Clinical and pharmacological observations on a new microcrystalline theophylline preparation.

Tablets containing 250 mg of microcrystalline theophylline were given at 6-hourly intervals for 6 days. Minimum plasma theophylline concentrations in eight patients averaged 36.6 +/- 5.4 mumol/l (1 mumol = 0.18 mg), and the corresponding maximum concentration were 81.8 +/- 10.6 mumol/l. In 11 patients, studied after a single 250 mg dose, significant improvements in PEF and FEV1 were observed, in spite of maximum concentrations averaging only 38.8 +/- 2.2 mumol/l, which is below the commonly regarded lower limits of the therapeutic range. Nine of the 11 patients complained of side effects and in three patients a reduction in dose was necessary. In four volunteers given a single dose of 250 mg the plasma concentration of theophylline were not particularly affected by whether the tablets were taken fasting or postprandial.