Development of a high pressure liquid chromatography method for the determination of mycophenolic acid and its glucuronide metabolite in small volumes of plasma from paediatric patients

Validated Simple HPLC-UV Method for Mycophenolic Acid (MPA) Monitoring in Human Plasma. Internal Standardization: Is It Necessary?

The aim of the work was to prepare a simple but reliable HPLC-UV method for the routine monitoring of mycophenolic acid (MPA). Sample preparation was based on plasma protein precipitation with acetonitrile. The isocratic separation of MPA and internal standard (IS) fenbufen was made on Supelcosil LC-CN column (150 × 4.6 mm, 5 µm) using a mobile phase: CH₃CN:H₂O:0.5M KH₂PO₄:H₃PO₄ (260:700:40:0.4, v/v). UV detection was set at 305 nm. The calibration covered the MPA concentration range: 0.1–40 µg/mL. The precision was satisfactory with RSD of 0.97–7.06% for intra-assay and of 1.92–5.15% for inter-assay. The inaccuracy was found between −5.72% and +2.96% (+15.40% at LLOQ) and between −8.82% and +5.31% (+19.00% at LLOQ) for intra- and inter-assay, respectively, fulfilling acceptance criteria. After a two-year period of successful application, the presented method has been retrospectively calibrated using the raw data disregarding the IS in the calculations. The validation and stability parameters were similar for both calculation methods. MPA concentrations were recalculated and compared in 1187 consecutive routine therapeutic drug monitoring (TDM) trough plasma samples from mycophenolate-treated patients. A high agreement (r² = 0.9931, p < 0.0001) of the results was found. A Bland–Altman test revealed a mean bias of −0.011 μg/mL (95% CI: −0.017; −0.005) comprising −0.14% (95% Cl: −0.39; +0.11), whereas the Passing–Bablok regression was y = 0.986x + 0.014. The presented method can be recommended as an attractive analytical tool for medical (hospital) laboratories equipped with solely basic HPLC apparatus. The procedure can be further simplified by disapplying an internal standard while maintaining appropriate precision and accuracy of measurements.

Pharmacokinetics, electrophysiological, and morphological effects of the intravitreal injection of mycophenolic acid in rabbits

PURPOSE

To determine the half-life of mycophenolic acid (MPA) in the vitreous of New Zealand albino rabbits after intravitreal injection and the retinal toxicity of different doses of MPA.

METHODS

Ten micrograms of MPA (Roche Bioscience, Palo Alto, CA) was injected in the vitreous of 16 rabbits, animals were sacrificed at different time-points, and vitreous samples underwent high-performance liquid chromatography. For functional and morphological studies, 5 doses of MPA (0.05, 0.5, 2, 10, and 100 μg) were injected in the vitreous of 20 rabbits. As control, contralateral eyes were injected with aqueous vehicle. Electroretinograms (ERGs) were recorded before injection and at days 7, 15, and 30. Animals were sacrificed on day 30 and retinas were analyzed under light microscopy.

RESULTS

MPA half-life in the vitreous was 5.0±0.3 days. ERG revealed photoreceptor functional impairment in eyes injected with 0.5 μg and higher on day 30, while eyes injected with 100 μg presented the same changes already from day 15. No morphological change was found.

CONCLUSIONS

MPA vitreous half-life is 5.0 days. Intravitreal injection of 0.5 μg MPA and higher causes dose- and time-related photoreceptor sensitivity decrease in rabbits. The MPA dose of 0.05 μg may be safe for intravitreal use in rabbits.

Vitreous pharmacokinetics and electroretinographic findings after intravitreal injection of acyclovir in rabbits

OBJECTIVES

Acute retinal necrosis is a rapidly progressive and devastating viral retinitis caused by the herpesvirus family. Systemic acyclovir is the treatment of choice; however, the progression of retinal lesions ceases approximately 2 days after treatment initiation. An intravitreal injection of acyclovir may be used an adjuvant therapy during the first 2 days of treatment when systemically administered acyclovir has not reached therapeutic levels in the retina. The aims of this study were to determine the pharmacokinetic profile of acyclovir in the rabbit vitreous after intravitreal injection and the functional effects of acyclovir in the rabbit retina.

