Early estimate of theophylline clearance during intravenous infusion

Wc cxamined two rapid methods of mcasuring thcophyllinc clcarancc using pairs of serum conccntration mcasurcments, and compared them with thc stcady-statc values in 31 patients with acute asthma. A constant intravenous aminophyllinc infusion was started at a rate given by current guidelines. Thcophyllinc clcarance was estimated from two scrum mcasurcmcnts madc with an intcrval of a t least 4 h, providing clcarancc estimatcs 5 h from commencement. Duplicate estimate;$ wcrc madc, using either a 3rd serum measurcment at 12 h or a 3rd and 4th at 7 and 14 h. A steady-state estimate was finally made aftcr 48 h constant infusion. Thc two rapid estimatcs agrccd well both between themselves and with the steady-statc dctcnnination despite wide variations in the clinical status of thc paticnts. These methods provide a rapid means ofmonitoring dosage in the individuai patient. This is partieularly important when the predieted dose is inappropriate.