Effect of recombinant factor VIIa variant (NN1731) on platelet function, clot structure and force onset time in whole blood from healthy volunteers and haemophilia patients

NN1731 is a novel variant of recombinant factor VIIa (rFVIIa) that binds to activated platelets, but has greater enzymatic activity than rFVIIa in generating FXa and thrombin. The effect of NN1731 on clot structure and platelet function was characterized ex vivo in whole blood from healthy volunteers and haemophilic patients. Blood samples from six healthy volunteers, nine haemophilia A patients with and without inhibitors and one acquired haemophilia A patient, were spiked with increasing concentrations (0.32, 0.64 and 1.28 microg mL(-1)) of rFVIIa and NN1731. Platelet contractile force (PCF) or platelet function, clot elastic modulus (CEM) or clot structure, and force onset time (FOT) or the thrombin generation time (TGT) were determined using the Hemodyne Hemostasis Analysis System (HAS). Baseline PCF, CEM and FOT values in patients were abnormal compared to healthy volunteers' baseline values. Overall, haemophilia blood samples with or without inhibitors spiked with NN1731 had significantly greater PCF, CEM and shorter FOT values relative to samples spiked with corresponding doses of rFVIIa. The variability in response to treatment between patients was greater with rFVIIa compared to NN1731. At 1.28 microg mL(-1) (90 microg kg(-1)), NN1731 normalized PCF, CEM and FOT in nine of 10 patients, while rFVIIa normalized these parameters in four of 10 patients. Increasing in vitro concentrations of NN1731 normalized platelet function, clot structure and thrombin generation consistently in haemophilia blood with or without inhibitors. NN1731 may be a promising haemostatic agent for patients with bleeding disorders. These results should be confirmed in an in vivo study.

Development of an Efficient Sampling Strategy to Predict Enoxaparin Pharmacokinetics in Stage 5 Chronic Kidney Disease

Patients with renal dysfunction are at greater risk for hemorrhagic events than patients with normal renal function. The objective of this study was to develop an efficient sampling strategy that optimally predicts anti-Xa activity exposure after enoxaparin administration in patients with chronic kidney disease to optimize enoxaparin therapy. The antifactor Xa activity data of 8 anuric patients who were administered 1 mg/kg enoxaparin immediately after hemodialysis were used for the development of the optimal sampling strategies. Maximum A Posteriori Bayesian (MAPB) priors were developed by pharmacokinetic analysis. The 2, 3, and 4 D-optimal sampling designs were determined and Monte Carlo simulations using the MAPB estimator were performed. The original model with the estimator was used to determine the predictive power of the sampling schemes. The most efficient sampling scheme (OSS-2) was accurate and precise in predicting apparent enoxaparin clearance (-3.2% bias, 6.5% precision). The addition of a third sampling time at 30 minutes (OSS-3) was more accurate (P < 0.01) and precise (P < 0.01) than OSS-2 at predicting the rate of absorption (ka) but did not improve the accuracy (P > 0.05) or precision (P = 0.20) of the CLs/F estimate. The determination of antifactor Xa activity at 5 and 24 hours, along with the Bayesian estimators generated from this study, accurately and precisely predict the apparent clearance of antifactor Xa activity. This sampling strategy may be used for therapeutic drug monitoring of enoxaparin and for future clinical trials in patients with chronic kidney disease.

The effect of uremia on platelet contractile force, clot elastic modulus and bleeding time in hemodialysis patients

INTRODUCTION

Uremic bleeding frequently occurs in dialysis patients. Although its mechanism is not well characterized, acquired platelet dysfunction has been implicated in its pathogenesis. Skin bleeding time has been used to characterize platelet dysfunction in this population. However, the bleeding time is prone to error. The goal of this study was to compare the bleeding time to the novel platelet function parameters platelet contractile force and clot elastic modulus as well as platelet aggregation studies in controls and patients receiving maintenance hemodialysis.

