GSK-1004723

Background: A therapeutic role for histamine H₃ receptor antagonism in allergic rhinitis has been proposed and may be complimentary to the well-known benefits of H₁ receptor antagonism. Combined H₁/H₃ blockade has therefore been investigated as a novel therapeutic approach that may enhance symptom relief, particularly nasal blockage. Methods: Two novel H₁/H₃ dual receptor antagonists were investigated in phase I and II safety and efficacy studies. One molecule (GSK1004723) was designed for intranasal administration as a suspension or solution and the other molecule (GSK835726) for oral administration. In phase I and II studies, both molecules were compared with an active control and/or placebo in randomised studies. In phase II studies, efficacy was assessed in an environmental allergen challenge chamber (ECC). Subjects with seasonal allergic rhinitis were exposed to allergen to induce symptoms. Efficacy and safety was measured over 4, 7 and 20–24 h post-dose. The endpoints included total nasal symptom score and nasal blockage. Results: Intranasal suspension of GSK1004723 and oral GSK835726 were well tolerated. Single-dose intranasal suspensions of GSK1004723 (220, 1,100 µg) failed to demonstrate clinically significant attenuation of symptoms of allergic rhinitis induced in the ECC. Single (10, 50, 100 mg) and 3-day repeat (10 mg) dose oral GSK835726 demonstrated clinically significant attenuation of symptoms in the ECC comparable to cetirizine 10 mg. Three-day repeat dosing of the intranasal solution GSK1004723 1,000 µg also demonstrated a statistically significant attenuation of nasal symptoms, but was less than seen with cetirizine and GSK835726 and caused initial nasal discomfort. Conclusions: Combined H₁/H₃ antagonism did not show differentiation from H₁ antagonism in reducing total nasal symptom score or nasal blockage.