Impact of extracorporeal blood flow rate on blood pressure, pulse rate and cardiac output during haemodialysis.

BACKGROUND: If blood pressure (BP) falls during haemodialysis (HD) [intradialytic hypotension (IDH)] a common clinical practice is to reduce the extracorporeal blood flow rate (EBFR). Consequently the efficacy of the HD (Kt/V) is reduced. However, only very limited knowledge on the effect of reducing EBFR on BP exists and data are conflicting. The aim of this study was to evaluate the effect and the potential mechanism(s) involved by investigating the impact of changes in EBFR on BP, pulse rate (PR) and cardiac output (CO) in HD patients with arteriovenous-fistulas (AV-fistulas). METHODS: We performed a randomized, crossover trial in 22 haemodynamically stable HD patients with AV-fistula. After a conventional HD session each patient was examined during EBFR of 200, 300 and 400 mL/min in random order. After 15 min when steady state was achieved CO, BP and PR were measured at each EFBR, respectively. RESULTS: Mean (SD) age was 71 (11) years. Systolic BP was significantly higher at an EBFR of 200 mL/min as compared with 300 mL/min [133 (23) versus 128 (24) mmHg; P < 0.05], but not as compared with 400 mL/min [133 (23) versus 130 (19) mmHg; P = 0.20]. At EBFR of 200, 300 and 400 mL/min diastolic BP, mean arterial pressure, PR and CO remained unchanged. CONCLUSION: Our study does not show any consistent trend in BP changes by a reduction in EBFR. Reduction in EBFR if BP falls during IDH is thus not supported. However, none of the patients experienced IDH. Further studies are required to evaluate the impact of changes in EBFR on BP during IDH.

A review of the immunosuppressive activity of cyclosporine metabolites: new insights into an old issue.

Cyclosporine A (CsA) is metabolized into a vast spectrum of metabolites. The potential immunosuppressive action of CsA's metabolites has been studied extensively in the early 1990's, with conflicting and inconclusive results. Since then, the pharmacological and clinical consensus guidelines recommend the use of specific monoclonal assays for measurement of CsA's concentrations thus avoiding metabolite interference. Nevertheless, clinical benefit or superiority of these assays was never convincingly demonstrated. We provide a review of the performed in vivo, in vitro and animal studies and their conclusions. During the last years, many transplantation centres have employed the C(2) monitoring of CsA (2 hours post-dose concentration). The metabolites / parent drug ratio two hours post dose is completely different from trough levels (predose concentration). Cyclosporine exerts its immunosuppressive action by inhibiting the enzyme calcineurin phosphatase (CaN). Currently, our laboratory, among others, is working on determination of the enzyme's inhibition and its potential use as a pharmacodynamic biomarker. Utilizing this novel pharmacodynamic approach, we have performed in vitro and in vivo studies investigating the immunosuppressive impact of CsA's metabolites on C2 monitoring and on various monitoring assays (mono-/polyclonal). Interestingly, even though we have estimated in vivo that the potential immunosuppressive action of metabolites is less than 10% of the parent drug, we have found assays that take metabolites into consideration to correlate stronger with calcineurin phosphatase inhibition. We believe that the old controversial issue of metabolite induced immunosuppressive action examined under the light of newer pharmacodynamic approaches is still intriguing. Instead of a priori neglecting CsA's metabolites maybe we should investigate the potential of utilizing them as an additional tool towards better therapeutic drug monitoring of cyclosporine.

The calcineurin activity profiles of cyclosporin and tacrolimus are different in stable renal transplant patients.

Cyclosporin and tacrolimus remain the cornerstone immunosuppressive drugs in organ transplantation. Dosing and monitoring these drugs is based on pharmacokinetic protocols, but measuring a pharmacodynamic parameter, calcineurin phosphatase (CaN) activity, could be a valuable supplement in determining optimal doses. Forty stable renal transplant patients were investigated three times in a 6-month period. Blood samples were drawn at 0, 1, 2, 3 and 4 h after oral intake of tacrolimus (FK) or cyclosporin at days 1 and 180. At day 90, one blood sample at trough level (FK) or C2 level (cyclosporin A, CsA) was drawn. CaN activity was determined in whole blood as the release of 32P from a phosphorylated peptide. Activity of the 32P was quantitated by liquid scintillation and results converted to Units CaN, utilizing a calibration curve with CaN. We demonstrated that calcineurin activity profiles at days 1 and 180 were the same for both drugs. Furthermore, we found that patients treated with tacrolimus or cyclosporin displayed different calcineurin activity profiles. We found that cyclosporin displayed greater calcineurin inhibition than tacrolimus. We have demonstrated that the two drugs exert significantly different effects on calcineurin activity in renal transplant patients with stable, well-functioning grafts and that tacrolimus-treated patients can maintain good, stable graft function with minimal CaN inhibition.

