Background and purpose: The primary objective of this study was to assess the feasibility of applying in situ UV spectroscopy in combination with multicomponent analysis (MCA) to simultaneously quantify the dissolution of a drug and its coformer from a cocrystal. A secondary objective was to determine whether this approach can support a mechanistic understanding of cocrystal dissolution. Experimental approach: The rotating-vessel μDISS system equipped with an in situ UV probe was used for dissolution tests. Carbamazepine (CBZ) cocrystals with saccharin, nicotinamide, and 2,4-dihydroxybenzoic acid were used as model compounds. The concentrations of CBZ and each coformer were simultaneously quantified using MCA of the in situ UV spectra. Key results: The concentrations of CBZ and the coformer were successfully quantified by MCA throughout the dissolution process. In the absence of a polymeric precipitation inhibitor (PPI), the dissolution of CBZ from the cocrystal reached only 20%, and no supersaturation was observed, whereas the coformers were rapidly released. In contrast, in the presence of PPIs, the dissolution of CBZ from the cocrystal increased to supersaturated levels, while the dissolution of the coformer decreased. Supersaturation of CBZ was achieved when CBZ and the coformer dissolved congruently. A PPI may interfere with the molecular dissociation of CBZ and the coformer from the cocrystal surface, resulting in a slower release of both CBZ and the coformer. This effect may have reduced the local CBZ concentration at the particle surface and, consequently, slowed the precipitation of CBZ dihydrate on the particle surface. Conclusion: MCA enables the simultaneous quantification of a drug and its coformer from in situ UV spectra during cocrystal dissolution testing. This analytical approach provides valuable insights into the dissolution mechanisms of cocrystals.

Background and purpose: In the compendial dissolution test, the overhead rotating paddle method (ORP) has been used for stirring, whereas the magnetic stirring bar method (MSB) has been employed for small-scale dissolution tests, such as the μDISS ProfilerTM (μDISS). Previous reports have indicated that differences exist in the precipitation profiles of a drug between ORP and MSB, because the latter causes contact-induced nucleation. However, it has been difficult to use an ORP and an in situ UV probe simultaneously in μDISS. In this study, a novel stirring method, the rotating vessel method (RV), was developed for μDISS. The dissolution and precipitation profiles of model drugs in RV-μDISS were then compared with those in MSB-μDISS, as well as with the results of conventional dissolution tests using an ORP. Experimental approach: In RV-μDISS, a small paddle (approximately 1/4 of the conventional paddle) was fixed to the UV probe, and the glass vessel was rotated to produce a flow pattern similar to that of ORP. The dissolution and bulk-phase precipitation tests were per­formed for ibuprofen sodium (IBU Na) and carbamazepine (CBZ), respectively, using RV-μDISS and MSB-μDISS, as well as ORP with the conventional vessel (500 mL, for IBU Na) (CV) or the mini-vessel (50 mL, for CBZ) (MV). Key results: The dissolution rate of IBU Na was similar in all methods. Rapid precipitation of crystalline IBU free acid was observed in the MSB-μDISS method. In contrast, no crystalline precipitation was observed in RV-μDISS and ORP-CV, and the drug phase-separated as a liquid (oil) phase (liquid-liquid phase separation). The precipitation rate of CBZ in RV-μDISS was similar to that in ORP-MV, but slower than that in MSB-μDISS. Conclusion: The precipitation profile in RV-μDISS was close to those in ORP-CV and ORP-MV. RV-μDISS would be a useful tool for the assessment of the precipitation profiles of drugs.