MATERIALS AND METHODS

Forty-five subjects completed this study (25 controls, 20 dialysis). All subjects had the Ivy skin bleeding time procedure performed, as well as the collection of whole blood samples for the determination of platelet contractile force, clot elastic modulus, % von Willebrand Factor antigen, and platelet aggregation studies. Pearson's correlation determined the relationships between skin bleeding time and platelet function and clot structure parameters and markers of renal dysfunction.

RESULTS

Bleeding time was significantly prolonged in the dialysis group relative to controls. The platelet function parameters were not significantly different between groups. There was a significant relationship between bleeding time and creatinine concentration, however, no relationship existed between bleeding time and platelet function parameters.

CONCLUSIONS

Skin bleeding time poorly correlates with measurements of platelet function. There were no significant differences noted in platelet function between the groups despite the prolongations in bleeding time in the dialysis group. These data may suggest that the bleeding time reflects perturbations in platelet adhesion or secretion, and not aggregation. Further study is needed to characterize platelet function in dialysis patients.

Thrombin generation time is a novel parameter for monitoring enoxaparin therapy in patients with end-stage renal disease

BACKGROUND

Patients with end-stage renal disease (ESRD) who receive enoxaparin are at increased risk for adverse bleeding episodes. This phenomenon appears to occur despite judicious monitoring of antifactor Xa (aFXa) activity. Better monitoring parameters are needed to quantify the anticoagulant effects of enoxaparin in the ESRD population.

OBJECTIVES

The objective of this study was to determine the utility of using thrombin generation time (TGT), platelet contractile force (PCF) and clot elastic modulus (CEM) to monitor the degree of anticoagulation in ESRD subjects, and to compare these results to aFXa activity, the current gold-standard monitoring parameter.

METHODS

Eight healthy volunteers without renal dysfunction and eight ESRD subjects were enrolled into this study. Subjects received a single dose of enoxaparin 1 mg kg(-1) subcutaneously, and blood samples were obtained for the determination of aFXa activity, TGT, PCF and CEM at baseline, 4, 8, and 12 h postdose.

RESULTS

Baseline, 4, 8, and 12-h aFXa activity concentrations were not different between groups. However, the corresponding TGT at 8 and 12 h was significantly prolonged in the ESRD group (P = 0.04, and P = 0.008, respectively). The 4-h peak TGT trended toward significance (P = 0.06). There were no differences in PCF or CEM across time.

CONCLUSIONS

These data suggest that the parameter aFXa activity is a poor predictor of the anticoagulant effect of enoxaparin in patients with ESRD. Thrombin generation time appears to be more sensitive to the antithrombotic effects of enoxaparin in this population. Further large-scale trials are needed to corroborate these data.

Darbepoetin Alfa Therapeutic Interchange Protocol for Anemia in Dialysis

BACKGROUND

Erythropoiesis-stimulating proteins, such as erythropoietin alfa and darbepoetin alfa, have positively impacted anemia management. These medications improve patient outcomes and quality of life. Their costs, however, remain a major barrier for health systems.

OBJECTIVE

To evaluate the development, implementation, and cost-effectiveness of an inpatient therapeutic interchange protocol for erythropoiesis-stimulating proteins at a large, tertiary care, university-affiliated health system.

METHODS

Virginia Commonwealth University Health System (VCUHS) developed and implemented a therapeutic interchange program to convert therapy for all inpatients undergoing dialysis from erythropoietin alfa to darbepoetin alfa for treatment of chronic kidney disease–related anemia. An evaluation of the economic impact of this program on drug expenditures over a fiscal quarter (2003) was conducted using historical comparator data (2002).

RESULTS

Preliminary evaluation of the program demonstrated cost-savings and reduced drug utilization of erythropoiesis-stimulating proteins in hospitalized dialysis patients. For the first quarter of 2003 compared with the first quarter of 2002, VCUHS realized a cost-savings of nearly $10 000, which was related to the program's aggressive screening procedure. When these data were normalized for equal numbers of patients in each group receiving one of the drugs, the actual cost-savings was over $2000. These cost-savings are largely due to reduced utilization of these expensive biotechnology products with implementation of a dosing protocol.

