Using SDi2 to characterise swelling and drug release profiles
The SDi2 surface dissolution imaging system provides unique insights into physical phenomena that occur at the interface of a drug product and dissolution medium. These phenomena are by necessity overlooked using compendial dissolution techniques, because concentration measurements are usually taken downstream of the dissolution process, yet they are key to understanding the full picture of how a formulation will perform in vivo. The SDi2 is used to observe and measure such effects of erosion, swelling, disintegration and drug release from API compacts or formulated whole dosages in a single experiment, enabling rapid, informed decisions to be made during dosage form selection/optimization.
Validation of the SDi2 intrinsic dissolution rate measurement
Here we present a validation study whereby IDR measurements using the SDi2 are compared with published values from using the USP rotating disk method. The SDi2 is a unique small-scale flow-through instrument for biorelevant IDR measurement of compacts, employing real-time UV/Vis imaging to create a video of the dissolution process directly at the solid-dissolution medium interface.
Estimating Food Effect on Drug Absorption using Flux Experiments through Artificial Lipophilic membranes
This work aimed to introduce an in vitro method for qualitatively estimating food effect in early stages of pre-formulation and formulation based on the differences in the flux through artificial lipophilic membranes of two chamber dissolution-permeability system.
Application of MacroFLUX™ Apparatus for Screening Formulations before Bioequivalence Studies
For generic drug development traditional (USP) dissolution tests have been used in the pharmaceutical industry to compare performance of different drug product formulations before or instead of conducting bioequivalence studies. Although dissolution tests provide a simple way of testing formulations, the in vivo predictive power of these tests are questionable. Namely, when a poorly water-soluble API is formulated to enhance its dissolution, additives, such as surfactants and polymers have an effect not only on dissolution profile, but also on flux through the membrane. The aim of this study was to represent the importance of simultaneous dissolution-absorption studies using MacroFLUX apparatus before conducting bioequivalence studies.
Study of Danazol Cocrystal Using Trans-Membrane Flux Measurements
Pharmaceutical cocrystals have emerged as one of the potential strategies to enable supersaturation for poorly soluble drugs and as a result to improve their oral absorption and bioavailability . Flux across a membrane provides a better understanding of passive absorption of solutes from supersaturated solutions, since solute activity rather than concentration is the driving force. This study was aimed at investigating how supersaturation of model drug danazol released from its cocrystal in biorelevant media affects the trans-membrane flux of this low soluble compound.
Degree and Extent of Supersaturation of Amorphous Pharmaceuticals and Their Flux through Lipophilic Membrane
Amorphous Solid Dispersions (ASD) of low soluble drugs has become one of the favorite technologies in attempt for improving gastro‐intestinal (GIT) absorption and as a result bioavailability of insoluble compounds. The goal of this study was to apply in situ concentration monitoring for quick assessment of degree and extent of supersaturation that can be achieved by amorphization of the drug. In addition the comparison of the flux through artificial lipophilic membrane from drug loaded below and above their amorphous solubility threshold was investigated.
Understanding drug release mechanisms from diclofenac tablets using the SDi2
The SDi2 (Surface Dissolution imaging) instrument combines high resolution UV/vis imaging with a USP IV type flow through cell to study drug product performance. Biorelevant buffer systems and pH shifts may be incorporated to generate meaningful data. The dual wavelength capability allows for the study of drug concentration in solution, and physical processes such as disintegration and swelling in a single experiment. In this study, a quantitative in vitro comparison of drug release between different dosage forms was linked to formulation composition.
Pion SDi2 and Raman spectroscopy – study of diclofenac sodium salt
Salt formation is often used to improve solubility of acidic drugs at low pH. When studying the dissolution of acidic active pharmaceutical ingredient (API) salt forms, results are often hard to interpret using a single technique due to their varying stability and eventual solid form conversion. Raman spectroscopy has been used in parallel with the Pion SDi2 to study the real-time surface dissolution of compacted diclofenac Na and monitor an associated solvent-mediated form transition.
AN418 Using Scissor as a platform to analyze non-protein subcutaneous formulations
Subcutaneous (SC) therapies have gained more importance over the years due to their favourable ability to administer chronic therapies in comparison to their intravenous (IV) counterparts. Furthermore, with the ageing of the world population, it is of particular importance to reduce the burden of the health services. Since SC formulations do not require supervision by medical professionals to be administered, they present an excellent alternative to the current intravenous therapies.
Even though the majority of SC formulations consist of biopharmaceuticals, some formulations contain a non-protein molecule as an Active Pharmaceutical Ingredient (API).
