Antagonism of picumast and ketotifen against histamine, acetylcholine, LTC4, slow-reacting substance of anaphylaxis and barium chloride in the guinea pig ileum bioassay

The actions of ketotifen on intestinal smooth muscles

Ketotifen is a tricyclic drug with a wide spectrum of pharmacological effects. We studied the actions of ketotifen on the mechanical activity of isolated segments of guinea-pig ileum, guinea-pig colon and mouse colon. In the guinea-pig ileum ketotifen induced small contractions and inhibited the contractions induced by carbachol and by electric field stimulation. Responses to bradykinin (in the absence or in the presence of atropine 1 microM) were similarly inhibited by ketotifen, with an IC50 of 23 microM. In the guinea-pig colon ketotifen evoked non-cholinergic contractions with a pD2 of 4.5, but still it inhibited responses to bradykinin (IC50 = 75 microM). Ketotifen relaxed the unstimulated mouse colon with a pD2 of 4.2. This effect persisted in the presence of propranolol and phentolamine (each 10 microM). Incubation of the mouse colon with the nitric oxide synthase inhibitors NG-nitro-L-Arginine methyl ester hydrochloride (L-NAME), or L-NG-nitro-arginine (L-NNA) (100-500 microM) did not alter the inhibitory action of ketotifen. The histamine H1 receptor antagonist chlorpheniramine (5 microM) or the nerve blocker tetrodotoxin (1 microM) did not alter the inhibitory effects of ketotifen. It is concluded that the actions of ketotifen are mediated by a non-cholinergic, non-histaminergic mechanisms.

High performance liquid chromatographic determination of Picumast and two active metabolites in plasma using on-line sample preparation

A method for determining Picumast, an antiallergic drug, in plasma by HPLC and column switching has been developed. The system consisted of two precolumns, an analytical column, three pumps, an autosampler and a fluorescence detector. The precolumns (17 x 4.6 mm i.d.) were packed with LiChroprep RPR (a moderately polar reversed phase) and the analytical column with Nucleosil ODS (RP 18, 5 microns). The columns were connected according to the alternating precolumn technique. The mobile phase consisted of 30% CH3CN/70% 0.05 M KH2PO4, pH 2.5, with a flow gradient. Detection wavelengths were 333 nm for excitation and 383 nm for emission. The retention times of Picumast, M1 and M2 were 12, 3.6 and 4.0 min, respectively. Total run time was 15 min. The limit of detection was 3 ng/mL for M1 and 1 ng/mL for M2 and Picumast using an injection volume of 150 microL. The recoveries vary between 89% and 97% with standard deviations between 2.4 and 3.3%.