Chapter 52: Pregnancy & Preterm Labor Drug Therapy

Pregnancy & Preterm Labor Drug Therapy begins by exploring the unique physiology of drug use during pregnancy, detailing how hormonal changes affecting liver metabolism, reduced gastrointestinal motility, increased glomerular filtration rates, and expanded blood volume alter pharmacokinetics. The text clarifies that the placenta acts as an organ of exchange rather than a barrier, allowing drug transfer based on molecular weight, ionization, and protein binding. A significant portion of the chapter is dedicated to nutritional supplementation, specifically the administration of iron to prevent maternal anemia and folic acid to avert neural tube defects like spina bifida, including specific instructions on maximizing iron absorption with Vitamin C while avoiding antacids and milk. The summary covers the management of minor pregnancy discomforts, outlining the hierarchy of treatment for nausea and vomiting (starting with nonpharmacologic measures and progressing to pyridoxine/vitamin B6 and doxylamine), heartburn (utilizing aluminum and magnesium-based antacids), and constipation (favoring bulk-forming agents and docusate sodium). Pain management is critically reviewed, identifying acetaminophen as the safest analgesic while strictly warning against aspirin and ibuprofen in the third trimester due to risks of premature closure of the ductus arteriosus and hemorrhage. The discussion transitions to high-risk complications, specifically Preterm Labor (PTL), detailing tocolytic therapies used to delay birth. This includes the off-label use of beta-sympathomimetics like terbutaline (noting the Black Box warning regarding maternal cardiac risks with prolonged use) and magnesium sulfate, which serves as both a tocolytic and a neuroprotective agent. The essential role of antenatal corticosteroids, such as betamethasone and dexamethasone, in accelerating fetal lung maturity and surfactant production to prevent respiratory distress syndrome is also explained. Finally, the chapter addresses gestational hypertension and preeclampsia, describing the pathophysiology of vasospasm and the use of antihypertensives like methyldopa, hydralazine, and labetalol. It provides a comprehensive protocol for using magnesium sulfate to prevent eclamptic seizures, stressing the importance of nursing assessments for toxicity—such as respiratory depression and absent deep tendon reflexes—and the immediate availability of the antidote, calcium gluconate.