Liquid chromatography‐mass spectrometric method for determination of the non‐imidazole H 3 ‐receptor antagonist UPR1056 in rat plasma

The non‐imidazole H3 receptor antagonist UPR1056 was dosed in plasma samples from rats individually administered with a single i.p. dose of 1.25 mg/kg by means of a newly validated HPLC‐MS method. UPR1056 was extracted from rat plasma by protein precipitation with acetonitrile and was separated by linear gradient elution, employing water and methanol both additioned with 0.05% trifluoroacetic acid as mobile phases. UPR1056 was detected in MS using an electrospray ion source operating in positive ion mode. Acquisition was performed in single ion monitoring mode at m/z =349.3. The method was validated over the concentration range of 17.43–1743 ng/mL (50–5000 pmol/mL). Within‐ and between‐run precision for the low, mid and high quality controls (QC) levels were 6.75% or less and accuracy ranged from 95.8 to 107.6%. The lower limit of quantification was 17.43 ng/mL. The analysis of the time course of UPR1056 concentrations over the 24‐h period revealed a C max of 1147 ng/mL after 2 h from peripheral administration of the non‐imidazole H 3 ‐receptor antagonist, with a prolonged elimination half‐life of over 9 h.