Tacrolimus Exposure Before and After a Switch From Twice-Daily Immediate-Release to Once-Daily Prolonged Release Tacrolimus: The ENVARSWITCH Study.

LCP-tacrolimus displays enhanced oral bioavailability compared to immediate-release (IR-) tacrolimus. The ENVARSWITCH study aimed to compare tacrolimus AUC0-24 h in stable kidney (KTR) and liver transplant recipients (LTR) on IR-tacrolimus converted to LCP-tacrolimus, in order to re-evaluate the 1:0.7 dose ratio recommended in the context of a switch and the efficiency of the subsequent dose adjustment. Tacrolimus AUC0-24 h was obtained by Bayesian estimation based on three concentrations measured in dried blood spots before (V2), after the switch (V3), and after LCP-tacrolimus dose adjustment intended to reach the pre-switch AUC0-24 h (V4). AUC0-24 h estimates and distributions were compared using the bioequivalence rule for narrow therapeutic range drugs (Westlake 90% CI within 0.90-1.11). Fifty-three KTR and 48 LTR completed the study with no major deviation. AUC0-24 h bioequivalence was met in the entire population and in KTR between V2 and V4 and between V2 and V3. In LTR, the Westlake 90% CI was close to the acceptance limits between V2 and V4 (90% CI = [0.96-1.14]) and between V2 and V3 (90% CI = [0.96-1.15]). The 1:0.7 dose ratio is convenient for KTR but may be adjusted individually for LTR. The combination of DBS and Bayesian estimation for tacrolimus dose adjustment may help with reaching appropriate exposure to tacrolimus rapidly after a switch.

New perspectives for the therapeutic drug monitoring of tacrolimus: Quantification in volumetric DBS based on an automated extraction and LC-MS/MS analysis.

Volumetric microsampling devices have been developed for home-based capillary blood sampling and are now increasingly proposed for the therapeutic drug monitoring (TDM) of immunosuppressive drugs. Our objective was to validate a LC-MS/MS method for tacrolimus quantification based on both a manual and an automated extraction of dried blood spots (DBS) collected with a volumetric microsampling device. DBS collection was performed by placing a drop of whole blood (WB) pre-spiked with tacrolimus onto a sealing film and placing the hemaPEN® device (Trajan Scientific and Medical, Melbourne, Australia) into the drop according to the device specifications. Tacrolimus was quantified using a fully automatic preparation module connected to a LCMS system (CLAM-3020® and LCMS-8060®, Shimadzu, Marne-la-Vallée, France). The method was validated analytically and clinically in accordance with the EMA and IATDMCT guidelines. The method was linear from 1 to 100 µg/L. Within- and between-run accuracy and precision fulfilled the validation criteria (biases and imprecision <15% or 20% for the lower limit of quantification). No hematocrit effect, matrix effect or carry-over was observed. No selectivity issue was identified and dilution integrity was confirmed. Tacrolimus in DBS was stable for 14 days at room temperature and +4°C, and for 72h at +60°C. There was a good correlation between tacrolimus concentrations measured in WB and in DBS of 20 kidney and liver transplant recipients (r=0.93 and 0.87, for manual and automated extraction respectively). A method for tacrolimus measurement in DBS collected with volumetric micro-sampling device, based on a fully automated process from pre-treatment to LC-MS/MS analysis was developed and validated according to analytical and clinical criteria. This performing sampling and analytical procedure opens the perspective of an easier, faster and more efficient TDM of tacrolimus for patients, clinicians and laboratories.

Quantitative impact of pre-analytical process on plasma uracil when testing for dihydropyrimidine dehydrogenase deficiency.

AIMS: Determining dihydropyrimidine dehydrogenase (DPD) activity by measuring patient's uracil (U) plasma concentration is mandatory before fluoropyrimidine (FP) administration in France. In this study, we aimed to refine the pre-analytical recommendations for determining U and dihydrouracil (UH2 ) concentrations, as they are essential in reliable DPD-deficiency testing. METHODS: U and UH2 concentrations were collected from 14 hospital laboratories. Stability in whole blood and plasma after centrifugation, the type of anticoagulant and long-term plasma storage were evaluated. The variation induced by time and temperature was calculated and compared to an acceptability range of ±20%. Inter-occasion variability (IOV) of U and UH2 was assessed in 573 patients double sampled for DPD-deficiency testing. RESULTS: Storage of blood samples before centrifugation at room temperature (RT) should not exceed 1 h, whereas cold (+4°C) storage maintains the stability of uracil after 5 hours. For patients correctly double sampled, IOV of U reached 22.4% for U (SD = 17.9%, range = 0-99%). Notably, 17% of them were assigned with a different phenotype (normal or DPD-deficient) based on the analysis of their two samples. For those having at least one non-compliant sample, this percentage increased up to 33.8%. The moment of blood collection did not affect the DPD phenotyping result. CONCLUSION: Caution should be taken when interpreting U concentrations if the time before centrifugation exceeds 1 hour at RT, since it rises significantly afterwards. Not respecting the pre-analytical conditions for DPD phenotyping increases the risk of DPD status misclassification.

Neurotoxicity Despite a Renal Function-Adjusted Cefepime Regimen: A Case Study.

