Fludarabine pharmacokinetics after subcutaneous and intravenous administration in patients with lupus nephritis

An Explanation of Why Dose-Corrected Area Under the Curve for Alternate Administration Routes Can Be Greater than for Intravenous Dosing

It is generally believed that bioavailability (F) calculated based on systemic concentration area under the curve (AUC) measurements cannot exceed 1.0, yet some published studies report this inconsistency. We teach and believe, based on differential equation derivations, that rate of absorption has no influence on measured systemic clearance following an oral dose, i.e., determined as available dose divided by AUC. Previously, it was thought that any difference in calculating F from urine data versus that from systemic concentration AUC data was due to the inability to accurately measure urine data. A PubMed literature search for drugs exhibiting F > 1.0 and studies for which F was measured using both AUC and urinary excretion dose-corrected analyses yielded data for 35 drugs. We show and explain, using Kirchhoff's Laws, that these universally held concepts concerning bioavailability may not be valid in all situations. Bioavailability, determined using systemic concentration measurements, for many drugs may be overestimated since AUC reflects not only systemic elimination but also absorption rate characteristics, which is most easily seen for renal clearance measures. Clearance of drug from the absorption site must be significantly greater than clearance following an iv bolus dose for F(AUC) to correctly correspond with F(urine). The primary purpose of this paper is to demonstrate that studies resulting in F > 1.0 and/or greater systemic vs urine bioavailability predictions may be accurate. Importantly, these explications have no significant impact on current regulatory guidance for bioequivalence testing, nor on the use of exposure (AUC) measures in making drug dosing decisions.

Immunosuppressive treatment for proliferative lupus nephritis

BACKGROUND

Cyclophosphamide, in combination with corticosteroids, has been first-line treatment for inducing disease remission for proliferative lupus nephritis, reducing death at five years from over 50% in the 1950s and 1960s to less than 10% in recent years. Several treatment strategies designed to improve remission rates and minimise toxicity have become available. Treatments, including mycophenolate mofetil (MMF) and calcineurin inhibitors, alone and in combination, may have equivalent or improved rates of remission, lower toxicity (less alopecia and ovarian failure) and uncertain effects on death, end-stage kidney disease (ESKD) and infection. This is an update of a Cochrane review first published in 2004 and updated in 2012.

OBJECTIVES

Our objective was to assess the evidence and evaluate the benefits and harms of different immunosuppressive treatments in people with biopsy-proven lupus nephritis. The following questions relating to management of proliferative lupus nephritis were addressed: 1) Are new immunosuppressive agents superior to or as effective as cyclophosphamide plus corticosteroids? 2) Which agents, dosages, routes of administration and duration of therapy should be used? 3) Which toxicities occur with the different treatment regimens?

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Specialised Register up to 2 March 2018 with support from the Cochrane Information Specialist using search terms relevant to this review. Studies in the Specialised Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs comparing any immunosuppressive treatment for biopsy-proven class III, IV, V+III and V+VI lupus nephritis in adult or paediatric patients were included.

DATA COLLECTION AND ANALYSIS

Data were abstracted and the risks of bias were assessed independently by two authors. Dichotomous outcomes were calculated as risk ratio (RR) and measures on continuous scales calculated as mean differences (MD) with 95% confidence intervals (CI). The primary outcomes were death (all causes) and complete disease remission for induction therapy and disease relapse for maintenance therapy. Evidence certainty was determined using GRADE.

