Plasma Total Concentrations Research Articles

Plasma protein binding of arsenic species in acute promyelocytic leukemia patients and their relationships with hepatic and renal function

ABSTRACT Objectives Percentage protein binding (%PB) of arsenic species in acute promyelocytic leukemia (APL) patients treated with arsenic trioxide remains unclear. It can be different depending on the status of hepatic or renal function. Methods This study obtained steady-state blood samples from normal APL patients and those with hepatic or renal impairment. %PB of inorganic arsenic (iAs), monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV) was determined by analyzing free and total plasma concentrations using ultrafiltration method by HPLC-HG-AFS. Results There is a linear relationship between free and total plasma concentrations for iAs (r2 = 0.952), MMAV (r2 = 0.603), and DMAV (r2 = 0.945). For patients with normal hepatic and renal function, mean %PB was as follows: iAs at 26.7 ± 14.3%, MMAV at 53.3 ± 11.9%, and DMAV at 24.7 ± 7.8%. %PB decreased in patients with renal impairment, with MMAV and DMAV showing statistically significant differences (p < 0.05 for MMAV, p < 0.01 for DMAV). No significant differences in %PB between normal and hepatic impairment group were observed. Conclusion Free arsenic species fraction can be estimated by total concentration. DMAV and iAs present low %PB, while MMAV exhibits a relatively high %PB in plasma. Level of %PB is more likely to be affected by renal function and age.

Development and Validation of an Improved HPLC-MS/MS Method for Quantifying Total and Unbound Lenalidomide in Human Plasma.

This study aimed to develop a fully validated HPLC-MS/MS method for quantifying total and unbound lenalidomide concentrations in human plasma. Unbound concentrations were measured using plasma ultrafiltrate prepared with Amicon® Centrifugal Filters. Lenalidomide and lenalidomide-d5 (internal standard) were extracted from 50 μL of human plasma using liquid-liquid extraction. Chromatography was conducted with a Halo® C18 column using 0.1% formic acid and methanol (20:80, v/v) as the mobile phase. The mass spectrometer was operated in a positive ion mode with an electrospray ionization interface and multiple reaction monitoring modes. Calibration curves were linear over the range of 5 to 1000 ng/mL (r2 > 0.996) for both the total and unbound lenalidomide. For total lenalidomide concentrations, between-run precision (coefficients of variation) and accuracy were 1.70-7.65% and 94.45-101.10%, respectively. For unbound concentrations, inter-day precision and accuracy were 1.98-10.55% and 93.95-98.48%, respectively. We developed a highly reproducible, sensitive, and efficient bioanalytical method using a smaller volume of plasma sample (50 μL) with a relatively short run time (2.5 min). The proposed analytical method was successfully applied to measure total and unbound lenalidomide concentrations at various time points in multiple myeloma patients with renal impairment.

Therapeutic drug monitoring of imatinib: is there a rationale for also quantifying its active metabolite ?

Therapeutic drug monitoring of imatinib is widely performed to individualize imatinib dosage. While N-desmethyl imatinib is an active metabolite of imatinib, its concentrations are not routinely determined. Imatinib and N-desmethyl imatinib trough plasma concentrations at steady-state were obtained from 295 patients with either chronic myeloid leukemia or gastrointestinal stromal tumor to see whether N-desmethyl imatinib provided additional information. Pharmacokinetic data were analyzed using a nonlinear mixed effect approach. Correlations between several pharmacokinetic metrics of drug exposure were evaluated. The mean value of the N-desmethyl imatinib/imatinib ratio of trough concentrations was 0.31 with half of the values between 0.23-0.37. N-desmethyl imatinib and total (i.e., N-desmethyl imatinib plus imatinib) trough plasma concentrations or area-under-the curve values were closely correlated with imatinib values. The distribution of imatinib or total concentrations between patients requiring imatinib dosage adjustment, or not, were similar. These results do not clearly support routine N-desmethyl monitoring since it does not provide additional information to imatinib data.

