Eradication of meticillin-resistant Staphylococcus aureus from human skin by the novel LL-37-derived peptide P10 in four pharmaceutical ointments.

Skin bacterial colonization/infection is a frequent cause of morbidity in patients with chronic wounds and allergic/inflammatory skin diseases. This study aimed to develop a novel approach to eradicate meticillin-resistant Staphylococcus aureus (MRSA) from human skin. To achieve this, the stability and antibacterial activity of the novel LL-37-derived peptide P10 in four ointments was compared. Results indicate that P10 is chemically stable and antibacterial in hypromellose gel and Softisan-containing cream, but not in Cetomacrogol cream (with or without Vaseline), at 4 °C for 16 months. Reduction in MRSA counts on Leiden human epidermal models (LEMs) by P10 in hypromellose gel was greater than that of the peptide in Cetomacrogol cream or phosphate buffered saline. P10 did not show adverse effects on LEMs irrespective of the ointment used, while Cetomacrogol with Vaseline and Softisan cream, but not hypromellose gel or Cetomacrogol cream, destroyed MRSA-colonized LEMs. Taking all this into account, P10 in hypromellose gel dose-dependently reduced MRSA colonizing the stratum corneum of the epidermis as well as biofilms of this bacterial strain on LEMs. Moreover, P10 dose-dependently reduced MRSA counts on ex-vivo human skin, with P10 in hypromellose gel being more effective than P10 in Cetomacrogol and Softisan creams. P10 in hypromellose gel is a strong candidate for eradication of MRSA from human skin.

Pharmacodynamics of Cefepime Combined with Tazobactam against Clinically Relevant Enterobacteriaceae in a Neutropenic Mouse Thigh Model.

The lack of new antibiotics has prompted investigation of the combination of two existing agents-cefepime, a broad-spectrum cephalosporin, and tazobactam-to broaden their efficacy against extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae We determined the pharmacokinetic (PK) and pharmacodynamic (PD) properties of the combination in a murine neutropenic thigh model in order to establish its exposure-response relationships (ERRs). The PK of cefepime were determined for five doses; that of tazobactam was determined in earlier studies (Melchers et al., Antimicrob Agents Chemother 59:3373-3376, 2015, https://doi.org/10.1128/AAC.04402-14). The PK were linear for both compounds. The estimated mean (standard deviation [SD]) half-life of cefepime was 0.33 (0.12) h, and that of tazobactam was 0.176 (0.026) h; the volumes of distribution (V) were 0.73 liters/kg and 1.14 liters/kg, respectively. PD studies of cefepime administered every 2 h (q2h) with or without tazobactam, including dose fractionation studies of tazobactam, were performed against six ESBL-producing isolates. A sigmoidal maximum-effect (Emax) model was fitted to the data. In the dose fractionation study, the q2h regimen was more efficacious than the q4h and q6h regimens, indicating time-dependent activity of tazobactam. The threshold concentration (CT ) best correlating with tazobactam efficacy was 0.25 mg/liter, as evidenced by the best fit of the percentage of time above the threshold concentration (%fT>CT ) and response. A mean %fT>CT of 24.6% (range, 11.4 to 36.3%) for a CT of 0.25 mg/liter was required to obtain a bacteriostatic effect. We conclude that tazobactam enhanced the effect of cefepime in otherwise resistant isolates of Enterobacteriaceae and that the %fT>CT of 0.25 mg/liter best correlated with efficacy. These studies provide the basis for the development of human dosing regimens for this combination.

Antimicrobial Peptide P60.4Ac-Containing Creams and Gel for Eradication of Methicillin-Resistant Staphylococcus aureus from Cultured Skin and Airway Epithelial Surfaces.

