Anti-allergic activity of H1 blockers.

Terfenadine is an H1 blocker that may also have anti-allergic properties, as it inhibits the release of mediators from mast cells. Oral terfenadine reduces the release of prostaglandin D2 (PGD2) and, to a lesser extent, the release of histamine in patients after nasal challenge with allergen. The effect of terfenadine on the release of mediators from mast cells isolated from human lung was examined. The cells were challenged with anti-immunoglobulin E after pretreatment with 0, 0.1, 1 or 10 microM terfenadine, and the release of PGD2, leukotriene C4/D4 and histamine was assessed. Release of both eicosanoids was observed in the absence of terfenadine. Inhibition of the release of both eicosanoids was seen with 1 and 10 microM terfenadine. The release of histamine was not affected by terfenadine. These anti-allergic properties of terfenadine are likely to be involved in the therapeutic efficacy of the drug.