Pharmacology Flashcards
Indications to promote UTERINE CONTRACTIONS
Postpartum hemorrhage 2° to uterine atony. Induction of labor, cervical ripening, and pregnancy termination are secondary indications.
Pitocin (Dosing)
Promotes Uterine Contractions
Dosing: Uterine Atony- 20 to 40 units in 1 liter of crystalloid solution administered over 15-30 minutes. Induction of labor- 1 to 40 milliunit per minute.
Look out for: ↓BP and ↑HR 2° vasodilation with bolus.
Methergine (methylergonovine)
Dosing
Promotes Uterine Contractions.
Dosing: 0.2mg intramuscularly, NEVER IV! 15 minute intervals to max dose of 0.8mg.
Look out for: ↑↑BP leading to pulmonary edema, cerebral hemorrhage, MI, emesis and/or retinal damage.
Contraindicated: chronic hypertension, preeclampsia, peripheral vascular disease, and ischemic heart disease.
Hemabate/Carboprost (15-methyl PGF2α) and Misoprostol (PGE1 analog)
Dosing
Promotes Uterine Contractions
Dosing: Hemabate for uterine atony- 250µg (micrograms) intramuscularly or intramyometrially, NEVER IV! 15 minute intervals to max dose of 1mg.
Look out for: Bronchoconstriction and hypoxemia
Contraindicated: reactive airway disease, cardiac disease and pulmonary hypertension.
Indications to promote UTERINE RELAXATION
Preterm labor, uterine inversion, uterine tetany, retained placenta, and fetal head entrapment.
Magnesium Sulfate (Dosing)
Promotes Uterine Relaxation
Dosing: IV bolus of 4-6g over 20 minutes, continued as infusion of 1-2g per hour.
Look out for: ↓BP after bolus. Muscle weakness. Defasciculating dose of NDNMB should be avoided, succinylcholine dose should not be changed but maintenance dose of NDNMB should be decreased. If magnesium toxicity occurs: Calcium Chloride (10-15mg/kg) or Calcium Gluconate (10-15mg/kg) over 10 minutes IV.
Magnesium Sulfate Levels
Level (mEq/L) Effects
1.5-2 Normal plasma level
4.0-9.0 Therapeutic Level
5.0-10.0 ECG changes (P-Q interval prolongation,
widened QRS complex)
10 Loss of deep tendon reflexes
15 SA and AV block, respiratory paralysis
25 Cardiac Arrest
Ritodrine and Terbutaline (Dosing)
Promotes Uterine Relaxation
Dosing: Uterine hypertonus or non-reassuring fetal status- 0.25mg IV or SQ. Infusion of 0.01 to 0.08mg/minute titrated to a maternal HR of 20% above baseline.
Look out for: Vasodilation. Maternal/fetal ↑HR, MI, dysrhythmia, or pulmonary edema (from β-2 mediated increased in pulmonary capillary permeability). Gluconeogenesis and glycogenolysis. Avoid agents that increase HR. Contraindicated: Significant cardiac disease or uncontrolled diabetes.
Nifedipine and Nicardipine (Dosing)
Promotes Uterine Relaxation
Dosing: Nifedipine 10-20 mg PO or SL q4-6 hours. Large bore IV (18 gauge or greater) and type and screen should be obtained.
Look out for: ↓BP, refractory postpartum hemorrhage.
Indomethacin and Ketorolac (Dosing)
Promotes Uterine Relaxation
Dosing: Indomethacin- 50mg loading dose PO or PR, followed by 25mg q4-6h. Ketorolac 30mg q6h IV or IM.
Contrainidcations: renal insufficiency, bleeding diathesis, and aspirin induced asthma. Administration prior to 32 weeks gestation.
Nitroglycerin (Dosing)
Promotes Uterine Relxation
Dosing: Profound, short duration uterine relaxation- 50-200µg (micrograms) IV. May repeat up to 500µg (micrograms). 2.5mL in 250mL bag = 50mcg/mL.
Look out for: transient hypotension and maternal headache.
Stadol (Butorphanol)
Dosing
Breakthrough pain- 1-2mg IV/IM q3-4h.
Look out for: Dysphoria, increased cardiac work, and increased pulmonary artery pressure.
Nubain (Nalbuphine)
Dosing
Pruritus- 3-4mg q3-6hrs IV. Breakthrough pain- 10-20mg q3-6hrs IV.