We previously found the LL-37-derived peptide P60.4Ac to be effective against methicillin-resistant Staphylococcus aureus (MRSA) on human epidermal models (EMs). The goal of this study was to identify the preferred carrier for this peptide for topical application on skin and mucosal surfaces. We prepared P60.4Ac in three formulations, i.e., a water-in-oil cream with lanolin (Softisan 649), an oil-in-water cream with polyethylene glycol hexadecyl ether (Cetomacrogol), and a hydroxypropyl methylcellulose (hypromellose) 4000 gel. We tested the antimicrobial efficacy of the peptide in these formulations against mupirocin-resistant and -sensitive MRSA strains on EMs and bronchial epithelial models (BEMs). The cytotoxic effects of formulated P60.4Ac on these models were determined using histology and WST-1 and lactate dehydrogenase assays. Moreover, we assessed the stability of the peptide in these formulations with storage for up to 3 months. Killing of MRSA by P60.4Ac in the two creams was less effective than that by P60.4Ac in the hypromellose gel. In agreement with those findings, P60.4Ac in the hypromellose gel was highly effective in eradicating the two MRSA strains from EMs. We found that even 0.1% (wt/wt) P60.4Ac in the hypromellose gel killed >99% of the viable planktonic bacteria and >85% of the biofilm-associated bacteria on EMs. Hypromellose gels containing 0.1% and 0.5% (wt/wt) P60.4Ac effectively reduced the numbers of viable MRSA cells from BEMs by >90%. No cytotoxic effects of P60.4Ac in the hypromellose gel with up to 2% (wt/wt) P60.4Ac on keratinocytes in EMs and in the hypromellose gel with up to 0.5% (wt/wt) P60.4Ac on epithelial cells in BEMs were observed. High-performance liquid chromatography analysis showed that P60.4Ac was stable in the Softisan cream and the hypromellose gel but not in the Cetomacrogol cream. We conclude that P60.4Ac formulated in hypromellose gel is both stable and highly effective in eradicating MRSA from colonized EMs and BEMs.

The Effect of Tamoxifen Dose Increment in Patients With Impaired CYP2D6 Activity.

BACKGROUND: The effect of tamoxifen dose elevation on endoxifen serum concentration was investigated in patients with reduced CYP2D6 activity resulting from genetic variation and/or CYP2D6 inhibitor use. Additionally, baseline differences in endoxifen concentrations between the different CYP2D6 phenotypes were studied. METHODS: Patients, treated with tamoxifen 20 mg once daily (QD) for at least 4 weeks, were classified as phenotypic extensive (EM), intermediate (IM), or poor (PM) metabolizer based on their genotype and comedication. In patients with an IM or PM phenotype, the tamoxifen dose was increased to 40 mg QD for 4 weeks. Tamoxifen, 4-OH-tamoxifen, N-desmethyltamoxifen, and endoxifen serum concentrations were measured at baseline and 4 weeks after the dose increment. Side effects of tamoxifen were assessed using the validated Functional Assessment of Cancer Therapy-Endocrine Symptom subscale (FACT-ESS-19). RESULTS: The median baseline endoxifen concentration differed between EMs (11.4 mcg/L: n = 19), IMs (8.3 mcg/L: n = 16), and PMs (4.0 mcg/L: n = 7), P = 0.040. Tamoxifen dose elevation significantly increased the median endoxifen concentrations in 12 IMs from 9.5 to 17.4 mcg/L (P < 0.001) and in 4 PMs from 3.8 to 7.8 mcg/L (P = 0.001), without influencing median FACT-ESS-19 scores. CONCLUSIONS: Raising the tamoxifen dose to 40 mg QD significantly increased endoxifen concentrations in IMs and PMs without increasing side effects. The tamoxifen dose increment in PMs was insufficient to reach endoxifen concentrations equal to those observed in EMs. Future studies will clarify the direct effect of endoxifen exposure on tamoxifen efficacy and may reveal a threshold endoxifen concentration that is critical for its efficacy.

Dried blood spot analysis for therapeutic drug monitoring of pazopanib.

