Effect of using an incorrect elimination rate constant in application of the Wagner–Nelson method to theophylline data in cases of zero order absorption

Some authors have used an elimination rate constant derived from one theophylline treatment (e.g. the elixir) to apply the Wagner–Nelson method to concentration–time data from another treatment (e.g. a sustained‐release form). Since there is considerable intrasubject variation in the elimination rate constant of theophylline such a practice usually involves use of an incorrect rate constant. By means of theoretical treatment and simulations the effects of such a practice are shown and illustrated.