2018B13 List the drugs which affect uterine tone and outline the adverse effects of these agents.



·      Oxytocics table

·      Tocolytic table


Oxytocics: *Note risk foetal asphyxia antepartum*


Mechanism of action (MoA) and adverse effects (AE)


·   Bind oxytocin receptor, a Gq G protein coupled receptor (GPCR)

·   ↑IP3 -> ↑ICF [Ca2+] (also ↑DAG)

·   At low dose: intermittent contraction

·   At high dose: tonic contraction

·   Receptors upregulated from from 36/40

·   AE: N&V, vasodilatation, slightly ADH effect on kidney (V2) -> H2O reabsorption, hyponatraemia


·   Synthetic analogue of oxytocin


·   Oxytocic mechanism unclear

·   Causes tonic contraction at any dose cf. oxytocin

·   Known receptor effects:

o α1: ↑SVR, ↑BP, risk of APO (contra-indicated in pre-eclampsia)

o 5HT2 agonist: N&V

o DA agonist: N&V


·   PGE1 analogue

·   Binds PGE2-R -> multiple G protein-coupled receptor subtypes

·   AE: diarrhoea


·   MoA: binds Gq protein-coupled receptor -> ↑ICF Ca2+

·   AE: bronchoconstriction, hypertension, nausea




Mechanism of action and adverse effects:


·   β2 agonist / Gs GPCR -> ↑cAMP -> ↑inhibition of MLCK

·   AE: ↑HR (cardiac B2) ↓K+ (↑Na+K+ATPase activity), lactic acidosis (β2 liver and skeletal muscle), tremor (β2 skeletal muscle)


·   Inhibit L-Ca2+ -> ↓ICF [Ca2+]

·   AE: reflex ↑HR, peripheral oedema


·   Prodrug

·   Reacts with endothelial ICF sulfhydryl groups -> NO -> activate GC -> ↑cGMP -> ↑MLCP activity, ↑Ca2+ reuptake, ↑K+ efflux

·   AE: ↓BP (vascular SM), reflex HR, flushing, headache, metHbaemia (bad in foetus)

·   Note tachyphylaxis (depletion of sulfhydryl groups)


·   Nonapeptide

·   Competitive antagonist at oxytocin receptor

·   AE: headache, nausea&vomiting

Volatile anaesthetics

·   Inhibit L-Ca2+ -> ↓ICF [Ca2+]

·   Note ↑risk sedated neonate

·   ↑Risk PPH if GA Caesarean

·   Supplement with N2O

·   AE: maternal and foetal anaesthesia, respiratory and cardiovascular depression, nausea and vomiting



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