Which of the following is a uterine relaxant?
Ans. B. Ritodrine. (Ref. KDT, Pharmacology, 6th ed., p 125; 323)SELECTIVE b2 STIMULANTSThese include, salbutamole, terbutaline, salmeterol, formoterol and ritodrine. They cause bronchodilatation, vasodilatation and uterine relaxation, without producing significant cardiac stimulation. b2 selectivity is only relative. Salbutamol has b2:bj action ratio of about 10. They are primarily used in bronchial asthma. Other uses are:# As uterine relaxant to delay premature labour. Ritodrine is the preferred drug;# In hyperkalemic familial periodic paralysis - benefit by enhancing K+ uptake into muscles a lowering plasma K+ levels.The most important side effect is muscle tremor; tachycardia and arrhythmias are less likely.THERAPEUTIC CLASSIFICATION OF ADRENERGIC DRUGSI.Pressor agentsNoradrenalineMethoxaminePhenylephrineDopamineeEphedrineMephentermineII.Cardiac stimulantsAdrenalineeDobutamineeIsoprenalineeIII.BronchodilatorsAdrenalineSalmeterolTerbutalineSalbutamoleIsoprenalineFormoterolIV.Nasal decongestantsPhenylephrineePseudoephedrineNaphazolineOxymetazolineXylometazolinePhenylpropanolamineV.CNS stimulantsAmphetamineMethamphetamineDexamphetamineVI.AnorecticsFenfluramineSibutramineDexfenfluramineVII.Uterine relaxant and vasodilatorsRitodrineSalbutamol IsoxsuprineeTerbutalineeTocolytic drugsSr. no.Tocolytic AgentsComments1Isosuprine (DUVADILAN)It is an orally effective long acting selective b receptor stimulant, which has direct smooth muscle relaxant property as well. It has been used as uterine relaxant for threatened abortion and dysmenorrhoea, but efficacy is poor.Side effects: nausea, tachycardia, flushing, dizziness, and tremor. Isoxsuprine has been used in threatened abortion and dysmenorrhoea, but efficacy is doubtful.2Ritodrine (Selective b2 stimulants)infused i.v. have been successfully used to postpone labour but maternal morbidity and mortality may be increased due to their cardiac and metabolic actions and incidents of pulmonary edema.3Atosiban & nifedipineAlthough atosiban and nifedipine seem equally effective in delaying preterm labour, there is increasing concern in twin pregnancies about the adverse CVS effects of nifedipine. Nifedipine should not be used in multiple pregnancies due to fear of pul edema. However, atosiban, which is principally an AVP receptor antagonists is oxytocin receptor antagonist, used for the treatment of preterm labour.4Magnesium sulphateAlso acts as a tocolytic agent. With the withdrawal of sympathomimetic drugs and the failure of atosiban, an oxytocinantagonist, to obtain FDA approval, magnesium sulphate is therefore in commonly used tocolytic drug.Educational points:# Tolterodine is being developed as a vasicoselective antimuscarinic.# Tiotropiumbromide Congener of ipratropium bromide, which binds very tightly to bronchial M1/M3 muscarinic receptors producing long lasting bronchodilatation. Binding to M2 receptors is less tight confering relative M1/M3 selectivity. Like ipratropium, it is not absorbed from respiratory and g. i. mucosa and has exhibited high bronchial selectivity of action.
Tolterodine
Ritodrine
Tiotropium
Salmeterol
Miscellaneous (Gynae)