A nurse is reviewing a patient’s medications before administration. Which drug-to-drug interactions will most concern the nurse in a patient with a history of heart failure and a potassium level of 5.5 mEq/L?

Choice A reason: Lipid-soluble drugs cross cell membranes quickly due to their affinity for lipid bilayers, leading to predictable, rapid absorption. Their onset is not unpredictable but typically faster than water-soluble drugs, especially via routes like intravenous or transdermal, making this choice incorrect for lipid-soluble drugs.

Choice B reason: Lipid-soluble drugs, like fentanyl, rapidly cross lipid-rich cell membranes, including the blood-brain barrier, leading to quick onset of action. This is due to their high partition coefficient, allowing fast diffusion into tissues, making rapid effect onset the correct expectation for the nurse.

Choice C reason: Lipid-soluble drugs have faster onset than water-soluble drugs due to easier membrane penetration. Slow effects are more typical of water-soluble or poorly absorbed drugs. Lipid solubility enhances rapid distribution and action, making this choice incorrect for the expected effect timeline.

Choice D reason: Osmosis refers to water movement across membranes, not drug absorption. Lipid-soluble drugs diffuse through lipid bilayers, not via osmosis, which is irrelevant to their pharmacokinetics. This choice is scientifically inaccurate for describing the onset of lipid-soluble drug effects.

Choice A reason: A 25-year-old man typically has mature liver and kidney function, efficiently metabolizing and excreting CNS depressants like benzodiazepines. Toxicity risk is lower compared to neonates, whose immature systems impair drug clearance, making this choice less critical for close toxicity monitoring.

Choice B reason: A 15-year-old boy has relatively mature metabolic pathways, though not fully adult-like. CNS depressants are cleared more effectively than in neonates, reducing toxicity risk. Adolescents are less vulnerable than infants to accumulation, making this choice less concerning for drug toxicity observation.

Choice C reason: A 3-week-old neonate has immature liver enzymes (e.g., CYP450) and reduced renal clearance, increasing the risk of CNS depressant toxicity (e.g., respiratory depression, sedation). Their low body mass and underdeveloped metabolism necessitate close monitoring, making this the correct choice for heightened toxicity vigilance.

Choice D reason: A 25-year-old woman, like men of the same age, typically has efficient drug metabolism and excretion. CNS depressants pose lower toxicity risk compared to neonates, whose immature systems lead to drug accumulation, making this choice less critical for close toxicity monitoring.