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Difficulties encountered in controlling theophylline blood concentrations in an asthmatic patient on hemodialysis prompted us to study the effect of hemodialysis on theophylline kinetics. Plasma theophylline extraction ratios, clearances, and half-lives were determined during dialysis for 11 adults given an intravenous infusion of 4 mg/kg aminophylline. For comparison, eight of these patients were evaluated for theophylline half-lives when not dialyzed. Extraction ratios of theophylline during dialysis ranged from 0.22 to 0.51 (0.35 +/- 0.08) for these patients, indicating that a mean of 36 per cent plasma theophylline was removed during each pass through the dialyzer. This compares with a mean extraction ratio of urea of 0.63 +/- 0.07. Plasma clearance of theophylline during dialysis ranged from 52 to 124 ml/min (83 +/ 20 ml/min). Plasma theophylline half-lives during dialysis ranged from 1.6 to 3.4 hours (2.3 +/- 0.5 hours). Theophylline half-lives when not on dialysis ranged from 3.5 to 8.2 hours (5.0 +/- 1.7). Theophylline clearance was significantly faster in every patient during dialysis. Asthmatics requiring hemodialysis should receive additional theophylline during dialysis if therapeutic blood levels are to be maintained. Routine hemodialysis will significantly increase clearance in a toxic patient in whom life-threatening toxicity is occurring and charcoal hemoperfusion is unavailable.

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