19B19: Exam Report
SAQ 19 Describe the pharmacology of Atropine
53% of candidates passed this question.
Most candidates used a good structure to compose their answer. Better candidates understood that CNS effects occur as atropine is a tertiary amine that crosses the blood brain barrier. The mechanism of action wa required. Indication for use should have included bradcardia, organophosphate poisoning, drying of secretions etc. Reasonably extensive details regarding pharmacodynamics was expected, including potential toxic effects. There was limited knowlwdge regarding pharmacokinetics.
M2i / 19B19: Describe the pharmacology of Atropine
Chemical
Naturally occurring tertiary amine, which is the ester of tropic acid & tropine
NB: the ester is essential for binding at ACh R’s
Use
- Tx bradycardia
- Counter muscarinic effects of anticholinesterases
- Bronchodilation (nebulised)
Presentation
Clear colourless solution 600mcg/ml
Tablets 600mcg
Dose
300 – 600mcg
3mg for complete vagal blockade
Well matched to Edrophonium (when given at reversal of neuromuscular blockade)
Route
IM/IV/PO
Onset
Rapid – 1min
DoA
Short – 30mins
MoA (mechanism)
competitive antagonist at muscarinic cholinergic receptors
PD
CVS
↑ HR
↑ CO
↓ AV conduction time
RESP
Bronchodilation
↓ bronchial secretions
CNS
Central Anticholinergic Syndrome → somnolence, confusion, amnesia, agitation, delirium, mydriasis
GI
↓ gastric secretions
↓salivation
↓gut tone & peristalsis
Antispasmodic at biliary tree
↓LOS
PK
A
rapidly absorbed, lipid soluble, 20% OA
D
50% PPB, VD 2 – 4L/kg, crosses BBB & placenta
M
hydrolysed in liver & tissues to TROPINE + TROPIC ACID
E
95% dose excreted in 24hrs. Some IM ∆
Adverse Effects
Painful IM
Dry mouth
Inhibition of sweating → hyperpyrexia in elderly & children
Elderly high risk of Central Anticholinergic Syndrome
Glaucoma (↑IOP)