Toxicology

Barbiturate Poisoning

Barbara

• Urethane an urea derivative acted as hypnotic so other urea derivatives tested
• Derivatives of Malonyl urea(barbituric acid) were found to be effective and in 1903 Barbitone(Veronal) introduced
• Phenobarbitone(luminal) was next
• 1000 barbiturates were synthesized and nearly 100 tested
• All of these have qualitatively same action from mild sedation to surgical anaesthesia

Traditional Classification

• Long acting- 10 to 14 days
• Barbitone (Not metabolised), Phenobarbitone (25% excreted unchanged)
• Intermediate acting- 3-5 days
• Nembutol (Pentobarbitone), Soneryl (Butobarbitone), Amytal (Amylobarbitone)
• Short acting- 2 to 4 days
• Seconal (Hexabarbitone)
• Ultra short acting
• Pentothal

Clinical picture

• Classical clinical picture of severe metabolic brain disease
• Depression- Bilateral symmetrical
• Respiration & Circulation controlling centres in lower brain stem are affected late or not at all
• Pupillary light reflex is preserved

Clinical Picture(Cont.)

• General
• Nausea, vomiting, headache, or drowsiness to coma
• Fast pulse, low B.P. temperature may be raised sometimes hyperpyrexia
• There may be cyanosis or slow, superficial and stertorous respiration
• CNS
• Varying depth of coma,
• Pupil-dilated, constricted or unequal

Clinical Picture (Cont.)

• CVS
• Inverted and flattened T wave and depressed ST segment
• Muscles & reflexes
• Flaccid, Reflexes lost, Babinsky Positive,
• Metabolism
• Temperature subnormal
• Skin
• Anoxic Skin Bullae

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Management

• No specific antidote
• Keep the patient alive & Complication free
• Threat to life - Shock due to
• Circulatory failure
• Head down position,
• If B.P. under 80mm then Dopamine
• Digitalis if heart failure

Management

• Resp. failure
• No action if pharyngeal reflex present & cyanosis absent
• Use of Respiratory stimulant
• Ideally to keep alive till artificial resp. being arranged
• Evidence that it will benefit the patient is weak
• Watch for convulsion, twitching in face-STOP
• Ventilatory support- Mechanical Invasive Ventilation should be considered.
• Where ventilator not available:- With manual ventilatory support
• If cough reflex absent then cuffed endotracheal tube-48 hrs
• Tracheostomy Suction every ½ hr Humidified 25% O₂

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Prevention of Complication

Patient placed in semiprone position

The bed raised in the middle

Changed from side to side but not on back

Broad spectrum antibiotic to prevent pneumonia

Nasal Feeding

Fluid & electrolyte balance

Care of Bladder & Bowel

Other Measures

• Gastric lavage & Aspiration
• Induce vomiting if the patient conscious
• Gastric lavage done
• if Patient Unconscious
• Or Vomiting does not take place
• Cuffed endotracheal tube to prevent aspiration
• Initial lavage with plane water and preserve in 2 bottles one sealed to be sent to FSL and the other to the local lab for identification of poison.
• Use activated charcoal/ Tannic acid or Pot. permanganate

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Enhancing Excretion

• Forced Alkaline Diuresis
• Indications
• Deep coma
• Hypoventilation
• Hypotension
• 1/6 Molar Lactate or 1.2% Sodibicarb Soln.
• + Lasix and 5% dextrose
• Urine output of 500ml per hr, pH-7.5 to 8.5
• Serum electrolyte & ECG monitored
• Contraindications- Shock, CCF, Renal damage

Enhancing Excretion

• Peritoneal dialysis
• More effective than diuresis
• Haemodialysis
• 5 to 10 times more effective than peritoneal d.
• Barbiturates removed 10-60 times faster
• Especially useful in patients with renal damage
• Exchange transfusion

Medico-Legal

• Fatal dose- 20 times the hypnotic dose
• Fatal period-4 hrs to 2 weeks or more
• P.M.Findings- Nothing characteristic
• External cyanosis, internal congestion found
• Lungs pneumonic, UTI, bedsores
• Brain should also be preserved
• Suicidal generally in old people or accidental, rarely homicidal

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