Poblaciones especiales: embarazo

Pharmacokinetics in Pregnancy and Lactation
📌 Physiological modifications during pregnancy alter pharmacokinetic parameters, though the clinical implication of these changes is often limited due to lack of robust studies.
💧 Increased plasma volume (up to 50% in the third trimester) and cardiac output (up to 30%) affect drug distribution.
📉 Serum albumin decreases by 80%, which can lead to an overestimation of the free, active drug concentration if plasma monitoring is performed without considering current protein levels.
⬆️ Renal excretion is affected, with glomerular filtration increasing up to 50% in the first trimester, necessitating dose adjustments for renally excreted drugs.

Placental Transfer and Fetal Risk
🔑 The primary determinant of fetal drug risk is placental passage, influenced by the placenta's surface area, thickness, integrity, and blood flow.
⚖️ Drugs with lower molecular weight, high liposolubility, and low protein binding tend to pass the placenta more easily.
⚖️ Fetal pH is slightly lower ($\text{pH}_{\text{fetal}} \approx \text{pH}_{\text{maternal}} - 0.1$), favoring the passage and accumulation of basic drugs.

Drug Use in Pregnancy and Teratogenicity
⚠️ The popular myth that pregnant women should use no medications is false; studies show high consumption rates, with one local study indicating 83.3% usage among pregnant women.
💊 Essential medications like folic acid and iron should be administered preconceptionally/early in pregnancy and throughout, though proper adherence (e.g., 50% not receiving folic acid 12 weeks prior) is often lacking.
❌ Teratogenicity is defined as adverse morphological or biochemical effects during fetal life, depending on genetic susceptibility, dose, mechanism, and developmental phase (organogenesis occurs in the first trimester).
🚫 The historical FDA category system (A, B, C, D, X) is considered obsolete since 2015 because it lacks clinical context, doesn't account for dose-dependency, and groups disparate risks together (e.g., Thalidomide was category B).

Drug Selection and Risk-Benefit Analysis
⚖️ Prescribing during pregnancy often means prescribing without conclusive evidence; a rational approach requires an individual risk-benefit balance.
✅ For chronic conditions like asthma or autoimmune diseases requiring corticosteroids, the risk of untreated disease often outweighs potential fetal risks, necessitating careful drug selection (e.g., choosing corticosteroids inactivated by the placenta like prednisone if only maternal effect is desired).
🚫 Medications without proven efficacy, such as antitussives, should generally be avoided regardless of safety profile due to lack of demonstrated benefit.
🛡️ When selecting drugs, use those with the longest clinical experience; for instance, Omeprazole (Category C by old FDA standards) is preferred over more expensive, newer proton pump inhibitors (Category B) due to extensive safety data.

Lactation Considerations
🍼 Generally, less than 2% of the maternal drug concentration passes into breast milk, but specific drug characteristics, transport systems, and infant elimination capacity matter.
🤱 To minimize infant exposure, it is recommended to breastfeed prior to the next drug dose.
👶 Preterm infants have a reduced capacity to eliminate many drugs, requiring caution even if the drug transfers minimally to milk.
🚫 Radioactive compounds are a mandatory exception requiring cessation of breastfeeding.

Key Points & Insights
➡️ Avoid self-medication in pregnant women, as no drug is entirely innocuous, demanding careful individual risk-benefit assessment.
➡️ Prioritize using drugs with greater clinical experience over newer agents when efficacy and safety profiles are being weighed.
➡️ When choosing medications like corticosteroids for maternal conditions, select agents that are inactivated by the placenta (e.g., prednisone) if the desired therapeutic effect is not intended for the fetus.
➡️ For conditions requiring chronic medication like epilepsy, continue treatment, aim for monotherapy at the lowest effective dose, and avoid polytherapy; consider higher folic acid doses for neural tube defect prophylaxis.

📸 Video summarized with SummaryTube.com on Mar 07, 2026, 21:18 UTC