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DRUGS ACTING ON UTERINE MUSCLE CONTRACTILITY

DRUGS ACTING ON UTERINE MUSCLE CONTRACTILITY. Haitham M. Al-Wali Ph.D Pharmacology & Therapeutics Al-Nahrain college of Medicine. Terminology. Uterotonics: are drugs that stimulate the contraction of the uterus, they are mainly used to induce labor. Tocolytics :

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DRUGS ACTING ON UTERINE MUSCLE CONTRACTILITY

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  1. DRUGS ACTING ON UTERINE MUSCLE CONTRACTILITY Haitham M. Al-Wali Ph.D Pharmacology & Therapeutics Al-Nahrain college of Medicine

  2. Terminology Uterotonics: are drugs that stimulate the contraction of the uterus, they are mainly used to induce labor. Tocolytics : are drugs that relax the uterus, they use them mainly to stop preterm labor.

  3. DRUGS PRODUCING UTERINECONTRACTIONS( Oxytocic Drugs ) • OXYTOCIN • ERGOT ALKALOIDS Ergometrine (Ergonovine) • PROSTAGLANDINS dinoprostone (PGE2) dinoprost (PGF2α)

  4. OXYTOCIN(SyntocinonR) Synthesis • Is a posterior pituitary hormone secreted by the posterior pituitary gland. • Oxytocin secretion occurs by sensory stimulation from cervix ,vagina , and from suckling at breast.

  5. Physiological Effects ★Stimulation of milk ejection (milk letdown) mammary alveoli ★ Stimulation of uterine smooth muscle contraction during birth ★ Establishment of maternal behavior

  6. Pharmacokinetics of oxytocin Absorption ,Metabolism and Excretion • Not effective orally • Administered intravenously • Also as nasal spray • Not bound to plasma proteins • Catabolized by liver & kidneys • Half life = 5 minutes

  7. Role of oxytocin Uterus • Stimulates both the frequency and force of uterine contractility particularly of the fundus segment of the uterus. • These contractions resemble the normal physiological contractions of uterus (contractions followed by relaxation)

  8. Immature uterus is resistant to oxytocin. • Contract uterine smooth muscle only at term. • Sensitivity increases to 8 fold in last 9 weeks and 30 times in early labor. • Clinically oxytocin is given only when uterine cervix is soft and dilated.

  9. Clinical uses • Induction (abortion) or Augmentation (birth) I.Vd 1mU/min initially and increased to 5-20 mU/min gradually contraindications: ﹡malposition ﹡cephalopelvic disproportion ﹡birth canal abnormality • postpartum hemostasia &uterus restoration I.M 5-10 U each time • Impaired milk ejection One puff in each nostril 2-3 min before nursing

  10. Side Effects: a) Hypertension b) Uterine rupture c) Fetal death(ischaemia) d) Water intoxication e) Neonatal jaundice

  11. Contraindications a) Hypersensitivity b) Prematurity c) Abnormal fetal position d) Evidence of fetal distress e) Cephalopelvic disproportion Precautions a) Multiple pregnancy b) Previous c- section c) Hypertension

  12. Ergot Alkaloids Fungus grows on rye • Ergometrine (Ergonovine) • Methylergonovine

  13. Effects on the Uterus • Alkaloid derivatives induce TETANIC CONTRACTION of uterus without relaxation in between. These does not resemble the normal physiological contractions • It causes contractions of uterus as a whole i.e. fundus and cervix(tend to compress rather than to expel the fetus) Difference between oxytocin & ergots??

  14. Clinical uses • ★uterus hemorrhage • ★postpartum uterus restoration • ergometrine po 0.2-0.5 mg, im or iv 0.1-0.3 mg, 1-2/d • ★migraine • ergotamine po 1-2 mg, im 0.25-0.5 mg, <10 mg/w

  15. Side effects a) Nausea, vomiting, diarrhea b) Hypertension Vasoconstriction of peripheral blood vessels ( toes & fingers) c) Gangrene , angina

  16. * Contraindications: a) 1st and 2nd stage of labor b) vascular disease c) impaired hepatic and renal functions * Precautions: a) Cardiac diseases b) Hypertension c) Multiple pregnancy

  17. PROSTAGLANDINS (PGE2 & PGF2α) • Drugs • dinoprostone (PGE2) dinoprost (PGF2α) • carboprost (15-methylPGF2α) and gemeprost or misoprostol (PGE1 analogues). • Effects • Stimulation of rhythmic uterine contraction • Clinical use • Inducing abortion • Postpartum hemorrhage • contraindications • ﹡ Similar to oxytocin • ﹡ PGF2α is banned for patient with asthma • ﹡ PGE2 is banned for patient with glaucoma .

  18. Difference B/w Oxytocin and Prostaglandins

  19. Difference (cont’d)

  20. Difference b/w Oxytocin and Ergometrine

  21. UTERINE RELAXANTS

  22. DRUGS PRODUCING UTERINE RELAXATION( Tocolytic Drugs ). Action and Uses Relax the uterus and arrest threatened abortion or delay premature labor. 1. β-ADRENOCEPTOR AGONISTS** Ritodrine, i.v. drip Selective β2 receptor agonist used specifically as a uterine relaxant.

  23. β- adrenoceptor agonists • Mechanism of action Bind to β-adrenoceptors , activate enzyme Adenylate cyclase , increase in the level of cAMP reducing intracellular calcium level and decreasing the sensitivity of actin myosin contractile unit.

  24. Side effects: • Tremor • Nausea , vomiting • Flushing • Sweating • Tachycardia (high dose) • Hypotension • Hyperglycemia • Hypokalaemia

  25. 2.CALCIUM CHANNEL BLOCKERS e.g., Nifedipine • Causes relaxation of myometrium • Markedly inhibits the amplitude of spontaneous and oxytocin-induced contractions

  26. Unwanted effects • Headache, dizziness • Hypotension • Flushing • Constipation • Ankle edema • Coughing • Wheezing • Tachycardia

  27. 3. Prostaglandin synthetase inhibitors • The depletion of prostaglandins prevents stimulation of uterus NSAID,s e.g. Aspirin Indomethacin Ibuprofen

  28. Adverse effects ulceration • premature closure of ductus arterious.

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