Paracetamol and its metabolites in saliva and plasma in chronic dialysis patients

1 Many pharmacokinetic studies on paracetamol are based on saliva paracetamol concentrations. The utility of saliva in patients with chronic renal failure is unclear. In this study, concentrations of saliva and plasma paracetamol and its major metabolites, sulphate and glucuronide conjugates were determined at 0.5, 1, 2 and 3 h after the ingestion of 1 g paracetamol in 20 patients with endstage renal failure. Ten haemodialysis patients were studied on a non-haemodialysis day and during a haemodialysis session. The other 10 patients were on chronic ambulatory peritoneal dialysis. 2 The plasma paracetamol concentrations attained in all groups were not different from those reported previously in healthy subjects. Mean +/- s.d. plasma paracetamol concentrations at 0.5 h in haemodialysis patients on a non-haemodialysis day, during haemodialysis and in those on chronic ambulatory peritoneal dialysis were 15.3 +/- 8.2, 21.5 +/- 10.9 and 18.2 +/- 12.3 mu g ml(-1) respectively. 3 The saliva paracetamol concentrations were highly variable and unpredictable. Saliva paracetamol concentrations at 1, 2 and 3 h after ingestion in the haemodialysis group during haemodialysis were 31.5 +/- 20.1, 14.1 +/- 10.4 and 7.3 +/- 3.8 mu g ml(-1) respectively, significantly (P < 0.05; paired t-test) higher than the corresponding plasma paracetamol concentrations which were 11.0 +/- 2.8 6.5 +/- 2.8 and 3.2 +/- 0.9 mu g ml(-1) respectively. 4 Correlation coefficients between saliva and plasma paracetamol concentrations in haemodialysis patients on a non-haemodialysis day and during haemodialysis and in chronic ambulatory peritoneal dialysis patients were poor; r=0.58 (P < 0.0002); r = 0.40 (P < 0.02); and r = 0.13 (P = 0.49) respectively. 5 Three hours after paracetamol ingestion, plasma paracetamol, sulphate and glucuronide concentrations were significantly (P < 0.05) reduced in haemodialysis patients during haemodialysis when compared with the same patients on a non-haemodialysis day (paired t-test) and to the chronic ambulatory peritoneal dialysis group (Kruskal-Wallis ANOVA) except for plasma glucuronide. This indicates the effective removal of paracetamol and metabolites by haemodialysis. In contrast, chronic ambulatory peritoneal dialysis seemed to remove glucuronide only. 6 In the light of the poor correlation between saliva and plasma paracetamol in dialysis patients in this study, we would like to caution against using saliva paracetamol concentrations for pharmacokinetic studies in this group of patients.