METHODS

Acyclovir (Acyclovir; Bedford Laboratories, Bedford, OH, USA) 1 mg in 0.1 mL was injected into the right eye vitreous of 32 New Zealand white rabbits, and 0.1 mL sterile saline solution was injected into the left eye as a control. The animals were sacrificed after 2, 9, 14, or 28 days. The eyes were enucleated, and the vitreous was removed. The half-life of acyclovir was determined using high-performance liquid chromatography. Electroretinograms were recorded on days 2, 9, 14, and 28 in the eight animals that were sacrificed 28 days after injection according to a modified protocol of the International Society for Clinical Electrophysiology of Vision.

RESULTS

Acyclovir rapidly decayed in the vitreous within the first two days after treatment and remained at low levels from day 9 onward. The eyes that were injected with acyclovir did not present any electroretinographic changes compared with the control eyes.

CONCLUSIONS

The vitreous half-life of acyclovir is short, and the electrophysiological findings suggest that the intravitreal delivery of 1 mg acyclovir is safe and well tolerated by the rabbit retina.

UPLC MS/MS method for quantification of mycophenolic acid and metabolites in human plasma: Application to pharmacokinetic study

BACKGROUND

We described the development and full validation of a rapid, high throughput sensible and accurate UPLC method using tandem mass spectrometry detection for mycophenolate acid (MPA) and its metabolites, MPA glucuronide (MPAG) and acyl MPA glucuronide (AcMPAG) concentration determination with MPA-D3 as internal standard in human plasma.

METHODS

Plasma pretreatment involved a one-step protein precipitation with acetonitrile. The separation was performed by reverse-phase chromatography on a Waters BEH HSST3 100 mm*2.1 mm*1.8 μm column. The multiple reaction monitoring transitions used for quantification were m/z 321.04→303.02 for MPA, 524.09→303.02 for AcMPAG and MPAG and 324.03→306.04 for MPA-D3 in the electrospray positive ionization mode.

RESULTS

The method was linear over the concentration range of 0.1-20mg/L for MPA and AcMPAG and 1-200mg/L for MPAG respectively. The intra- and inter-day precision values were below 14% and accuracy was from 94.0 to 103.3% at all quality control levels. The lower LOQ was 0.1 mg/L for MPA and AcMPAG, 1 mg/L for MPAG.

CONCLUSION

Sample analysis time was reduced to 7 min including sample preparation. The present method was successfully applied to a pharmacokinetic study following oral administration of enterocoated sodium mycophenolate in de novo renal transplantation.

Determination of total, free and saliva mycophenolic acid with a LC-MS/MS method: application to pharmacokinetic study in healthy volunteers and renal transplant patients

Mycophenolic acid (MPA) is the active moiety of mycophenoate mofetil (MMF), an ester prodrug widely used as an immunosuppressant. Therapeutic drug monitoring (TDM) of MPA is becoming mandatory for transplant patients received MMF therapy in the routine clinical practice because of large individual variability, dose-related toxicity and the risk of acute rejection. In this study, a rapid, sensitive and selective LC-MS/MS method was developed and validated for the quantitative analysis of total and free MPA in plasma and in saliva that uses one identical liquid chromatographic and mass spectrometric condition. Following protein precipitation for total and saliva MPA, and ultrafiltration for free MPA, chromatographic separation was performed on an Allure PFP Propyl analytical column (100 x 2.1 mm, 5 microm, RESTEK Co., Bellefonte, PA, USA) with 0.1% formic acid in acetonitrile and 0.1% formic acid in water (45:55, v/v) as the mobile phases. The compounds were quantified by positive electrospray ionization tandem mass spectrometry. Selectivity, linearity, accuracy, precision, recovery, matrix effect, and saliva stability were evaluated during method validation. The validated method was applied to a pharmacokinetic study of MPA after an oral administration of a single 1000 mg of MMF to eight healthy male volunteers and 750 mg bid of MMF to nine renal transplant patients.

