Question

A target plasma theophylline concentration (TC) of 10 mg/L is desired to relieve acute bronchial asthma in a patient. The patient is a nonsmoker and otherwise normal except for asthma. The Vd (volume of distribution) of theophylline is 35L and the mean clearance (Cl) is 2.8L/h for a 70kg man. The oral bioavailability (F) is 0.96. If the drug is taken twice a day, calculate its loading and maintenance doses.

Answer 1

To calculate the loading dose, multiply the target concentration by the volume of distribution. To calculate the maintenance dose, multiply the target concentration by the clearance, dosing interval, and divide by the oral bioavailability.

Step-by-step explanation:

To calculate the loading and maintenance doses of theophylline, we need to consider the target plasma concentration, volume of distribution (Vd), clearance (Cl), and oral bioavailability (F).

The loading dose is a one-time dose administered to quickly achieve the desired plasma concentration. To calculate the loading dose, we use the formula: Loading dose = TC * Vd, where TC is the target concentration and Vd is the volume of distribution. In this case, the loading dose would be 10 mg/L * 35 L = 350 mg.

The maintenance dose is the dose that needs to be administered regularly to maintain the desired plasma concentration. To calculate the maintenance dose, we use the formula: Maintenance dose = TC * Cl * dosing interval / F, where dosing interval is the time between doses. In this case, the dosing interval is twice a day, so the maintenance dose would be 10 mg/L * 2.8 L/h * 12 h / 0.96 = 290 mg per dose.