Mathematical models for prescription and delivery in peritoneal dialysis

Population pharmacokinetics of intra-peritoneal gentamicin and the impact of varying dwell times on pharmacodynamic target attainment in patients with acute peritonitis undergoing peritoneal dialysis

While the use of intraperitoneal (i.p.) gentamicin is common in the treatment of peritoneal dialysis (PD)-related infections, the ability of these regimens to attain pharmacodynamic target indices of interest in blood and dialysate has not been widely reported. Pharmacokinetic (PK) data was obtained and analyzed from a multiple-dose PK study of i.p. gentamicin with 24 patients who received the drug at 0.6 mg/kg dose of body weight. The probability of target attainment (PTA) for indices of treatment success (i.p. peak/MIC ratio >10) and toxicity (plasma AUC < 120 mg*h/L) was determined for 0.3 to 1.2 mg/kg i.p. regimens every 24 h for dwell times of 2 to 6 hours and for the duration of 2-week course. In the peritoneum, successful PTA was achieved by all of the simulated regimens up to an MIC of 1 mg/L, and by doses equal to or greater than 0.6 mg/kg up to the MIC of 2 mg/L. At the susceptibility break point of 4 mg/L only the highest dose of 1.2 mg/kg is likely to provide adequate PTA. Probability of achieving exposure below the threshold of 120 mg*h/L in the daily AUC in plasma seems acceptable for all regimens at or below 0.6 mg/kg. Based on the model we developed, a gentamicin dose of 0.6 mg/kg is sufficient to treat organisms with an MIC of ≤2 mg/L without the risk of significant systemic exposure. The 1.2 mg/kg dose necessary to reach the pharmacodynamic target for efficacy at the clinical break point of 4 mg/L is likely to produce early toxic levels of exposure that is expected to be detrimental to the renal system.

Icodextrin Simplifies PD Therapy by Equalizing UF and Sodium Removal Among Patient Transport Types During Long Dwells: A Modeling Study

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BACKGROUND

In recent years, results from clinical studies have changed the focus of peritoneal dialysis (PD) adequacy from small solute clearance to volume control, resulting in continued efforts to improve fluid and sodium removal in PD patients. We used a modified 3-pore model to theoretically predict fluid and solute removal using glucose-based and icodextrin solutions for a wide range of transport characteristics with automated PD (APD) and continuous ambulatory PD (CAPD) therapies. ♦

METHODS

Simulations were performed for the day (APD: 15-hr, 2.27% glucose and 7.5% icodextrin; CAPD: 3x5-hr, 1.36% and 2.27% glucose) and night (APD: 9-hr, 1.36% glucose; CAPD: 9-hr, 2.27% glucose and 7.5% icodextrin) dialysis periods separately. During APD, the number of night exchanges (N) was varied from 3 to 7. Ultrafiltration (UF), sodium removal (NaR), total carbohydrate absorption (CHO), UF efficiency (UFE), and sodium removal efficiency (NaRE) were calculated. Typical patients in fast (i.e. high, H), average (high-average, HA; low-average, LA), and slow (low, L) transport groups with no residual kidney function were considered. ♦

RESULTS

The effective dwell times varied between 1.0 and 14.7 hours depending on the number of exchanges. With glucose-based solutions, differences in UF and NaR between H and L transport patients ranged from 140 mL and 2 mmol (APD night, n = 7) to 778 mL and 56.4 mmol (CAPD day, 2.27%). With icodextrin, differences in UF and NaR ranged from 1 mL and 1.1 mmol (CAPD night) to 59 mL and 6.1 mmol (APD day). The use of icodextrin resulted in greater CHO than 2.27% glucose (APD: 27.1 - 35.6 g more; CAPD: 17.1 - 17.5 g more). The UFE and NaRE were greater for all patients with icodextrin than with glucose-based solution in both therapy modalities, except for slow transport patients in CAPD. ♦

CONCLUSION

This modeling study shows that the dependence of UF and NaR on patient transport type observed with glucose-based solutions can be minimized using icodextrin during the long dwells of APD and CAPD. While this approach simplifies the PD prescription by minimizing the dependencies of ultrafiltration and sodium removal on patient transport type when using icodextrin, it improves fluid and sodium removal efficiencies in fast and average transport patients without any added glucose exposure.