An 83-year-old man, presenting decreased renal function (estimated glomerular filtration rate 21 mL/min/1.73 m), was treated for a bone and joint infection (on a trans-metatarsal right foot amputation) caused by Klebsiella Pneumonia sensitive to cefepime. The starting dose (1 g bid) was based on recommendations for patients presenting severe infections. One week after treatment initiation, the patient developed neurotoxicity, exhibiting extremely high plasma cefepime concentrations. Based on TDM, the dose was reduced by 8 times the original dose. This case report highlights the importance of therapeutic drug monitoring for cefepime, especially in patients presenting altered renal functions, as typical recommendations are estimated for standard patients.

Phenotyping of Uracil and 5-Fluorouracil Metabolism Using LC-MS/MS for Prevention of Toxicity and Dose Adjustment of Fluoropyrimidines.

BACKGROUND: Plasma concentrations of fluoropyrimidine exhibit a wide interindividual variability that depends mainly on the activity of dihydropyrimidine dehydrogenase, its major catabolic enzyme. Patients with low dihydropyrimidine dehydrogenase activity are at an increased risk of overexposure and often severe, sometimes lethal, toxicity. This study aimed to develop a quick and easy bioanalytical method for the simultaneous determination of endogenous uracil (U), exogenous 5-fluorouracil (5-FU), and their respective 5,6-dihydro-metabolite in human plasma using Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). METHODS: After protein precipitation, the compounds were purified using liquid-liquid extraction. Chromatographic separation was conducted using a Cortecs T3 column and binary gradient elution. Detection and quantification were performed in the positive electrospray ionization and selected the reaction monitoring mode after 2 transitions per analyte and 1 per internal standard. The data obtained with this technique were retrospectively gathered for uracil metabolism phenotyping before fluoropyrimidine treatment (as enforced by national regulations) in a large group of 526 patients. RESULTS: The analytical response was linear (r > 0.99 for all compounds), and it yielded a lower limit of quantification of 2 ng·mL for U and UH2 as well as 4 ng·mL for 5-FU and 5,6-dihydro-5-FUH2. The median uracil concentration in 526 patients was 10.6 mcg/L, with extreme values of 3.9 and 81.6 mcg/L; 78 patients (15%) had uracil concentration ≥16 mcg/L, that is, above the threshold of decreased enzyme activity and initial dose reduction.

Automatic quantification of uracil and dihydrouracil in plasma.

Fluoropyrimidines-based chemotherapies are the backbone in the treatment of many cancers. However, the use of 5-fluorouracil and its oral pre-prodrug, capecitabine, is associated with an important risk of toxicity. This toxicity is mainly due to a deficiency of dihydropyrimidine dehydrogenase (DPD). This deficiency may be detected by using a phenotypic approach that consists in the measurement of uracilemia or the calculation of dihydrouracil (UH2)/uracil (U) ratio. For uracilemia, a threshold value of 16 ng/ml has been proposed for partial deficiency, while a value of 150 ng/ml has been proposed for complete deficiency. We have developed a rapid, accurate and fully-automated procedure for the quantification of U and UH2 in plasma. Sample extraction was carried out by a programmable liquid handler directly coupled to a liquid chromatography - tandem mass spectrometry (LC-MS/MS) system. The method was validated according to the EMA guidelines and ISO 15189 requirements and was applied to real patient samples (n = 64). The limit of quantification was 5 and 10 ng/ml for U and UH2 respectively. Imprecision and inaccuracy were less than 15% for inter and intra-assay tests. Comparison with dedicated routine method showed excellent correlation. An automated procedure perfectly fulfills the need of low inaccuracy and CVs at the threshold values (less than 5% at 16 ng/ml) and is highly suitable for the characterization of DPD deficiency. Automatization should guaranty reliable and robust performances by minimizing the sources of variation such as volume inaccuracies, filtration or manual extraction related errors.

Acute visual loss following dapsone-induced methemoglobinemia and hemolysis.

OBJECTIVE: While methemoglobinemia is a possible complication of chronic dapsone therapy or of acute overdose, serious adverse manifestations related to methemoglobin formation remain rare. We present an unusual case with severe ischemic retinal injury. CASE REPORT: A 30-year-old African woman presented with a sudden decrease of visual acuity secondary to retinal ischemia. She was chronically treated with dapsone (50 mg/day) for a dermatologic disease and denied any drug overdose. However, the determination of serum dapsone level on admission revealed a largely supratherapeutic concentration (20,044 µg/ml compared with 1-3.5 ± 0.5 µg/ml for therapeutic levels). The methemoglobin level at admission was 32% (sulfhemoglobin 1.2%), with hemoglobin level, 7.4 g/dl, schistocytes count, 2-5%, lactate dehydrogenase level, 580 IU/l, and haptoglobin level, < 10 mg/dl. The patient had both alpha-thalassemia and sickle cell trait. She was treated with methylene blue, vitamin C, and exchange transfusion. There was no improvement in visual symptoms over time. CONCLUSIONS: In a patient with supratherapeutic serum levels of dapsone, the severity of visual injury was associated with dapsone-induced methemoglobinemia and hemolysis, and perhaps also with some hematologic predisposing factors.