This document summarizes drugs acting on the genitourinary system, including uterine stimulants and relaxants. It describes the classification, mechanisms of action, uses, and side effects of various oxytocics (uterine stimulants) like oxytocin, ergot alkaloids, and prostaglandins that are used to induce or accelerate labor. It also discusses uterine relaxants (tocolytics) like ritodrine, nifedipine, magnesium sulfate, and atosiban that inhibit uterine contractions to delay premature labor. The document provides details on the pharmacokinetics, dosing, and administration of these important drugs used in obstetrics.

1. 5/3/2018
DRUGS ACTING ON
GENITOURINARY
SYSTEM

2. GENITOURINARY SYSTEM
Genitourinary is a word that refers to the urinary and genital organs.
Urology is the branch of medicine concerned with the urinary tract in both
genders and the genital tract of the reproductive system in males.
DRUGS ACTING ON GENITOURINARY SYSTEM
UTERINE STIMULANTS UTERINE RELAXANTS
 Uterine stimulants (uterotonics
or abortifacients) are
medications given to cause a
woman’s uterus to contract, or
 Uterine relaxants (tocolytic
drugs) relax the uterus and
arrest threatened abortion or
delay premature labor.
DRUGS
ENDOMETRIUM
ESTROGEN
PROGESTERONE
MYOMETRIUM
INDIRECTLY
ACTING
SYMPATHOMIMETIC
PARASYMPATHOMIMET
IC
DIRECTLY
ACTING
UTERINE
STIMULANTS
(OXYTOCICS)
UTERINE RELAXANTS
(TOCOLYTICS)

3. to increase the frequency or
intensity of contractions.
 These drugs are used to
induce labor.
 And to reduce postpartum
bleeding.
 These drugs inhibit uterine
contractions.
CLASSIFICATION OF UTERINE STIMULANTS
Classified as:
Posterior Pitutary Hormone: Oxytocin, Desamino oxytocin
Prostaglandins: PGE2, PGE1, PGF2α ,15-methyl PGF2α(Carboprost),
Misoprostol (Methyl ester of PGE1)
Ergot Alkaloids: Ergometrine (Ergonovine), Methylergometrine,
Miscellaneous: Ethacridine, Quinine
Anti Progestin: Mifepristone
OXYTOCIN
MECHANISM OF ACTION:
 Action mediated through specific G-protein coupled oxytocin
receptors.
 On Activation, these receptors mediate the response:

4. o By depolarization of muscle fibres and influx of Ca++ ions (main
mechanism)
o Through phosphoinsitide hydrolysis and IP3 mediated
intracellular release of Ca++ ions.
 Number of oxytocin receptors increases markedly during later part of
pregnancy.
 Also increases Prostaglandin (PG) synthesis and release by the
endometrium.
PHARMACOKINETICS
 Not absorbed orally.
 Administered by i.v. , i.m. ,rarely nasal route.
 Plasma t1/2- approx. 15 mins .
 It is primarily inactivated in the KIDNEY and the LIVER.
 DOSAGE- OXYTOCIN, SYNTOCINON 2 IU/2ml and 5 IU/ml inj.
PITOCIN 5 IU/0.5ml inj.
OXYTOCIN USES
Drug of Choice

5.  Induction of Labour (slow i.v. infusion 5IU in 500 ml glucose or NS;
10milli IU/mL: 0.2-2.0 mL/min)
 Uterine Inertia
 Postpartum Haemorrhage
 Breast Engorgement (inefficient milk ejection reflex; intra-nasally)
 Oxytocin Challenge Test (risky and rarely performed)
Side Effects
 Injudicious use: maternal and foetal soft tissue injury, ruptured uterus,
foetal asphyxia/death
 Water intoxication
DESAMINO OXYTOCIN
 Buccal formulation, uses same as oxytocin, less consistent action.
INDICATIONS:
 Induction of labour :
 50 IU every 10min, max 10 tablets
 Uterine inertia : 25 IU every 30 mins
 Promotion of uterine involution: 25-50 IU
 Breast engorgement : 25-50 IU before breast feeding
CARBETOCIN
 long acting structural analogue of human oxytocin
 given as a single IV bolus following the delivery of baby at Elective or
Emergency caesarean section.

6.  Carbetocin is as effective as an oxytocin infusion with respect to
blood loss following delivery
 DOSE: Dilute 100mcg Carbetocin with 10mls Saline. Administer over
one minute following delivery of the baby.
ERGOMETRINE AND METHYL ERGOMETRINE
 Ergot alkaloids obtained from clavicepspurpura.
 Amine ergot alkaloid and methyl derivative. duration of uterine
contractions
 Methyl ergometrine more potent action on uterus and less on CVS,
CNS, GIT etc.
MECHANISM OF ACTION:
 They increase force, frequency and duration of uterine contractions.
 Gravid uterus is more sensitive and involves the lower segment as
well.
 Partial agonist action on 5-HT2 and α adrenergic receptors.
USES:
 Post Partum Haemorrahge(PPH )→ After anterior shoulder
presentation
 Prevention → 0.2-0.3 mg i.m
 Treatment → 0.5 mg i.v.
 Prevent uterine atony
 To promote involution in multipara → 0.125mg TDS -7days.
 Diagnosis of variant angina during Coronary angiography.