AN501 A novel in vitro model for subcutaneous injection
The Scissor is a new instrument designed to simulate the physiological conditions of the hypodermis, to be used as an in vitro model of the physical behaviour of biopharmaceutical formulations undergoing subcutaneous (SC) injection.
Often biopharmaceuticals are formulated under non-physiological conditions with the aim of improving stability and prolonging shelf-life. Biopharmaceuticals intended for SC injection are typically formulated at low pH to mitigate decomposition, and in the presence of various stabilising agents and excipients.
AN502 IN vitro studt of subcutaneous injection of two insulin formulations
Insulin is a peptide hormone produced in the pancreas. It is used to regulate blood glucose levels by promoting the absorbance of glucose from the blood stream and inhibiting the production of glucose by the liver.
AN503 Investigation of subcutaneous monoclonal antibody formulations
There is a strong patient preference for subcutaneous (SC) delivery of parenteral drugs. SC therapies are safer to administer and less time-consuming than intravenous (IV) therapies and they do not require supervision by medical professionals, making them
suitable for self-managed home care treatments.
AN01 High quality measurements for small sample amounts
A comprehensive validation study conducted using the SiriusT3 instrument has demonstrated that highly accurate and repeatable data are obtained for key physico-chemical parameters using sub milligram amounts for pKa and logP measurements and from as little as 2 mg for solubility measurements. The study compared results obtained from Pion standard assays with literature values and excellent agreement was demonstrated.
AN02 PKa measurements in 15 minutes – the SiriusT3 Fast UV pKa method
Understanding the ionisation properties of a molecule is an essential requirement for drug development. SiriusT3 technology provides the capability to perform pKa measurements in 15 minutes using only 5 µL of a 10 mM stock solution. This method requires that the molecule exhibits discernable UV absorption changes on ionisation and possesses an intrinsic aqueous solubility greater than 30 µM. Compounds having a lower aqueous solubility can be accommodated using a cosolvent assay.
The SiriusT3 Fast UV pKa method has been validated against results reported in the literature and produces results that are of comparable quality to those obtained by traditional methods. Measurement repeatability is typically within 0.01 pKa units. A complete summary of the data collected in this study is available on request.
Blank titrations enable calibration of the pH electrode using the Four-Plus method. The Four-Plus values describe the theoretical shape of the blank titration curve that best fit the experimental curve and are used to set up the pH concentration scale.
The determination of pKas outside of the range 3 – 11 using potentiometric methods can prove problematic, due to the high buffer capacity of water and the relatively poor performance of pH electrodes at the extremes of the pH range. Capillary electrophoresis methods also perform poorly in this range.
It is also true that predicted pKa values are less reliable at the extremes of the pKa range. This application note describes some experimental designs for the SiriusT3 which may be used to overcome these problems, giving reliable pKa values between 0.7 and >13.
AN06 The use of cosolvent pKa assays for poorly soluble compounds
The ionisation constant or pKa is a solution property of a compound. The formation of a precipitate during a pKa acid/base
titration therefore prevents the accurate measurement of pKa. However, drug-like molecules are often poorly soluble in water. In these cases, a cosolvent mixture comprising water and a water-miscible organic solvent can be used to enhance solubility. By performing titrations in several different solvent / water ratios, the pKas of water-insoluble compounds can be derived using the well-known Yasuda-Shedlovsky extrapolation.
An understanding of the dissolution and precipitation behaviour of active pharmaceutical ingredients is of fundamental importance in designing formulation approaches for successful drug delivery. The Pion GI Dissolution Assay has been designed as a formulation tool to conduct low volume, multi pH assays to give insight into how the dissolution of a drug is influenced by changes in pH1. By incorporating different excipients in the assay, methods of maintaining enhanced levels of drug in solution can be investigated to maintain supersaturation and avoid precipitation issues. Additionally, the assay can accommodate a lipid
sink to further mimic drug absorption.
AN08 Solubility and Supersaturation – A Brief Introduction
Solubility is a key pharmaceutical parameter. For pharmaceuticals, the solubility in two types of media are important: aqueous based fluids such as the gastrointestinal tract fluid and blood, and lipid based media such as cell membranes and micelles.
Most biochemical and pharmacological processes occur in aqueous media and determining the solubility of a drug in an aqueous based medium is a very important part of drug development. This application note briefly introduces some relevant
terminology and methods of determining solubility.
AN09 The Determination of Solubility – Pion CheqSol Explained
The CheqSol method accurately determines the kinetic and intrinsic solubilities of ionizable compounds. It generates detailed information about the extent and duration of supersaturation and a pH-solubility profile from a single, highly automated assay which takes less than 2 hours. This application note provides a brief overview of the technique and should be read alongside Application Note 08/12, Solubility and Supersaturation —A Brief Introduction, which describes some terminology associated with solubility determination.
