Question: A patient is begun on a continuous infusion of theophylline for treatment of refractory status asthmaticus. The patient accidentally receives the theophylline for 1 hr at a rate of 80 mg/hour; 12 hours later she is noted to be experiencing apparent theophylline toxicities and a serum concentration is measured and found to be 36 mg/L. If the half- life of theophylline is 6 hours in this patient, how long will it take for the patient to reach a "nontoxic" concentration of 20 mg/L once the infusion is discontinued?