PA 5111: Factors Affecting Drug Action - Pharmacokinetics and Teratology

Comprehensive vocabulary flashcards covering the pharmacokinetics of special populations (pediatric, geriatric, sex-related, pregnancy-induced changes), common teratogenic agents, and old vs. new FDA pregnancy risk classification systems from PA 5111 Pharmacology.

Minimum Effective Concentration (MEC)

The lowest plasma concentration of a drug required to produce the desired therapeutic effect.

Maximum Tolerated Concentration (MTC)

Also termed the minimum toxic concentration; the highest plasma concentration of a drug that can be tolerated without producing dose-limiting toxicity.

Elimination Half-Life ($t_{1/2}$)

The time required for the plasma concentration of a drug to decrease by half through metabolism and excretion.

Pediatric Pharmacokinetic Characteristics

Physiological traits in newborns and children that alter drug response, including immature metabolic and elimination systems, an incomplete blood-brain barrier, immature hepatic enzymes, a higher body water percentage, and susceptibility to drug-induced growth impacts.

Geriatric Pharmacokinetic Alterations

Age-related physiological changes that typically necessitate lower drug doses, including reduced renal clearance, decreased hepatic blood flow, altered body composition (reduced muscle mass and increased adipose tissue), heightened central nervous system sensitivity, and elevated risk of orthostatic hypotension.

Sex-Based Differences in Drug Distribution

Females typically possess a higher percentage of body fat and lower body water content than males of similar weight, resulting in an increased volume of distribution for lipophilic drugs.

Sex-Based Metabolic Variations

The slower metabolic clearance observed in females compared to males for specific substances, including opioids, alcohol, diazepam, and zolpidem, often requiring doses at the lower end of the recommended range.

Gastrointestinal Changes in Pregnancy

Pharmacokinetic alterations beginning in the first trimester and peaking in the second trimester, characterized by nausea and vomiting (mediated by hCG), progesterone-induced delayed gastric emptying, and increased gastric pH, all of which alter drug absorption.

Hemodynamic and Volume Changes in Pregnancy

Physiological expansions where maternal plasma volume, cardiac output, and glomerular filtration rate increase by $30\%$ to $50\%$ or higher, which can significantly reduce the plasma concentrations of renally eliminated drugs.

Protein Binding Changes in Pregnancy

A physiological reduction in plasma albumin concentrations that increases the free (unbound) fraction of highly protein-bound medications, accompanied by enhanced hepatic and renal clearance that typically results in minimal net change in total drug concentration.

Pregnancy-Induced Hepatic Enzyme Changes

Differential shifts in cytochrome P450 enzyme activity during pregnancy, specifically involving increased activity of CYP3A4, CYP2C9, and CYP2D6 (leading to faster metabolism) alongside decreased activity of CYP1A2 and CYP2C19 (leading to slower metabolism).

Renal Clearance Changes in Pregnancy

An approximate $50\%$ increase in glomerular filtration rate (GFR) and elevated renal blood flow during gestation that shortens the elimination half-life of renally excreted medications (such as ampicillin and penicillins), often requiring increased dosing frequency.

Lamotrigine (LTG) Clearance in Pregnancy

An antiepileptic drug whose clearance increases significantly due to elevated sex steroids stimulating Phase II glucuronidation, potentially dropping plasma levels by $50\%$ during pregnancy and causing rapid rebound toxicity postpartum as clearance normalizes within days.

Valproic Acid (VPA) Monitoring in Pregnancy

An antiepileptic agent whose total plasma concentration can drop by as much as $50\%$ during pregnancy; guidelines recommend monthly monitoring of free and total plasma concentrations and maintaining doses preferably below $1000\,\text{mg/d}$ to minimize congenital malformation risks.

Teratogen

Any substance capable of producing structural, physical, or functional defects in an embryo or fetus following maternal exposure during pregnancy.

Congenital Abnormalities Etiology

The distribution of known and unknown causes of human birth defects, consisting of $80\%$ unknown etiology and $20\%$ known etiology (comprising $15\%$ chromosomal abnormalities, $4\%$ genetic abnormalities, $1\%$ teratogens, and $0\%$ twinning).

Determinants of Placental Drug Transfer

Physicochemical properties dictating maternal-fetal exchange across placental membranes: low molecular weight ($< 500\,\text{Da}$), high lipid solubility, unionized electrical state (determined by pKa and maternal-fetal pH), and low maternal protein binding.

Organogenesis Window of Vulnerability

The critical developmental timeframe spanning the first $6\text{ to }8\,\text{weeks}$ of gestation (within the first trimester) during which embryonic tissues are most susceptible to major structural malformations, carcinogen-induced cancer, or miscarriage.

