Dissolution comparisons using a Multivariate Statistical Distance (MSD) test and a comparison of various approaches for calculating the measurements of dissolution profile comparison

The f ₂ test is generally used for comparing dissolution profiles. In cases of high variability, the f ₂ test is not applicable, and the Multivariate Statistical Distance (MSD) test is frequently proposed as an alternative by the FDA and EMA. The guidelines provide only general recommendations. MSD tests can be performed either on raw data with or without time as a variable or on parameters of models. In addition, data can be limited—as in the case of the f ₂ test—to dissolutions of up to 85% or to all available data. In the context of the present paper, the recommended calculation included all raw dissolution data up to the first point greater than 85% as a variable—without the various times as parameters. The proposed MSD overcomes several drawbacks found in other methods.     

Effect of Gastric Fluid Volume on the <Emphasis Type="Italic">In Vitro</Emphasis> Dissolution and <Emphasis Type="Italic">In Vivo</Emphasis> Absorption of BCS Class II Drugs: a Case Study with Nifedipine

Nifedipine is a BCS Class II drug used for treatment of hypertension and preterm labor. Large inter-patient variability in nifedipine absorption results in variable exposure among different patients. We conducted in vitro dissolution studies to compare nifedipine dissolution from immediate release (IR) capsules with different volumes of dissolution media. Results from dissolution studies were used to design a crossover study in healthy volunteers to evaluate the effect of coadministered water volume with nifedipine 10 mg IR capsules on nifedipine pharmacokinetics, especially absorption (C _max, t _max, and AUC_0-6). Dissolution studies demonstrated that larger gastric fluid volumes result in enhanced nifedipine dissolution from 10 mg IR cosolvent capsules (73 vs. 17% in 200 and 100 mL simulated gastric fluid, respectively, at 30 min). The pharmacokinetic crossover study in healthy volunteers (N?=?6) did not show a significant effect of the water volume administered with the capsule (50 vs. 250 mL) on C _max, t _max, or AUC_0-6 of orally administered nifedipine IR capsules (10 mg). However, administration of large water volumes resulted in lower variability in nifedipine C _max (47 vs. 70% for 250 and 50 mL, respectively). Administration of large water volumes with nifedipine 10 mg IR cosolvent capsules may reduce inter-individual variability in plasma exposure. Evaluation of similar effects in other BCS Class II drugs is recommended.     

Development of a Novel Simplified PBPK Absorption Model to Explain the Higher Relative Bioavailability of the OROS® Formulation of Oxybutynin

A new minimal Segmented Transit and Absorption model (mSAT) model has been recently proposed and combined with intrinsic intestinal effective permeability (P _eff,int ) to predict the regional gastrointestinal (GI) absorption (f _abs ) of several drugs. Herein, this model was extended and applied for the prediction of oral bioavailability and pharmacokinetics of oxybutynin and its enantiomers to provide a mechanistic explanation of the higher relative bioavailability observed for oxybutynin’s modified-release OROS® formulation compared to its immediate-release (IR) counterpart. The expansion of the model involved the incorporation of mechanistic equations for the prediction of release, transit, dissolution, permeation and first-pass metabolism. The predicted pharmacokinetics of oxybutynin enantiomers after oral administration for both the IR and OROS® formulations were in close agreement with the observed data. The predicted absolute bioavailability for the IR formulation was within 5% of the observed value, and the model adequately predicted the higher relative bioavailability observed for the OROS® formulation vs. the IR counterpart. From the model predictions, it can be noticed that the higher bioavailability observed for the OROS® formulation was mainly attributable to differences in the intestinal availability (F _G ) rather than due to a higher colonic f _abs , thus confirming previous hypotheses. The predicted f _abs was almost 70% lower for the OROS® formulation compared to the IR formulation, whereas the F _G was almost eightfold higher than in the IR formulation. These results provide further support to the hypothesis of an increased F _G as the main factor responsible for the higher bioavailability of oxybutynin’s OROS® formulation vs. the IR.     

