The loading dose (D_L) of a drug is usually based on the

Correct Answer: D

Rationale: The loading dose (D_L) is based on the apparent volume of distribution (V_D) and desired plasma concentration (D), calculated as D_L = V_D × C_p, ensuring rapid therapeutic levels (e.g., digoxin). Clearance (A) affects maintenance, not loading. Protein binding (B) and urinary excretion (C) influence free drug but aren't primary. AUC (original E) is outcome-based. V_D reflects tissue distribution, critical for initial dosing in drugs with large V_D, balancing speed and safety.

Correct Answer: A

Rationale: Hydrolases (A) uncouple peptide linkages, cleaving bonds with water (e.g., pepsin in digestion), breaking proteins into amino acids. Ligases (B) form bonds. Oxidoreductases (C) handle redox. Transferases (D) move groups. Isomerases (original E) rearrange. Hydrolases' role in proteolysis impacts drug metabolism (e.g., prodrugs like enalapril) and digestion, central to biochemistry and pharmacology, affecting bioavailability and clearance.

Correct Answer: A

Rationale: IgG (A) has the longest serum half-life (~21 days) and opsonizes antigens via Fc receptors and complement activation, enhancing phagocytosis (e.g., bacterial clearance). IgM (B) is short-lived, pentameric. IgA (C) protects mucosae. IgE (D) drives allergies. No original E. IgG's persistence and dual opsonization (FcγR and C3b) make it key in immunity and monoclonal antibody drugs (e.g., rituximab), impacting pharmacokinetics and therapeutic longevity.

Correct Answer: B

Rationale: Diazepam (B) does not undergo hydrolysis; it's metabolized by CYP450 oxidation and glucuronidation (e.g., to nordazepam). Procaine (A), aspirin (C), and lidocaine (D) hydrolyze via esterases (e.g., procaine to PABA), cleaving ester bonds. No original E. Hydrolysis, a phase I reaction, increases polarity for excretion, but diazepam's oxidative path prolongs its action, impacting its use as a long-acting anxiolytic, distinct in metabolism profiles.

Correct Answer: C

Rationale: ⁹⁹ᵐTc (C) is most commonly used in nuclear pharmacy, a gamma-emitter (t₁/₂ 6h) ideal for imaging (e.g., bone scans), produced via generators. ⁶⁷Ga (A) is for infection. ²⁰¹Tl (B) is cardiac-specific. ¹²³I (D) and ¹³³Xe (original E) are less versatile. Tc-99m's short half-life and gamma emission suit diagnostics, dominating nuclear medicine for its availability and imaging clarity, a staple in radiopharmaceuticals.