Antiemetics, Obstetrics, Dexamethasone

Question 1

oxytocin (MOA, SEs, dosing)

Answer 1

MOA: (octapeptide) lowers depolarization threshold for uterine smooth muscle - ↑ activation of Ca++ channels, ↑ prostaglandin production
Indications: 1st-line tx of uterine atony following fundal massage, or prophylactically to reduce blood loss after delivery, uterotonic
Contraindications:
SEs: synthetic oxytocin causes less SEs than endogenous oxytocin (related to ADH).
Causes vasodilation or ↓ SVR, which can result in significant hypotension/tachycardia (mostly with boluses, so just don’t do that and you’ll avoid these SEs)
Dosing: 20-40 units/L of isotonic solution, over 15-20 minutes
“As soon as the cord is cut, you start the gtt. The goal is to make sure you get good uterine contraction so that you stop bleeding post-delivery.

Question 2

hemabate (MOA, SEs, dosing)

Answer 2

MOA: (Prostaglandin) - ↑myometrial Ca++ levels and increases MLCK (myosin light-chain kinase activity) and causes uterine contraction (↓s need for postop hysterectomy d/t uterine atony)
Indications: 80-90% effective in PPH refractory to oxytocin and ergot alkaloids, uterotonic
Contraindications: “Detrimental SEs” -
SEs: (listed for carboprost – which was in the same class) if used in reactive AW disease women, can cause bronchospasm, ventilation-perfusion mismatch and hypoxemia, so use misoprostol instead
Dosing: 250 mcg IM (or DIRECTLY INTO THE MYOMETRIUM OH GOD), q15-30 minutes, total dose 2 mg (so 8 possible doses)

Question 3

methergine (MOA, SEs, dosing)

Answer 3

“Methergine, ergot I-M”
MOA: (ergot alkaloid uterotonic) – MOA unclear but “α-adrenergic effect”
Indications: uterotonic - tx for uterine atony. WANT a contraction. Decrease postpartum blood loss and PPH (but tetanic uterine contractions restricts their use postdelivery)
Contraindications: HTN (preexisting/chronic or pregnancy-induced), PVD, ischemic heart dz (r/f MI)
SEs: (Need vasodilating drugs nearby), N/V (effect on vomiting ctr), usually give BP meds rather than Zofran bc hypotension is usually causing the nausea
Dosing: 0.2 mg IM q15 minutes, total 0.8 mg (so 4 possible doses) – never give IV!!

Question 4

zofran (MOA, SEs)

Answer 4

MOA: selective Serotonin Type 3 (5-HT3) receptor Antagonist. Inhibit the stimulation of 5HT3 receptors are gated Na+/K+ channels in the CNS and PNS, which work on the chemoreceptor trigger zone of the area postrema and NTS
Dosing: 4 or 8 mg IV or SL
SEs: headache, prolonged QTc

Question 5

promethazine / Phenergan (MOA, SEs)

Answer 5

MOA: H1 antagonist, muscarinic blocker
Dosing: IM preferred (bc IV is a vesicant) 12.5 mg q4-6hr

Clinical pearls
● CONTRAINDICATIONS: >65 yo pts (confusion)
● Can cause significant sedation, esp w/opioids

Question 6

metoclopraminde / Reglan (MOA, SEs)

Answer 6

MOA: centrally acting dopamine (D2) receptor antagonist in CTZ/vomiting center, peripherally acting as cholinomimetic in GI tract – facilitates ACh transmission at muscarinic receptors (prokinetic - increases gastric motility, increase lower esophageal sphincter tone) – can pee, can spit, can shit
Dosing: 10 mg IV, or 0.1-0.25 mg/kg IV q6-8 hours
Can be given PO, IVP, IV infusion or IM
SEs: rapid injection  abdominal cramping! Too much GI motility haha.

Question 7

dexamethazone (decadron)

Answer 7

MOA: stimulates changes in transcription of 456 DNA, changes synthesis of proteins. Target cells have 11 B-hydroxylase
hydroxysteroid dehydrogenase
Indications: antiemetic, immunosuppression, decreasing post-intubation laryngeal edema
Stress Dosing: 0.75 mg IV

Don’t actually know the stress dose bc we were given stress doses using hydrocortisone, 25 mg IV for minor surgery, 50-75 mg for moderate surgery (colon resxn, hip repl), and 100-150 mg for major surgery. Hydrocortisone = cortisol. 20 mg hydrocortisone = 0.75 mg dexamethasone