Insights into the Release Mechanisms of ITZ:HPMCAS Amorphous Solid Dispersions: The Role of Drug-Rich Colloids.

Understanding the dissolution mechanisms of amorphous solid dispersions (ASDs) and being able to link enhanced drug exposure with process parameters are key when formulating poorly soluble compounds. Thus, in this study, ASDs composed by itraconazole (ITZ) and hydroxypropylmethylcellulose acetate succinate (HPMCAS) were formulated with different polymer grades and drug loads (DLs) and processed by spray drying with different atomization ratios and outlet temperatures. Their in vitro performance and the ability to form drug-rich colloids were then evaluated by a physiologically relevant dissolution method. In gastric media, drug release followed a diffusion-controlled mechanism and drug-rich colloids were not formed since the solubility of the amorphous API at pH 1.6 was not exceeded. After changing to intestinal media, the API followed a polymer dissolution-controlled release, where the polymer rapidly dissolved, promoting the immediate release of API and thus leading to liquid-liquid phase separation (LLPS) and consequent formation of drug-rich colloids. However, the release of API and polymer was not congruent, so API surface enrichment occurred, which limited the further dissolution of the polymer, leading to a drug-controlled release. ASDs formulated with M-grade showed the highest ability to maintain supersaturation and the lowest tendency for AAPS due to its good balance between acetyl and succinoyl groups, and thus strong interactions with both the hydrophobic drug and the aqueous dissolution medium. The ability to form colloids increased for low DL (15%) and high specific surface area due to the high amount of polymer released until the occurrence of API surface enrichment. Even though congruent release was not observed, all ASDs formed drug-rich colloids that were stable in the solution until the end of the dissolution study (4 h), maintaining the same size distribution (ca. 300 nm). Drug-rich colloids can, in vivo, act as a drug reservoir replenishing the drug while it permeates. Designing ASDs that are prone to form colloids can overcome the solubility constraints of Biopharmaceutics Classification System (BCS) II and IV drugs, posing as a reliable formulation strategy.

A high-sensitivity HPLC-ELSD method for HPMC-AS quantification and its application in elucidating the release mechanism of HPMC-AS based amorphous solid dispersions.

Hydroxypropyl methylcellulose acetate succinate (HPMC-AS) is one of the most widely used polymers used in amorphous solid dispersions (ASD) for solubility and bioavailability enhancement of poorly water-soluble drugs. Once released from ASDs, HPMC-AS was often found to be highly effective in maintaining drug supersaturation, and this capability is dependent on the concentration and substitution types of this pH-dependent polymer. Therefore, accurate quantification of different grades of HPMC-AS allows us to better understand the release and supersaturation mechanisms of HPMC-AS based ASDs. Since previously reported analytical methods were unable to quantify HPMC-AS in a complex medium with enough sensitivity, we hereby developed a high-sensitivity HPLC-ELSD (evaporative light scattering detector) method with satisfactory specificity, linearity, accuracy and precision, to quantify HPMC-AS down to 20 µg/mL in dissolution media, with the presence of various commonly used pharmaceutical excipients. With the assistance of this method, we compared the intrinsic dissolution rates (IDR) of both the drug and the polymer of posaconazole ASDs based on different types of HPMC-AS. We observed that: 1) For ASDs that were spray dried and uniformly mixed, drug and polymer released simultaneously into the medium with practically identical IDRs slower than the IDR of pure HPMC-AS; 2) For ASDs that were heterogeneously mixed, IDRs of the drug and polymer were significantly slower or faster than the IDRs of the drug and polymer of the uniform ASDs, respectively. In summary, the high sensitivity HPLC-ELSD method established here can be readily applied to quantify HPMC-AS in various dissolution media, thus helps to reveal the release kinetics and mechanisms of different HPMC-AS based ASDs.

Dissolution performance of binary amorphous drug combinations--Impact of a second drug on the maximum achievable supersaturation.