A-068 Development of GIP ELISAs: The Next Level of DiabetesManagement

Abstract Background To develop sensitive and specific ELISAs for the quantitative measurement of total and intact GIP in human plasma, and other biological fluids. Glucose-dependent insulinotropic polypeptide (GIP) is a peptide hormone consisting of 42 amino acids (1-42aa). This undergoes processing by a dipeptidyl peptidase-4 (DPP-4) and produces GIP (3-42aa) and GIP (3-30aa) fragments. The processed forms have higher affinity and very efficiently inhibits GIP receptor (GIPR) activity with no intrinsic activity. It has also been observed that the GIP response is dependent not only on meal size but also on meal composition. GIP has been found to have physiological and pharmacological relevance in the development of obesity and the pathogenesis of cardiovascular disease besides its involvement in type 2 diabetic pathophysiology. GIP acts in the entero-insular axis as an anabolic hormone that increases insulin levels, which in return increases glycogen and fatty acid synthesis and inhibits the breakdown of fat. GIP also has extra-pancreatic functions as well as roles in the stomach to reduce acid secretion by the parietal cells. On the bone, GIP has a dual effect as it causes the proliferation of osteoblasts as well as inhibits osteoclastic bone resorption. The widespread expression of GIP-R in the brain suggests that GIP might play an essential function in neuro-signaling mechanisms. Methods Highly specific and reproducible total GIP (AL-1013) and Intact GIP (AL-1022) ELISAs have been developed using specific monoclonal antibodies to help estimate the total and intact GIP concentrations in plasma in the respective immunoassays. Results Total and intact GIP ELISAs have been validated using well-characterized sample set and the peptide preparations. The total GIP ELISA detects 1-42aa, 3-42aa, 1-30aa, and 3-30aa in the sample. The intact GIP assay detects GIP (1-42aa) and the most abundant 3-42aa fragment equally in the human plasma. The intact GIP assay does not detect truncated C-terminal fragments(1-30aa). These assays did not cross-react to GRPP, Glucagon, Oxyntomodulin, GLP-1, and GLP-2. Method comparison between intact and total GIP assays using 388 samples yielded a slope of 0.8154 (r=0.958, p &amp;lt; 0.0001). Both the assays are highly reproducible with the total coefficient of variation less than 10%. GIP concentrations were measured in both assays in lean and obese subjects on fat-rich diet at 30-minute intervals. Average concentrations in intact GIP assay at 0 minutes (baseline) in lean and obese subjects (n=10) were 115.6 and 88.5 pg/mL, respectively. Average concentrations in total GIP assay at 0 minutes (baseline) in lean and obese subjects (n=10) were 151.5 and 125.9 pg/mL, respectively. Both total and intact GIP had steep increase in concentrations up to 90 minutes and then flattened up to 180 minutes. The GIP results have been also compared to the mean plasma concentrations of Glucagon, GLP-1, C-Peptide between lean and obese subjects on fat-rich meal. Conclusions Highly sensitive and specific total and intact GIP ELISAs have been developed to reliably quantify these important endocrine and local regulators in physiological and pathophysiological studies for metabolic disorders.

Physiologically-Based Pharmacokinetic Modeling of Total and Unbound Valproic Acid to Evaluate Dosing in Children With and Without Hypoalbuminemia.

Valproic acid (VPA) demonstrates nonlinear pharmacokinetics (PK) due to a capacity-limited protein binding, which has potential implications on its total and unbound plasma concentrations, especially during hypoalbuminemia. A physiologically based pharmacokinetic (PBPK) model was developed to assess the nonlinear dose-exposure relationship of VPA with special emphasis on pediatric patients with hypoalbuminemia. A PBPK model was first developed and evaluated in adults using PK-Sim® and MoBi® (v.11) and the scaled to children 1 year and older. The capacity-limited protein binding was characterized by second-order kinetics between VPA and albumin with a 2:1 molar ratio. All drug-specific parameters were informed by literature and optimized using published PK data of VPA. PK simulations were performed in virtual populations with normal and low albumin levels. The reported concentration-time profiles of total and unbound VPA were adequately predicted by the PBPK model across the age and dose range (3-120 mg/kg). The model was able to characterize the nonlinear PK, as the concentration-dependent fraction unbound (fu) and the related dose-dependent clearance values were well predicted. Simulated steady-state trough concentrations of total VPA were less than dose-proportional and were within the therapeutic drug monitoring range of 50-100 mg/L for doses between 30 and 45 mg/kg per day in children with normal albumin concentrations. However, virtual children with hypoalbuminemia largely failed to achieve the target exposure. The PBPK model helped assess the nonlinear dose-exposure relationship of VPA and the impact of albumin concentrations on the achievement of target exposure.

Whole Body PhysiologicallyBased Pharmacokinetic Model to Explain A Patient With Drug-Drug Interaction Between Voriconazole and Flucloxacillin.

