SN4 SHORT NOTE 5M ★ High-yield

Describe barbiturate and benzodiazepine poisoning.

Forensic Medicine · 2nd Professional — Para-Clinical

Barbiturates

Barbiturates — phenobarbitone, thiopentone, butobarbitone — act at the GABA-A receptor, where they increase the duration of chloride channel opening. Crucially, at high doses they can open the channel directly, without GABA, which is why there is NO ceiling to their respiratory depression and why they are so much more lethal than benzodiazepines
Features of overdose — progressive drowsiness to coma with flaccidity and absent reflexes; respiratory depression; hypotension and shock; hypothermia, which is characteristic; the pupils are usually constricted early and dilate terminally; and barbiturate blisters ("barb burns") — tense bullae over the pressure areas, particularly between the knees, on the buttocks and the heels, which are highly suggestive though also seen with other deep coma
Treatment — there is NO antidote. Supportive care with airway protection and ventilation, which is what determines survival; activated charcoal, and multiple-dose charcoal for phenobarbitone; urinary alkalinisation with sodium bicarbonate for phenobarbitone, which is a weak acid; warming; and haemodialysis in severe cases
Withdrawal is dangerous — unlike opioid withdrawal, barbiturate and benzodiazepine withdrawal may cause convulsions and death, and must be managed by gradual reduction

Benzodiazepines

Benzodiazepines — diazepam, alprazolam, nitrazepam, midazolam — also act at the GABA-A receptor, but increase the frequency of channel opening and require GABA to be present. This gives them a ceiling effect and makes them far safer in overdose
Taken alone, benzodiazepines rarely kill an adult. The patient is drowsy or comatose but usually maintains the airway, with a normal or slightly depressed respiration and preserved reflexes. Deaths occur when they are combined with alcohol, opioids or other depressants, and that combination is the usual finding at autopsy
Flumazenil is the specific antagonist — but is used with great caution and rarely, because it precipitates convulsions in a person dependent on benzodiazepines or who has co-ingested a tricyclic antidepressant, in whom the benzodiazepine may be the only thing preventing seizures. Its half-life is also short, so resedation follows

CLINICAL PEARL

Benzodiazepines alone almost never kill; the combination does. The ceiling effect means an adult who takes only benzodiazepines usually survives with nothing more than airway care. When one of these deaths reaches the mortuary, the question is what else was taken — alcohol, an opioid, a tricyclic — and the toxicology must be broad rather than confirmatory.

Medicolegal Aspects and Applied Aspects

Manner — suicidal is much the commonest, these being among the most frequently used drugs in self-poisoning because they are prescribed so widely; accidental, particularly in the elderly, in children and in combination with alcohol; and criminal — for stupefaction
Stupefaction for robbery and for sexual assault — alprazolam and other benzodiazepines are widely used in India to drug travellers for robbery, charged under BNS 123; and in drug-facilitated sexual assault, where the drug is added to a drink. The agents are rapidly cleared, so an early urine sample is essential and the opportunity is lost within hours
These drugs are schedule H1 under the Drugs and Cosmetics Rules and several are covered by the NDPS Act, requiring a prescription and a separate register kept for three years
Take an early urine sample in any suspected drugging; benzodiazepines are cleared within hours and a delayed sample is negative even where the drug was given
Assume a co-ingestant in every benzodiazepine death and screen broadly; the drug alone rarely kills an adult
Avoid flumazenil unless the ingestion is known to be a benzodiazepine alone in a non-dependent person; the risk of precipitating convulsions outweighs the benefit, and supportive care suffices
Never stop a barbiturate or benzodiazepine abruptly in a dependent patient; withdrawal causes convulsions and death, unlike opioid withdrawal
Look for barbiturate blisters over the pressure areas at autopsy; they are suggestive, though not specific to barbiturates
Barbiturates open the chloride channel directly at high dose, which is why they have no ceiling and are so much more lethal
Benzodiazepines need GABA to be present, which gives the ceiling effect and makes them relatively safe alone
Urinary alkalinisation helps phenobarbitone, which is a weak acid, and multiple-dose charcoal is also effective for it
Hypothermia is characteristic of barbiturate coma, along with flaccidity and absent reflexes, and the patient must be warmed
Alprazolam is widely used for stupefaction in India, charged under BNS 123, and clears from urine within hours
Withdrawal from either can kill, unlike opioid withdrawal, so neither is ever stopped abruptly in a dependent patient
Screen broadly at autopsy; a benzodiazepine death almost always involves alcohol, an opioid or another depressant as well

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