Dried blood spot (DBS) sampling is potentially a more patient-friendly and flexible alternative to venous sampling of pazopanib. This study determined the agreement between pazopanib DBS and plasma concentrations to facilitate implementation of pazopanib DBS sampling into clinical practice. Paired DBS and plasma samples were collected in 12 patients. Pazopanib plasma concentrations were calculated from DBS concentrations using the formula: plasma concentration = DBSconcentration /(1 - hematocrit). Passing-Bablok and Bland-Altman analyses were used to determine the agreement between calculated and measured plasma concentrations. We predefined a clinical acceptance limit of 25% for the Bland-Altman analysis. Passing-Bablok analysis showed a small constant (intercept estimate, -8.53 [95%CI, -12.22 to -4.41]) and slightly proportional (slope estimate, 1.15 [95%CI, 1.04-1.24]) bias between calculated and measured concentrations. This bias was clinically nonrelevant, as shown by Bland-Altman analysis; the mean ratio of calculated to measured concentrations was 0.94 (95%CI, 0.65-1.23). The clinical acceptance limits were well within these 95% limits of agreement. More specifically, 92.6% of the data points were within the predefined acceptance limits. Pazopanib plasma concentrations can be accurately calculated from DBS concentrations. Although validation of DBS cards prepared by patients themselves is required, these results show that DBS sampling can be used to monitor pazopanib therapy in clinical practice.

Individualized dosing of tyrosine kinase inhibitors: are we there yet?

Tyrosine kinase inhibitors (TKIs) are registered at a fixed oral dose, despite their large variability in pharmacokinetics (PK). Given that the evidence for a relation between drug exposure and treatment outcome is growing, this one-dose-fits-all approach can unintentionally lead to under- and overexposure. Dose individualization could lower this variability and thereby beneficially effect treatment outcome. In this article, we explore whether TKIs used for solid tumors meet the criteria for dose individualization. Despite limitations such as retrospective analysis, current data suggest that the following Ctrough levels could be used: imatinib 1100ng/ml, sunitinib when continuously dosed 37.5ng/ml, intermittent 50ng/ml and pazopanib 20µg/ml. A comprehensive review of the literature also shows that prospective trials investigating the influence of dose individualization on treatment outcome are warranted.

Development of a pharmacokinetic model of mitotane: toward personalized dosing in adrenocortical carcinoma.

BACKGROUND: Mitotane is the drug of choice in medical treatment of adrenocortical carcinoma. The antineoplastic effect seems to be correlated with a minimum plasma level of 14 mg/L, but plasma concentration build-up is in general slow due to the long elimination half-life. Consequently, the therapeutic effect sets in after weeks or even months. The objective of this study was to develop a pharmacokinetic model that enables clinicians to adjust dosing based on a target drug exposure, which facilitates personalized therapy. METHODS: Data on dosing and plasma level measurements performed throughout mitotane therapy were retrospectively collected in a population of 29 patients from 2 hospitals. A population pharmacokinetic model was constructed based on data from 20 patients using iterative 2-stage Bayesian fitting (MWPharm). The model was validated in an independent sample of 9 patients. RESULTS: The concentration-time data were best described by a 3-compartment model. The model estimated mitotane clearance at 0.94 ± 0.37 L/h and a volume of distribution in the steady state at 161 ± 68 L/kg of lean body mass. The mean prediction error was 14% ± 13%. CONCLUSIONS: A pharmacokinetic model was developed, which characterized mitotane by slow clearance and large volume of distribution. The model seems to be able to predict mitotane levels in individual patients with an error margin of 14%. The model enables one to adapt dosing based on individual plasma level measurements in prospective setting, which improves the accuracy of the prediction. We expect that individualization of mitotane dosing leads to anticipated and more rapid attainment of the therapeutic levels and potentially to improved clinical management of mitotane treatment.

Therapeutic drug monitoring to individualize the dosing of pazopanib: a pharmacokinetic feasibility study.