MAIN RESULTS

In this review update, 26 new studies were identified, to include 74 studies involving 5175 participants overall. Twenty-nine studies included children under the age of 18 years with lupus nephritis, however only two studies exclusively examined the treatment of lupus nephritis in patients less than 18 years of age.Induction therapy Sixty-seven studies (4791 participants; median 12 months duration (range 2.5 to 48 months)) reported induction therapy. The effects of all treatment strategies on death (all causes) and ESKD were uncertain (very low certainty evidence) as this outcome occurred very infrequently. Compared with intravenous (IV) cyclophosphamide, MMF may have increased complete disease remission (RR 1.17, 95% CI 0.97 to 1.42; low certainty evidence), although the range of effects includes the possibility of little or no difference.Compared to IV cyclophosphamide, MMF is probably associated with decreased alopecia (RR 0.29, 95% CI 0.19 to 0.46; 170 less (129 less to 194 less) per 1000 people) (moderate certainty evidence), increased diarrhoea (RR 2.42, 95% CI 1.64 to 3.58; 142 more (64 more to 257 more) per 1000 people) (moderate certainty evidence) and may have made little or no difference to major infection (RR 1.02, 95% CI 0.67 to 1.54; 2 less (38 less to 62 more) per 1000 people) (low certainty evidence). It is uncertain if MMF decreased ovarian failure compared to IV cyclophosphamide because the certainty of the evidence was very low (RR 0.36, 95% CI 0.06 to 2.18; 26 less (39 less to 49 more) per 1000 people). Studies were not generally designed to measure ESKD.MMF combined with tacrolimus may have increased complete disease remission (RR 2.38, 95% CI 1.07 to 5.30; 336 more (17 to 1048 more) per 1000 people (low certainty evidence) compared with IV cyclophosphamide, however the effects on alopecia, diarrhoea, ovarian failure, and major infection remain uncertain. Compared to standard of care, the effects of biologics on most outcomes were uncertain because of low to very low certainty of evidence.Maintenance therapyNine studies (767 participants; median 30 months duration (range 6 to 63 months)) reported maintenance therapy. In maintenance therapy, disease relapse is probably increased with azathioprine compared with MMF (RR 1.75, 95% CI 1.20 to 2.55; 114 more (30 to 236 more) per 1000 people (moderate certainty evidence). Multiple other interventions were compared as maintenance therapy, but patient-outcome data were sparse leading to imprecise estimates.

AUTHORS' CONCLUSIONS

In this review update, studies assessing treatment for proliferative lupus nephritis were not designed to assess death (all causes) or ESKD. MMF may lead to increased complete disease remission compared with IV cyclophosphamide, with an acceptable adverse event profile, although evidence certainty was low and included the possibility of no difference. Calcineurin combined with lower dose MMF may improve induction of disease remission compared with IV cyclophosphamide, but the comparative safety profile of these therapies is uncertain. Azathioprine may increase disease relapse as maintenance therapy compared with MMF.

Personalized fludarabine dosing to reduce nonrelapse mortality in hematopoietic stem-cell transplant recipients receiving reduced intensity conditioning

Patients undergoing hematopoietic cell transplantation (HCT) with reduced intensity conditioning (RIC) commonly receive fludarabine. Higher exposure of F-ara-A, the active component of fludarabine, has been associated with a greater risk of nonrelapse mortality (NRM). We sought to develop a model for fludarabine dosing in adult HCT recipients that would allow for precise dose targeting and predict adverse clinical outcomes. We developed a pharmacokinetic model from 87 adults undergoing allogeneic RIC HCT that predicts F-ara-A population clearance (Clpop) accounting for ideal body weight and renal function. We then applied the developed model to an independent cohort of 240 patients to identify whether model predictions were associated with NRM and acute graft versus host disease (GVHD). Renal mechanisms accounted for 35.6% of total F-ara-A Clpop. In the independent cohort, the hazard ratio of NRM at day 100 was significantly higher in patients with predicted F-ara-A clearance (Clpred) <8.50 L/h (P < 0.01) and area under the curve (AUCpred) >6.00 μg × h/mL (P = 0.01). A lower Clpred was also associated with more NRM at month 6 (P = 0.01) and trended toward significance at 12 months (P = 0.05). In multivariate analysis, low fludarabine clearance trended toward higher risk of acute GVHD (P = 0.05). We developed a model that predicts an individual's systemic F-ara-A exposure accounting for kidney function and weight. This model may provide guidance in dosing especially in overweight individuals and those with altered kidney function.

Pharmacokinetic modeling of therapies for systemic lupus erythematosus

With the increasing use of different types of therapies in treating autoimmune diseases such as systemic lupus erythematosus (SLE), there is a need to utilize pharmacokinetic (PK) strategies to optimize the clinical outcome of these treatments. Various PK analysis approaches, including population PK modeling and physiologically based PK modeling, have been used to evaluate drug PK characteristics and population variability or to predict drug PK profiles in a mechanistic manner. This review outlines the PK modeling of major SLE therapies including immunosuppressants (methotrexate, azathioprine, mycophenolate and cyclophosphamide, among others) and immunomodulators (intravenous immunoglobulin). It summarizes the population PK modeling, physiologically based PK modeling and model-based individualized dosing strategies to improve the therapeutic outcomes in SLE patients.