The purpose of this study was to investigate the theoretical and in vitro experimental prediction of food effects on oral drug absorption, focusing on solubility-epithelial membrane permeation-limited cases (SL-E). Bosentan, fidaxomicin, pranlukast, and rifaximin were employed as model SL-E drugs. Celecoxib and danazol were employed as solubility-unstirred water layer permeation-limited cases (SL-U) for comparison. Theoretical predictions of food effects were based on the rate-limiting steps of the fraction of a dose absorbed (Fa) (FaRLS) (Fa rate-limiting step). μFLUX was used as a dissolution-permeation flux (JμFLUX) experiment. Fasted and fed state simulated intestinal fluids (FaSSIF and FeSSIF, respectively) were employed as the donor solution. For all SL-E drugs, the food effect on Fa was theoretically predicted to be 1.2, irrespective of bile micelle solubilization (FaSSIF/FeSSIF: bosentan (2.1), fidaxomicin (2.3), pranlukast (9.1), and rifaximin (3.5)). Theoretically, an increase in solubility by bile micelles is counterbalanced by a decrease in effective permeability (Peff) due to a decrease in the free fraction (Peff is defined based on unbound + bound drug concentration (CD)). This prediction was consistent with the clinical data (fed/fasted AUC ratio: 1.1, 1.0, 1.3, and 1.6, respectively). In μFlux, even though CD was markedly higher in FeSSIF than in FaSSIF (1.9, 3.1, 20, and 3.3-fold, respectively), JμFLUX was less enhanced (0.91, 0.81, 2.4, and 0.81-fold, respectively). For the SL-U drugs, as theoretically expected, JμFLUX was increased as CD was increased, which was consistent with the clinical data. FaRLS appropriately predicted the food effect for the SL-E drugs. The mechanism was experimentally confirmed by μFlux.

Background and purpose: The pH value of the small intestine is physiologically maintained by bicarbonate buffer (BCB). However, the effect of BCB on the membrane permeation of drugs has not been investigated. The purpose of this study was to investigate the effect of BCB on the passive membrane permeation of drugs. Experimental approach: The μFlux apparatus (pION Inc.) was used for permeability measurements. To avoid a pH change of BCB, a floating lid was newly developed for μFlux. The membrane filter was coated with a 10 % soybean lecithin-decane solution. The flux measurement was performed in an iso-pH condition (pH 6.5, BCB = 10 mM, buffer capacity ()= 4.4 mM pH-1). Phosphate buffer (PPB) with the same pH and β was used for comparison (PPB = 8 mM). Key results: The floating lid suppressed the pH increase to less than 0.1 for 120 min. The effective permeability (Pe) values of lipophilic weakly acidic and basic drugs were lower in BCB than in PPB (ketoprofen, naproxen, and propranolol). On the other hand, the Pe values in BCB and PPB were similar for unionizable drugs (caffeine and antipyrine) and hydrophilic weakly basic drugs (metoprolol and procainamide). Conclusion: Passive membrane permeation of lipophilic weakly acidic and basic drugs was slower in BCB than in PPB. This was suggested to be attributed to the slow neutralization rate of BCB, which affects the pH value adjacent to the membrane surface.

Computational approaches are increasingly explored in development of drug products, including the development of lipid-based formulations (LBFs), to assess their feasibility for achieving adequate oral absorption at an early stage. This study investigated the use of computational pharmaceutics approaches to predict solubility changes of poorly soluble drugs during dispersion and digestion in biorelevant media. Concentrations of 30 poorly water-soluble drugs were determined pre- and post-digestion with in-line UV probes using the MicroDISS Profiler™. Generally, cationic drugs displayed higher drug concentrations post-digestion, whereas for non-ionized drugs there was no discernible trend between drug concentration in dispersed and digested phase. In the case of anionic drugs there tended to be a decrease or no change in the drug concentration post-digestion. Partial least squares modelling was used to identify the molecular descriptors and drug properties which predict changes in solubility ratio in long-chain LBF pre-digestion (R2 of calibration = 0.80, Q2 of validation = 0.64) and post-digestion (R2 of calibration = 0.76, Q2 of validation = 0.72). Furthermore, multiple linear regression equations were developed to facilitate prediction of the solubility ratio pre- and post-digestion. Applying three molecular descriptors (melting point, LogD, and number of aromatic rings) these equations showed good predictivity (pre-digestion R2 = 0.70, and post-digestion R2 = 0.68). The model developed will support a computationally guided LBF strategy for emerging poorly water-soluble drugs by predicting biorelevant solubility changes during dispersion and digestion. This facilitates a more data-informed developability decision making and subsequently facilitates a more efficient use of formulation screening resources.