Voriconazole administered concomitantly with flucloxacillin may result in subtherapeutic plasma concentrations as shown in a patient with Staphylococcus aureus sepsis and a probable pulmonary aspergillosis. After switching our patient to posaconazole, therapeutic concentrations were reached. The aim of this study was to first test our hypothesis that flucloxacillin competes with voriconazole not posaconazole for binding to albumin ex vivo, leading to lower total concentrations in plasma. A physiologicallybased pharmacokinetic (PBPK) model was then applied to predict the mechanism of action of the drug-drug interaction (DDI). The model included non-linear hepatic metabolism and the effect of a severe infectious disease on cytochrome P450 (CYP) enzymes activity. The unbound voriconazole concentration remained unchanged in plasma after adding flucloxacillin, thereby rejecting our hypothesis of albumin-binding site competition. The PBPK model was able to adequately predict the plasma concentration of both voriconazole and posaconazole over time in healthy volunteers. Upregulation of CYP3A4, CYP2C9, and CYP2C19 through the pregnane X receptor (PXR) gene by flucloxacillin resulted in decreased voriconazole plasma concentrations, reflecting the DDI observations in our patient. Posaconazole metabolism was not affected, or was only limitedly affected, by the changes through the PXR gene, which agrees with the observed plasma concentrations within the target range in our patient. Ex vivo experiments reported that the unbound voriconazole plasma concentration remained unchanged after adding flucloxacillin. The PBPK model describes the potential mechanism driving the drug-drug and drug-disease interaction of voriconazole and flucloxacillin, highlighting the large substantial influence of flucloxacillin on the PXR gene and the influence of infection on voriconazole plasma concentrations, and suggests a more limited effect on other triazoles.

Effect of protein binding on the pharmacokinetics of the six substrates in the Basel phenotyping cocktail in healthy subjects and patients with liver cirrhosis

Phenotyping serves to estimate enzyme activities in healthy persons and patients in vivo. Low doses of enzyme-specific substrates are administered, and activities estimated using metabolic ratios (MR, calculated as AUCmetabolite/AUCparent). We administered the Basel phenotyping cocktail containing caffeine (CYP1A2 substrate), efavirenz (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), metoprolol (CYP2D6) and midazolam (CYP3A) to 36 patients with liver cirrhosis and 12 control subjects and determined free and total plasma concentrations over 24 h. Aims were to assess whether MRs reflect CYP activities in patients with liver cirrhosis and whether MRs calculated with free plasma concentrations (MRfree) provide better estimates than with total concentrations (MRtotal). The correlation of MRtotal with MRfree was excellent (R2 >0.910) for substrates with low (<30 %, caffeine and metoprolol) and intermediate protein binding (≥30 and <99 %, midazolam and omeprazole) but weak (R2 <0.30) for substrates with high protein binding (≥99 %, efavirenz and flurbiprofen). The correlations between MRtotal and MRfree with CYP activities were good (R2 >0.820) for CYP1A2, CYP2C19 and CYP2D6. CYP3A4 activity was reflected better by midazolam elimination than by midazolam MRtotal or MRfree. The correlation between MRtotal and MRfree with CYP activity was not significant or weak for CYP2B6 and CYP2C9. In conclusion, MRs of substrates with an extensive protein binding (>99 %) show high inter-patient variabilities and do not accurately reflect CYP activity in patients with liver cirrhosis. Protein binding of the probe drugs has a high impact on the precision of CYP activity estimates and probe drugs with low or intermediate protein binding should be preferred.

A Physiologically-Based Pharmacokinetic Simulation to Evaluate Approaches to Mitigate Efavirenz-Induced Decrease in Levonorgestrel Exposure with a Contraceptive Implant.

Background: Levonorgestrel implant is a highly effective hormonal contraceptive, but its efficacy may be compromised when used with cytochrome enzyme inducers such as efavirenz. The primary aim of this study was to evaluate methods of mitigating the drug interaction. Methods: Using a physiologically-based pharmacokinetic (PBPK) model for levonorgestrel that we developed within the Simcyp® program, we evaluated a higher dose of levonorgestrel implant, a lower dose of efavirenz, and the combination of both, as possible methods to mitigate the interaction. In addition, we investigated the impact on levonorgestrel total and unbound concentrations of other events likely to be associated with efavirenz coadministration: changes in plasma protein binding of levonorgestrel (as with displacement) and high variability of efavirenz exposure (as with genetic polymorphism of its metabolism). The range of fraction unbound tested was 0.6% to 2.6%, and the range of efavirenz exposure ranged from the equivalent of 200 mg to 4800 mg doses. Results: Levonorgestrel plasma concentrations at any given time with a standard 150 mg implant dose are predicted to be approximately 68% of those of control when given with efavirenz 600 mg and 72% of control with efavirenz 400 mg. With double-dose levonorgestrel, the predictions are 136% and 145% of control, respectively. A decrease in levonorgestrel plasma protein binding is predicted to primarily decrease total levonorgestrel plasma concentrations, whereas higher efavirenz exposure is predicted to decrease total and unbound concentrations. Conclusions: Simulations suggest that doubling the dose of levonorgestrel, particularly in combination with 400 mg daily efavirenz, may mitigate the drug interaction. Changes in levonorgestrel plasma protein binding and efavirenz genetic polymorphism may help explain differences between model predictions and clinical data but need to be studied further.

Effect of midostaurin on the pharmacokinetics of P-gp, BCRP, and CYP2D6 substrates: assessing potential drug-drug interactions in healthy participants : Brief title: Drug-drug interaction of midostaurin.