BACKGROUND: Patients treated with the standard dose of pazopanib show a large interpatient variability in drug exposure defined as the area under the plasma concentration-time curve (AUC0-24h). The primary objective of this study was to evaluate the feasibility of pharmacokinetics (PK)-guided individualized dosing to reduce the interpatient variability in pazopanib exposure. METHODS: Thirteen patients were treated with pazopanib for 3 consecutive periods of 2 weeks. During the first period, all patients received 800 mg of pazopanib once daily to reach steady-state exposure. During the second period, the patients either received a PK-guided individualized pazopanib dose or the registered fixed 800-mg dose. During the third period, these 2 dosing regimens were switched. RESULTS: The interpatient variability in pazopanib AUC0-24h during fixed dosing (27.3 coefficient of variation) was not significantly different when compared with the variability in AUC0-24h during PK-guided dosing (24.8 coefficient of variation). The percentage of patients within the target window during PK-guided dosing (53.9%) was not significantly different from the percentage during fixed dosing (46.2%). Both Ctrough and C24 were significantly (P < 0.001) correlated to pazopanib AUC0-24h (R = 0.596 and R = 0.940, respectively). Pazopanib AUC0-24h decreased 17% over time. CONCLUSIONS: PK-guided dosing did not reduce the interpatient variability in pazopanib exposure. In this study, the intrapatient variability in pazopanib exposure was relatively large compared with interpatient variability. This makes it challenging to achieve a target exposure within a predefined window. The causes of intrapatient variability must first be better understood and controlled, before PK-guided dosing can reduce the interpatient variability.

Pharmacokinetics of treosulfan in pediatric patients undergoing hematopoietic stem cell transplantation.

BACKGROUND: High-dose treosulfan is used in conditioning regimens before hematopoietic stem cell transplantation in children. Pharmacokinetic data to optimize treosulfan dosing are scarce in this patient population. The aims of this study were the development and validation of an analytical method for treosulfan in human serum and the development of a pharmacokinetic model for treosulfan in pediatric patients. Furthermore, we aimed to develop a limited sampling strategy to estimate treosulfan systemic exposure with a minimum of inconvenience and risk for the patient. METHODS: A reversed phase high-performance liquid chromatography method using ultraviolet detection to determine treosulfan in human serum samples was developed and validated according to food and drug administration guidelines. Serum pharmacokinetics after the first treosulfan administration was investigated in 20 children using nonlinear mixed-effect modeling, and a limited sampling strategy was developed and validated. RESULTS: The assay was validated in a 10-500 mg/L concentration range with a lower limit of quantification of 10 mg/L. Accuracies were within the 90%-110% limit. The coefficients of variation of the within-day imprecision and between-days imprecision were less than 5%. Pharmacokinetics was adequately described with a 1-compartment model. The population estimates for clearance (CL) and volume of distribution were 6.85 L/h and 13.2 L for a typical patient of 20 kg, respectively. Treosulfan exposure could be adequately quantified with 2 samples, at 4 and 7 hours after the start of a 3-hour treosulfan infusion, with a mean deviation of 3% of individual CL and area under the curve based on limited sampling in comparison with the full data set in a total cohort. CONCLUSIONS: In this study, a bioanalytical method, PK model, and limited sampling model were developed and validated. Furthermore, PK parameters of 20 pediatric patients were analyzed, demonstrating an interpatient variability in area under the curve of 14.5%. This study demonstrates the essential developments in the optimization of treosulfan therapy based on PK data.

Limited sampling model for advanced mycophenolic acid therapeutic drug monitoring after liver transplantation.

BACKGROUND: The immunosuppressive drug mycophenolate mofetil (MMF), with mycophenolic acid (MPA) as active metabolite, is a nonnephrotoxic alternative to calcineurin inhibitors. Therapeutic drug monitoring (TDM) of MPA may improve clinical benefit from MMF therapy, especially in MMF monotherapy or with reduced dose of a calcineurin inhibitor. Limited data are available on TDM strategies for MPA in orthotopic liver transplantation (OLT). The authors here describe the pharmacokinetic (PK) behavior of MPA after OLT and developed a Bayesian limited sampling model for monitoring MMF after OLT. METHODS: PK data were obtained from 57 stable patients, and trapezoidal area under the curve (AUC(0-12h)) was calculated. The effect of the covariates kidney function and serum albumin concentration was studied. A TDM strategy was developed based on individualized population PKs using Bayesian estimations and limited sampling models to predict the MPA AUC. RESULTS: A relationship between MMF dose and MPA AUC was found and a 8-fold apparent clearance range of MPA was observed at the same dose level. Significant relationships of albumin concentration and creatinine clearance with MPA plasma clearance were identified (respectively, r² = 0.12 and 0.24; P < 0.05). A model with limited sampling at 0, 0.5, 1, 2, and 3 hours after drug administration showed very good correlation with trapezoidal AUC(0-12h) with acceptable bias and precision (r² = 0.92, mean prediction error = 1, mean absolute prediction error = 13; P < 0.05). CONCLUSIONS: Remarkable variability of MPA clearance in stable OLT patients exists, which can be partially explained by the patients' albumin serum levels and creatinine clearance. Systemic exposure in these patients can be accurately assessed by the Bayesian limited sampling TDM strategy.

