The following drugs have an elimination half-life of less than 4 hours in a healthy adult:

Correct Answer: A

Rationale: Dopamine (A) has a half-life <4 h (~2 min), used IV for rapid hemodynamic effects. Heparin (B) is ~1-2 h, also correct but A is chosen. Amiodarone (C) is weeks-long. Gentamicin (D) is ~2-3 h, close. Diazepam (original E) is ~20-70 h. Short half-lives like dopamine's enable tight control in critical care, contrasting long-acting drugs, a key pharmacokinetic trait for acute interventions, requiring frequent dosing or infusion.

Correct Answer: A

Rationale: Potassium chloride (A) commonly causes phlebitis IV due to its high osmolarity and irritation (e.g., >10 mEq/L), requiring dilution. Hydrocortisone (B) and diazepam (C) can irritate but less so. 50\% glucose (D) is hypertonic, also correct but A is chosen. 5\% glucose (original E) is isotonic. Phlebitis risk, critical in IV therapy, demands careful administration (e.g., central lines), minimizing vascular damage, a key consideration in hospital settings.

Correct Answer: D

Rationale: Amitriptyline (D) decreases gastric emptying via anticholinergic effects, delaying absorption (e.g., of co-drugs). Aspirin overdose (A) may slow it, correct but D is chosen. Migraine (B) does too. Fluoxetine (C) has minimal effect. Metoclopramide (original E) increases it. Slowed emptying, critical in pharmacokinetics, alters drug onset, a key factor in tricyclic antidepressant use, impacting bioavailability.

Correct Answer: C

Rationale: Drugs reducing placental blood flow (e.g., NSAIDs) can lower birth weight (C), impairing fetal nutrient delivery. Option A is false (passive diffusion dominates). Option B is incorrect (un-ionized cross better). Option D is wrong (BBB forms early). Option E (original) is true (placenta metabolizes steroids). Placental flow effects, critical in pharmacology, highlight drug safety, impacting fetal growth, a key pregnancy consideration.

Correct Answer: B

Rationale: In pharmacology, drug clearance refers to the volume of blood or plasma that is completely cleared of a drug per unit time. Option B is the correct answer because when the extraction ratio (the fraction of drug removed by an organ during a single pass) is less than 0.2, the clearance is primarily enzyme-dependent. This means that the drug is not efficiently removed by the organ and depends more on enzymatic metabolism for clearance. Option A is incorrect because drug clearance is not directly used in the calculation of loading doses; rather, it helps in determining the maintenance dose. Option C is incorrect as clearance is directly proportional, not inversely proportional, to the blood flow to the clearing organ. The higher the blood flow, the higher the clearance. Option D is incorrect because lipid solubility generally decreases renal excretion of drugs by promoting reabsorption in the renal tubules rather than increasing excretion. Understanding drug clearance is crucial in pharmacology as it influences dosing regimens, drug interactions, and overall drug efficacy and safety. Knowing how different factors affect drug clearance helps healthcare professionals optimize drug therapy for individual patients based on their pharmacokinetic profile.