Midostaurin, approved for FLT3-mutated acute myeloid leukemia and advanced systemic mastocytosis, is mainly metabolized by cytochrome P450 (CYP) 3A4. Midostaurin exhibited potential inhibitory effects on P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), organic anion-transporting polyprotein 1B1, and CYP2D6 in in vitro studies. This study investigated the pharmacokinetic (PK) effects of midostaurin on P-gp (digoxin), BCRP (rosuvastatin) and CYP2D6 (dextromethorphan) substrates in healthy adults. This was an open-label, single-sequence, phase I clinical study evaluating the effect of single-dose midostaurin (100mg) on the PK of digoxin and rosuvastatin (Arm 1), and dextromethorphan (Arm 2). Participants were followed up for safety 30 days after last dose. In addition, the effect of midostaurin on the PK of dextromethorphan metabolite (dextrorphan) was assessed in participants with functional CYP2D6 genes in Arm 2. The effect of midostaurin on digoxin was minor and resulted in total exposure (AUC) and peak plasma concentration (Cmax) that were only 20% higher. The effect on rosuvastatin was mild and led to an increase in AUCs of approximately 37-48% and of 100% in Cmax. There was no increase in the primary PK parameters (AUCs and Cmax) of dextromethorphan in the presence of midostaurin. The study treatments were very well tolerated with no occurance of severe adverse events (AEs), AEs of grade ≥ 2, or deaths. Midostaurin showed only a minor inhibitory effect on P-gp, a mild inhibitory effect on BCRP, and no inhibitory effect on CYP2D6. Study treatments were well tolerated in healthy adults.

Exploring the contribution of genetic variants to high sunitinib exposure in patients with cancer.

Sunitinib exhibits considerable interindividual variability in exposure. While the target total plasma concentration of sunitinib and its active metabolite is 50-87.5ng/mL for the intermittent dosing schedule, ~10-21% of patients experience higher exposures (>87.5ng/mL), correlated with an increased risk for toxicity. Previous research identified single nucleotide variants (SNVs) in genes from the sunitinib pharmacokinetic pathway to be associated with efficacy and toxicity. However, significant interindividual variability in exposure remains unexplained. Our aim was to identify genetic variants associated with supratherapeutic exposure of sunitinib. This was a genome-wide association study. Cases were identified during routine therapeutic drug monitoring and consisted of patients with dose-normalized sunitinib plasma concentrations >87.5 ng/mL (intermittent dosing) or >75 ng/mL (continuous dosing). Controls were sampled from the historical cohort EuroTARGET who tolerated the standard dose of 50 mg in an intermittent schedule. SNVs were tested for an association with sunitinib exposure. A P-value ≤5 × 10-8 was considered significant and a P-value between 5 × 10-8 and 5 × 10-6 was considered suggestive. Sixty-nine cases and 345 controls were included for association analysis. One SNV (rs6923761), located on the gene glucagon-like peptide 1 receptor, was significantly associated with increased sunitinib exposure (P = 7.86 × 10-19). Twelve SNVs were suggestive for an association with sunitinib exposure (P≤ 5 × 10-6). While rs6923671 is associated with high sunitinib exposure, the underlying mechanism is not yet clarified and warrants further investigation. We could not confirm the earlier found associations between SNVs in candidate genes involved in the pharmacokinetic pathway of sunitinib and its efficacy and toxicity.

Pharmacokinetics of carprofen in lactating dogs after intravenous treatment

Analgesia is an important component of veterinary care with nonsteroidal antiinflammatory drugs, particularly carprofen (Rimadyl®) commonly used for dogs. Pharmacokinetic studies of carprofen in lactating dogs have not been examined fully, questioning the use and safety of carprofen. The extent to which lactation changes the pharmacokinetics is unknown, nor is the extent of transfer into milk of lactating dogs and their neonates or pups. We hypothesized that after a single dose of intravenous (4.4 mg/kg) to dogs, concentrations in milk are low and not high enough to produce harmful exposure in pups. We tested our hypothesis in healthy, adult lactating dogs (n = 4) using pharmacokinetic methods and nonchiral and chiral specific assays measuring total, R-, and S-enantiomer carprofen concentrations with high performance liquid chromatography in maternal plasma, milk, and neonatal plasma samples. The CMAX, elimination half-life, and clearance for maternal plasma were 9.09 and 7.3 µg/ml (R-, S+), 6.82 and 6.22 hours (R-, S+), and a higher clearance rate of 95.81 ml/hr/kg (R-) and 73.87 ml/hr/kg (S+) than reported. None of the neonatal plasma concentrations at any time point were more than 10% of the total maternal plasma concentrations and milk:plasma ratio was &lt; 1. This study confirmed the approved dose is appropriate for perioperative and chronic pain in lactating dogs and is safe with reduced exposure to nursing pups. This study suggested that the pharmacokinetics of carprofen in lactating dogs may be different from their nonlactating counterparts. However, further pharmacokinetic studies with more dogs are needed to confirm these findings.

