An Integrated Paediatric Population PK/PD Analysis of dDAVP: How do PK Differences Translate to Clinical Outcomes?

INTRODUCTION: The bioequivalence of two formulations of desmopressin (dDAVP), a vasopressin analogue prescribed for nocturnal enuresis treatment in children, has been previously confirmed in adults but not in children. In this study, we aimed to study the pharmacokinetics (PK) and pharmacodynamics (PD) of these two formulations, in both fasted and fed children, including patients younger than 6 years of age. METHODS: Previously published data from one PK study and one PK/PD study in children aged between 6 and 16 years were combined with a new PK/PD study in children aged between 6 months and 8 years, and analysed using population PK/PD modelling. Simulations were performed to further explore the relative bioavailability of both formulations and evaluate current dosing strategies. RESULTS: The complex absorption behaviour of the lyophilizate was modelled using a double input, linked to a one-compartmental model with linear elimination and an indirect response model linking dDAVP concentration to produced urine volume and osmolality. The final model described the observed data well and elucidated the complexity of bioequivalence and therapeutic equivalence of the two formulations. Simulations showed that current dosing regimens using a fixed dose of lyophilizate 120 µg is not adequate for children, assuming children to be in the fed state when taking dDAVP. A new age- and weight-based dosing regimen was suggested and was shown to lead to improved, better tailored effects. CONCLUSIONS: Bioequivalence and therapeutic equivalence data of two formulations of the same drug in adults cannot be readily extrapolated to children. This study shows the importance of well-designed paediatric clinical trials and how they can be analysed using mixed-effects modelling to make clinically relevant inferences. A follow-up clinical trial testing the proposed dDAVP dosing regimen should be performed. CLINICAL TRIAL REGISTRATION: This trial has been registered at www.clinicaltrials.gov (identifier NCT02584231; EudraCT 2014-005200-13).

Pharmacokinetics and safety profile of desmopressin oral tablet formulations in healthy Chinese subjects under fasting and fed conditions.

OBJECTIVE: Desmopressin acetate (DDAVP®) is a synthetic analogue of the pituitary hormone vasopressin. Until now, few studies of desmopressin have focused on the pharmacokinetics (PK) or food effects in Asian populations. This study aimed to assess the effect of food intake on the PK of desmopressin and bioequivalence of two tablet formulations in Chinese subjects. MATERIALS AND METHODS: A single-center, single-dose, randomized, open-label, two-period crossover study was conducted in 104 healthy Chinese volunteers under fasted or fed conditions (52 volunteers for each condition). Blood samples were collected up to 14 hours after administration of oral desmopressin tablets (0.6 mg; 0.2 mg × 3) in each period. Plasma desmopressin concentrations were analyzed by validated liquid chromatography-tandem mass spectrometry (LC-MS/MS). PK and bioavailability parameters were calculated. Adverse events (AEs) were also recorded. RESULTS: No significant differences in mean (standard deviation, SD) PK parameters were observed between formulation 1 (F1) and formulation 2 (DDAVP®; F2) under both fasted and fed conditions. All AEs observed were mild and resolved quickly without treatment. The maximum concentration (Cmax) and area under the curve (AUC) were significantly decreased (p < 0.01) when the drug was taken with food, compared with fasted subjects. CONCLUSION: These findings suggest that both tablet formulations were well tolerated. Food can significantly decrease the exposure of desmopressin.
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Claiming desmopressin therapeutic equivalence in children requires pediatric data: a population PKPD analysis.

PURPOSE: For a new formulation of a drug, only pharmacokinetic bioequivalence with the original formulation has to be demonstrated in healthy, young adults. However, "children are not small adults," and to guarantee a safe and effective treatment, age-adapted drug development is required. Desmopressin, a vasopressin analogue prescribed for nocturnal enuresis in children, was studied as an example formulation first developed in adults and then extrapolated to a pediatric indication. METHODS: Population pharmacokinetic and pharmacodynamic modeling was used to analyze previously published desmopressin data of 18 children suffering from nocturnal enuresis. The main objective was the comparison of the therapeutic equivalence of two desmopressin formulations: tablet and lyophilisate. The measurements for pharmacokinetics and pharmacodynamics were respectively plasma desmopressin concentration and urine osmolality and diuresis. RESULTS: The half maximal inhibitory concentration for inhibition of urine production was 0.7 pg/mL lower for the lyophilisate than for the tablet. The effect of formulation on the half maximal inhibitory concentration seems to suggest that the 120-µg lyophilisate has a more pronounced effect on the urine volume and osmolality than the 200-µg tablet, even when the same exposure is achieved. CONCLUSIONS: A new indirect response model for desmopressin was constructed and validated, using a previously built pharmacokinetic model and additional pharmacodynamic data. In order to draw solid conclusions regarding the efficacy and safety of desmopressin in children, pharmacokinetics and pharmacodynamics data should be analyzed together. This study adds proof to potential differences in pediatric and adult pharmacokinetic and pharmacodynamic properties of desmopressin and exemplifies the need for pediatric clinical trials, not only for every new drug but also for every new formulation.