CONCLUSIONS

VCUHS has successfully developed and implemented a darbepoetin alfa therapeutic interchange protocol for hospitalized dialysis patients. This has translated into reduced use of erythropoiesis-stimulating proteins, resulting in cost-savings for the health system.

Venous Thromboembolism Prevention in Acutely Ill Nonsurgical Patients

OBJECTIVE

To review recent advances in the prevention of venous thromboembolism (VTE) in acutely ill nonsurgical inpatients.

DATA SOURCES

A MEDLINE search (1966–March 2005) was done to identify relevant articles relating to prevention of VTE in acutely ill nonsurgical inpatients.

STUDY SELECTION AND DATA EXTRACTION

Four major prophylaxis trials, one registry, one guideline, and supporting articles representative of the subject matter from the last few years were included.

DATA SYNTHESIS

Enoxaparin, dalteparin, fondaparinux, and unfractionated heparin 5000 units every 8 hours are effective in reducing the risk of VTE in acutely ill medical patients, but such prophylaxis is currently underused. Barriers to be overcome include recognition of the importance of VTE in this population, definition of the optimal strategy to assess risks, optimal timing of the risk assessment, optimal prophylactic regimen for a given level of risk or disease state, and optimal duration of prophylaxis. We recommend that acutely ill medical inpatients should be risk-stratified early in their hospitalization. At this time, the specific risk-assessment protocol should be derived from the trial(s) of the available formulary agent(s). Decisions about providing prophylaxis must also be made considering anticoagulant contraindications and renal function. Mechanical methods of prophylaxis should be considered as monotherapy only if an anticoagulant contraindication exists. The optimal duration of prophylaxis is not known, but 14 days was used in recent studies.

CONCLUSIONS

Prophylaxis of VTE in acutely ill medical inpatients is underused. Data provide some guidance for increasing awareness and optimizing patient care.

A hypothesis-generating study to evaluate platelet activity in diabetics with chronic kidney disease

Background

It is well described that diabetes mellitus is a hypercoagulable state. It is also known that patients with renal dysfunction have impaired platelet aggregation and function. It is not well described how renal dysfunction affects the hypercoagulability associated with diabetes. This post-hoc sub-group analysis compares platelet function, clot structure and thrombin generation time at baseline, and following enoxaparin exposure in three groups of subjects.

Methods

30 total subjects were evaluated in the three groups: Group I: normal controls (n = 10), Group II: subjects with renal dysfunction but without diabetes (n = 13), and Group III: subjects with concomitant diabetes and renal dysfunction (n = 7). For each subject, platelet contractile force (PCF), clot elastic modulus (CEM) and thrombin generation time (TGT) were simultaneously measured in whole blood at baseline, and following increasing enoxaparin antifactor Xa activity exposure. The group means for each parameter were determined and compared using one-way analysis of variance, with post-hoc Tukey-Kramer test.

Results

At baseline, subjects in Group III (diabetics with concomitant renal dysfunction) display significantly enhanced platelet activity, as measured by PCF (p = 0.003) and CEM (p = 0.03), relative to the non-diabetic Groups I and II. Subjects in Group II (renal dysfunction without diabetes) had significantly prolonged TGT values relative to controls when the antifactor Xa activity concentration reached 0.5 (p = 0.007), 1.0 (p = 0.005) and 3.0 IU/mL (p < 0.0001), respectively. There were no differences between Group II and Group III with respect to TGT at these antifactor Xa activity concentrations. When the antifactor Xa activity concentration reached 3.0 IU/mL, Groups II and III formed significantly less rigid blood clots (CEM p = 0.003) and also trended toward reduced PCF (p = 0.06) relative to Group I.

Conclusion

This hypothesis-generating sub-group analysis suggests that at baseline, patients with concomitant diabetes and renal dysfunction have significantly enhanced platelet activity (PCF), and form more rigid blood clots (CEM) compared to controls and subjects with renal dysfunction but no diabetes. This may suggest that the presence of renal dysfunction does not ameliorate the hypercoagulable state associated with diabetes. Secondly, it appears that subjects with renal dysfunction but without diabetes have an enhanced response to enoxaparin relative to controls.

