Cisplatin Concentrations in Long and Short Duration Infusion: Implications for the Optimal Time of Radiation Delivery

INTRODUCTION

Cisplatin has radiosensitizing properties and the best sensitization to radiotherapy occurs with a higher plasma concentration of cisplatin. To our knowledge the optimal time sequence between chemotherapy and administration of radiation therapy, to obtain maximum effect from concurrent chemoradiation is unclear.

AIM

The aim of this study was to measure the two cisplatin infusion regimens in order to determine the total and free cisplatin post infusion concentration changes over time. These changes may have clinical implications on the optimum time of administration of post infusion radiation therapy.

MATERIALS AND METHODS

Two cohorts of patients were recruited and both, total and free plasma concentration of cisplatin following long and short durations of intravenous infusion was determined. Blood samples were collected at 0.5, 1, 1.5, 2, 3 and 5 hours from the start of the infusion in the 1hour infusion group and at 2, 3, 3.5, 4, 6 and 24 hours from the start of the infusion, in the 3 hour infusion group. Total and free cisplatin concentrations were measured using a validated HPLC-UV method.

RESULTS

The highest concentration of total and free cisplatin was achieved at the end of the infusion in both regimens. Total cisplatin concentration declined 30 minutes after the end of infusion in both the groups. After 1hour of discontinuing cisplatin, the free cisplatin concentration also declined significantly.

CONCLUSION

We conclude that radiation should be administered within 30 minutes of completion of the infusion irrespective of the duration of infusion.

Development and validation of limited sampling strategy equation for mycophenolate mofetil in children with systemic lupus erythematosus

The aim of this study was to establish a limited sample strategy (LSS) to predict the mycophenolic acid (MPA) area under the curve (AUC)_(0-12) in children with systemic lupus erythematosus (SLE). Three months after initiation of mycophenolate mofetil (MMF) 26 children with SLE presented for therapeutic drug monitoring of MPA. On the day of the test, 10 specimens were collected, analyzed, and MPA AUC_(0-12) was calculated. Using step-wise regression analysis, LSS equations were developed. Using bootstrap validation, the predictive performance was calculated. The measured mean (standard deviation) for the trough concentration and AUC_(0-12) were 2.55 (1.57) μg/ml and 62.6 (21.67) mg.h/L, respectively. The range of trough concentrations and AUC_(0-12) were 0.7-5.54 μg/ml and 22.1-104.8 mg.h/L, respectively. The interindividual variability (%CV) for dose normalized AUC_(0-12) and dose normalized C_trough was 46.5% and 61.1%, respectively. The correlation between the concentrations at the different time points and MPA AUC_(0-12) ranged from 0.05 (1.5 h) to 0.56 (4 h). Two LSS equations that included 4 or 5 time points up to 3 h were developed and validated. The 4 point LSS had a correlation (R²) of 0.88 and the 5 point LSS an R² of 0.87. With respect to the 4 point and 5 point MPA LSS AUC_(0-12), the bias was 1.92% and 1.96%, respectively, and the imprecision was 11.24% and 11.28%, respectively. A 4 point LSS which concludes within 3 h after the administration of the MMF dose was developed and validated, to determine the MPA AUC_(0-12) in children with SLE.

Combined approach with therapeutic drug monitoring and pharmacogenomics in renal transplant recipients

In patients undergoing renal transplantation, dose individualization for tacrolimus is routinely achieved with therapeutic drug monitoring (TDM). The patient started on 5.5 mg/day of tacrolimus had a significantly elevated tacrolimus trough concentration. The tacrolimus dose was regularly reduced following TDM at many time periods in the post transplant period but the tacrolimus concentration was consistently elevated. Genomic analysis done after four years revealed mutations in the genes encoding for CYP3A5 and MDR1 (2677G > T). Pharmacogenomics alongside TDM, will soon emerge as the backbone of dose individualization. But for genomics to be beneficial, it should be advocated in the pre-transplant or early post transplant period.

Mycophenolic acid area under the curve recovery time following rifampicin withdrawal

Renal transplant patients prescribed mycophenolate mofetil (MMF) may require treatment for tuberculosis with a regimen including the tuberculocidal drug rifampicin. MMF is an ester prodrug which is rapidly hydrolysed to the active compound, mycophenolic acid (MPA). Therapeutic drug monitoring of mycophenolate involves the measurement of MPA area under the curve (MPA-AUC_0-12). Rifampicin is known to increase the metabolism and decrease enterohepatic recirculation of mycophenolic acid, (MPA). When MPA is monitored after the discontinuation of rifampicin, an important factor is the time required for the MPA area under the curve to return to the pre-rifampicin value. At present this is not known. This report describes one such renal allograft patient, on long term MMF and prescribed rifampicin by a local physician. As expected there was a clinically significant decrease in MPA-AUC_0-12 Three weeks after rifampicin was discontinued the MPA-AUC_0-12 was still only 65% of the pre-rifampicin value and only 55% of the steady state MPA-AUC_0-12 measured six months later.