Active cyamemazine metabolites in patients treated with cyamemazine (Tercian<Emphasis Type="Bold">®</Emphasis>): influence on cerebral dopamine D<Subscript>2</Subscript> and serotonin 5-HT<Subscript>2A</Subscript> receptor occupancy as measured by positron emission tomography (PET)

Rationale

Cyamemazine (Tercian®) is an antipsychotic agent blocking central dopamine D₂ receptors, which induces few extrapyramidal adverse effects, due to a potent antagonistic action at serotonin 5-HT_2A receptors. In vitro studies showed that the desmethyl metabolite of cyamemazine (N-desmethyl cyamemazine) has similar affinity for 5-HT_2A receptors as cyamemazine, whereas its D₂ receptor affinity is eight times lower (Benyamina et al. in Eur J Pharmacol 578(2–3):142–147, 2008). Moreover, cyamemazine sulfoxide showed modest affinity for 5-HT_2A receptors.

Objectives

The objective of this study is to measure steady-state plasma levels of N-desmethyl cyamemazine and cyamemazine sulfoxide in patients treated with clinically relevant doses of cyamemazine and correlate them with dopamine D₂ and serotonin 5-HT_2A receptor occupancies (RO) assessed by positron emission tomography (PET).

Methods

Eight patients received Tercian® 37.5, 75, 150, or 300 mg/day according to their symptoms. Dopamine D₂ and serotonin 5-HT_2A RO were assessed at steady-state cyamemazine plasma levels using [¹¹C]raclopride and [¹¹C]N-methyl-spiperone, respectively, for PET. Plasma levels of cyamemazine metabolites were determined using a validated high-performance liquid chromatography (PerkinElmer) associated with a mass spectrometry detection (API 365, PE SCIEX). The apparent equilibrium inhibition constant (K _i) was estimated by fitting RO with plasma levels of cyamemazine metabolites at the time of the PET scan.

Results

After 6 days of cyamemazine administration, plasma N-desmethyl cyamemazine reached steady-state levels at 2 to 12 times higher than those previously found for cyamemazine (Hode et al. in Psychopharmacology (Berl) 180:377–384, 2005). Plasma levels of N-desmethyl cyamemazine were closely related to striatal D₂ RO (r ²?=?0.942) and extrastriatal 5-HT_2A RO (r ²?=?0.901). The estimated K _i(app) value of N-desmethyl cyamemazine for striatal D₂ receptors was about fivefold higher than that for extrastriatal 5-HT_2A receptors (48.7 vs. 10.6 nM). Striatal D₂ RO increased with the plasma levels of N-desmethyl cyamemazine but remained below 75% even at its highest levels. At steady state, plasma cyamemazine sulfoxide levels were about double those of N-desmethyl cyamemazine. However, these cyamemazine sulfoxide levels should not contribute significantly to in vivo 5-HT_2A and D₂ receptor occupancy.

Conclusions

In patients orally given cyamemazine, N-desmethyl cyamemazine, but not cyamemazine sulfoxide, should significantly contribute to in vivo frontal 5-HT_2A and striatal D₂ receptor occupancy. The higher in vivo affinity of cyamemazine and its desmethyl metabolite for serotonin 5-HT_2A receptors compared with dopamine D₂ receptors should explain the low incidence of extrapyramidal adverse effects.

     

Simulation-Based Evaluation of PK/PD Indices for Meropenem Across Patient Groups and Experimental Designs

Purpose

Antibiotic dose predictions based on PK/PD indices rely on that the index type and magnitude is insensitive to the pharmacokinetics (PK), the dosing regimen, and bacterial susceptibility. In this work we perform simulations to challenge these assumptions for meropenem and Pseudomonas aeruginosa.

Methods

A published murine dose fractionation study was replicated in silico. The sensitivity of the PK/PD index towards experimental design, drug susceptibility, uncertainty in MIC and different PK profiles was evaluated.

Results

The previous murine study data were well replicated with fT?>?MIC selected as the best predictor. However, for increased dosing frequencies fAUC/MIC was found to be more predictive and the magnitude of the index was sensitive to drug susceptibility. With human PK fT?>?MIC and fAUC/MIC had similar predictive capacities with preference for fT?>?MIC when short t_1/2 and fAUC/MIC when long t_1/2.