AN11 Evaluating Solid Dispersion using Small-Scale Dissolution Testing
In their efforts to enhance the bioavailability of poorly soluble drugs in BCS Class II, formulators often work with amorphous forms, which are many times more soluble than crystals of the same substance. The problem is, how can the amorphous drug be preserved, even though its natural tendency is to crystallise? One way is to prepare it as a solid dispersion.
AN12 Introduction to logP and logD Measurement Using SiriusT3
The ability of a drug to permeate biological membranes is influenced by log P, an important pharmaceutical parameter. It is described as the ratio of the concentration of compound dissolved in a lipid layer, which is usually modelled by octanol, over the concentration of compound dissolved in water.
AN15 Determination of pKa Measurement or Prediction?
Pion has extensive experience in measuring pKa values of novel drugs for our Analytical Service customers. Where we know the compound’s structure, we use computational methods to predict the number of pKas and the type (acidic or basic); this information helps us to design optimal experiments.
AN410 Measuring the isoelectric point pf peptides by potentiometric titration
The isoelectric point (pI) is the pH at which biological amphoteric molecules such as peptides and proteins carry no net electrical charge. Biopharmaceutical drug formulations that are intended for subcutaneous injection are often prepared at about pH 4 to enhance shelf life but when they are injected into the body the pH swiftly moves to 7.4. If the isoelectric point is between these pH values, there is increased risk of precipitation and aggregation after injection, which could diminish bioavailability.
Pion inForm Intrinsic Dissolution Rate of Ibuprofen and its Sodium Salt
The Pion InForm platform (figure 1) was used to determine the intrinsic dissolution rate (IDR) of ibuprofen and its sodium salt at pH 6.5. The IDR of a compound is the surface specific dissolution rate of a compound measured under the conditions of the study.
AN405 Controlled supersaturation by solvent-quench
Controlled Supersaturation experiments on Pion inForm provide a way to create supersaturated solutions which can then be monitored to determine the time when precipitation starts, and the precipitation rate.
Overcoming the difficulties posed by BCS Class II and IV APIs, where oral bioavailability is typically poor, is a challenge for modern formulation development. Although dissolution instrumentation is prevalent, most types of apparatus are not designed to simulate physiological conditions and their in vivo predictive power is poor. An instrument that has the ability to predict formulation behaviour in vivo would, therefore, be a useful tool for formulators looking to understand how their formulation was likely to perform in animal testing and clinical trials. The Pion inForm is an automated robotic, titrator that has the capability to test multiple formulation types using a variety of assays designed to mimic the dynamic chemical environment of the GI tract.
This poster reports on two biphasic studies of felodipine. In the first, partition rates were measured at concentrations above and below its amorphous solubility to understand the impact of different dose levels on absorption. In the second, solid dispersions of API of two different particle sizes were created in order to investigate dissolution‐limited aspects of drug absorption. Experiments were performed using Pion inForm, an instrument for biorelevant solubility and dissolution testing.
A pH stat method to measure the dissolution rate of nano- and microparticle suspensions
Measuring the dissolution performance of nanoparticle suspensions presents some practical challenges as (i) the rate of dissolution is often very fast, reaching maximum concentration within seconds and, (ii) depending on the concentration of the suspension, turbidity may be encountered. For ex-situ analytical techniques, such as HPLC, a fast sample collection rate and reliable phase separation is required in order to measure the kinetics of the dissolution process, which is often not achievable. Therefore an in-situ technique is preferable.
The selection of an appropriate salt form for a potential drug candidate is an opportunity to modulate its characteristics to improve bioavailability, stability and manufacturability. The intrinsic dissolution rate (IDR) and the dissolution profile of a free base and four complementary salts were investigated in order to understand the effect of the counterions on the dissolution of the API, using the Pion inForm.
Biphasic dissolution experiments can be used to study the lipid absorption of drugs and are performed using the Pion inForm platform (right). The Pion inForm contains dispensers for volumetrically dispensing reagents via capillaries into the measurement cell. For this study, 40 mL of an aqueous acetate-phosphate buffer was dispensed and adjusted to pH 6.5, after which 30 mL of decanol was added as a lipid phase. Stirring was continuous and at a constant rate of 100 rpm.
µDISS Profiler™ in Early Pharmaceutical Development: Miniaturized Intrinsic Dissolution Rate (Mini-IDR™) Measurement of GRISEOFULVIN and CARBAMAZEPINE
Because of its well characterized fluid hydrodynamics, the rotating disk method is a useful tool for mechanistic dissolution studies. The disk intrinsic dissolution rate (DIDR) measurements have been used to characterize solid drugs, including studies of dissolution-pH rate profiles in the presence of buffers, complexing agents, and various excipients. It is currently debated at the FDA whether the DIDR method can be used to determine solubility class membership in the Biopharmaceutics Classification System, with encouraging early indications.