Effect of Carbamazepine on the Pharmacokinetics of Erdafitinib in Healthy Participants.

Erdafitinib, a selective and potent oral pan-FGFR inhibitor, is metabolized mainly through CYP2C9 and CYP3A4 enzymes. This phase 1, open-label, single-sequence, drug-drug interaction study evaluated the pharmacokinetics, safety, and tolerability of a single oral dose of erdafitinib alone and when co-administered with steady state oral carbamazepine, a dual inducer of CYP3A4 and CYP2C9, in 13 healthy adult participants (NCT04330248). Compared with erdafitinib administration alone, carbamazepine co-administration decreased total and free maximum plasma concentrations of erdafitinib (Cmax) by 35% (95% CI 30%-39%) and 22% (95% CI 17%-27%), respectively. The areas under the concentration-time curve over the time interval from 0 to 168hours, to the last quantifiable data point, and to time infinity (AUC168h, AUClast, AUCinf), were markedly decreased for both total erdafitinib (56%-62%) and free erdafitinib (48%-55%). The safety profile of erdafitinib was consistent with previous clinical studies in healthy participants, with no new safety concerns when administered with or without carbamazepine. Co-administration with carbamazepine may reduce the activity of erdafitinib due to reduced exposure. Concomitant use of strong CYP3A4 inducers with erdafitinib should be avoided.

Phase I study of the pharmacokinetics and safety of rezafungin in subjects with moderate/severe hepatic impairment and matched control subjects.

Rezafungin is a second-generation, once-weekly echinocandin antifungal approved for the treatment of invasive candidiasis, including candidemia. In phase II/III studies of rezafungin versus caspofungin, patients with severe hepatic impairment were excluded due to lack of caspofungin data in this population. This open-label, single-dose, phase I study evaluated the pharmacokinetics (primary objective) and safety of rezafungin in subjects with moderate or severe hepatic impairment versus matched, healthy subjects with normal hepatic function. Eight subjects each with moderate (Child-Pugh B) or severe (Child-Pugh C) hepatic impairment were matched 1:1 with healthy subjects for age, sex, and body mass index. Each subject received a single 400-mg, intravenous, 1-h infusion of rezafungin. Plasma pharmacokinetic sampling was performed at various time points through 336 h postdose. Pharmacokinetic parameters were derived by non-compartmental analysis. Safety was assessed throughout. All 32 subjects received study treatment and were included in all analyses. Despite overlapping distributions of total plasma concentrations, based on geometric least-squares (LS) mean ratios, the area under the plasma concentration-time curve from time zero (prior to the start of infusion) to infinity (AUC0-∞) was 32% lower in subjects with moderate (LS mean ratio, 67.55; 90% confidence interval [CI]: 53.91, 84.65) and severe (LS mean ratio, 67.84; 90% CI: 57.49, 80.05) hepatic impairment versus matched healthy subjects. The maximum plasma concentration (Cmax) was 12% lower in moderate hepatic impairment and 28% lower in severe hepatic impairment groups. Linear regression showed no significant trend in the degree of hepatic impairment (based on Child-Pugh score) on AUC0-∞ or Cmax (p > 0.05). Treatment-emergent adverse events were reported in seven subjects (21.9%; three subjects in each of the hepatic impairment groups, and one healthy subject), none of which were severe, serious, or resulted in withdrawal. Rezafungin is well tolerated and can be administered to patients with moderate or severe hepatic impairment without the need for dose adjustment. The modest reduction in exposures in subjects with hepatic impairment is not clinically meaningful and is unlikely to impact efficacy.

Retrospective analysis of a flucloxacillin oral absorption test in patients requiring flucloxacillin therapy: results and determination of factors associated with adequate absorption

ABSTRACT Objectives Flucloxacillin has the most narrow spectrum to treat staphylococcal infections, but has a large variability in bioavailability which hampers its intravenous (iv) to oral switch. To identify patients with adequate absorption, the use of an oral absorption test (OAT) measuring total plasma concentrations of flucloxacillin before and after an oral dose of 1 gram flucloxacillin, was previously published. The current pilot study aims to evaluate the fraction of patients with adequate absorption using a similar OAT; to assess the therapeutic consequences and to identify potential factors associated with adequate absorption. Methods Demographic data of adult patients treated with iv flucloxacillin and requiring prolonged therapy were collected retrospectively between May 2020 and November 2021 at Ghent University Hospital. A previously published OAT protocol was used, with addition of a protocol for intermittent dosing of iv flucloxacillin. Adequate absorption was defined as an increase in plasma concentration of at least 10 mg/L. Results The flucloxacillin OAT was performed in 99 patients, of which 62% were men, with a median age of 58 years and 95% received intermittent dosing of iv flucloxacillin. Of the 99 patients, 55% had a result indicating an adequate absorption and 49% of all patients were switched to oral flucloxacillin afterwards. Inadequate absorption was found to be associated with higher Body Mass Index and higher flucloxacillin baseline concentration, while co-administration of acetylsalicylic acid was associated with an adequate absorption. Conclusions Based on the OAT, 49% of all patients were switched to oral flucloxacillin instead of broader-spectrum anti-staphylococcal antibiotics. This implicates that an OAT could be a valuable antimicrobial stewardship measure by restricting the use of broad-spectrum antibiotics. For each of the associations found, a hypothesis was formulated about the underlying reason or mechanism; these should be confirmed in future studies with prospective and multicentric design.