A fast ultra-performance liquid chromatography method for simultaneous quantification of mycophenolic acid and its phenol- and acyl-glucuronides in human plasma

Several studies have demonstrated a close relationship between mycophenolic acid (MPA) exposure and the risk for graft rejection or side effects. Measurements of MPA and its metabolites plasma levels are therefore recommended. A new chromatographic method has been developed using ultra-performance liquid chromatography (UPLC) to improve both analytical throughput and sensitivity. MPA and its phenol-glucuronide and acyl-glucuronide were extracted from plasma using Isolute C2 solid phase extraction (SPE) cartridges (100 mg, 3 mL). UPLC separations were performed with a Waters BEH C18 column (50 x 2.1 mm, 1.7 microm) maintained at 65 degrees C on a Waters Acquity instrument equipped with a photodiode array detector. The total UPLC run time was 3.5 minutes. The method was linear in the range of 0.1-40 microg/mL for MPA and acyl-glucuronide, and 1-400 microg/mL for phenol-glucuronide. Relative standard error and mean relative prediction error were <15% for all tested quality controls (in-house and external proficiency panels). UPLC performances are characterized by a dramatic reduction in retention times together with an improvement of the sensitivity without affecting peak resolution. Further validations have been obtained by analyzing routine and clinical trial patients' samples. Significant improvement of the analytical throughput (reduction of run time from >10 to 3.5 minutes) was obtained using UPLC for MPA analyses. This retention time reduction was accompanied by an improvement of other analytical performances such as sensitivity.

Influence of lansoprazole and rabeprazole on mycophenolic acid pharmacokinetics one year after renal transplantation

Peptic ulcer disease is a common complication after organ transplantation, and long-term administration of antiulcer agents is needed in many renal transplant recipients. Although several drug interactions with mycophenolic acid (MPA), the active metabolite of the prodrug mycophenolate mofetil (MMF), have been reported, little is known about the interaction between MPA and proton pump inhibitors (PPIs). The present study investigated the drug interaction between MMF and lansoprazole or rabeprazole and the impact of cytochrome (CYP) 2C19, and multidrug resistance (MDR)1 C3435T polymorphisms on these drug interactions at 1 year after renal transplantation. Retrospectively, 61 recipients were divided into 3 groups: MMF and tacrolimus as combination immunosuppressive therapy, together with either 30 mg lansoprazole (n = 22) or 10 mg rabeprazole (n = 17), or without PPI (n = 22). One year after transplantation, plasma concentrations of MPA were measured by high-performance liquid chromatography. The mean dose-unadjusted and -adjusted Cmax of MPA with 30 mg lansoprazole were significantly lower than those without PPI (11.8 vs. 17.8 microg/mL, P = 0.0197, and 22.6 vs. 33.1 ng/mL/mg MMF, P = 0.0222, respectively). In recipients having the CYP2C19 *1/*2+*1/*3 or MDR1 C3435T CC genotype, the mean dose-adjusted AUC0-12 of MPA with 30 mg lansoprazole was significantly smaller than that with 10 mg rabeprazole or without PPI. The plasma concentration of MPA was influenced by 30 mg lansoprazole but not 10 mg rabeprazole. Because of the greater gastric acid secretion-inhibitory effect of 30 mg lansoprazole in recipients having the CYP2C19 *1/*2+*1/*3 (intermediate metabolizer) or MDR1 C3435T CC genotype, the elution and hydrolysis of MMF might be decreased. Although the clinical relevance might be minor, the fact that administration of 30 mg lansoprazole in patients having the CYP2C19 *2 or *3 allele or the MDR1 C3435T CC genotype diminishes the absorption of MPA in the maintenance stage after renal transplantation should be taken into consideration with regard to the MPA pharmacokinetics.

Sensitive high-performance liquid chromatography–tandem mass spectrometry method for quantitative analysis of mycophenolic acid and its glucuronide metabolites in human plasma and urine

A method to determine total and free mycophenolic acid (MPA) and its metabolites, the phenolic (MPAG) and acyl (AcMPAG) glucuronides, using HPLC and mass spectrometry was developed. Mean recoveries in plasma and urine samples were >85%, and the lower limits of quantification for MPA, MPAG and AcMPAG were 0.05, 0.05 and 0.01 mg/L, respectively. For plasma, the assay was linear over 0.05-50 mg/L for MPA and MPAG, and from 0.01 to 10mg/L for AcMPAG. A validation study demonstrated good inter- and intra-day precision (CV<or=11%) and accuracy (bias<or=16%) and satisfactory specificity and stability. Pharmacokinetic parameters were assessed in plasma and urine from healthy volunteers after an oral dose of mycophenolate mofetil.

Therapeutic drug measurement of mycophenolic acid derivatives in transplant patients

INTRODUCTION

Mycophenolic acid, the active metabolite of the prodrug mycophenolate mofetil, is widely used as an immunosuppressive agent in transplant patients for the prophylaxis of acute rejection. Recent prospective trials suggested the need for therapeutic drug monitoring, which raises the necessity to acquire accurate methods to measure MPA and its metabolites.