Conclusions

A longitudinal PKPD model based on in vitro data successfully predicted a previous in vivo study of meropenem. The type and magnitude of the PK/PD index were sensitive to the experimental design, the MIC and the PK. Therefore, it may be preferable to perform simulations for dose selection based on an integrated PK-PKPD model rather than using a fixed PK/PD index target.

     

Population <Emphasis Type="BoldItalic">In Vitro-In Vivo</Emphasis> Correlation Model Linking Gastrointestinal Transit Time,pH, and Pharmacokinetics: Itraconazole as a Model Drug

Purpose

To establish an in vitro-in vivo correlation (IVIVC) model for Sporanox and SUBA-itraconazole formulations and to understand the impact of gastrointestinal (GI) pH and transit times on itraconazole dissolution and absorption.

Methods

IVIVC was developed based on fed/fasted pharmacokinetic data from randomized cross-over trials, in vitro dissolution studies, and prior information about typical and between subject variability of GI pH and transit times. Data were analysed using the population modelling approach as implemented in NONMEM.

Results

Dissolution kinetics were described using first order models. The in vivo pharmacokinetics of itraconazole was described with a 2-compartment model with 4-transit absorption compartments. Pharmacokinetic profiles for fasted itraconazole periods were described based on the in vitro dissolution model, in vivo disposition model, and the prior information on GI pH and transit times. The IVIVC model indicated that drug dissolution in the fed state required an additional pH-independent dissolution pathway. The IVIVC models were presented in a ‘Shiny’ application.

Conclusion

An IVIVC model was established and internally evaluated for the two itraconazole formulations. The IVIVC model provides more insight into the observed variability of itraconazole pharmacokinetics and indicated that GI pH and transit times influence in vivo dissolution and exposure.

     

Inflation of Type I Error in the Evaluation of Scaled Average Bioequivalence,and a Method for its Control

Purpose

To verify previously reported findings for the European Medicines Agency’s method for Average Bioequivalence with Expanding Limits (ABEL) for assessing highly variable drugs and to extend the assessment for other replicate designs in a wide range of sample sizes and CVs. To explore the properties of a new modified method which maintains the consumer risk ≤0.05 in all cases.

Methods

Monte-Carlo simulations of three different replicate designs covering a wide range of sample sizes and intra-subject variabilities were performed.

Results

At the switching variability of CV _wR 30% the consumer risk is substantially inflated to up to 9.2%, which translates into a relative increase of up to 84%. The critical region of inflated type I errors ranges approximately from CV _wR 25 up to 45%. The proposed method of iteratively adjusting α maintains the consumer risk at the desired level of ≤5% independent from design, variability, and sample size.

Conclusions

Applying the European Medicines Agency’s ABEL method at the nominal level of 0.05 inflates the type I error to an unacceptable degree, especially close to a CV _wR of 30%. To control the type I error nominal levels ≤0.05 should be employed. Iteratively adjusting α is suggested to find optimal levels of the test.

     

Application of the Stable Isotope Label Approach in Clinical Development—Supporting Dissolution Specifications for a Commercial Tablet Product with Tafenoquine,a Long Half-life Compound

