Based on the information below, what equivalent oral daily dose, in milligrams of theophylline, should the patient receive upon discharge?

Question

The drug aminophylline is 80% theophylline. A patient to be discharged from the hospital has been receiving aminophylline 40 mg/hour by IV infusion. Upon discharge, the physician orders oral theophylline tablets. The pharmacist recognizes that the prescribed tablets have 85% bioavailability. What equivalent oral daily dose, in milligrams of theophylline, should the patient receive upon discharge?

Answer 1

Theophylline is the prescribed drug. We want to identify the correct daily dosage of theophylline to match what was given in the hospital.

To answer this question, we need to use the given information about the % composition theophylline in amino phylline as well as the rate of IV infusion the patient was receiving.

40mg/hour x 24 hours = 960mg per day of aminophylline, which is 80% theophylline. 960 x 0.80 = 768mg of theophylline per day.

The patient was receiving 768mg of theophylline per day while in the hospital. This is what we want to match with the prescribed drug, but the drug has only 85% bioavailability as indicated in the question. So what we need to figure out 85% of what number = 768. A few ways to do this, but easiest way to explain here would be 0.85x = 768 and solve for x. You would need to give about 903.5mg per day of the drug to match the daily dose received at hospital .

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