Effects of Food and Pharmaceutical Formulation on Desmopressin Pharmacokinetics in Children.

INTRODUCTION: Desmopressin is used for treatment of nocturnal enuresis in children. In this study, we investigated the pharmacokinetics of two formulations-a tablet and a lyophilisate-in both fasted and fed children. METHODS: Previously published data from two studies (one in 22 children aged 6-16 years, and the other in 25 children aged 6-13 years) were analyzed using population pharmacokinetic modeling. A one-compartment model with first-order absorption was fitted to the data. Covariates were selected using a forward selection procedure. The final model was evaluated, and sensitivity analysis was performed to improve future sampling designs. Simulations were subsequently performed to further explore the relative bioavailability of both formulations and the food effect. RESULTS: The final model described the plasma desmopressin concentrations adequately. The formulation and the fed state were included as covariates on the relative bioavailability. The lyophilisate was, on average, 32.1 % more available than the tablet, and fasted children exhibited an average increase in the relative bioavailability of 101 % in comparison with fed children. Body weight was included as a covariate on distribution volume, using a power function with an exponent of 0.402. Simulations suggested that both the formulation and the food effect were clinically relevant. CONCLUSION: Bioequivalence data on two formulations of the same drug in adults cannot be readily extrapolated to children. This was the first study in children suggesting that the two desmopressin formulations are not bioequivalent in children at the currently approved dose levels. Furthermore, the effect of food intake was found to be clinically relevant. Sampling times for a future study were suggested. This sampling design should result in more informative data and consequently generate a more robust model.

Temporal delays and individual variation in antidiuretic response to desmopressin.

This study aimed to estimate the relationship between pharmacokinetics and the antidiuretic effect of desmopressin. In the investigator-blind, randomized, parallel group study, 5 dose groups and 1 placebo group, each consisting of 12 healthy, overhydrated, nonsmoking male subjects 18-55 yr of age were infused intravenously over 2 h with placebo or 30, 60, 125, 250, and 500 ng desmopressin in 50 ml of normal saline. Plasma desmopressin and urine osmolality rose by variable amounts during the infusions of 60, 125, 250, and 500 ng desmopressin. Plotting mean urine osmolality against the concurrent mean plasma desmopressin yielded a temporal delay between pharmacokinetic (PK) and -dynamic (PD) responses in all dose groups. Using simulation from the indirect-response model, assuming a constant (4 ng/ml) desmopressin concentration, this delay between PK and PD was estimated at 4 h (10th-90th percentile: 1.8-8.1). Within each group, however, there were large individual variations (2- to 10-fold) in the magnitude and duration of the antidiuretic effect. The antidiuretic effect of intravenous desmopressin in water-loaded healthy adults varies considerably due largely to factors other than individual differences in pharmacokinetics. The antidiuretic effect is time as well as dose dependent and may be self-amplifying. The most likely explanation for these findings is that the time required for a given level of plasma desmopressin to exert its maximum antidiuretic effect varies markedly from person to person due to individual differences in the kinetics of one or more of the intracellular mechanisms that promote the reabsorption of solute-free water by principal cells in renal collecting tubules.

[Hyaluronidase activity of Wistar rat blood plasma: effect of dehydration and vasopressin].

Effect of dehydration and arginine vasopressin treatment (Arg-VP Sigma, USA, 50 ng/100 g b.wt. ip.) on the blood plasma hyaluronidase activity in Wistar rats was studied. It was found that the pH optimum of the enzyme activity was in the range of 3.5-3.7 that is characteristic for the hyaluronidase type 1. Water deprivation for 1 day was followed by significant increase in the blood plasma hyaluronidase activity. The same response was observed under vasopressin treatment. The possible role of increased plasma hyaluronidase activity in the regulation of water balance is discussed.

[Osmoregulating effect of vasopressin with prolonged action on Brattleboro rats with hypothalamic diabetes insipidus].