Correlations between calcineurin phosphatase inhibition and cyclosporine metabolites concentrations in kidney transplant recipients: implications for immunoassays.

Cyclosporine exhibits a wide spectrum of metabolites that vary considerably in the extent to which they interfere with the various parent drug monitoring immunoassays. There is no consensus regarding the clinical significance of metabolites. Cyclosporine exerts its immunosuppressive action by inhibiting the enzyme calcineurin phosphatase. Determination of the enzyme's activity is one of the most promising pharmacodynamic markers. It is unknown how calcineurin phosphatase inhibition correlates with various cyclosporine monitoring assays and what is the potential impact of metabolites in this perspective? The aim of the present study was to determine the concentration of cyclosporine (by means of three different assay methods) and the four most significant metabolites (AM1, AM4N, AM9, and AM1C) in relation to calcineurin phosphatase inhibition. Twelve randomly selected cyclosporine-treated renal transplant patients were included in the study. Blood samples were drawn before, 1, 2, 3, 4, 6, 8, and 12 hr after oral intake of cyclosporine. Parent drug and metabolites were determined by liquid chromatography/tandem mass spectrometry (LC/MSMS). Additionally, cyclosporine concentration was determined by the enzyme multiplied immunoassay technique (EMIT) and by the polyclonal fluorescence polarization immunoassay (pFPIA). Calcineurin phosphatase activity was measured by its ability to dephosphorylate a previously phosphorylated 19-amino acid peptide. We found that calcineurin phosphatase inhibition correlates strongly with parent cyclosporine metabolites concentrations determined by all three assay methods. Determination methods that took metabolites into consideration exhibit stronger correlations with calcineurin phosphatase inhibition (sum of cyclosporin plus metabolites r=-0.93, LC/MSMS; pFPIA r=-0.94, P

The hemodynamic effect of calcium ion concentration in the infusate during predilution hemofiltration in chronic renal failure.

BACKGROUND: It is the prevailing view that convective dialysis techniques stabilize blood pressure. Calcium concentration in the substitution fluid may be important in this respect. The aim of this study is to investigate the influence of calcium ion concentration in the substitution fluid on hemodynamic stability during predilution hemofiltration (HF). METHODS: We conducted a randomized, crossover, blinded, controlled trial with 12 stable long-term hemodialysis patients without diabetes. Each patient was randomly assigned to substitution fluid with a calcium ion (iCa) concentration of 2.5 mEq/L (1.25 mmol/L; low-calcium session [L-HF]) or 3.5 mEq/L (1.75 mmol/L; high-calcium session [H-HF]) during 4.5 hours of predilution HF with a volume of 1.24 +/- 0.09 L/kg dry body weight and a temperature of 37 degrees C. Ultrafiltration was kept constant in each patient. Blood pressure (mean, systolic [SBP], and diastolic blood pressure [DBP]), pulse rate, arterial and venous temperature, energy transfer, and relative blood volume were measured at 15-minute intervals. Cardiac output, total peripheral resistance, stroke volume, and iCa were measured hourly. The 2 treatments were matched with the exception of iCa concentration. RESULTS: A significant intratreatment reduction in cardiac output and stroke volume was shown to the same extent for both groups. Intertreatment comparisons showed a significantly lower mean arterial pressure, SBP, DBP, and total peripheral resistance in the L-HF compared with the H-HF group. CONCLUSION: iCa concentration of 3.5 versus 2.5. mEq/L (1.75 versus 1.25 mmol/L) in the infusate during predilution HF stabilized blood pressure, possibly because of greater peripheral resistance rather than through changes in cardiac performance.

Predilution hemodiafiltration displays no hemodynamic advantage over low-flux hemodialysis under matched conditions.

