Pharmacokinetic changes in children that affect drug dosing include:

Correct Answer: D

Rationale: Choice D is correct because children have higher gastric pH (affects absorption), slower liver metabolism (prolongs drug action), and more body water (alters distribution), all impacting dosing per pediatric pharmacology. Choice A is incorrect alone as pH is one factor. Choice B is wrong by itself because metabolism is just part. Choice C is incorrect solo since body water is only one aspect.

Correct Answer: A

Rationale: Choice A is correct because protein intake affects albumin levels, altering drug binding and free drug availability, directly impacting action. Choice B is incorrect as iron intake influences absorption of some drugs (e.g., tetracyclines), not action broadly. Choice C is wrong because vitamin D affects bone health, not drug action directly. Choice D is incorrect since only protein has a widespread pharmacokinetic impact.

Correct Answer: B

Rationale: Choice B is correct because St John's wort induces P-glycoprotein and CYP3A4, reducing digoxin levels and efficacy, a significant interaction. Choice A is incorrect as ginkgo biloba doesn't notably affect digoxin. Choice C is wrong because valerian root has minimal impact on digoxin pharmacokinetics. Choice D is incorrect since only St John's wort interacts markedly.

Correct Answer: B

Rationale: Choice B is correct because Schedule III drugs (e.g., anabolic steroids) have moderate abuse potential, less than Schedule II, with medical use, per DEA. Choice A is incorrect as high potential is Schedule II. Choice C is wrong because low potential is Schedule IV. Choice D is incorrect since only B applies.

Correct Answer: C

Rationale: The correct answer is C because preterm infants (32-35 weeks) under 3 months at RSV season start need three Synagis doses. Choice A is incorrect (one dose insufficient). Choice B is wrong (prophylaxis indicated). Choice D is inaccurate (three doses, not until April).

Correct Answer: A

Rationale: Choice A is correct because protein intake affects albumin levels, altering drug binding and free drug availability, directly impacting action. Choice B is incorrect as iron intake influences absorption of some drugs (e.g., tetracyclines), not action broadly. Choice C is wrong because vitamin D affects bone health, not drug action directly. Choice D is incorrect since only protein has a widespread pharmacokinetic impact.

Correct Answer: C

Rationale: The correct answer is C because a higher concentration (500 mg/5 mL) and bid dosing simplifies administration, enhancing compliance. Choice A is incorrect (lower concentration, less convenient). Choice B is wrong (tid less convenient). Choice D is inaccurate (tid and lower dose inconvenient).

Correct Answer: B

Rationale: The correct answer is B because pharmacokinetics studies how the body processes drugs, including excretion affected by age, race, and gender. Choice A is incorrect as bioavailability focuses on drug availability, not excretion. Choice C is wrong since pharmacodynamics studies drug effects, not excretion. Choice D is inaccurate as it’s too broad and not specific to drug processing.

Correct Answer: B

Rationale: Choice B is correct because codeine is a prodrug activated by CYP2D6 into morphine for pain relief; genetic variants affect its efficacy or safety. Choice A is incorrect as acetaminophen isn't activated by CYP2D6—it's metabolized differently. Choice C is wrong because ibuprofen doesn't require CYP2D6 activation—it's active as administered. Choice D is incorrect since only codeine relies on this enzyme for activation.