
Intravenous lorazepam or intravenous diazepam (pre-
ferably in emulsion form)
may be required to treat
convulsions.
Activated charcoal
given within 1 hour of
the overdose reduces absorption of the drug.
Although
arrhythmias are worrying, some will respond to correc-
tion of hypoxia and acidosis. The use of anti-arrhythmic
drugs is best avoided,
but intravenous infusion of sod-
ium bicarbonate can arrest arrhythmias or prevent them
in those with an extended QRS duration.
Diazepam
given by mouth is usually adequate to sedate delirious
patients but large doses may be required.
Selective serotonin re-uptake inhibitors (SSRIs)
Symptoms of poisoning by selective serotonin re-uptake
inhibitors include nausea,
vomiting,
agitation,
tremor,
nystagmus,
drowsiness,
and sinus
tachycardia;
con-
vulsions may occur.
Rarely,
severe poisoning results in
the serotonin syndrome,
with marked neuropsychiatric
effects,
neuromuscular
hyperactivity,
and autonomic
instability;
hyperthermia,
rhabdomyolysis,
renal
failure,
and coagulopathies may develop.
Management of SSRI poisoning is supportive. Activated
charcoal
given within 1 hour of
the overdose reduces
absorption of the drug. Convulsions can be treated with
lorazepam, diazepam, or buccal midazolam [unlicensed
use] (see p.
33).
Contact the National
Poisons Informa-
tion Service for the management of hyperthermia or the
serotonin syndrome.
Antimalarials
Overdosage
with quinine,
chloroquine,
or
hydroxy-
chloroquine is
extremely hazardous
and difficult
to
treat. Urgent advice from the National Poisons Informa-
tion
Service
is
essential.
Life-threatening
features
include
arrhythmias
(which can have
a very rapid
onset) and convulsions (which can be intractable).
Beta-blockers
Therapeutic overdosages with beta-blockers may cause
lightheadedness,
dizziness,
and possibly syncope as a
result of bradycardia and hypotension; heart failure may
be precipitated or exacerbated. These complications are
most likely in patients with conduction system disorders
or
impaired myocardial
function.
Bradycardia is
the
most
common arrhythmia caused by beta-blockers,
but
sotalol
may induce ventricular
tachyarrhythmias
(sometimes of the torsade de pointes type). The effects
of massive overdosage can vary from one beta-blocker
to another;
propranolol
overdosage in particular
may
cause coma and convulsions.
Acute massive overdosage
must be managed in hospital
and expert advice should be obtained. Maintenance of a
clear airway and adequate ventilation is mandatory. An
intravenous injection of
atropine is required to treat
bradycardia
(3 mg
for
an
adult,
40 micrograms/kg
(max.
3 mg) for a child).
Cardiogenic shock unrespon-
sive to atropine is probably best treated with an intra-
venous
injection
of
glucagon
2–10 mg
(
CHILD
50–
150 micrograms/kg, max. 10 mg) [unlicensed indication
and dose] in glucose 5% (with precautions to protect the
airway in case of vomiting) followed by an intravenous
infusion of
50 micrograms/kg/hour.
If
glucagon is not
available, intravenous isoprenaline (available from ‘spe-
cial-order’
manufacturers or specialist importing com-
panies,
see p.
988)
is an alternative.
A cardiac pace-
maker can be used to increase the heart rate.
Calcium-channel blockers
Features of calcium-channel
blocker poisoning include
nausea,
vomiting,
dizziness,
agitation,
confusion,
and
coma
in severe
poisoning.
Metabolic
acidosis
and
hyperglycaemia may occur.
Verapamil
and diltiazem
have a profound cardiac depressant effect causing hypo-
tension
and
arrhythmias,
including
complete
heart
block and asystole.
The dihydropyridine calcium-chan-
nel
blockers cause severe hypotension secondary to
profound peripheral vasodilatation.
Activated charcoal
should be considered if the patient
presents within 1 hour of
overdosage with a calcium-
channel
blocker;
repeated doses of
activated charcoal
are
considered if
a
modified-release
preparation is
involved. In patients with significant features of poison-
ing,
calcium chloride or
calcium gluconate (section
9.5.1.1) is given by injection; atropine is given to correct
symptomatic bradycardia.
In severe cases,
an insulin
and glucose infusion may be required in the manage-
ment
of
hypotension and myocardial
failure.
For
the
management
of
hypotension,
the choice of
inotropic
sympathomimetic depends on whether hypotension is
secondary to vasodilatation or
to myocardial
depres-
sion—advice should be sought from the National
Poi-
sons Information Service.
Hypnotics and anxiolytics
Benzodiazepines
Benzodiazepines taken alone cause
drowsiness,
ataxia,
dysarthria,
nystagmus,
and occa-
sionally respiratory depression,
and coma.
Activated
charcoal
can be given within 1 hour
of
ingesting a
significant
quantity of
benzodiazepine,
provided the
patient is awake and the airway is protected. Benzodiaz-
epines potentiate the effects of
other central
nervous
system depressants
taken concomitantly.
Use of
the
benzodiazepine antagonist flumazenil
[unlicensed indi-
cation]
can be hazardous,
particularly in mixed over-
doses involving tricyclic antidepressants or in benzodia-
zepine-dependent patients. Flumazenil may prevent the
need for ventilation, particularly in patients with severe
respiratory disorders; it should be used on expert advice
only and not
as a diagnostic test
in patients with a
reduced level of consciousness.
BNF 61
Emergency treatment of poisoning
37
Emergency treatment of poisoning