Morphine induces hyperalgesia without involvement of µ-opioid receptor or morphine-3-glucuronide.

Opioid-induced hyperalgesia (OIH) is a paradoxical increase in pain perception that may manifest during opioid treatment. For morphine, the metabolite morphine-3-glucuronide (M3G) is commonly believed to underlie this phenomenon. Here, in three separate studies, we empirically assess the role of M3G in morphine-induced hyperalgesia. In the first study, CD-1 mice injected with morphine (15 mg/kg subcutaneously) after pretreatment with the opioid receptor antagonist naltrexone (NTX) (15 mg/kg) showed tail withdrawal latency reductions indicative of hyperalgesia (2.5 ± 0.1 s at t = 30 min, P < 0.001 versus baseline). In these mice, the morphine/M3G concentration ratios versus effect showed a negative correlation (r(p) = -0.65, P < 0.001), indicating that higher morphine relative to M3G concentrations are associated with increased OIH. In the second study, similar hyperalgesic responses were observed in mice lacking the multidrug resistance protein 3 (MRP3) transporter protein (Mrp3(-/-) mice) in the liver and their wild-type controls (FVB mice; latency reductions: 3.1 ± 0.2 s at t = 30 min, P < 0.001 versus within-strain baseline). In the final study, the pharmacokinetics of morphine and M3G were measured in Mrp3(-/-) and FVB mice. Mrp3(-/-) mice displayed a significantly reduced capacity to export M3G into the systemic circulation, with plasma M3G concentrations just 7% of those observed in FVB controls. The data confirm previous literature that morphine causes hyperalgesia in the absence of opioid receptor activation but also indicate that this hyperalgesia may occur without a significant contribution of hepatic M3G. The relevance of these data to humans has yet to be demonstrated.

Population pharmacokinetics and pharmacogenetics of everolimus in renal transplant patients.

BACKGROUND AND OBJECTIVE: Everolimus is a novel macrolide immunosuppressant used in the prevention of acute and chronic rejection of solid organ transplants. Everolimus is being actively investigated worldwide as a non-nephrotoxic alternative for calcineurin inhibitors. Its highly variable pharmacokinetics and narrow therapeutic window make it difficult to maintain an adequate exposure to prevent serious adverse effects. The primary objective of this study was to improve prediction of everolimus systemic exposure in renal transplant patients by describing the pharmacokinetics of everolimus and identifying the influence of demographic factors and a selection of polymorphisms in genes coding for ABCB1, CYP3A5, CYP2C8 and PXR. The secondary objective of this study was to develop a limited sampling strategy to enable prediction of everolimus exposure in an efficient way and to compare it with the widely used trough blood concentration (C(trough)) monitoring. METHODS: A total of 783 blood samples were obtained from 53 renal transplant patients who had been switched from a triple therapy of ciclosporin, mycophenolate mofetil and prednisolone to a calcineurin inhibitor-free dual therapy of everolimus (twice daily) and prednisolone. Everolimus blood concentrations were analysed in whole blood using liquid chromatography-tandem mass spectrometry during routine therapeutic drug monitoring targeting an area under the blood concentration-time curve from time zero to 12 hours (AUC(12)) of 120 µg · h/L. A population pharmacokinetic model was developed and demographic factors and genetic polymorphisms in genes coding for ABCB1, CYP3A5, CYP2C8 and PXR were included as covariates. In addition, a limited sampling strategy was developed. RESULTS: Maintaining everolimus systemic exposure at an AUC(12) of 120 µg · h/L resulted in low rejection rates but considerable numbers of adverse events and toxicity. Everolimus pharmacokinetics were best described by a two-compartment model with lag-time (oral clearance = 17.9 L/h; volume of distribution of the central compartment after oral administration [V(1)/F] = 148 L and first-order absorption rate constant [k(a)] = 7.36 h-1). Ideal body weight was significantly related to V(1)/F. None of the selected polymorphisms in genes coding for enzymes involved in distribution and metabolism of everolimus had a significant influence on everolimus pharmacokinetics. The pharmacokinetic limited sampling model (C(trough) and whole blood drug concentration at 2 hours postdose [C(2)]) resulted in a significantly improved prediction of everolimus exposure compared with the widely used C(trough) monitoring. CONCLUSION: A two-compartment pharmacokinetic model with lag-time describing the concentration-time profile of oral everolimus in renal transplant patients has been developed using pharmacokinetic modelling. Ideal body weight significantly influenced V(1)/F of everolimus; however, the selected polymorphisms in genes coding for ABCB1, CYP3A5, CYP2C8 and PXR had no clinically relevant effect on everolimus pharmacokinetics. Everolimus C(trough) and C(2) as a limited sampling model can be used to accurately estimate everolimus systemic exposure, an improvement over the widely used C(trough) monitoring.

