A Textbook of Clinical Pharmacology and Therapeutics

● Intentional self-poisoning 444
● Accidental poisoning 449
INTENTIONAL SELF-POISONING
CHAPTER 54
DRUG OVERDOSE AND
POISONING
Self-poisoning creates 10% of the workload of Accident and
Emergency departments in the UK. Opioids (diamorphine
(heroin), morphine and methadone), compound analgesics
(e.g. codeine plus paracetamol), paracetamol alone and antidepressants
are the most common drugs used in fatal overdose.
Temazepam, cocaine, MDMA/ecstasy, lithium, paraquat,
salicylates, digoxin and aminophylline continue to cause fatalities.
This list of agents that cause death from overdose does not
reflect the drugs on which individuals most commonly overdose.
Self-poisoning often involves multiple drugs and alcohol.
Benzodiazepines (often taken with alcohol) are commonly
taken in an overdose, but are seldom fatal if taken in isolation.
Around 75% of deaths from overdose occur outside hospital,
with the mortality of those treated in hospital being less than
1%. The majority of cases of self-poisoning fall into the psychological
classification of suicidal gestures (or a cry for help).
However, the prescription of potent drugs with a low therapeutic
ratio can cause death from an apparently trivial overdose.
DIAGNOSIS
HISTORY
Self-poisoning may present as an unconscious patient being
delivered to the Accident and Emergency Department with or
without a full history available from the patient or their companions.
Following an immediate assessment of vital functions, as
full a history as possible should be obtained from the patient, relatives,
companions and ambulance drivers, as appropriate. A
knowledge of the drugs or chemicals that were available to the
patient is invaluable. Some patients in this situation give an unreliable
history. A psychiatric history, particularly of depressive illness,
previous suicide attempts or drug dependency, is relevant.
EXAMINATION
A meticulous, rapid but thorough clinical examination is essential
not only to rule out other causes of coma or abnormal
behaviour (e.g. head injury, epilepsy, diabetes, hepatic
● Criminal poisoning 449
encephalopathy), but also because the symptoms and signs
may be characteristic of certain poisons. The clinical manifestations
of some common poisons are summarized in Table 54.1.
The effects may be delayed.
LABORATORY TESTS
Routine investigation of the comatose overdose patient
should include blood glucose (rapidly determined by stick
testing) and biochemical determination of plasma electrolytes,
Table 54.1: Clinical manifestations of some common poisons
Symptoms/signs of Common poisons
acute overdose
Coma, hypotension, flaccidity Benzodiazepines and other
hypnosedatives, alcohol
Coma, pinpoint pupils, Opioids
hypoventilation
Coma, dilated pupils, Tricyclic antidepressants,
hyper-reflexia, tachycardia phenothiazines; other drugs
with anticholinergic properties
Restlessness, hypertonia, Amphetamines, MDMA,
hyper-reflexia, pyrexia anticholinergic agents
Convulsions Tricyclic antidepressants,
phenothiazines, carbon
monoxide, monoamine
oxidase inhibitors, mefenamic
acid, theophylline,
hypoglycaemic agents, lithium,
cyanide
Tinnitus, overbreathing, Salicylates
pyrexia, sweating, flushing,
usually alert
Burns in mouth, dysphagia, Corrosives, caustics, paraquat
abdominal pain
MDMA, methylenedioxymethylamphetamine.