Aspects of osseous, peritoneal and renal handling of bisphosphonate during peritoneal dialysis: a methodological...

The accumulation of methylene bisphosphonate (MBP) in increased bone turnover is an index of the total skeletal turnover. Accordingly, a model has been described where uptake of the osseous tracer can be estimated, regardless of renal function. In the present study, the model was adapted to continuous ambulatory peritoneal dialysis (CAPD). The aims were: to assess the kinetics of 99m-technetium MBP (99mTc-MBP) in CAPD, and to evaluate the correctness of the assumption that the peritoneal and renal clearances of 99mTc-MBP equal the total plasma clearance of 51-chromium ethylenediamine tetra-acetic acid (51Cr-EDTA). Eight patients on CAPD were studied cross-sectionally. The mean plasma clearances of 99mTc-MBP and 51Cr-EDTA in the steady state (4h) were 38.2 and 12.2 ml min-1 (p < 0.01), the peritoneal clearances (0-4 h) were 5.2 and 7.2 ml min-1 (p < 0.01), and the renal clearances (0-4 h) were 2.5 and 2.8 ml min-1 (not significant), respectively. The bone bisphosphonate clearance (BBC) at steady state was 26.0 ml min-1, a value which was significantly higher than that at infinity (16.5 ml min-1, p < 0.01). We conclude that the assumption that the sum of peritoneal and renal clearances of 99mTc-MBP equal the clearances of 51Cr-EDTA is correct from a clinical point of view. We found that the uptake of the tracers in soft tissue and the renal handling of 51Cr-EDTA and 99mTc-MBP are also similar. The differences between the clearance values for 51Cr-EDTA and 99mTc-MBP may be explained by their different molecular weight. The differences in the BBCs at infinity and at steady state are most probably due to late recirculation of MBP from the bone compartment. Hence, the BBC technique can be applied in the CAPD setting.