Dose loading with delayed-release mesalazine: a study of tissue drug concentrations and standard pharmacokinetic parameters

Abstract

Aims: Tissue concentrations of 5-aminosalicylic acid (5ASA) and its metabolites may influence the clinical course of inflammatory bowel disease. Since the factors that determine tissue drug concentrations are unknown we have studied the relationships between the oral dose of delayed-release mesalazine, rectal tissue drug concentrations and standard pharmacokinetic parameters.

Methods: Twelve healthy volunteers were studied following 7 days treatment with 1.2, 2.4 and 4.8 g of delayed-release mesalazine daily. 5-aminosalicylic acid and N-acetyl 5-aminosalicylic acid concentrations were measured in serum, urine, stool and rectal tissue biopsies.

Results: Serum concentrations and 24 h urinary excretion of 5ASA and N-acetyl 5ASA increased as the oral dose of mesalazine was increased from 1.2 g through 2.4 g to 4.8 g daily (serum area under curve (AUC):5ASA = 3. 9, 15.4 and 46.8 microg ml-1 h, P < 0.0001; N-acetyl 5ASA = 17.2, 30. 9 and 57.8 microg ml-1 h, P < 0.0001: urinary excretion: 5ASA = 1.8, 85.5 and 445 mg, P < 0.0001; N-acetyl 5ASA = 250, 524 and 1468 mg, P < 0.0001, respectively). Faecal 5ASA excretion increased as the oral dose increased from 1.2 g to 2.4 g but did not increase further with 4.8 g daily dosing whereas faecal N-acetyl 5ASA excretion was similar at all three doses. Rectal tissue concentrations of 5ASA increased markedly, and N-acetyl 5ASA increased modestly, as the dose of oral mesalazine increased from 1.2 g to 2.4 g daily but neither increased further with 4.8 g daily dosing.

Conclusions: The relationship between the ingested dose of delayed-release mesalazine and rectal tissue drug concentrations is complex. Factors other than dose are likely to be important determinants of rectal tissue drug concentrations.

Figure 1

(a) Serum 5ASA time concentration profiles (median and interquartile range) and (b) serum N-Acetyl 5ASA time concentration profiles (median and interquartile range). ○ mesalazine 400 mg three times daily; ▪ mesalazine 800 mg three times daily; ▵ mesalazine 1600 mg three times daily.

Figure 2

(a)24 h urinary excretion of 5ASA (□) and N-acetyl 5ASA () (box and whisker plots) *P < 0.05 and (b) 24 h faecal excretion of 5ASA and N-acetyl 5ASA (box and whisker plots)*P < 0.05.

Figure 3

(a) Rectal tissue time-concentration profiles of 5ASA (median and interquartile range) and (b) rectal tissue time-concentration profiles of N-acetyl 5ASA (median and interquartile range). ○ mesalazine 400 mg three times daily; ▪ mesalazine 800 mg three times daily; ▵ mesalazine 1600 mg three times daily.

Figure 4

(a) Correlations between 5ASA serum AUC and 24 h urinary excretion (5ASA, r = 0.84, P < 0.0001) and (b) correlations between N-acetyl 5ASA serum AUC and 24 h urinary excretion (N-acetyl 5ASA, r = 0.74, P < 0.0001).