Elevated Plasma Histamine in Chronic Uremia Effects of Ketotifen on Pruritus

: A role for histamine in the pathogenesis of uremic pruritus was investigated in maintenance hemodialysis patients. Venous plasma histamine levels, as determined by radioenzymatic assay, were significantly higher (p < 0.05) in hemodialysis patients with pruritus (368 ± 103 pg/ml [mean ± SEM], n = 6) than in those without pruritus (146 ± 22 pg/ml, n = 5) and in normal controls (142 ± 16, n = 5). Arteriovenous fistula histamine levels (202 ± 52 pg/ml, n = 6) were significantly lower (p < 0.05) than simultaneously drawn venous samples. Markedly elevated histamine‐degrading enzyme (histaminase) activities were found in both hemodialysis patients with (2.95 ± 0.18 pg histamine degraded/minute) and without (2.44 ± 0.28) pruritus, but was undetectable in normal controls. Histaminase activities did not significantly differ in simultaneously drawn venous and fistula samples. With hemodialysis, histaminase activities fell significantly (p < 0.01), whereas plasma histamine did not change. We further examined the effects of ketotifen, a putative mast cell stabilizer, on severe uremic pruritus. Five of five patients had significant (p