Antifactor Xa activity correlates to thrombin generation time, platelet contractile force and clot elastic modulus following ex vivo enoxaparin exposure in patients with and without renal dysfunction

Antifactor Xa activity is the gold standard monitoring parameter for low molecular weight heparin (LMWH) derivatives. It is frequently measured in high-risk populations, such as patients with renal dysfunction. Despite antifactor Xa monitoring, however, bleeding in renal dysfunction patients receiving LMWH remains a problem. This study determined the relationship between antifactor Xa activity and three novel coagulation monitoring parameters: thrombin generation time (TGT), platelet contractile force (PCF) and clot elastic modulus (CEM). This study also assessed the effect of renal dysfunction on these relationships. This was an ex vivo pharmacodynamic study of the relationship between antifactor Xa activity and TGT, PCF and CEM in subjects both with and without renal dysfunction. Thirty subjects completed this study (10 controls, 10 chronic kidney disease subjects, and 10 end-stage renal disease subjects receiving hemodialysis). Blood samples obtained from participants were spiked with increasing enoxaparin concentrations (0.25, 0.5, 1.0 and 3.0 IU mL(-1)). Samples were analyzed for TGT, PCF and CEM. The relationship between antifactor Xa activity and TGT, PCF and CEM was determined by Pearson's correlation. The effect of renal dysfunction on the relationship between antifactor Xa activity and TGT, PCF and CEM was determined by analysis of covariance. There is strong correlation between antifactor Xa activity and TGT, CEM and PCF. The presence of renal dysfunction significantly prolongs the TGT, and decreases the CEM relative to controls. These results suggest that patients with renal dysfunction have a greater pharmacodynamic response to LMWH, independent of the pharmacokinetics of LMWH.

Enhanced anticoagulant activity of enoxaparin in patients with ESRD as measured by thrombin generation time

BACKGROUND

Patients with renal dysfunction who undergo systemic anticoagulation with enoxaparin are at increased risk for bleeding. Although there is decreased renal clearance of enoxaparin in this population, the clinical utility of monitoring antifactor Xa activity is controversial because it is weakly correlated to bleeding. The goal of this study was to investigate the role of other novel anticoagulation markers, such as thrombin generation time, platelet contractile force, and clot elastic modulus, while controlling for antifactor Xa activity in patients with and without renal dysfunction.

METHODS

Thirty anticoagulant- and antiplatelet-naive subjects completed this trial (10 controls, 10 patients with chronic kidney disease, and 10 patients with end-stage renal disease [ESRD]). Blood samples were obtained and spiked ex vivo with increasing concentrations of enoxaparin antifactor Xa activity (0.25, 0.5, 1.0, and 3.0 IU/mL). Thrombin generation time, platelet contractile force, and clot elastic modulus were measured in each group at each antifactor Xa activity concentration.

RESULTS

Subjects with ESRD had an approximately 50% greater anticoagulant effect, determined by thrombin generation time prolongation, than controls at antifactor Xa activity concentrations of 0.5 to 3.0 IU/mL. This may explain why subjects with ESRD with seemingly therapeutic antifactor Xa levels still experience adverse bleeding. There were no intergroup differences in platelet function, determined by platelet contractile force and clot elastic modulus.

CONCLUSION

Antifactor Xa poorly predicts the degree of anticoagulation in patients with ESRD administered low-molecular-weight heparin (LMWH). Thrombin generation time may be a clinically useful anticoagulation monitoring tool to monitor LMWH therapy, especially in patients with renal dysfunction. Additional randomized prospective studies are needed to corroborate these findings.

