Intrinsic factors for unbound theophylline.

The developmental changes of the ratio of unbound theophylline to total serum concentration have been demonstrated, suggesting clinical usefulness. However, the molecules that can replace the theophylline binding sites of albumin could influence theophylline-binding affinity. We evaluated the intrinsic factors influencing the unbound theophylline ratio. The results suggested that physicians should note that a more intense response might be obtained in children with various intrinsic factors even at the same total theophylline concentration.