Liquid chromatography-tandem mass spectrometric assay for the PARP-1 inhibitor olaparib in combination with the nitrogen mustard melphalan in human plasma.

A bioanalytical assay for the new poly(ADP-ribose) polymerase-1 inhibitor olaparib in combination with melphalan was developed and validated. For the quantitative assay, human plasma samples were pre-treated on ice using protein precipitation with 2% (v/v) acetic acid in acetonitrile containing erlotinib and melphalan-d8 as internal standards. The extract was diluted with water and injected into the chromatographic system. This system consisted of a sub-2 µm particle, trifunctional bonded octadecyl silica column with an isocratic elution using 0.01% (v/v) of formic acid in a mixture of water and methanol. The eluate was transferred into the electrospray interface with positive ionization and the analyte was detected in the selected reaction monitoring mode of a triple quadrupole mass spectrometer. The assay was validated in a 10-5000 ng/ml calibration range for both drugs. The lowest level of this range corresponded to the lower limit of quantification. Within day precisions were 3.0-9.3%, between day precisions 6.0-9.8% and accuracies were between 101 and 110% for the whole calibration range. After validation the assay was used to assess the pharmacokinetics of olaparib in a patient with metastatic breast carcinoma. In addition, systemic exposure of melphalan was monitored in patients subjected to isolated hepatic perfusion with this drug. Both applications show that the new assay can be applied for human pharmacokinetic studies for both drugs.

Plasma concentrations of o,p'DDD, o,p'DDA, and o,p'DDE as predictors of tumor response to mitotane in adrenocortical carcinoma: results of a retrospective ENS@T multicenter study.

CONTEXT: In patients with adrenocortical carcinoma (ACC) mitotane activity has been suggested to depend on plasma levels 14 mg/liter or greater and metabolite formation. OBJECTIVE: The study was performed to confirm the correlation of the currently used mitotane (o,p'DDD) threshold of 14 mg/liter with tumor response and to evaluate the additional value of 1,1-(o,p'-dichlorodiphenyl) acetic acid (o,p'DDA) and o,p'DDE (1,1-(o,p'-dichlorodiphenyl)-2,2 dichloroethene) levels for predicting tumor response. SUBJECTS/METHODS: Plasma samples collected within 3 months of best response from 91 patients on mitotane therapy for advanced ACC were analyzed retrospectively. O,p'DDD and metabolites were assessed and related to tumor response and survival. Receiver operating characteristic curves were used. Sensitivity and specificity were calculated for different cutoff levels of o,p'DDD and metabolites. RESULTS: Objective tumor response was observed in 19% of patients. Median o,p'DDD level was higher in responders (P = 0.03). More responders were found among patients achieving o,p'DDD levels 14 mg/liter or greater (P = 0.02). Univariate and multivariate analysis showed significantly longer survival for patients with o,p'DDD levels 14 mg/liter or greater (hazard ratio 0.52, P = 0.04, hazard ratio 0.46, P = 0.03). An o,p'DDD cutoff value of 14 mg/liter was associated with a sensitivity of 65% and specificity 69%. An o,p'DDD level 20 mg/liter or greater or 14 mg/liter or greater combined with o,p'DDA level 92 mg/liter or greater was associated with a specificity of 90 and 92%, respectively. CONCLUSIONS: Our data confirm the value of o,p'DDD plasma monitoring as well as targeting the 14 mg/liter cutoff level in the therapeutic management of ACC patients. Furthermore, our results suggest additional benefit of higher levels of o,p'DDD and combined measurement of o,p'DDD and o,p'DDA.