Fetal Period Exposure Effects

Teratogenic insults occurring during the second and third trimesters that typically do not cause major gross structural malformations but result in growth retardation, functional defects, central nervous system abnormalities, or fetal demise.

Phocomelia

A severe congenital malformation involving the extreme shortening or absence of the long bones of the limbs (producing flipper-like appendages), classically induced by maternal exposure to thalidomide, lenalidomide, or leflunomide.

Fetal Warfarin Syndrome

A constellation of teratogenic anomalies resulting from in utero warfarin exposure, characterized by stippled calcification of the epiphyses, nasal hypoplasia, skeletal defects, low birth weight, developmental delay, deafness, and central nervous system or eye malformations.

Fetal Hydantoin Syndrome

A congenital disorder caused by gestational phenytoin exposure characterized by intrauterine growth restriction, microcephaly, craniofacial dysmorphisms (saddle nose, smooth philtrum, thin upper lip, cleft lip/palate), hypoplastic nails and distal phalanges, and cardiac anomalies.

ACE Inhibitor Fetopathy

Adverse fetal outcomes associated with angiotensin-converting enzyme inhibitor use during pregnancy, resulting from fetal hypotension and renal hypoperfusion, leading to renal hypoplasia, growth retardation, and fetal demise.

Retinoid Embryopathy

A pattern of severe congenital malformations linked to isotretinoin or topical retinoid exposure, including neural tube defects, exencephaly, spina bifida with meningocele, hydrocephalus, cleft palate, microtia/anotia, and conotruncal cardiovascular transposition.

Thionamide Teratogenicity (Methimazole / Propylthiouracil)

Adverse gestational drug effects manifesting as fetal goiter, hypothyroidism, choanal or esophageal atresia, and aplasia cutis (congenital absence of skin layers, most frequently localized to the scalp).

Quinolone-Induced Fetotoxicity

Adverse developmental effects from fluoroquinolone antibiotic exposure during pregnancy, notably damage to articular cartilage and impairment of fetal limb development.

Tetracycline Teratogenicity

Gestational toxicities involving permanent discoloration of teeth and bones, tooth enamel hypoplasia, and dose-dependent suppression of fetal skeletal bone growth.

NSAID Risks in Pregnancy

Adverse fetal and maternal outcomes resulting from second- and third-trimester NSAID use, including premature closure of the fetal ductus arteriosus, pulmonary hypertension, fetal renal impairment, oligohydramnios, platelet inhibition/intracranial hemorrhage, and prolonged labor.

Old FDA Pregnancy Category A

The classification assigned when adequate, well-controlled studies in pregnant women and animal models fail to demonstrate a risk to the fetus in the first trimester, rendering the possibility of fetal harm remote.

Old FDA Pregnancy Category B

The classification assigned when animal reproduction studies show no fetal risk without confirmed human studies, or when animal studies demonstrate an adverse effect that was not confirmed in controlled studies of pregnant women in their first trimester.

Old FDA Pregnancy Category C

The classification where animal reproduction studies show adverse fetal effects and adequate human studies are lacking, or no animal/human studies exist; the drug is given only if potential maternal benefits justify potential fetal risks.

Old FDA Pregnancy Category D

The classification indicating positive investigational or post-marketing human evidence of fetal risk exists, but potential clinical benefits may warrant use in pregnant women facing serious or life-threatening situations.

Old FDA Pregnancy Category X

The classification assigned when animal or human studies demonstrate definite fetal abnormalities or teratogenicity, rendering the agent strictly contraindicated for use in pregnancy under any clinical circumstance.

Prescription Drug Labeling Subsection 8.1 (Pregnancy)

The FDA Pregnancy and Lactation Labeling Rule (PLLR) section replacing letter categories; incorporates labor and delivery, provides an evidence-based pregnancy risk summary, clinical considerations, maternal and fetal adverse reactions, disease risks, dosing adjustments, and pregnancy exposure registry contact information.

Prescription Drug Labeling Subsection 8.2 (Lactation)

The PLLR section replacing 'Nursing Mothers' that outlines whether a drug and its metabolites are excreted in human breast milk, the potential effects on the breastfed infant, impacts on maternal milk production, and practical interventions to minimize infant exposure.

Prescription Drug Labeling Subsection 8.3 (Females and Males of Reproductive Potential)

The new PLLR subsection introduced in 2015 detailing drug effects on fertility, along with explicit clinical requirements for baseline pregnancy testing and recommended contraception usage.