Effect of Hepatic Impairment on the Pharmacokinetics of Fenfluramine and Norfenfluramine.

Fenfluramine (Fintepla®) is approved for the treatment of seizures associated with the rare epileptic encephalopathies Dravet syndrome and Lennox-Gastaut syndrome. Fenfluramine is extensively metabolized; thus, patients with hepatic impairment (HI) might experience changes in exposure to fenfluramine or its metabolites. In this phase 1 study, we investigated the pharmacokinetics (PK) and safety of a single oral dose of 0.35 mg/kg fenfluramine in subjects with mild (n = 8), moderate (n = 8), or severe (n = 7) HI (Child-Pugh A/B/C, respectively) and healthy control subjects (n = 22) matched for sex, age, and BMI. All subjects underwent serial sampling to determine total plasma concentrations of fenfluramine and its active metabolite, norfenfluramine. Hepatic impairment was associated with increases in fenfluramine exposures, mainly area-under-the-curve (AUC). Geometric least squares mean ratios (90% confidence intervals) for fenfluramine AUC0-∞ in mild, moderate, and severe HI versus healthy controls were 1.98 (1.36-2.90), 2.13 (1.43-3.17), and 2.77 (1.82-4.24), respectively. Changes in exposure to norfenfluramine in mild, moderate, and severe HI were minimal compared with normal hepatic function. Exposures to fenfluramine and norfenfluramine in all HI groups were within the ranges that have been characterized in the overall development program, including ranges examined in exposure-response relationships for efficacy and safety in patients, and determined to have an acceptable safety profile. Mild and moderate HI had a modest effect on fenfluramine exposure that was not clinically meaningful, whereas the higher fenfluramine exposure in severe HI may require dose reduction based on general caution in this population. The modest decrease in norfenfluramine exposure is not considered clinically relevant.

Abstract 597: Vebreltinib: A novel brain-penetrating MET kinase inhibitor demonstrates the mechanism of action and pharmacological anti-tumor activity in diverse patient-derived MET-dysregulated tumor models at clinically relevant drug levels

Abstract Background: Dysregulation of the MET signaling pathway drives oncogenesis in many human cancers, the majority of which have not been addressed by a MET targeted therapy albeit the emerging therapies for MET exon 14 skipping (MET ex14) NSCLC. We have developed a novel highly selective MET kinase inhibitor vebreltinib (APL-101, PLB1001, bozitinib) to address unmet medical need. Vebreltinib is being jointly investigated in ongoing pivotal Phase 2 and 2/3 studies in MET-dysregulated NSCLC, primary CNS cancers and basket solid tumors in China (as PLB-1001) and globally ex-China (as APL-101). The Phase 1 portion of both studies have been concluded with the same RP2D (200 mg BID by oral administration). Vebreltinib demonstrated blood-brain barrier permeability in PLB-1001 Phase 1 glioblastoma study as previously reported. Methods: MET enzyme kinetics and vebreltinib intrinsic potency were studied by a radiometric MET kinase assay. Selectivity was profiled by in vitro KINOME. Vebreltinib cellular activity on MET signaling and in vivo anti-tumor activity were assessed in tumor cell lines and patient-derived tumors (PDX) carrying MET alterations. Results: Vebreltinib is an ATP-competitive inhibitor with Ki of approximately 2.2 nM for recombinant MET kinase and inhibited the native form of activated MET with 0.52 nM IC50. Vebreltinib demonstrated exquisite selectivity in KINOMEscan selectivity panel. Vebreltinib inhibited HGF-dependent and -independent MET signaling in KP4 tumor cell lines with nanomolar concentrations. Vebreltinib inhibited IL-3 independent Ba/F3 cell lines carrying exogenous MET ex14 or with secondary mutations induced by other MET TKIs. Vebreltinib inhibited MKN45 gastric tumor xenograft in vivo with ED90 of 6 mg/kg PO/QD. Furthermore, Vebreltinib demonstrated strong anti-tumor activity in a variety of PDX tumor types carrying MET ex14, MET fusions, and MET amplification. In these preclinical studies, the total and unbound vebreltinib plasma concentration observed at steady state trough of RP2D was used as a clinically relevant drug level to interpret Vebreltinib efficacy in blocking oncogenic MET signaling, proliferation of Ba/F3 cell lines with a broad spectrum of MET mutations and in vivo tumor growth in PDXs carrying diverse MET alterations. We demonstrated the rationale for Vebreltinib to be an efficacious single-agent MET inhibitor in treating tumors carrying MET driver alterations beyond MET ex14 NSCLC. Conclusion: Vebreltinib is a novel potent MET kinase inhibitor showing promising preclinical activity against PDXs from diverse organs sites and genomic alterations such as MET ex14, MET fusion, MET amplification, or HGF over-expression at clinically relevant drug levels, providing proof-of-concepts for continued clinical development. Citation Format: Xiaoling Zhang, Elaine Liu, Yan Song, Peony Yu, Sanjeev Redkar, Guo-Liang Yu. Vebreltinib: A novel brain-penetrating MET kinase inhibitor demonstrates the mechanism of action and pharmacological anti-tumor activity in diverse patient-derived MET-dysregulated tumor models at clinically relevant drug levels [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 597.

