Increased urinary recycling decreases elimination rate constant, thus which statement is true?

Increased urinary recycling decreases elimination rate constant, thus which statement is true?

• A. Half life is decreased
• B. Shorter duration of pharmacologic response
• C. Increased therapeutic concentration in the body
• D. All of the above

Answer: (D)

When urinary recycling increases, more drug is reabsorbed and less is excreted, so the elimination rate constant (Ke) drops. The half-life (t1/2) is inversely related to Ke (t1/2 = 0.693/Ke), so a smaller Ke makes the half-life longer. A longer half-life means the drug stays in the body longer, extending the duration of effect. Slower elimination also lowers clearance (CL = Ke × Vd). With the same dose, reduced clearance raises overall exposure (higher AUC) and tends to push plasma concentrations higher, potentially increasing the therapeutic concentration achieved. Therefore, statements about half-life decreasing or the duration of effect shortening are incorrect, while the idea that therapeutic concentration in the body can increase is the true consequence.

When urinary recycling increases, more drug is reabsorbed and less is excreted, so the elimination rate constant (Ke) drops. The half-life (t1/2) is inversely related to Ke (t1/2 = 0.693/Ke), so a smaller Ke makes the half-life longer. A longer half-life means the drug stays in the body longer, extending the duration of effect. Slower elimination also lowers clearance (CL = Ke × Vd). With the same dose, reduced clearance raises overall exposure (higher AUC) and tends to push plasma concentrations higher, potentially increasing the therapeutic concentration achieved. Therefore, statements about half-life decreasing or the duration of effect shortening are incorrect, while the idea that therapeutic concentration in the body can increase is the true consequence.