Marginal increase of sunitinib exposure by grapefruit juice.

PURPOSE: The drug label of sunitinib includes a warning for concomitant use of grapefruit juice (GJ) but clinical evidence for this drug interaction is lacking. The aim of this study is to determine the effect of GJ, a potent intestinal cytochrome P450 (CYP) 3A4 inhibitor, on steady-state sunitinib pharmacokinetics (PK). METHODS: Sunitinib PK was evaluated in eight cancer patients receiving sunitinib monotherapy in a "4 weeks on-2 weeks off" dose regimen. Serial blood samples for PK analysis of sunitinib were collected on two separate days. On both PK days, patients received a single oral dose of 7.5-mg midazolam as a phenotypic probe for assessment of intestinal CYP3A4 activity. The first PK day was at steady-state sunitinib PK (between days 14-20), the second PK day was on day 28. On days 25, 26 and 27, 200-mL GJ was consumed 3 times a day. The effect of GJ on sunitinib exposure was assessed by comparing sunitinib PK with and without GJ. RESULTS: Concomitant use of GJ and sunitinib resulted in an 11% increase of the relative bioavailability of sunitinib (P < 0.05). The effect of GJ on CYP3A4 activity was confirmed by an increase of ~50% of mean midazolam exposure (AUC(0-24 h)) from 122.1 to 182.0 ng h/mL (P = 0.034). CONCLUSION: GJ consumption results in a marginal increase in sunitinib exposure which is not considered clinically relevant. There is no clinical evidence underscoring the warning in the sunitinib drug label regarding concomitant use of GJ.

Liquid chromatography-tandem mass spectrometry outperforms fluorescence polarization immunoassay in monitoring everolimus therapy in renal transplantation.

BACKGROUND: There is a need to monitor everolimus blood concentrations in renal transplant recipients as a result of its high pharmacokinetic variability and narrow therapeutic window. However, analytical methods to determine blood concentrations often differ in performance. Therefore, we investigated whether two commonly used therapeutic drug monitoring methods for everolimus were in agreement and to what extent their differences could lead to differences in dosage advice. DESIGN AND METHODS: Six hundred twelve whole blood samples were obtained from 28 adult renal transplant recipients receiving everolimus and prednisolone therapy. These samples included 286 everolimus trough concentrations. The remaining samples were obtained up to 6 hours post everolimus intake and allowed calculation of 84 AUCs0-12h. All samples were analyzed with fluorescence polarization immunoassay (FPIA) on an Abbott TDxFLx analyzer and liquid chromatography-tandem mass spectrometry (LC-MS/MS). RESULTS: Everolimus blood concentrations measured with FPIA and LC-MS/MS were not in agreement. Concentrations determined by FPIA were, on average, 23% higher than concentrations quantified by LC-MS/MS. Moreover, concentrations lower than 15 mug/L or AUC0-12h determined with FPIA could be twofold higher than with LC-MS/MS. This variability can lead to clinically relevant differences in dose adjustment of up to 1.25 mg everolimus despite using a correction factor of 23%. Finally, when trough concentrations were measured with FPIA, higher intrapatient variability was observed compared with the use of LC-MS/MS. CONCLUSION: LC-MS/MS outperforms FPIA for clinical drug monitoring and intervention of everolimus therapy in adult renal transplant recipients on dual therapy with prednisolone. Specifically, the use of FPIA can lead to clinically relevant differences in everolimus dosage advice and higher intrapatient variability.

Arterial and venous pharmacokinetics of morphine-6-glucuronide and impact of sample site on pharmacodynamic parameter estimates.