Understanding the effect of digestion on oral lipid-based drug formulations is a critical step in assessing the impact of the digestive process in the intestine on intraluminal drug concentrations. The classical pH-stat in vitro lipolysis technique has traditionally been applied, however, there is a need to explore the establishment of higher throughput small-scale methods. This study explores the use of alternative lipases with the aim of selecting digestion conditions that permit in-line UV detection for the determination of real-time drug concentrations. A range of immobilised and pre-dissolved lipases were assessed for digestion of lipid-based formulations and compared to digestion with the classical source of lipase, porcine pancreatin. Palatase (R) 20000 L, a purified liquid lipase, displayed comparable digestion kinetics to porcine pancreatin and drug concentration determined during digestion of a fenofibrate lipid-based formulation were similar between methods. In-line UV analysis using the MicroDISS ProfilerTM demonstrated that drug concentration could be monitored during one hour of dispersion and three hours of digestion for both a medium- and long-chain lipid-based formulations with corresponding results to that obtained from the classical lipolysis method. This method offers opportunities exploring the realtime dynamic drug concentration during dispersion and digestion of lipid-based formulations in a small-scale setup avoiding artifacts as a result of extensive sample preparation.

In 1997, the 'Rule of Five' (Ro5) suggested physicochemical limitations for orally administered drugs, based on the analysis of chemical libraries from the early 1990s. In this review, we report on the trends in oral drug product development by analyzing products launched between 1994 and 1997 and between 2013 and 2019. Our analysis confirmed that most new oral drugs are within the Ro5 descriptors; however, the number of new drug products of drugs with molecular weight (MW) and calculated partition coefficient (clogP) beyond the Ro5 has slightly increased. Analysis revealed that there is no single scientific or technological reason for this trend, but that it likely results from incremental advances are being made in molecular biology, target diversity, drug design, medicinal chemistry, predictive modeling, drug metabolism and pharmacokinetics, and drug delivery.

The objective of this study was to investigate the implications of changing dissolution parameters, including pH ramp time, absence and presence of simulated intestinal fluid (SIF), and the addition of a partitioning phase, using an automated dissolution-testing platform. The molar absorption coefficients, pKa, and dissolution characteristics of dipyridamole and piroxicam were investigated in the UV/Vis spectrophotometric and potentiometric platform, inForm (Pion Inc). Dissolution of dipyridamole and piroxicam from 10-mg compacts (tablets) was studied at pH 2.0 and 6.5 in fasted-state SIF version 2 (v2) and in biphasic media using decanol as the partitioning phase. Transfer through the gastrointestinal tract was simulated by shifting pH from 2.0 to 6.5 during dissolution testing. Dipyridamole (pKa 6.0) dissolved rapidly at pH 2.0; however, changing the pH to 6.5 brought dipyridamole into a supersaturated state, from which it precipitated. Precipitation was slower in the presence of SIF, and higher dipyridamole concentrations were maintained in solution compared with simple buffer systems. In the biphasic dissolution assay, rapid distribution of dipyridamole into the lipophilic partitioning phase minimized drug precipitation. For piroxicam (pKa1 1.9; pKa2 5.3), the dissolution rate increased with increasing pH. The inclusion of SIF and introduction of a partition phase had limited influence on piroxicam dissolution. The automated platform facilitated efficient exploration of dissolution conditions. Tailoring of dissolution assays including pH gradients, SIF, and biphasic partitioning enabled detailed drug characterization, increased biorelevance, and possibly in vivo predictability. The use of a biphasic dissolution assay had a large impact on the in vitro dissolution of dipyridamole. The incorporation of an absorptive sink might be key for unraveling the supersaturation and dissolution behavior of weakly basic drug compounds.