Pharmacoeconomic considerations in the health system management of anaemia in patients with chronic kidney disease and end stage renal disease

Anaemia is prevalent in patients with chronic kidney disease and end stage renal disease. If left untreated, it greatly affects patient survival, quality of life and functional status. Epoetin and darbepoetin are two biotechnology drugs that effectively stimulate the production of red blood cells. These drugs have been shown to significantly increase haemoglobin concentrations and improve quality of life. So far, there have been no head-to-head pharmacoeconomic studies that have compared epoetin to darbepoetin. Health system decision makers need to evaluate important considerations when comparing these agents. These considerations include drug acquisition costs, the patient population being treated, the location of drug administration (in-patient versus ambulatory) and federal government reimbursement. This review details these important pharmacoeconomic considerations.

Role of N-acetylcysteine in the prevention of radiocontrast-induced nephropathy

OBJECTIVE

To examine the role of N-acetylcysteine (NAC) in the prevention of radiocontrast-induced nephropathy (RIN).

DATA SOURCES

A literature search of MEDLINE (1966-December 2001) was performed using the following search terms: N-acetylcysteine, nephropathy, acute renal failure, and radiocontrast.

STUDY SELECTION

Pertinent English-language animal and human studies were reviewed.

DATA SYNTHESIS

Few small animal trials have demonstrated that NAC significantly prevents the development or reduces the severity of acute renal failure. Two human studies demonstrated NAC significantly reduces the occurrence of RIN.

CONCLUSIONS

NAC may reduce the occurrence of RIN in high-risk patients. Further large-scale studies are needed to corroborate findings from earlier trials.

The pharmacokinetics of subcutaneous enoxaparin in end-stage renal disease

STUDY OBJECTIVE

To evaluate the pharmacokinetics of enoxaparin in end-stage renal disease (ESRD), and determine if dosage reduction is necessary to maintain antifactor Xa activity concentrations within the therapeutic range.

DESIGN

Prospective, single-dose pharmacokinetic study.

SETTING

University-affiliated general clinical research center.

PATIENTS

Eight nonthrombosed patients with ESRD requiring hemodialysis.

INTERVENTION

All subjects received a single dose of enoxaparin sodium 1 mg/kg subcutaneously and had serial plasma antifactor Xa activity concentrations measured over 24 hours.

MEASUREMENTS AND MAIN RESULTS

The pharmacokinetics of enoxaparin were determined from plasma antifactor Xa activity concentrations, and various multiple-dose regimens were simulated. After administration of the drug, total body clearance was 14.6 ml/minute and there was a 2-fold prolongation in antifactor Xa activity half-life compared with values reported in healthy subjects. All other pharmacokinetic parameters were similar to those in healthy subjects and patients with chronic renal insufficiency. An accumulation ratio of 1.6 was estimated for a dosing interval of every 12 hours based on single-dose pharmacokinetics. When various therapeutic regimens were simulated to predict average steady-state antifactor Xa activity, standard enoxaparin dosages of 1 mg/kg subcutaneously every 12 hours and 1.5 mg/kg every 24 hours resulted in average steady-state concentrations within the therapeutic range.

CONCLUSIONS

Based on antifactor Xa activity, ESRD has little effect on the pharmacokinetics of enoxaparin, and dosing adjustments are unnecessary.

Pharmacokinetic Interaction between amprenavir and rifabutin or rifampin in healthy males