BACKGROUND: It is the prevailing view that convective dialysis techniques stabilize blood pressure. The aim of this study was to compare the intrasession hemodynamics during high-dose predilution hemodiafiltration (HDF) and low-flux hemodialsis, under strict controlled conditions. METHODS: Twelve stable hemodialysis patients were investigated in a randomized crossover blinded controlled trial. The patients were allocated to one session of predilution HDF (substitution fluid 1.20 +/- 0.10 L/kg body weight) and one session of hemodialysis at 4(1/2) hours. To eliminate confounding factors, dialysis dose, ultrafiltration volume and arterial temperature were matched. At the start of the dialysis the patients' core temperature was "locked" by an automatic feedback system regulating the dialysate temperature; thereby, patients' temperature was kept stable throughout the whole treatment. The calcium-ion concentration in the substitution/dialysis fluid was 1.25 mmol/L. Cardiac output was measured hourly by the ultrasound velocity dilution method. RESULTS: Mean blood pressure, cardiac output, stroke volume, cardiac work, and relative blood volume was significantly reduced in both treatments. Total peripheral resistance increased significantly in both groups. Ultrafiltration volume, cardiopulmonary recirculation, Kt/V, and total energy transfer were similar for hemodialysis and HDF. The pulse rate showed no significant change throughout both sessions. No significant differences were revealed between hemodialysis and HDF. CONCLUSION: The hemodynamics of predilution HDF and low-flux hemodialysis displayed a similar profile during matched conditions. An acute circulatory benefit of convective solute removal over diffusive could not be demonstrated.

Role of metabolites and calcineurin inhibition on C2 monitoring in renal transplant patients.

BACKGROUND: Many transplantation centres have switched to C2 monitoring of cyclosporin-treated renal transplant patients. The rationale is that the C2 correlates best with AUC0-4 (area under the concentration-time curve), which again correlates with rejection and nephrotoxicity. It has also been demonstrated that calcineurin phosphatase is inhibited maximally 1-2 h after intake of cyclosporin in patients receiving their first dose. Cyclosporin is metabolized to many compounds, which may influence the results of immunoassays. Some metabolites may have immunosuppressive activity. METHODS: Cyclosporin metabolites were added to whole blood from healthy volunteers and the calcineurin phosphatase activity (CaN) was determined. Twenty renal transplant patients at varying times after transplantation had blood samples drawn in the morning before and 1, 2, 3 and 4 h after intake of their usual dose of cyclosporin microemulsion. Whole blood samples were analysed by liquid chromatography/tandem mass spectrometry for cyclosporin blood concentration and for the cyclosporin metabolites AM1, AM9, AM1c and AM4n. All samples were analysed for CaN utilizing a 32P-labelled 19 amino-acid peptide. RESULTS: The concentrations of AM1c and AM4n were very low and cannot contribute to CaN inhibition. The ratio of AM1 and AM9 to cyclosporin was high before intake of the drug, but it was much lower during the following 4 h. The 2-h values of cyclosporin were the best predictors of AUC0-4. Calcineurin phosphatase was most inhibited in the 2-h samples and the 2-h value of CaN was the best predictor of CaN AUC0-4. The correlation with calcineurin inhibition seemed better for cyclosporin plus metabolites than for cyclosporin. CONCLUSIONS: Samples collected at 2 h are the best predictors of AUC0-4 for both cyclosporin and calcineurin inhibition. The impact of metabolites appears to be small; however, the temporal profile of calcineurin inhibition seemed to follow cyclosporin plus metabolites better than cyclosporin alone.

Validation of the calcineurin phosphatase assay.

BACKGROUND: The calcineurin inhibitors cyclosporine and tacrolimus are used as primary immunosuppressive drugs in transplant patients. Measuring calcineurin phosphatase (CaN) activity is a proposed pharmacodynamic approach to optimize dosing of these drugs. METHODS: Whole blood samples were obtained from 10 patients treated with calcineurin inhibitors and 20 healthy volunteers and frozen at -80 degrees C. CaN activity was measured by its ability to dephosphorylate a 19-amino acid peptide previously phosphorylated with [gamma-(32)P]ATP. Radioactivity was quantified by liquid scintillation, and results were converted from cpm to U of CaN. Validation of the assay included enzyme kinetics, linearity, precision (at low and normal CaN activities), analytical recovery, and limit of detection. RESULTS: The enzyme followed simple Michaelis-Menten-type kinetics: V(max) was estimated as 240 nmol (32)P x L(-1) x min(-1) and K(m) as 70 micromol/L. The assay was linear within the concentration range examined. Analytical recovery varied from 68% to 72%. The total analytical SD was 0.059 and 0.053 U of CaN for high and low CaN activity, respectively. The within-day SD for high and low activity was 0.032 and 0.039 U of CaN, respectively. The limit of detection was 0.04 U of CaN, which is far below the values measured in patients treated with CaN inhibitors. CONCLUSIONS: In addition to the pharmacokinetic monitoring applied today, the CaN assay can be used to monitor patients treated with calcineurin inhibitors, hopefully leading to prolonged graft survival.