Pharmacokinetics

Which of the following best describes the relationship between plasma protein binding and drug distribution volume (Vd)?

Which of the following drugs exhibits zero-order kinetics at therapeutic concentrations?

A 48-year-old woman with hepatic cirrhosis (Child-Pugh score 10) is prescribed warfarin 5 mg daily for atrial fibrillation. Her INR after 5 days is 4.8 (therapeutic range 2–3). She has normal renal function. Which pharmacokinetic mechanism best explains her exaggerated response to warfarin?

A 35-year-old man with obesity (BMI 38 kg/m²) and type 2 diabetes is started on metformin 500 mg twice daily. After 2 weeks, his plasma metformin concentration is lower than expected, and glycemic control is suboptimal. His renal function is normal (eGFR 95 mL/min/1.73m²). Which pharmacokinetic parameter is most likely responsible for the lower-than-expected plasma concentration?

A 62-year-old man with chronic kidney disease (eGFR 25 mL/min/1.73m²) is prescribed gentamicin 80 mg IV for a urinary tract infection. His serum creatinine is 3.2 mg/dL. On day 3 of therapy, his serum gentamicin peak level is 8 µg/mL (normal peak 4–10 µg/mL) but trough is 2.5 µg/mL (normal trough <2 µg/mL). Which pharmacokinetic parameter is primarily altered in this patient, leading to drug accumulation?