Volume of distribution of theophylline in acute exacerbations of reversible airway disease. Effect of body weight.
The literature is unclear as to whether theophylline loading doses should be based on total body weight (TBW) or ideal body weight (IBW). The objective of this study was to determine the most appropriate body weight for estimation of volume of distribution (Vd) in calculating theophylline loading dose in patients with acute bronchospasm. Fifty-four adult patients with acute bronchospasm requiring intravenous (IV) theophylline therapy were entered into the study. Patients were randomized into three theophylline loading dose groups based on (1) TBW, (2) IBW, and (3) adjusted body weight (ABW). Initial serum theophylline concentrations were used to determine an IV loading dose to reach a plasma concentration of 12 to 15 micrograms/ml. Percent prediction error was used to determine the appropriateness of each dosing group. Volumes of distribution were also determined for each group. There was a statistically significant difference at p less than 0.01 in the percent prediction error when patients in the TBW group were compared to the IBW and ABW groups. A statistically significant difference in the Vd was observed between the TBW and IBW group (p less than 0.01). We conclude that IBW is more appropriate than TBW or ABW for determining theophylline loading dose in patients with acute bronchospasm.