Quantification of human serum insulin concentrations in clinical pharmacokinetic or bioequivalence studies: what defines the "best method"?

BACKGROUND: Historically, quantitative clinical diagnostic assays (QCDAs) have not been accepted for use in pharmacokinetic or bioequivalence studies because they do not fully comply with the US Food and Drug Administration (FDA) Guidance for Industry: Bioanalytical Method Validation (e.g., full calibration curve not generated with each analytical run). Samples from a bioequivalence study were analysed for insulin and C-peptide concentrations with QCDAs and guidance-conforming radioimmunoassays (RIAs) and the results compared across and within assays. METHODS: Serum samples (n=1913) from study MKC-TI-142 were analysed first using the Roche E170 electrochemiluminescence immunoassay (ECLIA) for insulin concentration and the Immulite 2000 chemiluminescence immunoassay (CLIA) for C-peptide, and then using the corresponding Millipore RIAs. RESULTS: The insulin assays were highly correlated: r2=0.92 excluding samples requiring dilution and R2=0.88 including all samples. There was increasing negative bias of the ECLIA compared with the RIA with increasing insulin, especially with samples that required dilution for the RIA. The ECLIA had significantly fewer below-quantifiable-limit samples, a larger dynamic analysis range without dilution, and tighter agreement within incurred sample reanalysis (ISR) as compared with the RIA. The C-peptide assays showed good agreement but the CLIA method produced ISR results that were in closer agreement with the original values. CONCLUSIONS: The science indicates that the QCDAs are appropriate for the quantification of serum insulin (ECLIA) and C-peptide (CLIA) concentrations in human pharmacokinetic and bioequivalence studies even though the calibration curve is not generated in each analytical run.

Insulin lung deposition and clearance following Technosphere® insulin inhalation powder administration.

PURPOSE: To determine distribution and deposition of Technosphere® Insulin (TI) inhalation powder and the rate of clearance of fumaryl diketopiperazine (FDKP; major component of Technosphere particles) and insulin from the lungs. METHODS: Deposition and distribution of (99m)pertechnetate adsorbed onto TI immediately after administration using the MedTone® inhaler was quantified by gamma-scintigraphy. Clearance from the lungs was studied in a second experiment by serial bronchoalveolar lavage (BAL) after administration of TI inhalation powder and assay of the recovered fluid for FDKP and insulin. RESULTS: Following inhalation, ~60% of radioactivity (adsorbed on TI) emitted from the inhaler was delivered to the lungs; the remainder of the emitted dose was swallowed. Clearance from the lung epithelial lining fluid (ELF) of FDKP and insulin have a half-life of ~1 hour. CONCLUSION: TI inhalation powder administered via the MedTone inhaler was uniformly distributed throughout the lungs; ~40% of the initial cartridge load reached the lungs. Insulin and FDKP are quickly cleared from the lungs, mainly by absorption into the systemic circulation. The terminal clearance half-life from the lung ELF, estimated from sequential BAL fluid measurements for both components, was ~1 hour. Since there is an overnight washout period, the potential for accumulation on chronic administration is minimal.

Population pharmacokinetic model of human insulin following different routes of administration.

Multiple-compartment disposition of insulin has been demonstrated following intravenous administration; however, because of slow absorption and flip-flop kinetics, meal-time insulin pharmacokinetics have been described by a 1-compartment model. Technosphere insulin (TI) is an inhaled human insulin with rapid absorption and a distinct second compartment in its pharmacokinetics. The aim of this analysis was to develop a pharmacokinetic model for insulin administered via the intravenous, subcutaneous, and inhalation routes. A 2-compartment pharmacokinetic model with 1 (inhaled) or 2 sequential (subcutaneous) first-order absorption processes and first-order elimination was developed using data from 2 studies with a total of 651 concentrations from 16 healthy volunteers. Insulin was administered intravenously (5 U), subcutaneously (10 U), and via inhalation (25, 50, and 100 U). The data were modeled simultaneously with NONMEM VI, using ADVAN6 subroutine with FO. Typical values were clearance, 43.4 L/h; volume of distribution in the central compartment, 5.0 L; intercompartmental clearance, 23.9 L/h; volume of distribution in the peripheral compartment 30.7 L; TI first-order absorption rate constant, 2.35 h⁻¹; and first-order absorption rate constants associated with subcutaneously administered insulin, 0.63 and 1.04 h⁻¹, respectively. Absorption rate after subcutaneous dosing was found to decrease with increasing body mass index. Insulin pharmacokinetics were found to be consistent with 2-compartment disposition, regardless of route of administration, with insulin curve differences attributable to absorption differences.