Oral docetaxel plus encequidar – A pharmacokinetic model and evaluation against IV docetaxel

The development of optimized dosing regimens plays a crucial role in oncology drug development. This study focused on the population pharmacokinetic modelling and simulation of docetaxel, comparing the pharmacokinetic exposure of oral docetaxel plus encequidar (oDox + E) with the standard of care intravenous (IV) docetaxel regimen. The aim was to evaluate the feasibility of oDox + E as a potential alternative to IV docetaxel. The article demonstrates an approach which aligns with the FDA’s Project Optimus which aims to improve oncology drug development through model informed drug development (MIDD). The key question answered by this study was whether a feasible regimen of oDox + E existed. The purpose of this question was to provide an early GO / NO-GO decision point to guide drug development and improve development efficiency. Methods: A stepwise approach was employed to develop a population pharmacokinetic model for total and unbound docetaxel plasma concentrations after IV docetaxel and oDox + E administration. Simulations were performed from the final model to assess the probability of target attainment (PTA) for different oDox + E dose regimens (including multiple dose regimens) in relation to IV docetaxel using AUC over effective concentration (AUCOEC) metric across a range of effective concentrations (EC). A Go / No-Go framework was defined—the first part of the framework assessed whether a feasible oDox + E regimen existed (i.e., a PTA ≥ 80%), and the second part defined the conditions to proceed with a Go decision. Results: The overall population pharmacokinetic model consisted of a 3-compartment model with linear elimination, constant bioavailability, constant binding mechanics, and a combined error model. Simulations revealed that single dose oDox + E regimens did not achieve a PTA greater than 80%. However, two- and three-dose regimens at 600 mg achieved PTAs exceeding 80% for certain EC levels. Conclusion: The study demonstrates the benefits of MIDD using oDox + E as a motivating example. A population pharmacokinetic model was developed for the total and unbound concentration in plasma of docetaxel after administration of IV docetaxel and oDox + E. The model was used to simulate oDox + E dose regimens which were compared to the current standard of care IV docetaxel regimen. A GO / NO-GO framework was applied to determine whether oDox + E should progress to the next phase of drug development and whether any conditions should apply. A two or three-dose regimen of oDox + E at 600 mg was able to achieve non-inferior pharmacokinetic exposure to current standard of care IV docetaxel in simulations. A Conditional GO decision was made based on this result and further quantification of the “effective concentration” would improve the ability to optimise the dose regimen.

Amino acid distribution in blood following high-intensity interval exercise: a preliminary study.

This study investigated the effect of high-intensity interval exercise on total and individual amino acid concentrations in red blood cells (RBCs) and plasma. Seven males (31 ± 13yr) provided venous blood samples at rest, immediately and 15min and 30min following an 8-min high-intensity exercise bout. The exercise bout was 16 × 15s cycle efforts at 0.4N/kg of body mass and 90rpm, interspersed with 15s passive recovery. Total and individual amino acid concentrations of RBC and plasma and blood cell parameters were analysed. No significant differences for total amino acid concentrations between RBC and plasma were found. Individual amino acid analyses showed significant interaction effects for alanine and α-aminoadipic acid (P < 0.05), with plasma alanine significantly increased from baseline across the recovery period (P < 0.001). Blood fraction (group) effects showed greater concentrations of glycine, serine, asparagine, aspartic acid, glutamic acid, α-aminoadipic acid and ornithine in RBC, while greater concentrations of alanine, α-aminobutyric acid, valine, leucine, isoleucine, threonine, proline, phenylalanine, glutamine, tryptophan and cystine were found in plasma (P < 0.05). Comparable levels of histidine, lysine and tyrosine were observed between blood fractions. Significant differences in the variation of total amino acids in RBC were reported with higher variance at rest compared to following exercise (P = 0.01). Haemoglobin, pack cell volume and white blood cell count significantly increased immediately following exercise (P < 0.05) but returned to baseline after 15min recovery. These results support the notion of individualised amino acid transportation roles for RBC and plasma during exercise.