Treatment for lupus nephritis

BACKGROUND

Cyclophosphamide, in combination with corticosteroids has been used to induce remission in proliferative lupus nephritis, the most common kidney manifestation of the multisystem disease, systemic lupus erythematosus. Cyclophosphamide therapy has reduced mortality from over 70% in the 1950s and 1960s to less than 10% in recent years. Cyclophosphamide combined with corticosteroids preserves kidney function but is only partially effective and may cause ovarian failure, infection and bladder toxicity. Several new agents, including mycophenolate mofetil (MMF), suggest reduced toxicity with equivalent rates of remission. This is an update of a Cochrane review first published in 2004.

OBJECTIVES

To assess the benefits and harms of different immunosuppressive treatments in biopsy-proven proliferative lupus nephritis.

SEARCH METHODS

For this update, we searched the Cochrane Renal Group's Specialised Register (up to 15 April 2012) through contact with the Trials' Search Coordinator using search terms relevant to this review.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs comparing any treatments for biopsy-proven lupus nephritis in both adult and paediatric patients with class III, IV, V +III and V +IV lupus nephritis were included. All immunosuppressive treatments were considered.

DATA COLLECTION AND ANALYSIS

Data were abstracted and quality assessed independently by two authors, with differences resolved by discussion. Dichotomous outcomes were reported as risk ratio (RR) and measurements on continuous scales reported as mean differences (MD) with 95% confidence intervals (CI).

MAIN RESULTS

We identified 50 RCTs involving 2846 participants. Of these, 45 studies (2559 participants) investigated induction therapy, and six studies (514 participants), considered maintenance therapy.Compared with intravenous (IV) cyclophosphamide, MMF was as effective in achieving stable kidney function (5 studies, 523 participants: RR 1.05, 95% CI 0.94 to 1.18) and complete remission of proteinuria (6 studies, 686 participants: RR 1.16, 95% CI 0.85 to 1.58). No differences in mortality (7 studies, 710 participants: RR 1.02, 95% CI 0.52 to 1.98) or major infection (6 studies, 683 participants: RR 1.11, 95% CI 0.74 to 1.68) were observed. A significant reduction in ovarian failure (2 studies, 498 participants: RR 0.15, 95% CI 0.03 to 0.80) and alopecia (2 studies, 522 participants: RR 0.22, 95% CI 0.06 to 0.86) was observed with MMF. In maintenance therapy, the risk of renal relapse (3 studies, 371 participants: RR 1.83, 95% CI 1.24 to 2.71) was significantly higher with azathioprine compared with MMF. Multiple other interventions were compared but outcome data were relatively sparse. Overall study quality was variable. The internal validity of the design, conduct and analysis of the included RCTs was difficult to assess in some studies because of the omission of important methodological details. No study adequately reported all domains of the risk of bias assessment so that elements of internal bias may be present.

AUTHORS' CONCLUSIONS

MMF is as effective as cyclophosphamide in inducing remission in lupus nephritis, but is safer with a lower risk of ovarian failure. MMF is more effective than azathioprine in maintenance therapy for preventing relapse with no increase in clinically important side effects. Adequately powered trials with long term follow-up are required to more accurately define the risks and eventual harms of specific treatment regimens.

High fludarabine exposure and relationship with treatment-related mortality after nonmyeloablative hematopoietic cell transplantation

Despite its common use in nonmyeloablative preparative regimens, the pharmacokinetics of fludarabine are poorly characterized in hematopoietic cell transplantation (HCT) recipients and exposure-response relationships remain undefined. Our objective of this study was to evaluate the association between plasma F-ara-A exposure, the systemically circulating moiety of fludarabine, and engraftment, acute graft vs host disease (GVHD), treatment-related mortality (TRM) and survival after HCT. The preparative regimen consisted of cyclophosphamide 50 mg/kg/day i.v. day −6; plus fludarabine 30-40 mg/m²/day i.v. on days −6 to −2 and TBI 200 cGy on day −1. F-ara-A pharmacokinetics were performed with the first dose of fludarabine in 87 adult patients. Median (range) F-ara-A AUC _(0-∞) was 5.0 ug*hr/mL (2.0-11.0), clearance 15.3 L/hour (6.2-36.6), C_min 55 ng/mL (17-166), and concentration on day_zero 16.0 ng/mL (0.1-144.1). Despite dose reductions, patients with renal insufficiency had higher F-ara-A exposures. There was strong association between high plasma concentrations of F-ara-A and increased risk of TRM and reduced overall survival. Patients with an AUC_(0-∞) greater than 6.5 ug*hr/mL had 4.56 greater risk of TRM and significantly lower survival. These data suggest that clinical strategies are needed to optimize dosing of fludarabine to prevent overexposure and toxicity in HCT.