Applying transdermal patches to deliver active pharmaceutical ingredients (API) through the human skin provides numerous advantages compared to traditional dosage forms. Therefore, more and more efforts are devoted to the development of these formulations. To help the evolution of the patches, Skin PAMPA provides a unique opportunity to continuously estimate the performance of the patch during the early stages of development. This can help the formulator test various combinations, aiming to reach the most promising matrix for each API.
Studying semi-solid formulations of diclofenac using Skin PAMPA
Studying the permeation properties of formulations is crucial in all stages of dermal and transdermal formulation development. Most of the available methods suffer from being labor-intensive and having poor reproducibility. Skin PAMPA technology is a useful tool for the early stages of development as it is an easy-to-use, cost-effective, and standardized model with significantly lower variation compared to most of the available methods. This technical note provides an example of studying three commercially available diclofenac formulations using Skin PAMPA model.
The pKa determination by UV titration relies on the differences in molar absorptivity between charged and uncharged species present in solution. The traditional UV titration of a compound takes about 25–30 minutes. The fast UV titration method utilizes Pion’s linear universal buffer Prisma™ HT. It enables replacing a variable volume titrant addition with a constant volume addition that produces predictable pH change with each dispensed aliquot of KOH or HCl. This technical note demonstrates that reducing the number of titration points while keeping their uniform distribution along pH axis produces comparable results to the regular UV titrations while reducing the assay time to 7–10 minutes per titration. Additional potential benefit of fast titrations is that low-soluble compounds can stay supersaturated for a short period of time. That may enable aqueous pKa measurements for some low-soluble compounds that otherwise have to be determined only with the presence of cosolvent. It can also benefit compounds that are not stable and would decompose during the long assay.
Measuring Solubility of Nanoparticles by Zero Intercept Method
Nanoparticle formulations of active pharmaceutical ingredient (API) are often made in the form of a suspension with addition of surfactants to prevent nanoparticles from aggregating. The concentration of dissolved API in the nanosuspension is often unknown and determining the solubility of API when nanosuspension is added to the assay media is challenging. This technical note will describe the use of Zero Intercept Method (ZIM) implemented in Au PRO™ software to resolve these issues.
FLUX Measurements using Pion µFLUX™ and MacroFLUX™ Devices
This technical note introduces devices that can be utilized for flux measurements in a systematic and reproducible manner. The small volume apparatus called μFLUX is compatible with Pion’s mini-bath (MB-8) and can be used on various stages of formulation development when amount of API and/or its formulations is limited while many permutations of different formulation strategies have to be investigated. The other device MacroFLUX is an absorption chamber insert into USP 1 or 2 dissolution bath vessels. Both apparati would allow assessment of complex interplay between solubility, permeability and dissolution rate in formulation development and would provide valuable tools for in vivo predictive in vitro studies.
Using Integrated Absorption Chamber with USP II Dissolution Apparatus to Predict Risk of Drug‐Drug Interaction from pH‐Modifying Agents: Application Notes
It has been shown that a miniaturized two‐stage in vitro dissolution test can be used to understand why some low‐soluble weak basic drugs show reduced or highly variable absorption when co‐administered with pH‐modifying agents. The goal of this study was to demonstrate that an absorption chamber combined with USP I and II dissolution apparatus can be used to study similar drug‐drug interactions (DDI) of the final dosage forms.
Effect of Simulated Mucus Environment on the Supersaturation of Carvedilol and Its Flux through Artificial Lipophilic Membranes
It was hypothesized and then demonstrated that small intestinal mucus layer could stabilize supersaturated state of otherwise precipitating low solubility drugs. It was also concluded that flux measurements provide more in‐depth understanding of supersaturated systems than solute concentration measurements alone. This study used miniaturized dissolution – permeation apparatus (μFLUX) to compare flux of carvedilol through artificial membranes from a simple buffer system as well as from media simulating the mucus layer and/or containing solubilizing excipients like hydroxypropyl‐ß‐cyclodextrin.
Differentiating Itraconazole Formulations Based on the Flux through Artificial Lipophilic Membrane
It was demonstrated that flux measurements provide more in-depth understanding of supersaturated systems than solute concentration measurements alone. This study used miniaturized dissolution – permeation apparatus (μFLUX) to compare flux of itraconazole (Figure 1) from several formulations for which in-vivo rat PK data were available. The goal of the study was to evaluate the formulation benchmarking ability of the instrumental setup.