Bioavailability/bioequivalence studies supporting clinical drug development or commercial supply of drug formulations are often time, cost, and resource intensive. The drug’s pharmacokinetic (PK) variability, systemic half-life, and safety issues may pose additional challenges. The stable isotope label (SIL) approach provides a useful tool to significantly reduce the study size in clinical PK studies. Tafenoquine (TQ) is an 8-aminoquinoline under development for preventing Plasmodium vivax malaria relapse. This SIL study assessed the impact of differences in the in vitro dissolution profiles on in vivo exposure of TQ tablets. Fourteen healthy volunteers received a single dose of 300 mg TQ Intermediate Aged or 300 mg TQ Control formulations in this single-center, two-arm, randomized, open-label, parallel-group study. Endpoints included the geometric means ratio of the area under the concentration-time curve (AUC_(0-t) and AUC_(0-∞); primary endpoint) and maximum plasma concentration (C_max) for Intermediate Aged versus Control TQ; correlation of PK parameters for venous versus peripheral (via microsample) blood samples; and safety and tolerability endpoints. Geometric mean ratios for PK parameters (AUC and C_max) and their 90% confidence intervals fell well within standard bioequivalence limits (0.80–1.25). Only one mild adverse event (skin abrasion) was reported. In summary, this SIL methodology-based study demonstrates that the observed differences in the in vitro dissolution profiles between the Control and Intermediate Aged TQ tablets have no clinically relevant effect on systemic TQ exposure. The SIL approach was successfully implemented to enable the setting of a clinically relevant dissolution specification.Clinical trial: This study (GSK study number 201780) is registered at clinicaltrials.gov with identifier NCT02751294.     

Influence of Copolymer Composition on <Emphasis Type="Italic">In Vitro</Emphasis> and <Emphasis Type="Italic">In Vivo</Emphasis> Performance of Celecoxib-PVP/VA Amorphous Solid Dispersions

Previous studies suggested that an amorphous solid dispersion with a copolymer consisting of both hydrophobic and hydrophilic monomers could improve the dissolution profile of a poorly water-soluble drug compared to the crystalline form. Therefore, this study investigated the influence of the copolymer composition of polyvinylpyrrolidone/vinyl acetate (PVP/VA) on the non-sink in vitro dissolution behavior and in vivo performance of celecoxib (CCX) amorphous solid dispersions. The study showed that the hydrophilic monomer vinylpyrrolidone (VP) was responsible for the generation of CCX supersaturation whereas the hydrophobic monomer vinyl acetate (VA) was responsible for the stabilization of the supersaturated solution. For CCX, there was an optimal copolymer composition around 50–60% VP content where further replacement of VP monomers with VA monomers did not have any biopharmaceutical advantages. A linear relationship was found between the in vitro AUC_0-4h and in vivo AUC_0-24h for the CCX:PVP/VA systems, indicating that the non-sink in vitro dissolution method applied in this study was useful in predicting the in vivo performance. These results indicated that when formulating a poorly water-soluble drug as an amorphous solid dispersion using a copolymer, the copolymer composition has a significant influence on the dissolution profile and in vivo performance. Thus, the dissolution profile of a drug can theoretically be tailored by changing the monomer ratio of a copolymer with respect to the required in vivo plasma-concentration profile. As this ratio is likely to be drug dependent, determining the optimal ratio between the hydrophilic (dissolution enhancing) and hydrophobic (crystallization inhibiting) monomers for a given drug is imperative.     

Two different approaches for the prediction of <Emphasis Type="Italic">In Vivo</Emphasis> plasma concentration-time profile from <Emphasis Type="Italic">In Vitro</Emphasis> release data of once daily formulations of diltiazem hydrochloride

The aim of this study was to employ two different mathematical approaches: first, a convolution approach using computer software; second, a mathematical calculation exploiting Wagner-Nelson calculation to predict in vivo plasma concentration — time profile from the in vitro release study for the once daily formulations of a model drug diltiazem hydrochloride. The once daily extended release tablets (120 mg) were prepared by the wet granulation technique. Ethanol or ethanolic solutions of ethylcellulose (N22), were used as granulating agents along with hydrophilic matrix polymers like hydroxypropyl methylcellulose (HPMC) (K 15M). The granules showed satisfactory flow properties, compressibility, moisture content and drug content. All the tablet formulations showed acceptable properties and complied with pharmacopeial limits. The in vitro drug release study revealed that formula F7-T which contains drug: HPMC ratio 1:1 and 20 mg of ethylcellulose was able to sustain the drug release for 24 h and satisfied the USP dissolution limits. Fitting the in vitro drug release data to Korsmeyer-Peppas equation indicated that the mechanism of drug release could be zero-order. The capsule formulation F14-C which consists of drug: HPMC ratio 1:2, 12 mg of ethylcellulose and 20 mg of polyox 100 showed in vitro drug release similar to the tablet F7-T using the similarity factor (f ₂). The mechanism of drug release could be coupled diffusion, and polymer matrix relaxation. The percent dissolved data from the two formulations were used as input function to predict the in vivo plasma data by the two approaches (Convolution by Kinetica® software and Wagner-Nelson calculation). The two methods were validated by prediction of plasma data from in vitro release data of FDA approved 300 mg extended release capsule. Prediction errors were estimated for C _max and area under the curve (AUC) to determine the validity of the methods. The percent prediction error for each parameter is not exceeding 15%.     