International Society of Geriatric Oncology (SIOG) recommendations for the adjustment of dosing in elderly cancer patients with renal insufficiency

A SIOG taskforce was formed to discuss best clinical practice for elderly cancer patients with renal insufficiency. This manuscript outlines recommended dosing adjustments for cancer drugs in this population according to renal function. Dosing adjustments have been made for drugs in current use which have recommendations in renal insufficiency and the elderly, focusing on drugs which are renally eliminated or are known to be nephrotoxic. Recommendations are based on pharmacokinetic and/or pharmacodynamic data where available. The taskforce recommend that before initiating therapy, some form of geriatric assessment should be conducted that includes evaluation of comorbidities and polypharmacy, hydration status and renal function (using available formulae). Within each drug class, it is sensible to use agents which are less likely to be influenced by renal clearance. Pharmacokinetic and pharmacodynamic data of anticancer agents in the elderly are needed in order to maximise efficacy whilst avoiding unacceptable toxicity.

F-ara-A pharmacokinetics during reduced-intensity conditioning therapy with fludarabine and busulfan

Fludarabine is commonly used in combination with busulfan as part of conditioning regimens before allogeneic stem cell transplantation. So far, no data are available on busulfan-fludarabine drug interactions in transplant recipients. The pharmacokinetic (PK) properties of F-ara-A (9-beta-D-arabinosyl-2-fluoradenine) before and after application of busulfan were prospectively investigated in 16 patients with hematological malignancies. The conditioning regimen consisted of intravenous fludarabine 30 mg/m(2) over 30 min from day -6 to day -3, and oral busulfan given at 1 mg/kg every 6 h from day -5 to day -2. PK parameters of F-ara-A, derived from plasma and urine on day -6, -5, -4 and -3, were determined using high-performance liquid chromatography (HPLC). AUC, C(max), t(1/2), Cl(total) and V(SS) were 21.9 microMh, 3.5 microM, 13.0 h, 4.3 l/h/m(2), 60.0 l/m(2) on day -6 and 22.4 microMh, 3.5 microM, 14.0 h, 4.7 l/h/m(2), 69.0 l/m(2) on day -5 to (-2), respectively. Cl(renal) and the urine-recovery were 4.8 l/h, 43.7% of the fludarabine dose on day -6 and 3.9 l/h, 44.2% of the fludarabine dose on day -5 to (-2), respectively. There were no changes in PK parameters of fludarabine given before and after intake of busulfan. This implies that a clinically relevant busulfan-fludarabine drug interaction is unlikely.

Newer drugs for the treatment of lupus nephritis

This article first reviews the current treatment of lupus nephritis, with a focus on the most serious forms, that is, the proliferative subtypes. Current standards for treatment have been developed empirically. Corticosteroids form the basis of all regimens. Cyclophosphamide given intravenously for prolonged periods is the current gold standard. Azathioprine can be regarded as an effective drug for maintenance treatment of lupus nephritis. Studies on its efficacy in schedules for remission induction are in progress. It has been learned from studies on 'conventional' immunosuppression that randomised, clinical trials should comprise large numbers of patients and a follow-up of many years to elucidate differences between effective strategies. These requirements are not met by any of the 'new' treatments we discuss in this review. There is only limited experience in patients with lupus nephritis with drugs that are currently used for immunosuppression in other autoimmune diseases, such as methotrexate, cyclosporin and high-dose intravenous gammaglobulins, nor with new immunosuppressive drugs that have been developed for immunosuppression in organ transplantation (mycophenolate mofetil, tacrolimus, fludarabine and cladribine). Hormonal therapy with the weak androgen prasterone (dehydroepiandrosterone; DHEA) has no role in treatment of active lupus nephritis. There are interesting experiences with agents that have evolved from progress in immunobiology and in our understanding of immunological processes. These modalities enable more specific immunosuppression and include monoclonal antibodies directed at immune cells, cytokines and components of the complement system, constructs developed to induce tolerance in pathogenic B cells, and gene therapy. Finally, we review data on autologous bone marrow transplantation in patients with systemic lupus erythematosus. We conclude that some strategies (like mycophenolate mofetil) are good candidates for further investigation in large-scale, prospective, randomised trials with prolonged follow-up (which are almost by definition hard to perform). Most new biological agents still are in a pre-clinical phase.