Pharmacokinetics of theophylline in relation to increased pain sensitivity in the rat

In the rat, theophylline increases, in proportion to dose, the sensitivity to painful stimulation. A study of the pharmacological registration of this property combined with the determination of drug levels in plasma indicated that theophylline behaves according to a two-compartment open model. By relating the pharmacological activities to the drug level data using different pharmacokinetic types of calculation, it was concluded that the site of action of theophylline in the central nervous system lies closer to the central (plasma) compartment than to the peripheral one. The registered pharmacological effects of theophylline are thus directly reflected by the plasma concentration of this drug.