Time Scaling for <Emphasis Type="Italic">In Vitro-In Vivo</Emphasis> Correlation: the Inverse Release Function (IRF) Approach

In vitro-in vivo correlations (IVIVC) are methods used to create a link between biopharmaceutical properties such as dissolution and physiological response such as plasma concentration. Level A IVIVC defines 1:1 relationship between the percent absorbed in vivo and the percent dissolved in vitro. A successful level A IVIVC provides the capacity to predict in vivo behavior based only on in vitro data with application in formulation development and support of biowaivers recognized by regulatory agencies across the world. Level A regression may be complicated due to differences in time scales as well as the lack of coincident times of similar release in vitro and in vivo leading to approximate time-to-time links and subsequent loss of information. Here, a novel method to establish Levy’s plot and to provide time scaling for improved IVIVC predictive capacity is presented. The method is mathematically closed and is an inverse release function (IRF) characterizing the single (or more) phases of dissolution/absorption. It uses the complete set of information available from all time points both in vitro and in vivo. An extended-release formulation development situation is presented with three increasing release rate test products compared in a trial versus a reference product. First, the standard level A regression was made. Prediction errors for internal validation were higher than 10% for C_max. The IRF method was applied to obtain the in vitro times of percentage dissolved equivalent to percentage absorbed. The prediction errors from the IRF level A correlation were nearly negligible.     

Influence of Formulation Factors on the Aerosol Performance of Suspension and Solution Metered Dose Inhalers: A Systematic Approach

Metered dose inhalers (MDIs) are complex drug-device combination products widely used to treat pulmonary disorders. The efficacy, driven by aerosol performance of the products, depends on a multitude of factors including, but not limited to, the physicochemical properties of drug and nature and amount of excipient(s). Under the quality by design (QbD) paradigm, systematic investigations are necessary to understand how changes in critical quality attributes (CQAs) of formulation, device, and manufacturing process influence key product performance parameters, such as delivered dose (DD) and fine particle dose (FPD). The purpose of this work is to provide a better understanding of the effects of different levels of excipients and drug particle size distribution on the aerosol performance of MDI products, while using two fundamentally different MDI products as relevant model systems, Proventil® HFA (albuterol sulfate suspension) and Qvar® (beclomethasone dipropionate solution). These MDI products, as model systems, provided mid-points around which a design of experiments (DOE), consisting of 22 suspension and 9 solution MDI formulations, were defined and manufactured. The DOE included formulations factors with varying ethanol (2 to 20% w/w and 7 to 9% w/w for the suspension and solution, respectively) and oleic acid concentrations (0.005 to 0.25% w/w and 0 to 2% w/w for the suspension and solution, respectively) and drug volumetric median particle size distribution (PSD D₅₀, 1.4 to 2.5 μm for the suspension). The MDI formulations were analyzed using compendial methods to elucidate the effect of these formulation variables (ethanol, oleic acid, and PSD D₅₀) on DD and FPD. The outcomes of this study allowed defining design spaces for the formulation factors, such that DD and FPD would remain within specific pre-defined requirements. The systematic approach utilized in this work can contribute as a QbD tool to evaluate the extent to which the formulation factors govern the aerosol performance of MDI drug products, helping to design MDI formulations with desired product performance parameters.     