Efficacy of peritoneal dialysis during infusion and drainage procedures

BACKGROUND

Inadequate dialysis is still a major cause of technique failure in peritoneal dialysis (PD). Mathematical models provide the possibility of direct and precise assessment of peritoneal transport of urea and creatinine throughout the dwell and allow calculation of optimal schedules, dwell times, and predicted adequacy of a prescribed regimen. Kinetic modeling is particularly important for automated PD. If the effectiveness of uremic toxin removal that takes place during infusion and drainage of dialysis fluid is not taken into account, the predicted adequacy of the whole PD session may be underestimated. ♢

AIMS

To estimate the efficacy of urea and creatinine removal during the dialysis fluid exchange procedure. ♢

MATERIAL AND METHODS

17 patients treated with PD were included in the study. PD effectiveness during dialysate exchange was defined as the quotient k of removed amount of creatinine/BUN during the infusion and drainage of dialysate and during a dwell of the same duration as the dialysate exchange. ♢

RESULTS

The effectiveness of creatinine and urea removal was reduced during the exchange procedure (k(creat) = 0.68 ± 0.43 and k(BUN) = 0.87 ± 0.44) and differed between these 2 solutes (p = 0.0009). The k coefficients for urea and creatinine were well correlated (R(2) = 0.83). ♢

CONCLUSIONS

The effectiveness of peritoneal transport of creatinine and BUN during the inflow/outflow phase was relatively high compared to that during the same dwell time (68% and 87% respectively). This real effectiveness of the dialysate exchange procedure should be taken into account in the process of planning automated PD sessions, otherwise the predicted overall efficacy of creatinine and urea removal throughout the session may be underestimated. This underestimation is proportional to the number of dwells per day.

Evaluating peritoneal fluid transport in continuous peritoneal dialysis patients: a practical approach

BACKGROUND/AIMS

Evaluating the peritoneal fluid kinetics is of clinical importance in peritoneal dialysis treatment. We have previously developed a simple way to evaluate the peritoneal fluid transport characteristics in continuous ambulatory peritoneal dialysis patients which, however, cannot be applied to those patients on a fixed dialysis schedule. Therefore, in the present study, we tested the possibility to vary the peritoneal dwell time and tried to develop a more patient-friendly ultrafiltration (UF) collection protocol.

METHODS

The patients' UF volume was recorded for 10 days. All patients recruited were asked to perform their usual dialysis exchanges with, however, a special UF data collection protocol to improve the accuracy of computer simulation: at least one dwell of 2-4 h, one of 4-7 h, and one of more than 7 h. The fluid transport model was applied to the pooled UF volume for fluid kinetics simulation, and the data from the following day's UF records using the same glucose concentration and dwell time were used to evaluate reliability and accuracy of the simulated UF value.

RESULTS

Fifty-two chronic peritoneal dialysis patients were included in the present study. All of the UF data could be used in the computer simulation, and there was a significant negative correlation between fluid absorption rate (K(e); see text) and actual UF volume on the following day using a glucose concentration of 1.5% and a dwell time of 4 h (r = -0.336, p < 0.05). The estimated UF values correlated significantly with the actually measured UF values. The variability of the results, expressed by the width between the 95% limits of agreement, fell within -139.2 to 131.9 ml, while the mean difference was -3.7 ml.

CONCLUSIONS

Our present study showed that varying the peritoneal dwell time was a patient-friendly UF data collection protocol for continuous ambulatory peritoneal dialysis patients on a fixed dialysis schedule. Applying the fluid transport model and nonlinear least squares regression analysis to pooled UF values might be a good and simple way to predict the peritoneal UF capacity.

APD prescription: achieving the adequacy goals

In the last few years, automated peritoneal dialysis (APD) has undergone considerable improvements due to technological developments. The definition of a minimal dose of peritoneal dialysis (PD) has not yet been completely assessed. Appropriate use of APD requires an evaluation of dialytic efficiency in terms of dialytic indexes and their targets. Many dialytic treatment modalities have been performed in order to achieve adequacy targets. Some aspects have to be taken into consideration to reach the optimal dialytic dose: optimizing mass transfer in correlation with intraperitoneal volumes, prescribing tailored treatment modalities according to different characteristics of peritoneal membranes and individual patient needs, and performing more biocompatible treatments using different glucose profiling and alternative physiologic PD fluids. New high-flow techniques such as continuous flow PD can ensure better urea and creatinine clearances and ultrafiltration rates, leading to a higher utilization of the APD modality.