Effect of salivary phosphate-binding chewing gum on serum phosphate in chronic kidney disease.

Background/aims: Serum phosphate (P) has been linked to adverse events in patients with chronic kidney disease. Salivary phosphate (Psal) has been proposed as a potential target of therapy with a chitosan-containing chewing gum.

Methods: We conducted several pilot studies to characterize Psal and its relationship with kidney function and subsequently conducted two clinical efficacy studies: a double-blind placebo-controlled trial in patients with end-stage renal disease (ESRD) and an open-label trial in those with stage 3-4 CKD.

Results: Pilot studies demonstrated no relationship between the level of kidney function and Psal. Mean Psal was approximately 6.46 mmol/l across the entire spectrum of kidney function. Passive saliva collection demonstrated higher Psal concentration as compared to active collection. There was no evidence of diurnal variation in Psal. Twice daily 20 mg chitosan gum over 4 weeks reduced serum P by 0.065 mmol/l in the double-blind, placebo-controlled trial in ESRD (p = NS vs. placebo). In an open-label extension in these subjects, 40 mg chitosan gum three times daily reduced serum P by 0.065 mmol/l (p = 0.03 vs. end of washout). In a 2-week open-label trial in patients with CKD not on dialysis, 20 mg chitosan gum given three times daily reduced serum P by 0.05 mmol/l (p = 0.003 vs. day 1). Neither trial demonstrated any significant change in Psal with chitosan gum.

Conclusions: Psal concentration is approximately 4-5 times that of serum P and is not related to glomerular filtration rate. Chitosan chewing gum resulted in a reduction of serum P by approximately 0.05-0.065 mmol/l but had no effect on Psal concentration.