A small-scale two-stage biphasic system, a small-scale two-stage dissolution-permeation system, the Erweka mini-paddle apparatus, and the BioGIT system were evaluated for their usefulness in assessing the intraluminal performance of two low solubility drugs in the fasted state, one with weakly acidic properties (tested in a salt form, diclofenac potassium) and one with weakly alkaline properties [ritonavir, tested as an amorphous solid dispersion (ASD) formulation]. In all in vitro methods, an immediate-release tablet and a powder formulation of diclofenac potassium were both rapidly dissolved in Level II biorelevant media simulating the conditions in the upper small intestine. Physiologically based biopharmaceutics (PBB) modelling for the tablet formulation resulted in a successful simulation of the average plasma profile in adults, whereas for the powder formulation modelling indicated that gastric emptying and transport through the intestinal epithelium limit the absorption rates. Detailed information on the behaviour of the ritonavir ASD formulation under both simulated gastric and upper small intestinal conditions were crucial for understanding the luminal performance. PBB modelling showed that the dissolution and precipitation parameters, estimated from the Erweka mini-paddle apparatus data and the small-scale two-stage biphasic system data, respectively, were necessary to adequately simulate the average plasma profile after administration of the ritonavir ASD formulation. Simulation of the gastrointestinal transfer process from the stomach to the small intestine was necessary to evaluate the effects of hypochlorhydric conditions on the luminal performance of the ritonavir ASD formulation. Based on this study, the selection of the appropriate in vitro method for evaluating the intraluminal performance of ionisable lipophilic drugs depends on the characteristics of the drug substance. The results suggest that for (salts of) acidic drugs (e.g., diclofenac potassium) it is only an issue of availability and ease of operation of the apparatus. For weakly alkaline substances (e.g., ritonavir), the results indicate that the dynamic dissolution process needs to be simulated, with the type of requested information (e.g., dissolution parameters, precipitation parameters, luminal concentrations) being key for selecting the most appropriate method. Regardless of the ionisation characteristics, early in the drug development process the use of small-scale systems may be inevitable, due to the limited quantities of drug substance available.

Objective: To investigate the usefulness of four in vitro methodologies in screening for product related differences in tacrolimus exposure after oral administration of amorphous solid dispersions with modified release characteristics in the fasted state. Methods: Initially, Advagraf (R) (5 mg tacrolimus/capsule), Envarsus (R) (4 mg tacrolimus/tablet) and a modified release Test Tablet (5 mg tacrolimus/tablet) were subjected to in vitro biorelevant performance testing simulating fasted state conditions using a small-scale two-stage biphasic system, a small-scale two-stage dissolution - permeation (D-P) system, the compendial apparatus IV (open loop mode) and the biorelevant gastrointestinal transfer (BioGIT) system. Early and total exposure, after single dose administrations of the three products to twelve healthy adults in the fasted state on a crossover basis, were then evaluated. Subsequently, the usefulness of in vitro data in qualitatively predicting product related differences in early exposure and in total exposure were assessed. Results: Product related differences in tacrolimus early exposure were successfully predicted by data collected with compendial apparatus IV. The two-stage biphasic system was useful for predicting differences in early exposure between the non-disintegrating Envarsus (R) and the disintegrating products (Advagraf (R) or Test Tablet). BioGIT data were useful only for discussing clinical data early after administration of the two disintegrating products. Prediction of product related differences in total exposure was successful only when the compendial apparatus IV was used for comparing the two disintegrating products. Conclusions: Biorelevant in vitro performance testing with compendial apparatus IV was useful for qualitatively predicting differences in tacrolimus early and total exposure after administration of disintegrating products with modified release characteristics in the fasted state.