7. SIDE EFFECTS:
 Nausea, vomiting
 Rise in blood pressure
 Decrease milk secretion if used n higher dose for many days
postpartum
 Should be avoided in patients with:
 Vascular disease
 Presence of sepsis
 Liver and Kidney Disease
PROSTAGLANDINS
 Local Hormones, derived from breakdown of membrane
phospholipid (yielding arachidonic acid)
 PGE2 and PGF2α: commonly used clinically
 Dinoprostone (PGE2): cervical maturation/ripening (collagenolytic
proterty); 5 times potent than and less toxic than PGF2α; costly
 Dinoprost tromethammine(PGF2α): myometrial contractility
 Promotes myometrial contraction irrespective of duration of
gestation.
MECHANISM OF ACTION:
 Change in myometrial cell membrane permeability and/or alteration
of membrane bound Ca++
 Also sensitizes uterus to oxytocin

8. USES:
 Misoprostol PGE1: induction of abortion/labour; cervical ripening
 Termination of molar pregnancy
 Induction of labour (poor preinduction cervical score as in
Intrauterine Fetal Death, shorter period of gestation, early
primigravida: PGE1)
 Acceleration of labour
 Cervical ripening for induction of labour/abortion
 Management of atonic postpartum haemonrrrhage
 Refractive cases of Atonic uterus
 Medical management of tubal ectopic pregnancy
SIDE EFFECTS:
 On systemic use:
 Nausea, vomiting, diarrhoea, pyrexia, bronchospasm
 Cervical laceration when used as an abortifacient
 Tachysystole of uterus during induction
 Meconium passage by foetus (Foetal Distress)
 Rupture of uterus: Rare
 Should not be used in patients with previous history of Caesarean
Section.
ETHACRIDINE
 Available as 50 mg/ml solution
 For extra-amniotic infusion

9.  EMCREDIL , VECREDIL
CLASSIFICATION OF UTERINE RELAXANTS
Adrenergic agonists[β2 ]: ritodrine,salbutamol,isoxsuprine,terbutaline ,
orciprenaline, salbutamol etc
Calcium channel blockers: Nifedepine
Magnesium sulfate
Prostaglandin inhibiting agents:Indomethacin
Oxytocin antagonist:Atosiban
Ethyl alcohol
THERAPEUTIC USES:
 Delay or postpone labor – to allow fetus to mature and transfer of
mother to a healthcare centre
 Threatened abortion
 Dysmenorrhoea
RITODRINE
 A β2 selective agonist.
 It has a major uterine relaxant action.
 Doses given as I/V infusion of 50 mcg/min, dose may be increased
after every 10 minutes till tone is decreased.
 Causes postponement of delivery in 70% cases.

10. MECHANISM OF ACTION:
 Bind to β-adrenoceptors , activate enzyme Adenylatecyclase
 increase in the level of cAMP
 reducing intracellular calcium level and decreasing the sensitivity of
actin myosin contractile unit.
DOSES:
 50 mg of ritodrine in 500 ml of 5% glucose solution.
 Start by 10 drops per minute and increase by 5 drops every 10
minutes until uterine contractions cease.
 Infusion should be continued for 12-48 Hrs after cessation of
contractions.
 Oral therapy should be continued every 8 Hrs after food.
 Monitor maternal pulse, BP and FHS
ADVERSE EFFECTS:
 CVS effects like hypotension, tachycardia, arrhythmia etc and
metabolic effects like hyperglycemia, hyperinsulinemia and
hypokalaemia
CONTRAINDICATIONS:
 Heart disease - Hypertension or hypotension
 Hyperthyroidism and diabetes
 Antepartum haemorrhage (dilatation of the uterine arteries may
increase the bleeding)

11.  Rupture of membrane
PREPARATIONS:
 Available as Ritodie/yutopar
 Tablet 10 mg / tablet or injections 10 mg/ml – 1ml or 5 ml
 Isoxsuprine (duvadilan) is available as oral and injections (10, 20, 40
mg tablets)
OXYTOCIN ANTAGONIST(ATOSIBAN)
 Not FDA approved for the treatment of premature labor— historically
used in rural areas.
 Competitive antagonist at oxytocin receptors
 Decreases and stops uterine contractions
Mechanism of Action:
 Direct relaxant effect on the myometrium and inhibition of oxytocin
release
Indications/Therapeutic Effects:
 Inhibit premature labor
Pharmacokinetics:
 Loading dose (10% injection): 7.5 ml/kg/hr IV for two (2) hours with a
maintenance infusion rate of 1.5 ml/kg/hr IV for up to 10 hours.
NIFEDIPINE(Procardia®)

12.  Ca channel blocker
 Not FDA approved for the treatment of premature labor.
 acts by impairing entry of Ca into myometrial cells via voltage-dep Ca
channels (so inhibits contractility)
MECHANISM OF ACTION:
 All smooth muscles (uterus) use Ca2+ influx through L- type calcium
channels for contraction.
INDICATIONS/THERAPEUTIC EFFECTS:
 Starting to be used as a 1st line drug, especially with b2 agonists now
not available.
ADVERSE EFFECTS

13.  Flushing, headache, dizziness, transient hypotension.
CONTRAINDICATIONS/PRECAUTIONS:
 Concomitant use of calcium channel blocker.
MAGNESIUM SULPHATE
MECHANISM OF ACTION:
 Acts by competitive inhibition of Ca2+ ion either at the motor end
place at the cell membrane reducing calcium influx. es acetylcholine
release & its sensitivity at motor end plate.
 Direct depressant action on uterine muscle.
DOSES:
 Loading dose 4-6g IV (10-20% solution) over 20-30 mins
 followed by an infusion of 1-2g/hr to continue tocolysis for 12 hrs
after the contractions have stopped. Tocolytic effects is poor.
SIDE EFFECTS AND PRECAUTIONS:
 It is relatively safe.
 Common maternal side effects are flushing, perspiration, headache,
muscle weakness, rarely pulmonary oedema.
Neonatal side effects are lethargy, hypotonia, rarely respiratory
depression.

14. CONTRAINDICATIONS:
 Pts with myasthenia gravis & impaired renal function.