Development of <Emphasis Type="BoldItalic">In Vitro-In Vivo</Emphasis> Correlation for Potassium Chloride Extended Release Tablet Formulation Using Urinary Pharmacokinetic Data

Purpose

To develop and validate a Level A in vitro-in vivo correlation (IVIVC) for potassium chloride extended-release (ER) formulations.

Methods

Three prototype ER formulations of potassium chloride with different in vitro release rates were developed and their urinary pharmacokinetic profiles were evaluated in healthy subjects. A mathematical model between in vitro dissolution and in vivo urinary excretion, a surrogate for measuring in vivo absorption, was developed using time-scale and time-shift parameters. The IVIVC model was then validated based on internal and external predictability.

Results

With the established IVIVC model, there was a good correlation between the observed fraction of dose excreted in urine and the time-scaled and time-shifted fraction of the drug dissolved, and between the in vitro dissolution time and the in vivo urinary excretion time for the ER formulations. The percent prediction error (%PE) on cumulative urinary excretion over the 24 h interval (A_e0–24h) and maximum urinary excretion rate (R_max) was less than 15% for the individual formulations and less than 10% for the average of the two formulations used to develop the model. Further, the %PE values using external predictability were below 10%.

Conclusions

A novel Level A IVIVC was successfully developed and validated for the new potassium chloride ER formulations using urinary pharmacokinetic data. This successful IVIVC may facilitate future development or manufacturing changes to the potassium chloride ER formulation.

     

Translational Modeling in Schizophrenia: Predicting Human Dopamine D<Subscript>2</Subscript> Receptor Occupancy

Objectives

To assess the ability of a previously developed hybrid physiology-based pharmacokinetic-pharmacodynamic (PBPKPD) model in rats to predict the dopamine D₂ receptor occupancy (D₂RO) in human striatum following administration of antipsychotic drugs.

Methods

A hybrid PBPKPD model, previously developed using information on plasma concentrations, brain exposure and D₂RO in rats, was used as the basis for the prediction of D₂RO in human. The rat pharmacokinetic and brain physiology parameters were substituted with human population pharmacokinetic parameters and human physiological information. To predict the passive transport across the human blood–brain barrier, apparent permeability values were scaled based on rat and human brain endothelial surface area. Active efflux clearance in brain was scaled from rat to human using both human brain endothelial surface area and MDR1 expression. Binding constants at the D₂ receptor were scaled based on the differences between in vitro and in vivo systems of the same species. The predictive power of this physiology-based approach was determined by comparing the D₂RO predictions with the observed human D₂RO of six antipsychotics at clinically relevant doses.

Results

Predicted human D₂RO was in good agreement with clinically observed D₂RO for five antipsychotics. Models using in vitro information predicted human D₂RO well for most of the compounds evaluated in this analysis. However, human D₂RO was under-predicted for haloperidol.

Conclusions

The rat hybrid PBPKPD model structure, integrated with in vitro information and human pharmacokinetic and physiological information, constitutes a scientific basis to predict the time course of D₂RO in man.

     

Evaluation of ecotoxicological impact of new pyrrole-derived aminophosphonates using selected bioassay battery

Six new dimethyl N-arylamino(2-pyrrolyl)methylphosphonates 2a–f were synthesized by the modified aza-Pudovik reaction. Their ecotoxicological impact using battery of bioassay was assessed using Microtox and Ostracodtoxit tests as well as phytotoxicity towards two plants, dicotyledonous radish (Raphanus sativus) and monocotyledonous oat (Avena sativa) following the OECD 208 Guideline. Ecotoxicological properties of compounds 2a–f in aspect of acute and chronic toxicity were evaluated using Heterocypris incongruens and Aliivibrio fisheri tests. The obtained results showed that tested aminophosphonates 2a–f have moderate-to-high phyto- and ecotoxicological impact. They are toxic for both plants but more toxic against dicotyledonous. The investigated compounds showed important ecotoxicity against Heterocypris incongruens crustaceans and Aliivibrio fisheri bacteria. It was found that the substituents of the phenyl ring plays a key role in the degree of toxicity. Results showed that investigated compounds are ecologically toxic and that any of their application should be implemented with care.     