Computational approaches are increasingly utilised in development of bio-enabling formulations, including self-emulsifying drug delivery systems (SEDDS), facilitating early indicators of success. This study investigated if in silico predictions of drug solubility gain i.e. solubility ratios (SR), after dispersion of a SEDDS in biorelevant media could be predicted from drug properties. Apparent solubility upon dispersion of two SEDDS in FaSSIF was measured for 30 structurally diverse poorly water soluble drugs. Increased drug solubility upon SEDDS dispersion was observed in all cases, with higher SRs observed for cationic and neutral versus anionic drugs at pH 6.5. Molecular descriptors and solid-state properties were used as inputs during partial least squares (PLS) modelling resulting in predictive models for SRMC (r2 = 0.81) and SRLC (r2 = 0.77). Multiple linear regression (MLR) facilitated generation of simplified SR equations with high predictivity (SRMC r2 = 0.74; SRLC r2 = 0.69), requiring only three drug properties; partition coefficient at pH 6.5 (logD6.5), melting point (Tm) and aromatic bonds as fraction of total bonds (F-AromB). Through using the equations to inform developability classification system (DCS) classes for drugs that have already been licensed as lipid-based formulations, merits for development with SEDDS was predicted for 2/3 drugs.

OBJECTIVES To summarise key contributions of the Pharmaceutical Education and Research with Regulatory Links (PEARRL) project (2016-2020) to the optimisation of existing and the development of new biopharmaceutics tools for evaluating the in vivo performance of oral drug products during the development of new drugs and at the regulatory level. KEY FINDINGS Optimised biopharmaceutics tools: Based on new clinical data, the composition of biorelevant media for simulating the fed state conditions in the stomach was simplified. Strategies on how to incorporate biorelevant in vitro data of bio-enabling drug products into physiologically based pharmacokinetic (PBPK) modelling were proposed. Novel in vitro biopharmaceutics tools: Small-scale two-stage biphasic dissolution and dissolution-permeation setups were developed to facilitate understanding of the supersaturation effects and precipitation risks of orally administered drugs. A porcine fasted state simulated intestinal fluid was developed to improve predictions and interpretation of preclinical results using in vitro dissolution studies. Based on new clinical data, recommendations on the design of in vitro methodologies for evaluating the GI drug transfer process in the fed state were suggested. The optimized design of in vivo studies for investigating food effects: A food effect study protocol in the pig model was established which successfully predicted the food-dependent bioavailability of two model compounds. The effect of simulated infant fed state conditions in healthy adults on the oral absorption of model drugs was evaluated versus the fasted state and the fed state conditions, as defined by regulatory agencies for adults. Using PBPK modelling, the extrapolated fasted and infant fed conditions data appeared to be more useful to describe early drug exposure in infants, while extrapolation of data collected under fed state conditions, as defined by regulators for adults, failed to capture in vivo infant drug absorption. SUMMARY Substantial progress has been made in developing an advanced suite of biopharmaceutics tools for streamlining drug formulation screening and supporting regulatory applications. These advances in biopharmaceutics were achieved through networking opportunities and research collaborations provided under the H2020 funded PEARRL project.

