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Drugs acting on uterus, Oxytocin:, Post partum haemorrhage PPH:, Other…
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Oxytocin:
it is secreted by posterior pituitary along with ADH.
It increases the uterine contractions with complete relaxation in between.
It increases the contraction of upper segment(fundus and body) of uterus
whereas lower segment is relaxed facilitating the expulsion of the fetus.
Estrogen increases whereas the progesterone decreases the sensitivity of uterus to oxytocin.
Oxytocin is involved in milk ejection reflex whereas prolactin causes milk secretion.
High doses of oxytocin causes fall in BP due to vasodilation resulting in reflux tachycardia.
It also has ADH like action in high dose and can result in fluid retention.
It is used for the induction of labor in post-maturity and uterine inertia.
It is now drug of choice for the treatment as well as prevention of postpartum haemorrhage.
Methylergometrine and misoprostol are alternative drugs for this indication.
Oxytocin challenge test is performed to know the adequacy of uteroplacental circulation in high risk pregnancies.
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Other drugs:
Calcium channel blockers like nifedipine and oxytocin antagonist atosiban can also be used to delay premature labour.
Ethyl alcohol IV infusion, NSAIDs and progesterone also suppresses uterine contractions but are rarely used for this indication.
Halothane is an efficacious tocolytic agent and is the anaesthetic choice for version external or internal.
Hydroxyprogesterone has been used prophylactically to prevent pre-term labour.
However, teratogenic potential limits its use.
Calcium channel blockers and atosiban provides the best balance of successful delayed delivery with lesser risk to mother and baby.
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Ergot derivatives:
Ergometrine is derived from claviceps purpura and is used as an oxytocic agent.
It produces uterine contractions in the upper as well as lower segment and is used to control post partum haemorrhage.
Its derivative methylergometrine is more potent oxytocic and is preferred for this indication.
Latter is administered at the delivery of anterior shoulder.
These drugs are preferred over oxytocin for this indication.
Hypertension and sepsis are contraindications for their use.
Uterine relaxants:
These drugs decrease the uterine contractions and are known as tocolytics.
These are mainly used to delay labour when premature contractions are present.
Beta agonists:
Ritodrine, isoxsuprine and terbutaline are the selective B2 agonists useful as tocolytic agents.
These drugs should not be used in mother having heart disease or diabetes mellitus.
Pulmonary edema is a serious complication of these drugs at higher doses.
Beta 2 agonists can also produce tachycardia, palpitations, tremors, hyperglycemia and hypokalemia.
Magnesium sulphate:
It is mainly used to control convulsions in eclampsia.
It also possesses tocolytic activity and can be used.
It is preferred over beta 2 agonists in patients with cardiac problems, diabetes, hyperthyroidism and hypertension.
Toxicity is manifested initially as loss of patellar reflex followed by respiratory depression and finally cardiac arrythmias and arrest.
MgSO4 by IV or inhalational route has been utilized in the treatment of acute severe asthma.