An increased number of amorphous formulations of poorly water soluble drugs are being introduced into the market due to their higher transient solubility and thus faster absorption and higher bioavailability. While most amorphous drug products contain a single drug substance, there is a growing trend towards co-formulating compounds in the same dosage form to improve patient compliance. The purpose of the present work was to evaluate the dissolution behavior and maximum achievable solution concentrations of amorphous solid dispersions of co-formulated ritonavir and lopinavir, and to compare the results with individual amorphous solid dispersion formulations. Dispersions of ritonavir and lopinavir were prepared in polyvinylpyrrolidone (PVP) or hydroxypropylmethylcellulose acetate succinate (HPMCAS) at a 20% (w/w) total drug loading, both alone and in combination, at three different lopinavir:ritonavir weight ratios. Amorphous films containing both drugs, but no polymer, were also prepared. The dissolution behavior of the dispersions and the amorphous films in non-sink conditions was evaluated, using ultracentrifugation to separate any colloidal material from molecularly dissolved drug. Nanoparticle tracking analysis was used to characterize colloidal material formed during the dissolution process. Results from the dissolution study revealed that, although supersaturated solutions resulted following dissolution, the maximum achievable concentration of each drug, when present in combination, was dramatically lower than when the individual dispersions were dissolved. The maximum achievable solution concentration for systems containing both drugs was found to decrease as the mole fraction of the drug in the amorphous phase decreased. The type of polymer used to formulate the dispersion also appeared to influence the dissolution behavior whereby the HPMCAS dispersions dissolved rapidly, resulting in the generation of a nanodroplets, while the PVP dispersions did not produce as many colloidal species. These results highlight the need to consider potential decreases in achievable supersaturation for formulations containing more than one amorphous compound.

Charge profiling and stability testing of biosimilar by capillary isoelectric focusing.

CIEF was developed for the rapid analysis of charge heterogeneity of trastuzumab biosimilar using commercially available fluorocarbon-coated capillary. The CIEF master mix was composed of 0.30% w/v methyl cellulose, 2.3 M urea, 56.8 mM l-arginine, 1.52 mM iminodiacetic acid, 4.5% v/v carrier ampholytes (broad-range pI 3-10 and narrow-range pI 8-10.5 with ratio of 3:1), and 0.45% v/v 10.0, 9.5, 7.0, 5.5, 4.1 pI markers. To get a robust method to analyze charge heterogeneity, some separation parameters, including focusing time and separation temperature, were investigated and optimized. The optimized method gave good precision in estimated pI values of charge variants with RSDs of not more than 0.16% intraday analysis (n = 6) and < 0.18% interday analysis (n = 9). In addition, the applications of this method including purity, stability, lot consistency, peptide N-glycosidase F digest, and C-terminal lysine variants characterization were also investigated.

Optimization of HPMC and carbopol concentrations in non-effervescent floating tablet through factorial design.

This study was to optimize HPMC K4M and carbopol 934 concentration in the development of non-effervescent floating tablets (NEFTs) of glipizide as model drug using 3(2) factorial design. The time required for releasing drug of 50% and 80% and similarity factor were the target responses. HPMC K4M and carbopol 934 concentrations were the variables. The response surface methodology and optimized polynomial equations were used to select the optimal formulation with desired responses. The excipients used in tablets were compatible with glipizide as per the results of isothermal stress testing and DSC study. The drug release of entire NEFTs followed zero order kinetics and non-Fickian diffusion mechanism. Validation of the optimization technique demonstrated the reliability of the model. The optimized formulation containing 124.33 mg HPMC K4M and 25.76 mg carbopol 934 was prepared according to the software determined levels. The stability study of the optimized formulation proved the integrity of the developed formulation.

Evidence for the coexistence of interpenetrating permanent and transient networks of hydroxypropyl methyl cellulose.