Non-destructive Determination of Disintegration Time and Dissolution in Immediate Release Tablets by Terahertz Transmission Measurements

Purpose

The aim of this study was to establish the suitability of terahertz (THz) transmission measurements to accurately measure and predict the critical quality attributes of disintegration time and the amount of active pharmaceutical ingredient (API) dissolved after 15, 20 and 25 min for commercial tablets processed at production scale.

Methods

Samples of 18 batches of biconvex tablets from a production-scale design of experiments study into exploring the design space of a commercial tablet manufacturing process were used. The tablet production involved the process steps of high-shear wet granulation, fluid-bed drying and subsequent compaction. The 18 batches were produced using a 4 factor split plot design to study the effects of process changes on the disintegration time. Non-destructive and contactless terahertz transmission measurements of the whole tablets without prior sample preparation were performed to measure the effective refractive index and absorption coefficient of 6 tablets per batch.

Results

The disintegration time (R ²?=?0.86) and API dissolved after 15 min (R ²?=?0.96) linearly correlates with the effective refractive index, n _eff, measured at terahertz frequencies. In contrast, no such correlation could be established from conventional hardness measurements. The magnitude of n _eff represents the optical density of the sample and thus it reflects both changes in tablet porosity as well as granule density. For the absorption coefficient, α _eff, we observed a better correlation with dissolution after 20 min (R ²?=?0.96) and a weaker correlation with disintegration (R ²?=?0.83) compared to n _eff.

Conclusion

The measurements of n _eff and α _eff provide promising predictors for the disintegration and dissolution time of tablets. The high penetration power of terahertz radiation makes it possible to sample a significant volume proportion of a tablet without any prior sample preparation. Together with the short measurement time (seconds), the potential to measure content uniformity and the fact that the method requires no chemometric models this technology shows clear promise to be established as a process analyser to non-destructively predict critical quality attributes of tablets.

     

Effects of <Emphasis Type="Italic">CYP2C19</Emphasis> and <Emphasis Type="Italic">CYP2C9</Emphasis> genotypes on pharmacokinetic variability of valproic acid in Chinese epileptic patients: nonlinear mixed-effect modeling

Purpose

To evaluate the effects of CYP2C19 and CYP2C9 genotypes on the pharmacokinetic variability of valproic acid (VPA) in epileptic patients using a population pharmacokinetic (PPK) approach.

Methods

VPA concentrations were measured in 287 epileptic patients, who were genotyped for CYP2C19*2/*3 and CYP2C9*3. Patients who were on monotherapy with VPA were divided into two groups, a PPK-model group (n?=?177) and a PPK-valid group (n?=?110). The PPK parameter values for VPA were calculated in the PPK-model group by using the NONMEM software. Ultimately, a biological model and a final model were established. Each model was then used to independently predict the concentrations of the PPK-valid group to validate the two models.

Results

There was a significant effect of the CYP2C19 and CYP2C9 genotypes on the pharmacokinetic (PK) variability (P?<?0.01) in the final PPK model of CL/F. The interindividual CL was calculated according to the final model: CL/F?=?0.0951?×?(1?+?e^{0.0267?×?(3???genotype)})?+?0.0071?×?age (L/h). The coefficient of variation (CV) (omega CL/F) of the final model was 29.3%, while that of the biological model was 31.7%. Based on the genotype, the individual PK parameters can be calculated more accurately than before.

Conclusion

The CYP2C19 and CYP2C9 genotypes significantly influenced the PK variability of VPA, as quantified by NONMEM software.

     

Predicting Pulmonary Pharmacokinetics from <Emphasis Type="Italic">In Vitro</Emphasis> Properties of Dry Powder Inhalers

Purpose

The ability of two semi-mechanistic simulation approaches to predict the systemic pharmacokinetics (PK) of inhaled corticosteroids (ICSs) delivered via dry powder inhalers (DPIs) was assessed for mometasone furoate, budesonide and fluticasone propionate.

