Pharmacokinetics>Pk Parameter Calculation Practice Test

A 65-year-old man (80 kg, 176 cm) in the ICU is receiving a continuous IV infusion of theophylline at 40 mg/hr for COPD exacerbation. Liver enzymes are normal; SCr is 0.9 mg/dL; albumin 4.0 g/dL; vitals stable. After 48 hours of therapy, a steady-state serum theophylline concentration is reported as 10 mg/L (average concentration). No interacting medications are present. Assume one-compartment, linear kinetics and complete distribution at steady state. Based on the infusion rate and steady-state concentration, the drug's clearance can be determined.

A 62-year-old man (92 kg) with normal renal function is being treated with IV tobramycin for a gram-negative pneumonia. At steady state, two post-distribution serum concentrations were obtained 8 hours apart: 12 mg/L followed by 3 mg/L. No other nephrotoxic or interacting drugs are being administered, and the patient is hemodynamically stable. Assume one-compartment, first-order elimination and that distribution is complete for both samples. Calculate the drug's elimination half-life using these data.