NURSING 650 Exam 3 Study Guide

NURS 650 Exam 3 Study Guide I. What does ADME stand for? a. Absorption- i. GI tract 1. pH-dependent passive diffusion and gastric emptying time affect drug absorption a. Full-term newborn gastric acid pH is 6-8, but quickly declines to a pH of 1-3 within 24 hours b. Premature infants’ gastric acid stays elevated due to immature acid secretion c. gastric emptying time is SLOWED in premature infants, so drugs with limited absorption in adults may be efficiently absorbed in premature infants because it stays in contact with GI tract mucosa longer. ii. Intramuscular sites- 1. altered in premature infants (rare use except emergencies & can’t get IV) Premature infants: a. differences in relative muscle mass b. poor perfusion to various muscles c. peripheral vasomotor instability d. insufficient muscular contractions iii. Skin 1. Percutaneous absorption is INCREASED substantially in newborns. a. underdeveloped epidermal barrier called stratum corneum, and increased skin hydration 2. Total body surface area (BSA) to total body weight is highest in the very young. a. increased systemic exposure can be toxic; ex: hexachlorophene soaps & powder, salicylic acid ointment, and RUBBING ALCOHOL Drug Oral absorption (neonate vs. older children & adults) Acetaminophen Decreased Ampicillin Increased Diazepam Normal Digoxin Normal Penicillin G Increased Phenobarbital Decreased Phenytoin Decreased Sulfonamides Normal b. Distribution- determined by physiochemical properties of drugs which are constant, though physiologic functions often very between patient populations. i. Drug distribution in neonate depends on: 1. amount of body water a. Neonates (70%) have more body water than adults (50-60%) b. Full-term: 70-78% body wt is water c. Pre-term: 85% is body water i. ECF volume markedly different in premature infants 1. Pre-term- 50% body wt 2. 4-6-month infants -35% 3. 1 yr old- 25% 4. adults- 19% 2. body fat a. pre-term infants have much LESS fat than full-term b. Lipid soluble drugs may NOT accumulate in preterm 3. drug binding to plasma proteins a. binding of drugs to ALBUMIN is REDUCED b. drug competition for binding albumin may occur i. ex: Aminoglycosides (Tobramycin, Gentamicin, Erythromycin, Azithromycin and more) ii. ex: Volume of distribution of Gentamicin: 0.48L/kg in neonates, but only 0.20L/kg in adults (DOUBLE in neonates vs adults); so double the amount of drug is distributed in tissues rather than in free plasma. 1. higher doses required per kg; Tobramycin distribution volume is largest in most premature infants and decreases with increasing birth weight and gestational age 4. decreased drug binding to plasma proteins in newborns a. many drugs including phenobarbital, salicylates, and phenytoin have significantly LESS plasma protein binding in neonates than adults b. Increased apparent volume of distribution (Vd) i. because of increased Vd, premature infants require a larger loading dose than older children and adults to achieve a therapeutic serum level of drugs such as phenobarbital and phenytoin 5. Increased concentrations of free or unbound drug in the serum and tissues a. Pharmacologic and toxic effects directly related to the free drug concentration can occur ……………………………………..CONTINUED…………………………………..