Relative bioavailability of sodium cromoglycate to the lung following inhalation, using urinary excretion

Aims To determine if a urinary excretion method, previously described for s albutamol, could also indicate the relative bioavailability of sodium cromo glycate to the lung following inhalation from a metered dose inhaler. Method Inhaled (INH), inhaled + oral charcoal (INHC), oral (ORAL) and oral + oral charcoal (ORALC) 20 mg doses of sodium cromoglycate were given via a randomised cross-over design to 11 healthy volunteers trained on how to us e a metered dose inhaler. Urine samples were collected at 0.0, 0.5, 1.0 and up to 24 h post dosing and the sodium cromoglycate urinary concentration w as measured using a high performance liquid chromatographic method. Results No sodium cromoglycate was detected in the urine up to 24 h followi ng ORALC dosing. A mean (s.d.) of 3.6 (4.3) mu g, 10.4 (10.9) mu g and 83.7 (71.1) mu g of the ORAL dose was excreted, in the urine, during the 0.5, 1 .0 and 24 h post dose collection periods, respectively. Following INH dosin g, the renal excretion was significantly higher (P<0.01) with 32.9 (14.5) m u g, 61.2 (28.3) mu g and 305.6 (82.3) mu g excreted, respectively. The SCG excreted at 0.5, 1.0 and 24 h collection periods following INHC dosing wer e 26.3 (8.4) mu g, 49.3 (18.1) mu g and 184.9 (98.4) mu g, respectively. Th ere was no significant difference between the excretion rate of sodium crom oglycate following INHC when compared with INH dosing in the first 0.5 and 1.0 h. Conclusions The urinary excretion of sodium cromoglycate in the first 0.5 h post inhalation lan be used tu compare the relative lung deposition of two inhaled products or of the same product using different inhalation techniq ues. This represents the relative bioavailability of sodium cromoglycate to the lung following inhalation. Similar 24 h urinary excretion of sodium cr omoglycate can be use to compare the total dose delivered to the body from two different inhalation products/inhalation methods. This represents die r elative bioavailability of sodium cromoglycate to the body following inhala tion. Because of the lack of difference between the INH and INHC in tile fi rst 0.5 h, the use of activated charcoal is not necessary when this method is used to compare the relative lung bioavailability of different products or techniques.