Look out for: Dysphoria, increased cardiac work, and increased pulmonary artery pressure.
Remifentanil (Dosing)
Dosing: (100mcg/ml) start dosing at 20mcg/injection or 0.25mcg/kg IBW, increase 10-20mcg, delay 5-10 mins, NO BASAL rate.
Duration of action: 5-10 mins. Fetal esterases are nearly fully developed at birth. One on one nursing care, continuous pulseox.
Uterine Physiology
Blood flow increase from 75ml/min (pre-pregnancy) to 800ml/min (term) or 15% of cardiac output.
Vascular response: ↑ α-1 sensitivity and nitric oxide (NO) release, ↓ endogenous vasoconstrictor (angiotensin II and endothelin) sensitivity.
Oxytocin: ↑ in number of receptors later in pregnancy starting at 20 weeks.
Pitocin (Mechanism of Action)
Similar to the natural form (produced in hypothalamus, stored in the posterior pituitary), works directly on the G-protein uterine oxytocin receptor which increases calcium channel and local prostaglandin production. Less ADH effects than natural form.
Methergine (Mechanism of Action)
Ergot alkaloid. α-adrenergic stimulation promotes uterine contractions.
Methergine Contraindications
Chronic hypertension, preeclampsia, peripheral vascular disease, and ischemic heart disease.
Hemabate/Carboprost and Misoprostol (Mechanism of Action)
Prostaglandin. Works by increasing myosin light chain kinase activity and promotes uterine contraction. Works similar to endogenous prostaglandins.
Hemabate/Carboprost and Misoprostol (Contraindications)
Reactive airway disease, cardiac disease and pulmonary hypertension.
Magnesium Sulfate (Mechanism of Action)
Questionable efficacy in treating preterm labor. Used as seizure prophylaxis in severe pre-eclampsia.
Competes with calcium binding sites in the sarcoplasmic reticulum.
Increases PGI2 production in the vascular endothelium.
It blocks voltage dependent activation of the NMDA receptor working as an anticonvulsant, increased GMP production, and decreases angiotensin converting enzyme levels.
This promotes muscle relaxation and vasodilation.
Ritodrine and Terbutaline (Mechanism of Action)
β-2 selective agonist. Much better than magnesium for tocolysis but inferior to calcium channel blockers. Better for uterine hypertonus and nonreassuring fetal heart rate. Uterine smooth muscle contains β-2 adrenergic receptors. Stimulation of this receptor causes increased cAMP production, decreased intracellular calcium concentration, and smooth muscle relaxation.
Nifedipine and Nicardipine (Mechanism of Action)
Calcium Channel Blocker. Blocks entry of calcium into cell and release of calcium from sarcoplasmic reticulum.
Indomethacin and Ketorolac (Mechanism of Action)
Reversible COX-1 and 2 inhibitors (prostaglandin synthetase inhibitors). Decrease PGE2 and PGF2α production.
Nitroglycerin (Mechanism of Action)
Activates guanylate cyclase → ↑ cGMP → ↓Calcium influx.
Atosiban (Mechanism of Action)
Competitive inhibitor of oxytocin. Equivalent to β-agonist with tocolysis, second line after CCB.
Atosiban (Dosing)
300µg (micrograms) per minute IV infusion.
Look out for: no known side effects. Short duration of action allows myometrium to be sensitive to oxytocin after stopping infusion.
Stadol and Nubain (Mechanism of Action)
µ-1 and µ-2 antagonist, κ agonist. Equipotent to morphine. At lower dosing, keeps most of the analgesic effect of morphine while decreasing the pruritus associated with µ-receptor stimulus.
Hydralazine (Dosing)
Gold standard for hypertension as it promotes uterine and renal artery blood flow.
2.5 to 10 mg boluses, 10 to 15 minute onset.
Labetalol (Dosing)
Promotes Uterine Contractions and treats hypertension.
5 to 10 mg IV with 3-5 minute onset
Nipride (Dosing)
Hypertensive Crisis
0.25 to 2 mcg/kg/min
Nitroglycerin Hypertensive Crisis (Dosing)
Hypertensive Crisis
0.5 to 3 mcg/kg/min
Safe (Class B) Anesthetic Drugs
Propofol Desflurane or Sevoflurane Lidocaine or Ropivacaine Demerol Rocuronium or Cis-Atracurium
