Uterine Relaxants

Question 1

Oxytocin

Answer 1

1. cyclic oxtapeptide stored in post pituitary normally released in response to suckling and uterine pressure
2. Tx: DOC to induce labor at term if indicated
   - prevention of hemorrhate (IM route is preferred)
   - stimulation of milk let-down reflex (nasal application)
3. Circulates in the blood as free peptide very short t1/2, inactivated liver/kidney, IV/IM/nasal route admin
4. SE: H20 intoxication w/convulsions (ADH like effect)
   - uterine rupture w/large dose
   - allergy/anaphylaxis
   - sinus bradycardia of fetus
5. CI: malpresentation, cephalopelvic disproportion, complete placenta previa, uterine scar from previous C-section, unengaged head, cervical scaring

Question 2

Ergonovine maleate, Methylergonovine maleate

Answer 2

1. Ergot alkaloids: more uterus-specific than other ergots
2. Contraction of uterine smooth muscle through activation of 5HT and a-adrenergic receptors
3. Tx: used after completion of labor and delivery of placenta to produce firm uterine contractions and to dec uterine bleeding (2nd line drug after uterine massage and oxytocin therapy have failed to dec bleeding)
   - also used for same reasons following suction abortion
4. Rapid action, 30-40sec after IV, 10 min after oral, last several hours
5. SE: minimal due to brief dosing, transient HTN, angina/MI
6. CI: never used to induce labor! will cause fetal hypoxia
   - hepatic/renal disease
   - obliterative vascular or CAD

Question 3

Dinoprostone

Answer 3

1. Synthetic Prostaglandin E2
2. Tx: induce explusion of uterine contents in instances of intrauterine fetal death, missed abortion, elective abortion
   -cervical ripening at term
3. For abortion: one suppository inserted in vagina, subsequent inserted at 3-5 hr intervals until abortion occurs
   -For cervical ripening: apply gel to cervix
4. SE: GI disturbances: vomiting, DIARRHEA
   -Fever, chills, HA
5. CI: For cervical ripening: problems w/mother or fetus
   For abortions: similar to carboprost tromethamine

Question 4

Carboprost Tromethamine

Answer 4

1. Derivative of PGF2a
2. Tx: induce abortion btw 13th and 20th week
   - postpartum bleeding due to uterine atony that is unresponsive to conventional managment
3. IM admin
4. SE: not serious if used properly, systemic PG actions often diagnosed as anaphylactic shock
   - Vomiting and diarrhea
   - fever/rashes
5. CI: acute pelvic inflammation
   - acute cardiac, pulmonary, renal, hepatic diseases
   - asthma, HTN, anemia, Jaundice, epilepsy

Question 5

Magnesium Sulfate

Answer 5

1. MgSO4 relaxes the uterine muscle probably by direct effect on uterine cells, not FDA approved for this, 1st line drug
2. Tx: pre-eclamptic pts to prevent convulsions or as tx for eclamptic pts (FDA approved)
3. IV, slowly admin
4. SE: flushing, diaphoresis, hypotension
   - Depressed DTRs, muscle paralysis, wkness, lethargy, hypothermia
   - circulatory collapse and cardiac, CNS, respiratory depression

Question 6

Nifedipine

Answer 6

1. Ca channel blocker, not FDA approved for tx of premature labor
2. All smooth muscles use Ca influx through L-type Ca channels for contraction
3. Tx: starting to be used as 1st line drug, esp w/B2 agonists now not available
4. SE: flushing, HA, dizziness, transient hypotension
5. CI: concomitant use of Ca channel blockers and MgSO4 is potentially harmful and has resulted in CV collapse.

Question 7

Indomethacin

Answer 7

1. Not FDA approved for tx of premature labor.
2. Reduction of prostaglandin synthesis (prevent contractions)
3. SE: maternal GI irritation, peptic ulceration, thrombocytopenia, allergic rxns, HA/dizziness
   - partial closure of fetal ductus arteriosus, impaired fetal renal funciton, brochopulmonary dysplasia and persistent pulmonary hypertension in neonatal period.

Question 8

Progesterone

Answer 8

1. Not FDA approved, however still recommended by american college of obstetricians.
2. Tx: given prophylactically from 16th to 37th week of pregnancy or until delivery to maintain length of pregnancy
   - for use only in high risk women with history of spontaneous birth <37wks
   - not effective in acute managment of preterm labor
   - might be helpful to reduce repeated preterm labor occurrences if given after an episode of preterm labor
   - approved for used to supplement or replace progesterone as part of ART tx program to maintain luteal phase following IVFor ICSI.

Question 9

Nitroglycerin

Answer 9

1. Emergency use only-incases of uterine rupture only!
2. Tx: following 100ug IV bolus sudden cervicouterine relaxation within 45-90 seconds lasting abt 1 min.
3. CI: uncorrected hypovolemia, severe anemia (Hb,6 g/dL), increased intracranial pressure, constricitive pericarditis/pericaridal tamponade and hypersensitivity

Question 10

Ethanol

Answer 10

1. Not FDA approved for tx of premature labor, used in rural areas
2. Direct relaxant effect on myometrium and inhibition of oxytocin release
3. Tx: inhibit premature labor
4. Loading dose (10% inj): 7.5ml/kg/hr IV for 2 hrs with maintenance infusion rate of 1.5ml/kg/hr IV for up to 10hrs.