Daily maintenance dose of a long-acting theophylline from a single theophylline serum level

A single point method has recently been described whereby the daily maintenance dose of theophylline required to achieve a desired steady state serum concentration can be established from a nomogram with the aid of a single blood sample drawn after a test dose. This approach has been validated for intravenous administration and for a rapidly absorbed elixir (coefficient of absorption ka 2.3 h-1) given to children. In order to study whether this method could be applied to a slowly absorbed preparation (ka 0.44 h-1), we gave theophylline (Theo-Dur) to nine adults as a single dose and for one week. In applying a nomogram, we found that a sample taken nine hours after a test dose would more accurately predict the daily dose required to achieve a desired steady state concentration than a sample taken at six hours as has previously been recommended (error nine hours -16.8 percent to +29 percent, six hours -59.7 percent to +29.4 percent).