Antidotes

Question 1

Activated charcoal

Answer 1

Activated charcoal binds to drugs and poisons, thereby reducing absorption either by binding the substance before absorption in the GIT or by interrupting enterohepatic recirculation.

Question 2

Macrogol laxatives

Answer 2

Iso-osmotic solutions containing electrolytes and macrogol 3350, which clean the bowel by causing diarrhoea.

Question 3

Acetylcysteine

Answer 3

Precursor for glutathione synthesis; glutathione and acetylcysteine bind to reactive metabolite of paracetamol (and other drugs); repletion of glutathione also directly reduces oxidative cell injury. Acetylcysteine may also improve hepatic perfusion in established liver injury due to paracetamol or other insults.

Question 4

Atropine

Answer 4

Atropine competitively inhibits binding of acetylcholine to muscarinic receptors in the parasympathetic and central nervous systems. In normal circumstances atropine increases heart rate, causes mydriasis, inhibits smooth muscle contraction in the GI and genitourinary systems and inhibits secretion from a variety of glands.

When there is excessive acetylcholine, eg in organophosphate poisoning, the muscarinic effects of poisoning (eg miosis, salivation, sweating, bradycardia, vomiting and diarrhoea) are reversed by atropine.

Question 5

Calcium gluconate

Answer 5

Opposes blockade of calcium channels by drugs, eg verapamil, diltiazem; alters membrane polarisation; chelates fluoride ions.

Question 6

Digoxin-specific antibody

Answer 6

Immunoglobulin fragment that binds to digoxin with very high affinity, removing it from its site of action.

Question 7

Ethanol

Answer 7

Competitive inhibitor of alcohol dehydrogenase; prevents formation of toxic metabolites of ethylene glycol and methanol.

Question 8

Flumazenil

Answer 8

Competitive antagonist at benzodiazepine receptors.

Question 9

Fuller’s earth

Answer 9

Binds paraquat in the GIT and prevents absorption.

Question 10

Glucagon

Answer 10

Increases cyclic AMP independent of beta-receptors or calcium flux, positive chronotropic and inotropic effect.

Question 11

Naloxone

Answer 11

Competitive antagonist at opioid receptors.

Question 12

Pralidoxime

Answer 12

Reactivates cholinesterases inactivated by binding to organophosphates. This effect is most marked at the neuromuscular junction, with less effect on the parasympathetic nervous system. Data are limited but pralidoxime may also directly bind to some organophosphates and may reactivate other organophosphate target enzymes such as neurotoxic target esterase and pseudocholinesterase.

Question 13

Pyridoxine/Vitamin B6

Answer 13

Coenzyme in numerous reactions; required for GABA synthesis (glutamate decarboxylase), homocysteine metabolism (cystathionine beta-synthase) and haemoglobin synthesis (ALA synthetase).

Question 14

Thiamine/ Vitamin B1

Answer 14

Coenzyme in carbohydrate metabolism.