The absence of an intestinal absorption sink is a significant weakness of standard in vitro lipolysis methods, potentially leading to poor prediction of in vivo performance and an overestimation of drug precipitation. In addition, the majority of the described lipolysis methods only attempt to simulate intestinal conditions, thus overlooking any supersaturation or precipitation of ionizable drugs as they transition from the acidic gastric environment to the more neutral conditions of the intestine. The aim of this study was to develop a novel lipolysis method incorporating a two-stage gastric-to-intestinal transition and an absorptive compartment to reliably predict in vivo performance of lipid-based formulations (LBFs). Drug absorption was mimicked by in situ quantification of drug partitioning into a decanol layer. The method was used to characterize LBFs from four studies described in the literature, involving three model drugs (i.e., nilotinib, fenofibrate, and danazol) where in vivo bioavailability data have previously been reported. The results from the novel biphasic lipolysis method were compared to those of the standard pH-stat method in terms of reliability for predicting the in vivo performance. For three of the studies, the novel biphasic lipolysis method more reliably predicted the in vivo bioavailability compared to the standard pH-stat method. In contrast, the standard pH-stat method was found to produce more predictive results for one study involving a series of LBFs composed of the soybean oil, glyceryl monolinoleate (Maisine CC), Kolliphor EL, and ethanol. This result was surprising and could reflect that increasing concentrations of ethanol (as a cosolvent) in the formulations may have resulted in greater partitioning of the drug into the decanol absorptive compartment. In addition to the improved predictivity for most of the investigated systems, this biphasic lipolysis method also uses in situ analysis and avoids time- and resource-intensive sample analysis steps, thereby facilitating a higher throughput capacity and biorelevant approach for characterization of LBFs.

A small-scale biphasic dissolution setup and a small-scale dissolution-permeation (D-P) setup were evaluated for their usefulness in simulating the luminal precipitation of three lipophilic weak bases—dipyridamole, ketoconazole and itraconazole. The transition from the gastric to intestinal environment was incorporated into both experimental procedures. Emulsification during the biphasic dissolution experiments had a minimal impact on the data, when appropriate risk mitigation steps were incorporated. Precipitation parameters estimated from the in vitro data were inputted into the Simcyp® physiologically based pharmacokinetic (PBPK) modelling software and simulated human plasma profiles were compared with previously published pharmacokinetic data. Average Cmax and AUC values estimated using experimentally derived precipitation parameters from the biphasic experiments deviated from corresponding published actual values less than values estimated using the default simulator parameters for precipitation. The slow rate of transport through the biomimetic membrane in the D-P setup limited its usefulness in forecasting the rates of in vivo precipitation used in the modelling of average plasma profiles.

INTRODUCTION:In the development of bio-enabling formulations, innovative in vivo predictive tools to understand and predict the in vivo performance of such formulations are needed. Etravirine, a non-nucleoside reverse transcriptase inhibitor, is currently marketed as an amorphous solid dispersion (Intelence® tablets). The aims of this study were 1) to investigate and discuss the advantages of using biorelevant in vitro setups to simulate the in vivo performance of Intelence® 100 mg and 200 mg tablets in the fed state, 2) to build a Physiologically Based Pharmacokinetic (PBPK) model by combining experimental data and literature information with the commercially available in silico software Simcyp® Simulator V17.1 (Certara UK Ltd.), and 3) to discuss the challenges of predicting the in vivo performance of an amorphous solid dispersion and identify the parameters which influence the pharmacokinetics of etravirine most. METHODS:Solubility, dissolution and transfer experiments were performed in various biorelevant media simulating the fasted and fed state environment in the gastrointestinal tract. An in silico PBPK model for etravirine in healthy volunteers was developed in the Simcyp® Simulator, using in vitro results and data available from the literature as input. The impact of pre- and post-absorptive parameters on the pharmacokinetics of etravirine was investigated by simulating various scenarios. RESULTS:In vitro experiments indicated a large effect of naturally occurring solubilizing agents on the solubility of etravirine. Interestingly, supersaturated concentrations of etravirine were observed over the entire duration of dissolution experiments on Intelence® tablets. Coupling the in vitro results with the PBPK model provided the opportunity to investigate two possible absorption scenarios, i.e. with or without implementation of precipitation. The results from the simulations suggested that a scenario in which etravirine does not precipitate is more representative of the in vivo data. On the post-absorptive side, it appears that the concentration dependency of the unbound fraction of etravirine in plasma has a significant effect on etravirine pharmacokinetics. CONCLUSIONS:The present study underlines the importance of combining in vitro and in silico biopharmaceutical tools to advance our knowledge in the field of bio-enabling formulations. Future studies on other bio-enabling formulations can be used to further explore this approach to support rational formulation design as well as robust prediction of clinical outcomes.