Stability issues of mycophenolic Acid in plasma: from patient to laboratory

Although mycophenolate is widely prescribed in India, therapeutic drug monitoring of mycophenolic acid is not performed in most centers. This could be due to many factors such as the large investment and expertise required for high performance liquid chromatography, or the high costs involved as specialized refrigeration is required when transporting patient specimens to the laboratories with the facility to analyze MPA. The Clinical Pharmacology unit of the Christian Medical College Hospital routinely monitors the area under the curve of MPA. In order to determine if this unit could act as a central laboratory for MPA monitoring, the stability of MPA in plasma under a series of storage and transport conditions was assessed. The procedures involved the analysis of plasma specimens from patients on mycophenolate mofetil and blank plasma spiked with MPA reference standard. A range of low and high concentrations were separately analyzed to confirm long term and short term stability. The measured concentrations of MPA showed no significant change over 5 months when stored at -20 degrees or over five days under conditions encountered during transport.

A six-hour extrapolated sampling strategy for monitoring mycophenolic acid in renal transplant patients in the Indian subcontinent

BACKGROUND

Therapeutic drug monitoring for mycophenolic acid (MPA) is increasingly being advocated. The present therapeutic range relates to the 12-hour area under the serum concentration time profile (AUC).However, this is a cumbersome, tedious, cost restricting procedure. Is it possible to reduce this sampling period?

AIM

To compare the AUC from a reduced sampling strategy with the full 12-hour profile for MPA.

SETTINGS AND DESIGN

Clinical Pharmacology Unit of a tertiary care hospital in South India. Retrospective, paired data.

MATERIALS AND METHODS

Thirty-four 12-hour profiles from post-renal transplant patients on Cellcept were evaluated. Profiles were grouped according to steroid and immunosuppressant co-medication and the time after transplant. MPA was estimated by high performance liquid chromatography with UV detection. From the 12-hour profiles the AUC up to only six hours was calculated by the trapezoidal rule and a correction factor applied. These two AUCs were then compared.

STATISTICAL ANALYSIS

Linear regression, intra-class correlations (ICC) and a two-tailed paired t-test were applied to the data.

RESULTS

Comparing the 12-hour AUC with the paired 6-hour extrapolated AUC, the ICC and linear regression(r2) were very good for all three groups. No statistical difference was found by a two-tailed paired t-test. No bias was seen with a Bland Altman plot or by calculation.

CONCLUSION

For patients on Cellcept with prednisolone +/- cyclosporine the 6-hour corrected is an accurate measure of the full 12-hour AUC.

A Prospective Evaluation of Leflunomide Therapy for Cytomegalovirus Disease in Renal Transplant Recipients

AIM

A preliminary observation suggests leflunomide is effective in the treatment of cytomegalovirus (CMV) disease in renal transplant recipients. A prospective evaluation was conducted in renal transplant recipients to study the efficacy of leflunomide in the treatment of CMV disease.

PATIENTS AND METHODS

With prior approval and informed consent for therapy and follow-up, 17 consecutive consenting renal transplant recipients with proven CMV disease were treated with leflunomide. CMV disease was defined as a clinical syndrome of fever and/or symptoms of organ involvement, leukopenia, and a positive nested CMV quantitative PCR test at 0.001 microg/5 microL template input, with or without histologic evidence of tissue invasion. Leflunomide metabolite concentrations (A77 1726) were monitored.

RESULTS

Of the 17 patients, 14 patients were treated for 6 months for CMV disease the first time; the remaining 3 received leflunomide treatment for relapse after ganciclovir treatment, for a year. Seven patients had fever with viremia and no organ involvement, nine had viremia with involvement of gastrointestinal tract, and one had fever with CMV inclusions in the allograft, with no demonstrable viremia. The three patients with relapse treated with leflunomide responded. Overall, 15 patients (88%) clinically responded to leflunomide therapy and with viral clearance from blood and healing of involved organs. The cost of therapy with intravenous ganciclovir (Cymevene, Roche) for 2 weeks was US 721 dollars while that of leflunomide (Cleft, Cipla Ltd) for 6 months was US 64 dollars.

CONCLUSION

Leflunomide treatment for CMV disease in renal transplant recipients is effective, simple, and economical.