The particularities of urine osmotic concentration depending on hormonal background of vasopressin were studied in rats. It was found that WAG and Brattleboro lines of rats characterized respectively by normal level and absence of endogenous vasopressin, possess interline correlation of urine osmolality (p = 0.86) in various conditions between the extreme hydrating and dehydratation. Concentrating level of WAG rats varies from 747 +/- 94 to 2936 +/- 128 mOsm/kg, but that of Brattleboro rats changes more within the 160 +/- 9 being twice lower as isotonicity to 1305 +/- 142 mOcm/kg. Urine concentrating goes up to 1391 +/- 76 mOcm/kg in Brattleboro rats already on the day of the action of exogenous vasopressin secreted from ALZET minipump, however, in spite of constant work of this minipump during 4 hrs a week, further increasing of urine osmolality was not observed in Brattleboro rats.

Clinical study shows improved absorption of desmopressin with novel formulation.

PURPOSE: To create improved pharmaceutical formulations for nasal and sublingual administration of desmopressin and investigate their pharmacokinetic profiles in comparison with a commercial nasal liquid spray and finally to evaluate the volunteers' opinions on the different dosage forms. METHODS: Both formulations were based on the characteristics of interactive mixtures. The nasal powder spray was produced by a rotary evaporator technique with sodium starch glycolate as carrier material and the sublingual tablet by direct compression after dry mixing with mannitol as carrier. The clinical study was an open-label, randomised cross-over pharmacokinetic study in healthy volunteers. RESULTS: The nasal powder formulation gave a threefold increase in the absorption, unaltered time to maximum plasma concentration and a tendency to lower variability in the amount absorbed compared with the liquid spray. The powder was reported to be more irritating than the liquid but was still well accepted by the volunteers. The tablet did not improve the uptake of desmopressin, likely because of a poor disintegration sublingually. CONCLUSIONS: The nasal powder formulation is a promising new dosage form for the delivery of desmopressin and other compounds. The sublingual tablet has a beneficial means of production and may be further developed by decreasing its disintegration time.

Regulation of acid-base transporters by vasopressin in the kidney collecting duct of Brattleboro rat.

AIM: The objective of these studies was to examine the effects of long-term vasopressin treatment on acid-base transporters in the collecting duct of rat kidney. METHODS: Brattleboro rats were placed in metabolic cages and treated with daily injections of 1-desamino-8-D-arginine vasopressin (dDAVP), a selective V2-receptor agonist, or its vehicle (control) for up to 8 days. RESULTS: dDAVP treatment resulted in a significant reduction in serum bicarbonate concentration, and caused the upregulation of key ammoniagenesis enzymes, along with increased urinary NH4+ excretion. Northern hybridization and immunofluorescence labeling indicated a significant increase (+80%) in mRNA expression of the apical Cl-/HCO3- exchanger pendrin (PDS), along with a sharp increase in its protein abundance in B-type intercalated cells in the cortical collecting duct in dDAVP-treated rats. In the inner medullary collecting duct, the abundance of basolateral Cl-/HCO3- exchanger (AE1) and apical H+-ATPase was significantly reduced in dDAVP-treated rats. Kidney renin mRNA increased significantly and correlated with an increase in serum aldosterone levels in dDAVP-injected rats. Serum corticosterone levels were, however, reduced and correlated with increased mRNA levels of renal 11beta-hydroxysteroid dehydrogenase-2 (11beta-HSD2) and decreased mRNA expression of 11beta-hydroxylase in the adrenal gland of dDAVP-injected rats. CONCLUSION: Chronic administration of dDAVP to Brattleboro rats is associated with the upregulation of PDS and downregulation of H+-ATPase and AE1 in the collecting duct, along with increased ammoniagenesis. Stimulation of the renin-angiotensin-aldosterone system and/or decreased glucocorticoid levels likely plays a role in the transduction of these effects.

Sensitive liquid chromatography-tandem mass spectrometry method for quantification of hydrochlorothiazide in human plasma.

A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for quantification of hydrochlorothiazide (I), a common diuretic and anti-hypertensive agent. The analyte and internal standard, tamsulosin (II) were extracted by liquid-liquid extraction with diethyl ether-dichloromethane (70:30, v/v) using a Glas-Col Multi-Pulse Vortexer. The chromatographic separation was performed on a reversed-phase column (Waters symmetry C18) with a mobile phase of 10 mm ammonium acetate-methanol (15:85, v/v). The protonated analyte was quantitated in negative ionization by multiple reaction monitoring with a mass spectrometer. The mass transitions m/z 296.1 solidus in circle 205.0 and m/z 407.2 solidus in circle 184.9 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 0.5-200 ng/mL for hydrochlorothiazide in human plasma. The lower limit of quantitation was 500 pg/mL, with a relative standard deviation of less than 9%. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A run time of 2.5 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.