Pharmacokinetic profile of oral and subcutaneous administration of paracetamol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy.

The pharmacokinetic profile of paracetamol in koalas is described when administered orally at 15 mg/kg; followed by the same dose, administered every 12 hours (hrs), repeated five times. After the initial oral administration, the median (range) maximal plasma concentration (Cmax), the time Cmax was reached (Tmax) and elimination half-life (t1/2) were 16.93 μg/mL (13.66 to 20.25 μg/mL); 4 hrs (4 to 8 hrs) and 5.54 hrs (4.66 to 7.67 hrs), respectively. When paracetamol was administered orally at 15 mg/mL every 12 hrs, the trough total plasma concentration range remained comparable to the therapeutic range in humans i.e. 4 to 20 μg/mL that is known to provide some analgesia. However, there is a smaller proportion of free drug (i.e. not bound to plasma proteins; and the active form) available in koala plasma (approximately 40% unbound) compared to human plasma (approximately 80% unbound). Consequently, even when there are similar total drug plasma concentrations in both koala and human plasma, the therapeutic efficacy may be reduced in koalas compared to humans. The initial oral dose and subsequent twice daily doses resulted in no obvious adverse effects in any koala. Haematology, plasma electrolyte and biochemical analyte values remained within their reference ranges eight hrs after the last dose but there was a significant change in alanine transaminase (ALT) levels (an increase), and in total protein (a decrease) (both p = 0.03). A dose of 15 mg/kg was also administered as a subcutaneous injection, diluted 50:50 with saline, to two koalas. As the oral formulation and the subcutaneous administration resulted in comparable absorption, the study focused on the oral profile. Based on these results there is an argument to recommend a slight increase in the oral paracetamol dose for the koala, however further investigation is required to confirm whether repeated administration of a slightly higher dose may be associated with more severe or additional significant changes in haematology, electrolytes or biochemical analytes. However, a preferable recommendation would be to administer this dosage of paracetamol in combination with another analgesic such as tramadol, as a subcutaneous injection, to improve efficacy.

Semorinemab Pharmacokinetics and The Effect on Plasma Total Tau Pharmacodynamics in Clinical Studies.

Semorinemab is a monoclonal antibody that targets the N-terminal domain of the tau protein that is in clinical development for the treatment of Alzheimer's disease. To perform model-based evaluations of the observed pharmacokinetics in serum and the total plasma tau target-engagement dynamics from clinical studies evaluating semorinemab. The observed semorinemab pharmacokinetics and plasma tau target engagement from phase 1 and 2 clinical studies were modeled using a non-linear mixed effect target-mediated drug disposition model. The model was simulated to understand target engagement at clinical dose levels. The clinical studies testing semorinemab were evaluated in healthy volunteers, subjects with prodromal-to-mild Alzheimer's disease, and subjects with mild-to-moderate Alzheimer's disease. The data included a total of 8430 semorinemab serum concentrations and 4772 total tau protein plasma concentrations from 463 subjects treated with a range of single and multiple doses of semorinemab. Serum concentrations of semorinemab and the total plasma tau concentrations were measured after administration of a range of doses of semorinemab to subjects with Alzheimer's disease. A sensitivity analysis was performed wherein key target-mediated drug disposition model parameters were estimated separately between healthy volunteers, subjects with prodromal-to-mild Alzheimer's disease, and subjects with mild-to-moderate Alzheimer's disease. Serum concentrations of semorinemab were consistent across studies and showed a dose-proportional increase across the evaluated dose range. The pharmacokinetic profile was comparable between healthy volunteers and subjects with Alzheimer's disease. Total plasma tau concentrations increased in a dose-dependent non-linear manner upon semorinemab administration. The target-mediated drug disposition model adequately described the serum pharmacokinetics and protein dynamics with an estimated antibody-ligand binding strength, Kss, of 42.7 nM. The estimated values of clearance and central volume of distribution were 0.109 L/day/70 kg and 2.95 L/70 kg, respectively, and were consistent with typical values for IgG mAbs. In the sensitivity analysis, Kss (32 nM) and baseline tau protein (0.30 µM) were estimated to be lower for healthy volunteers compared to subjects with Alzheimer's disease but were comparable between subjects with Alzheimer's disease of different severities (Kss: 52-57 nM, baseline tau: 0.44-0.47 µM). The models suggested that peripheral target engagement was over 90% at the clinical doses in each of the diagnostic subgroups. Our target-mediated drug disposition model adequately described the serum pharmacokinetics and the peripheral non-linear increase with dose of the total tau. The model confirmed that these dose-response relationships were consistent across populations of healthy volunteers and subjects with different severities of Alzheimer's disease.