The objective of this study was to determine if there is a pharmacokinetic interaction when amprenavir is given with rifabutin or rifampin and to determine the effects of these drugs on the erythromycin breath test (ERMBT). Twenty-four healthy male subjects were randomized to one of two cohorts. All subjects received amprenavir (1,200 mg twice a day) for 4 days, followed by a 7-day washout period, followed by either rifabutin (300 mg once a day [QD]) (cohort 1) or rifampin (600 mg QD) (cohort 2) for 14 days. Cohort 1 then received amprenavir plus rifabutin for 10 days, and cohort 2 received amprenavir plus rifampin for 4 days. Serial plasma and urine samples for measurement of amprenavir, rifabutin, and rifampin and their 25-O-desacetyl metabolites, were measured by high-performance liquid chromatography. Rifabutin did not significantly affect amprenavir's pharmacokinetics. Amprenavir significantly increased the area under the curve at steady state (AUC(ss)) of rifabutin by 2.93-fold and the AUC(ss) of 25-O-desacetylrifabutin by 13.3-fold. Rifampin significantly decreased the AUC(ss) of amprenavir by 82%, but amprenavir had no effect on rifampin pharmacokinetics. Amprenavir decreased the results of the ERMBT by 83%. The results of the ERMBT after 2 weeks of rifabutin and rifampin therapy were increased 187 and 156%, respectively. Amprenavir plus rifampin was well tolerated. Amprenavir plus rifabutin was poorly tolerated, and 5 of 11 subjects discontinued therapy. Rifampin markedly increases the metabolic clearance of amprenavir, and coadministration is contraindicated. Amprenavir significantly decreases clearance of rifabutin and 25-O-desacetylrifabutin, and the combination is poorly tolerated. Amprenavir inhibits the ERMBT, and rifampin and rifabutin are equipotent inducers of the ERMBT.

Cost-effectiveness of sevelamer versus calcium carbonate plus atorvastatin to reduce LDL in patients with chronic renal insufficiency with dyslipidemia and hyperphosphatemia

We conducted a cost-effectiveness analysis to compare costs and clinical outcomes of sevelamer versus calcium carbonate plus atorvastatin for treatment of dyslipidemia in patients with chronic renal insufficiency. The model was from the third-party payer perspective. Efficacy and adverse event rates for each regimen were obtained from published clinical trials. Drug costs were based on average wholesale prices; monitoring costs were based on Medicare reimbursement rates. Our model suggests that the combination of calcium carbonate plus atorvastatin is substantially more cost-effective than sevelamer in reducing low-density lipoprotein (LDL) in these patients. One-way sensitivity analyses were performed to assess if 25% and 50% price reductions in sevelamer affected overall cost-effectiveness results. A 50% sevelamer price reduction was less expensive than combination therapy but remained less cost-effective. A two-way sensitivity analysis on the probability that a patient achieves the goal of a 35% LDL reduction resulted in calcium carbonate plus atorvastatin remaining more cost-effective. Further cost-effectiveness studies are necessary to corroborate our data.

Pharmacokinetic interaction between amprenavir and clarithromycin in healthy male volunteers

The P450 enzyme, CYP3A4, extensively metabolizes both amprenavir and clarithromycin. To determine if an interaction exists when these two drugs are coadministered, the pharmacokinetics of amprenavir and clarithromycin were investigated in healthy adult male volunteers. This was a Phase I, open-label, randomized, balanced, multiple-dose, three-period crossover study. Fourteen subjects received the following three regimens: amprenavir, 1,200 mg twice daily over 4 days (seven doses); clarithromycin, 500 mg twice daily over 4 days (seven doses); and the combination of the above regimens over 4 days (seven doses of each drug). Twelve subjects completed all treatments and the follow-up period. The erythromycin breath test (ERMBT) was administered at baseline, 2 h after the final dose of each of the three regimens and at the first follow-up visit. Coadministration of clarithromycin and amprenavir significantly increased the mean amprenavir AUC(ss), C(max,ss), and C(min,ss) by 18, 15, and 39%, respectively. Amprenavir had no significant effect on the AUC(ss) of clarithromycin, but the median T(max,ss)for clarithromycin increased by 2.0 h, renal clearance increased by 34%, and the AUC(ss) for 14-(R)-hydroxyclarithromycin decreased by 35% when it was given with amprenavir. Amprenavir and clarithromycin reduced the ERMBT result by 85 and 67%, respectively, and by 87% when the two drugs were coadministered. The baseline ERMBT value did not correlate with clearance of amprenavir or clarithromycin. A pharmacokinetic interaction occurs when amprenavir and clarithromycin are coadministered, but the effects are not likely to be clinically important, and coadministration does not require a dosage adjustment for either drug.

