Early estimate of theophylline clearance during intravenous infusion

We examined two rapid methods of measuring theophylline clearance using pairs of serum concentration measurements, and compared them with the steady-state values in 31 patients with acute asthma. A constant intravenous aminophylline infusion was started at a rate given by current guidelines. Theophylline clearance was estimated from two serum measurements made with an interval of at least 4 h, providing clearance estimates 5 h from commencement. Duplicate estimates were made, using either a 3rd serum measurement at 12 h or a 3rd and 4th at 7 and 14 h. A steady-state estimate was finally made after 48 h constant infusion. The two rapid estimates agreed well both between themselves and with the steady-state determination despite wide variations in the clinical status of the patients. These methods provide a rapid means of monitoring dosage in the individual patient. This is particularly important when the predicted dose is inappropriate.