Pharmacokinetic characterization of the novel pulmonary delivery excipient fumaryl diketopiperazine.

BACKGROUND: Technosphere® [Bis-3,6(4-fumarylaminobutyl)-2,5-diketopiperazine (FDKP)] microparticles, the integral component of the Technosphere inhalation system, deliver drugs to the deep lung and have been used to administer insulin and glucagon-like peptide-1 via inhalation in clinical studies. Three studies were conducted to characterize FDKP pharmacokinetics, including assessments in subjects with diabetic nephropathy (DNP), in subjects with chronic liver disease (CLD), and in healthy subjects. METHODS: An open-label, nonrandomized, two-period, fixed-sequence crossover absorption, distribution, metabolism, and excretion (ADME) study was conducted in six healthy nonsmoking men who received single intravenous and oral doses of [(14)C]FDKP solution, with serial sampling of blood, urine, feces, and expired air. Additionally, two single-dose, open-label, parallel-design studies with 20 mg of inhaled FDKP were conducted in (1) 12 diabetic subjects with normal renal function and 24 DNP subjects and (2) 12 healthy subjects and 21 CLD subjects. RESULTS: In the ADME study, >95% of the intravenous dose and <3% of the oral dose were recovered in urine, with no evidence of metabolism. No significant pharmacokinetic differences were observed between healthy subjects and CLD subjects [geometric mean (% coefficient of variation) area under the curve from time 0 to 480 minutes (AUC(0-480)): 26,710 (34.8) and 31,477 (28.8) ng/ml·min, respectively]. Maximum observed drug concentration (C(max)) and AUC(0-480) were higher in DNP subjects than in subjects with normal renal function [C(max): 159.9 (59.4) ng/ml versus 147.0 (44.3) ng/ml; AUC(0-480): 36,869 (47.2) ng/ml·min versus 30,474 (31.8) ng/ml·min]. None of the differences observed were considered clinically significant. CONCLUSIONS: Fumaryl diketopiperazine is predominantly cleared unchanged by the kidney with essentially no oral bioavailability. Technosphere is a safe delivery vehicle for medications administered via inhalation.

Insulin pharmacokinetics following dosing with Technosphere insulin in subjects with chronic obstructive pulmonary disease.

OBJECTIVES: Insulin exposure after inhalation has been reported to be altered significantly in subjects with chronic obstructive pulmonary disease (COPD). In this study, the rate and extent of insulin exposure was compared in healthy volunteers and subjects with COPD following administration of Technosphere * Insulin (TI), a dry powder insulin formulation for pulmonary delivery. METHODS: Insulin pharmacokinetics were evaluated in an open-label, single-dose, hyperinsulinemic-euglycemic glucose clamp study in 19 nondiabetic, nonsmoking healthy subjects (mean age [±SD] = 50.9 ± 14.1 years, body mass index = 29.1 ± 3.5 kg/m(2), forced expiratory volume in 1 second (FEV(1)) = 3.52 ± 1.02 L) and 17 nondiabetic subjects with mild-to-moderate COPD (mean age = 60.0 ± 9.0 years, body mass index = 28.5 ± 5 kg/m(2), FEV(1) = 2.56 ± 0.83 L). Subjects received a single 30-U dose of TI. Serial blood samples were obtained for insulin and C-peptide determination through 480 min after dosing. Insulin concentrations were adjusted for endogenous insulin by C-peptide correction; pharmacokinetic parameters were estimated using the corrected values. RESULTS: For the COPD and non-COPD groups, respectively, mean peak insulin (C(max)) was 34.7 µU/mL and 39.5 µU/mL (p = 0.29), median t(max) was 15 and 12 min (p = 0.24), and mean insulin exposure from time 0 to 240 min (AUC(0-240)) was 2037 µU/mL · min and 2279 µU/mL · min (p = 0.47). Cough was the most common respiratory adverse event observed. One instance of hypoglycemia was reported and was attributed to trial procedure. CONCLUSIONS: The rapid insulin absorption and the resulting insulin pharmacokinetic profile following TI inhalation were not significantly altered in the mild-to-moderate COPD population studied; however, long-term safety and efficacy of TI have not been established in patients with mild or moderate COPD. Longer-term experience is needed to fully characterize the effects of COPD on insulin PK following TI administration.