BACKGROUND: In pharmacokinetic-pharmacodynamic modeling studies, venous plasma samples are sometimes used to derive pharmacodynamic model parameters. In the current study the extent of arteriovenous concentration differences of morphine-6-glucuronide (M6G) was quantified. We used simulation studies to estimate possible biases in pharmacodynamic model parameters when linking venous versus arterial concentrations to effect. METHODS: Seventeen healthy volunteers received an IV 90-second infusion of 0.3 mg/kg morphine-6-glucuronide (M6G). Arterial and venous blood samples, from the radial artery and cubital vein, respectively, were obtained. An extended pharmacokinetic model was constructed linking arterial and venous compartments. The extent of bias in pharmacodynamic model parameter estimates was explored in simulation studies with NONMEM, simulating M6G effect using first-order effect-compartment-inhibitory sigmoid E(MAX) models. M6G effect was simulated at various values for the arterial blood-effect-site equilibration half-lifes (t(1/2)k(E0)), ranging from 5 to 240 minutes. RESULTS: Arteriovenous concentration differences were apparent, with higher arterial plasma concentrations just after infusion, whereas at later times (>60 minutes) venous M6G concentrations exceeded arterial concentrations. The extended pharmacokinetic model adequately described the data and consisted of 3 arterial compartments, 1 central venous compartment, and 1 peripheral venous compartment. The simulation studies revealed large biases in model parameters derived from venous concentration data. The biases were dependent on the value of t(1/2)k(E0). Assuming that the true values of M6G t(1/2)k(E0) range from 120 to 240 minutes (depending on the end point measured), we would have underestimated t(1/2)k(E0) by 30%, whereas the potency parameter would have been overestimated by about 40%, when using venous plasma samples. CONCLUSIONS: Because of large arteriovenous differences in M6G plasma, concentration biases in pharmacodynamic model parameters will occur when linking venous concentration to effect, using a traditional effect-compartment model.

Explaining variability in ciclosporin exposure in adult kidney transplant recipients.

PURPOSE: Optimal ciclosporin A (CsA) exposure in kidney transplant recipients is difficult to attain because of variability in CsA pharmacokinetics. A better understanding of the variability in CsA exposure could be a good means of individualizing therapy. Specifically, genetic variability in genes involved in CsA metabolism could explain exposure differences. Therefore, this study is aimed at identifying a relationship between genetic polymorphisms and the variability in CsA exposure, while accounting for non-genetic sources of variability. METHODS: De novo kidney transplant patients (n = 33) were treated with CsA for 1 year and extensive blood sampling was performed on multiple occasions throughout the year. The effects of the non-genetic covariates hematocrit, serum albumin concentration, cholesterol, demographics (i.e., body weight), CsA dose interval, prednisolone dose and genetic polymorphisms in genes encoding ABCB1, CYP3A4, CYP3A5, and PXR on CsA pharmacokinetics were studied using non-linear mixed effect modeling. RESULTS: The pharmacokinetics of CsA were described by a two-compartment disposition model with delayed absorption. Body weight was identified as the most important covariate and explained 35% of the random inter-individual variability in CsA clearance. Moreover, concurrent prednisolone use at a dosage of 20 mg/day or higher was associated with a 22% higher clearance of CsA, hence lower CsA exposure. In contrast, no considerable genotype effects (i.e., greater than 30-50%) on CsA clearance were found for the selected genes. CONCLUSIONS: It appears that the selected genetic markers explain variability in CsA exposure insufficiently to be of clinical relevance. Therefore, therapeutic drug monitoring is still required to optimize CsA exposure after administration of individualized doses based on body weight and, as this study suggests, co-administration of prednisolone.

Pancytopenia due to proguanil toxicity in a returning traveller with fever.

A patient known to have renal insufficiency was admitted to the hospital with fever and pancytopenia after returning from a trip to Mali. Pancytopenia was not caused by a tropical infection but was a side effect of atovaquone/proguanil used as malaria chemoprophylaxis. High and prolonged detectable proguanil serum levels can result in bone marrow suppression in patients with renal insufficiency. This should be taken into account in a returning traveller with fever and pancytopenia.