The pharmacokinetics and pharmacodynamics of losartan in continuous ambulatory peritoneal dialysis

The pharmacokinetics and pharmacodynamics of losartan and its active metabolite, E-3174, were studied in 8 stable, hypertensive continuous ambulatory peritoneal dialysis (CAPD) patients. Following a 1-week washout period, subjects received 100 mg of losartan orally for 7 days. On Days 1 and 7, hemodynamic and hormonal responses were determined, as were PK parameters on Day 7. Peritoneal equilibration testing was performed pre-Day 1 and on Day 7. AUC0-24 and t1/2 for losartan and E-3174 were 95 +/- 49.9 micrograms.min/mL and 176 +/- 82.1 micrograms.min/mL and 172.5 +/- 86.7 minutes and 628 +/- 575 minutes, respectively. These values are similar to those of normal subjects and subjects on hemodialysis. Peritoneal clearance of losartan and E-3174 was negligible. All subjects demonstrated a substantial reduction in blood pressure with at least a 10 mmHg drop in diastolic BP. Plasma renin activity (PRA) values increased, but aldosterone, endothelin, norepinephrine, and epinephrine values did not change following 7 days of losartan. Losartan was well tolerated in all study subjects.

Amiloride for the prevention of amphotericin B-induced hypokalemia and hypomagnesemia

OBJECTIVE

To review the published clinical data assessing the role of amiloride in the prevention of amphotericin B (AmB)induced electrolyte disorders.

DATA SOURCES

A MEDLINE search (January 1966-April 1999) of English-language literature pertaining to AmB, amiloride, potassium, and magnesium was performed. Tertiary sources were also used.

DATA EXTRACTION

In vivo and in vitro human and animal data and case reports were included due to the lack of published clinical trials.

DATA SYNTHESIS

AmB administration can result in severe hypokalemia and hypomagnesemia requiring chronic supplementation. In one prospective, controlled study of hypokalemia with AmB administration, patients receiving concomitant amiloride had significantly greater potassium concentrations (p < 0.01) and required significantly less potassium supplementation (p < 0.001). Amiloride may also reduce the amount of magnesium supplementation required by sparing elimination through the kidneys.

CONCLUSIONS

Amiloride may be considered for the prevention of AmB-induced hypokalemia and hypomagnesemia, especially in patients at high risk for complications resulting from these electrolyte disorders. Further studies are needed to assess concomitant use of other potassium-sparing diuretics and AmB.

Small and middle molecular weight solute clearance in nocturnal intermittent peritoneal dialysis

OBJECTIVES

To determine the dialysate-to-plasma (D/P) concentration ratios and peritoneal dialytic clearance (CI(D)) of substances with a wide range of molecular weights in subjects receiving a simulated nocturnal intermittent peritoneal dialysis (NIPD) session.

DESIGN

Open-label single-dose study.

SUBJECTS

Six end-stage renal disease patients undergoing peritoneal dialysis (PD).

SETTING

Clinical research center of a university-affiliated hospital.

INTERVENTIONS

Subjects received intravenous gentamicin and vancomycin on the first day of the study. Subjects received no PD until their return on the following day, when subjects underwent a simulated NIPD session utilizing four 2- to 2.5-L peritoneal dialysate dwells of 2 hours. Blood and dialysate samples were collected immediately before the session and after each dialysate dwell for determination of urea, creatinine, gentamicin, vancomycin, and beta2-microglobulin (beta2M) concentrations. Each solute's D/P concentration ratio and peritoneal CI(D) were calculated.

MEASUREMENTS AND MAIN RESULTS

The (mean +/- SD) 2-hour D/P concentration ratios were 0.78 +/- 0.05 (urea), 0.49 +/- 0.11 (creatinine), 0.38 +/- 0.08 (gentamicin), 0.11 +/- 0.06 (vancomycin), and 0.07 +/- 0.03 (beta2M). Peritoneal CI(D) values (mL/min of dialysis) were 19.0 +/- 2.8 (urea), 12.1 +/- 3.5 (creatinine), 8.4 +/- 2.8 (gentamicin), 2.7 +/- 1.5 (vancomycin), and 1.7 +/- 0.8 (beta2M). The D/P concentration ratios and peritoneal CI(D) values for urea, creatinine, and gentamicin were significantly different from vancomycin and beta2M (repeated measures ANOVA, p < 0.05). Beta2-microglobulin peritoneal CI(D) was strongly related to gentamicin peritoneal CI(D) (r = 0.96, p < 0.05).