OBJECTIVE

Present an overview of the reasons to monitor MPA and its metabolites as well as a review of the currently available methods for their determination.

METHODS

Articles published from January 1992 to December 2006 were reviewed.

RESULTS

Most of the cited references use either chromatographic or immunoassay techniques. Basic information about biological samples used for the analysis, sample preparation, stationary phase, mobile phase, detection mode and validation data are discussed. Current information suggests the feasibility to set up method(s) to monitor MPA and its metabolites in most centers.

New materials in sorptive extraction techniques for polar compounds

This paper provides an overview of the new developments in material and format technology that improve the extraction of polar compounds in several extraction techniques. They mainly include solid-phase extraction, but there are also other sorptive extraction techniques, such as stir bar sorptive extraction and solid-phase microextraction that use either fibers or in-tube devices. We focus on new synthesised materials that are both commercially available and "in-house". Most novel materials that enhance the extraction of polar compounds are hydrophilic and have large specific surface area; however, we also cover other leading technologies, such as sol-gel or monolith. We describe the morphological and chemical properties of these new sorbents so that we can better understand them and relate them to their capability of retaining polar compounds. We discuss the extraction efficiency for polar compounds when these polymers are used as sorptive material and compare them to other materials. We also mention some representative examples of applications.

Fully Automated Analytical Method for Mycophenolic Acid Quantification in Human Plasma Using On-line Solid Phase Extraction and High Performance Liquid Chromatography With Diode Array Detection

We have developed a new fully automated method for mycophenolic (MPA) acid quantification in plasma to optimize therapeutic drug monitoring of tranplant patients. This method involved solid-phase extraction on disposable extraction cartridges and reversed-phase high-performance liquid chromatography with diode array detection. Solid-phase extraction was performed automatically by an automated sample with extraction catridges system. After washing, MPA was eluted from the cartridge onto a Chromolith RP-18e column. MPA and the internal standard were detected at 306 nm. The retention time of MPA was 6.3 minutes. The developed method was linear from 0.2 to 20 microg/mL. The limit of quantification was 0.2 microg/mL. The method showed a good precision with intraday and interday variation coefficient less than 6%. The intraday accuracy ranged from 97.6% to 100.4% and the interday accuracy varied from 97.1% to 100.8%. The extraction efficiency was greater than 90%. This method is simple and shows a good specificity with respect to commonly co-prescripted drugs.

An isocratic high performance liquid chromatographic method for quantification of mycophenolic acid and its glucuronide metabolite in human serum using liquid–liquid extraction: Application to human pharmacokinetic studies

BACKGROUND

Mycophenolate mofetil (MMF) is a morpholinoethyl ester of mycophenolic acid (MPA), which is widely used as an immunosuppressive agent in renal transplant patients for the prophylaxis of acute rejection. We describe a fast and sensitive isocratic HPLC method for simultaneous quantification of the immunosuppressant mycophenolic acid, and its major metabolites in human serum.

METHODS

The analytes were extracted from serum using ethyl acetate/2 propanol (4-1, v/v) and subjected to an isocratic HPLC method using a phenyl analytical column. A mobile phase consisted of methanol-0.05 mol/l sodium phosphate buffer (46/54 v/v; pH 2.5) containing hexadecyl trimethylammonium bromide (100mg/l w/v) and triethylamine (0.25% v/v) was used.

RESULTS

The standard curve was linear from 0.050 to 51.2 microg/ml and 0.125 to 64 microg/ml, for mycophenolic acid and its metabolite, respectively. The method showed excellent selectivity, specificity, sensitivity, precision and accuracy. The respective limits of quantification for the drug and its metabolite were 0.050 and 0.125 microg/ml. This method was applied in a bioequivalence study following single dose administration of 2 different mycophenolate mofetil preparations in 24 healthy volunteers. Blood samples were analyzed and pharmacokinetic parameters of mycophenolic acid and its metabolite were compared.

CONCLUSION

This procedure is simple, and comparing to the previously published methods, more sensitivity is obtained and less time is needed for sample preparation. Less time was needed for the liquid-liquid extraction. Although, suitability of the method has been demonstrated in pharmacokinetic studies of MMF in normal subjects, its specificity in renal and hepatic transplant patients has not been established and the stated upper linearity of MPAG may not be sufficient for use in transplant patients.