Salivary excretion and pharmacokinetics of sulfapyridine after sulfasalazine.

The concentrations of sulfapyridine (SP) and N4-acetylsulfapyridine (AcSP) in the plasma and saliva of 5 healthy male adults (3 slow and 2 rapid acetylators) were determined as a function of time after a single 2.0-gm oral dose of sulfasalazine (salicylazosulfapyridine). SP absorption commenced 3.5 to 6 hr after sulfasalazine administration and occurred slowly (apparent absorption t1/2s ranged from 1.6 to 5 hr) irrespective of acetylator phenotype. Appreciable differences existed between slow and rapid acetylators with respect to the biologic t1/2 and total body clearance of SP. SP concentrations in the saliva correlated well with those in the plasma. The saliva:plasma concentration ratio for SP was 0.559 +/- 0.027 (mean of 5 subjects +/- SE) and was dependent of plasma concentration and saliva pH. The mean saliva:plasma concentration ratio for AcSP was lower (0.246 +/- 0.056), consistent with the pH-partition hypothesis, and showed considerably more intrasubject and intersubject variation than the ratio for SP. These findings suggest that measurement of SP concentrations in the saliva may be a convenient, noninvasive method for monitoring indirectly the steady-state plasma (serum) concentrations of SP in patients with ulcerative colitis or Crohn's disease who are receiving sulfasalazine.