Intrinsic dissolution rate (IDR) is the surface specific dissolution rate of a drug. In early drug development, this property (among other parameters) is measured in order to compare different polymorphs and salt forms, guide formulation decisions, and to provide a quality marker of the active pharmaceutical ingredient (API) during production. In this review, an update on different methods and small-scale techniques that have recently evolved for determination of IDR is provided. The importance of biorelevant media and the hydrodynamic conditions of dissolution are also discussed. Different preparation techniques for samples are presented with a focus on disc, particle- and crystal-based methods. A number of small-scale techniques are then described in detail, and their applicability domains are identified. Finally, an updated industrial perspective is provided about IDR’s place in the early drug development process.

Amorphous solid dispersions (ASDs) represent an important formulation technique to achieve supersaturation in gastrointestinal fluids and to enhance absorption of poorly water-soluble drugs. Drug release from such systems is complex due to emergence of different colloidal structures and potential drug precipitation, which can occur in parallel to absorption. The latter drug uptake from the intestinal lumen can be simulated by an organic layer in a biphasic in vitro test, which was employed in this work to mechanistically study the release of ketoconazole from ASDs produced by hot melt extrusion using different HPMCAS grades. A particular aim was to introduce diffusing wave spectroscopy (DWS) to biopharmaceutical testing of solid dispersions. Results indicated that amorphous formulations prevented crystallization of the weakly basic drug upon transfer into the intestinal medium. Microrheological differences among polymer grades and plasticizers were revealed in the aqueous phase, which affected drug release and subsequently uptake into the organic layer. The results indicate that DWS can be employed as a new non-invasive tool to better understand drug release from solid dispersions. This novel light scattering technique is highly promising for future biopharmaceutical research on supersaturating systems such as solid dispersions.

Objectives Drug precipitation in vivo poses a significant challenge for the pharmaceutical industry. During the drug development process, the impact of drug supersaturation or precipitation on the in vivo behaviour of drug products is evaluated with in vitro techniques. This review focuses on the small and full scale in vitro methods to assess drug precipitation in the fasted small intestine. Key findings Many methods have been developed in an attempt to evaluate drug precipitation in the fasted state, with varying degrees of complexity and scale. In early stages of drug development, when drug quantities are typically limited, small-scale tests facilitate an early evaluation of the potential precipitation risk in vivo and allow rapid screening of prototype formulations. At later stages of formulation development, full-scale methods are necessary to predict the behaviour of formulations at clinically relevant doses. Multicompartment models allow the evaluation of drug precipitation after transfer from stomach to the upper small intestine. Optimisation of available biopharmaceutics tools for evaluating precipitation in the fasted small intestine is crucial for accelerating the development of novel breakthrough medicines and reducing the development costs. Despite the progress from compendial quality control dissolution methods, further work is required to validate the usefulness of proposed setups and to increase their biorelevance, particularly in simulating the absorption of drug along the intestinal lumen. Coupling results from in vitro testing with physiologically based pharmacokinetic modelling holds significant promise and requires further evaluation.

Intrinsic dissolution rate (IDR) is the surface specific dissolution rate of a drug. In early drug development, this property (among other parameters) is measured in order to compare different polymorphs and salt forms, guide formulation decisions, and to provide a quality marker of the active pharmaceutical ingredient (API) during production. In this review, an update on different methods and small-scale techniques that have recently evolved for determination of IDR is provided. The importance of biorelevant media and the hydrodynamic conditions of dissolution are also discussed. Different preparation techniques for samples are presented with a focus on disc, particle- and crystal-based methods. A number of small-scale techniques are then described in detail, and their applicability domains are identified. Finally, an updated industrial perspective is provided about IDR’s place in the early drug development process.