Methods

Both approaches derived the total lung doses and the central to peripheral lung deposition ratios from clinically relevant cascade impactor studies, but differed in the way the pulmonary absorption rate was derived. In approach 1, the rate of in vivo drug dissolution/absorption was predicted for the included ICSs from in vitro aerodynamic particle size distribution and in vitro drug solubility estimates measured in an in vivo predictive dissolution medium. Approach 2 derived a first order absorption rate from the mean dissolution time (MDT), determined for the test formulations in an in vitro Transwell^® based dissolution system.

Results

Approach 1 suggested PK profiles which agreed well with the published pharmacokinetic profiles. Similarly, within approach 2, input parameters for the pulmonary absorption rate constant derived from dissolution rate experiments were able to reasonably predict the pharmacokinetic profiles published in literature.

Conclusion

Approach 1 utilizes more complex strategies for predicting the dissolution/absorption process without providing a significant advantage over approach 2 with regard to accuracy of in vivo predictions.

     

Effect of Cd<Superscript>+2</Superscript> on phosphate solubilizing abilities and hydrogen peroxide production of soil-borne micromycetes isolated from <Emphasis Type="Italic">Phragmites australis</Emphasis>-rhizosphere

The aims of this work were to evaluate the phosphate-solubilization and hydrogen peroxide (H₂O₂) production by the soil-borne micromycetes, Aspergillus japonicus, Penicillium italicum and Penicillium dipodomyicola, isolated from Phragmites australis rhizosphere and to study the effect of several concentrations of Cadmium (Cd²⁺) on both variables. Our results showed that P. italicum achieved a higher P-solubilization and H₂O₂ production than A. japonicus and P. dipodomyicola, as only P. italicum showed a positive correlation (R² = 0.71) between P-solubilization and H₂O₂ production. In dose–response assays, P. italicum was also more tolerant to Cd²⁺ (0.31 mM) in comparison to A. japonicus (0.26 mM). Analysis of the 2⁴ factorial experimental design showed that P-solubilization by P. italicum was negatively affected by increases in Cd²⁺ (p = 0.04) and yeast extract (p = 0.02) in the culture medium. The production of H₂O₂ was positively affected only by glucose (p = 0.002). Fungal biomass production was reduced significantly (p = 0.0009) by Cd²⁺ and increased (p = 0.0003) by high glucose concentration in the culture medium. The tolerance and correlation between P-solubilization and H₂O₂ production in the presence of Cd²⁺ was strain and species dependent. The effects of Cd²⁺, glucose, ammonium sulfate and yeast extract on those variables were evaluated through a two-level factorial design. P. italicum is promising for P-solubilization in soils contaminated with Cd²⁺ and may be an alternative for manufacture of biofertilizers to replace chemical fertilizers.     

Examining the Use of a Mechanistic Model to Generate an <Emphasis Type="Italic">In Vivo</Emphasis>/<Emphasis Type="Italic">In Vitro</Emphasis> Correlation: Journey Through a Thought Process

The attention and interest in establishing in vivo/in vitro correlations (IVIVCs) is grounded in its tremendous utility as a prognostic tool. It can be used to support formulation optimization, predict in vivo drug exposure across a potential patient population, select a biologically relevant in vitro dissolution test condition, and support the use of in vitro dissolution data as a surrogate for in vivo bioequivalence trials. The pharmacological and statistical implications of this correlation are linked to the method by which the IVIVC was determined and to the assumptions and optimization approaches integrated into the estimation procedure. Using previously published data generated in normal healthy volunteers, an IVIVC for metoprolol was established using a mechanistic modeling approach. Within that framework, we explored the consequences of (1) our method of fitting a single Weibull function to the in vivo dissolution, (2) our selection of weighting scheme and optimization approaches, (3) the impact of applying a fixed versus fitted gastric emptying time, and 4) the importance of factoring population variability into our IVIVC estimation and profile reconvolution. We identified those factors found to be critical in terms of their influence on the accuracy of our predicted systemic metoprolol concentration-time profiles. We considered the strengths and weaknesses of our approach and discussed how the results of this study may impact efforts to generate IVIVCs with compounds presenting physicochemical characteristics different from that of metoprolol.