CONCLUSION

Small molecular weight solutes have significantly greater D/P and peritoneal CI(D) than middle molecular weight solutes in NIPD. In NIPD, daily peritoneal CI(D) of beta2M is lower than that reported in continuous ambulatory PD. NIPD also results in lower drug CI(D) than that reported in continuous ambulatory PD studies.

Pharmacotherapy of dyslipidemia in postmenopausal women: weighing the evidence

In the United States, coronary heart disease (CHD) is the leading cause of death in women. The incidence of CHD rises dramatically in women following menopause, which can be partially attributed to a more atherogenic lipoprotein profile. For years, observational and epidemiological data have suggested that estrogen and progesterone therapy reduced CHD end points. However, the first prospective trial that evaluated hormone replacement therapy (HRT) for secondary CHD prevention demonstrated no positive cardiovascular benefit of HRT compared with placebo. In interventional studies, the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA)reductase inhibitors significantly reduced CHD outcomes in postmenopausal women, and these agents have emerged as the drugs of choice for primary and secondary CHD prevention. The selective estrogen receptor modulators (SERMs) may have a role in CHD prevention, but long-term clinical trials evaluating end points are needed. An evidence-based approach is necessary when deciding the appropriate pharmacotherapy of dyslipidemia in postmenopausal women.

Warfarin resistance in a patient with short bowel syndrome

Drug therapy in short bowel syndrome can be complicated by inadequate or incomplete absorption of drugs in the small intestine. Many case reports claim that warfarin absorption is not affected by the syndrome. We treated a patient with oral warfarin for recurring deep vein thrombosis; up to 20 mg/day was administered with no increase in the international normalized ratio. Drug-drug interactions that may prevent absorption, increase metabolism, or antagonize the effects of warfarin were ruled out. Intravenous lipid administration, which is anecdotally reported to precipitate warfarin resistance, may have contributed to the condition, but dosing was less frequent than in published reports. The most probable explanation of warfarin resistance is the reduced surface area for drug absorption secondary to surgical removal of the patient's duodenum and gastrojejunostomy.

Automated peritoneal dialysis: new implications for pharmacists

OBJECTIVE

To review the new automated peritoneal dialysis (APD) modalities that are available to patients with end-stage renal disease (ESRD), and to examine their potential pharmacokinetic and drug dosing consequences.

DATA SOURCES

A MEDLINE search (from January 1966 to June 1996) of English-language literature pertaining to peritoneal dialysis was performed. Additional references were obtained by reviewing the references of pertinent articles identified through the search. Tertiary sources were also used.

DATA EXTRACTION

Data regarding peritoneal dialysis techniques and pharmacokinetics were extracted from the literature. Data were evaluated according to the study design, population, results, and conclusions.

DATA SYNTHESIS

ESRD is the result of progressive chronic renal insufficiency and requires renal replacement therapy. APD is the fastest growing renal replacement therapy by percentage in the US and provides dialysis exchanges via a machine while the patient sleeps, thereby improving patient convenience, peritoneal dialysis compliance rates, and decreasing peritonitis rates. Well-designed pharmacokinetic studies involving APD have not been conducted. Consequently, no formal drug dosing recommendations are available for APD, and pharmacists must rely on established dosing guidelines for continuous ambulatory peritoneal dialysis (CAPD) when recommending dosing regimens. This article describes the new APD treatment modalities available and the potential pharmacokinetic differences between CAPD and APD.

CONCLUSIONS

Well-designed studies are needed to fully characterize the pharmacokinetic parameters of drugs in APD. Until then, pharmacists should recommend that intraperitoneally administered drugs be given during the longest peritoneal dialysate dwell of the day and that serum concentrations of drugs with narrow therapeutic indices be monitored closely.