Dynamic mechanical properties of aqueous solutions of hydroxypropyl methyl cellulose (HPMC) were investigated using oscillatory shear measurements. The structure was investigated with light scattering. A systematic investigation of the frequency dependence of the shear moduli showed that HPMC forms two distinct interpenetrating networks. A transient network is formed above about 0.3 wt % by reversible cross-linking of the chains. The elastic modulus of this network is independent of the temperature, but increases linearly with the concentration. An independent permanent network is formed involving a small fraction of the polymers and has an elastic modulus that increases with increasing temperature. Its elastic modulus is history dependent and evolves slowly with time. The transient network collapses at a critical temperature where micro phase separation occurs, but the permanent network is not influenced by this phenomenon. Light scattering showed that the pore size of the transient network is less than 40 nm, while probe diffusion measurements showed that the pore size of the permanent network is larger than 1 µm.

Comparative analysis of zaleplon complexation with cyclodextrins and hydrophilic polymers in solution and in solid state.

The aim of this work was to investigate the potential synergistic effect of water-soluble polymers (hypromellose, HPMC and polyvinylpyrrolidone, PVP) on zaleplon (ZAL) complexation with parent ß-cyclodextrin (ßCD) and its randomly methylated derivative (RAMEB) in solution and in solid state. The addition of HPMC to the complexation medium improved ZAL complexation and solubilization with RAMEB (K(ZAL/RAMEB)=156±5M(-1) and K(ZAL/RAMEB/HPMC)=189±8M(-1); p<0.01), while such effect was not observed for ßCD (K(ZAL/ßCD)=112±2M(-1) and K(ZAL/ßCD/HPMC)=119±8M(-1); p>0.05). Although PVP increased the ZAL aqueous solubility from 0.22 to 0.27mg/mL, it did not show any synergistic effects on ZAL solubilization with the cyclodextrins tested. Binary and ternary systems of ZAL with ßCD, RAMEB and HPMC were prepared by spray-drying. Differential scanning calorimetry, X-ray powder diffraction and scanning electron microscopy demonstrated a partial ZAL amorphization in spray-dried binary and ternary systems with ßCD, while the drug was completely amorphous in all samples with RAMEB. Furthermore, inclusion complex formation in all systems prepared was confirmed by solid-state NMR spectroscopy. The in vitro dissolution rate followed the rank order ZAL/RAMEB/HPMC>ZAL/RAMEB=ZAL/ßCD/HPMC>ZAL/ßCD≫ZAL, clearly demonstrating the superior performance of RAMEB on ZAL complexation in the solid state and its synergistic effect with HPMC on drug solubility. Surprisingly, when loaded into tablets made with insoluble microcrystalline cellulose, RAMEB complexes had no positive effect on drug dissolution, because HPMC and RAMEB acted as a binders inside the tablets, prolonging their disintegration. Oppositely, the formulation with mannitol, a soluble excipient, containing a ternary RAMEB system, released the complete drug-dose in only 5min, clearly demonstrating its suitability for the development of immediate-release oral formulation of ZAL.

Detecting endotoxin contamination of ophthalmic viscosurgical devices: intracameral versus intravitreal assays in rabbits.

OBJECTIVE: To compare the sensitivities of intracameral and intravitreal assays in the rabbit model to determine the relative adequacy of these methods in detecting bacterial endotoxin contamination of ophthalmic viscosurgical devices (OVDs). DESIGN: Experimental, randomized animal study. PARTICIPANTS: Twenty New Zealand white rabbits. METHODS: Rabbits were randomized into 4 groups to receive a cohesive or a dispersive OVD via intracameral or intravitreal injection. All 40 treated eyes (10 eyes of 5 animals in each group) received bilateral injection of OVD spiked with bacterial endotoxin at 7.0 endotoxin units/ml. All eyes were evaluated by slit-lamp biomicroscopy for inflammatory response at 3, 6, 9, 24, 48, and 72 hours after exposure. Eyes that received intravitreal injection were also dilated at 24, 48, and 72 hours and were re-examined by slit-lamp biomicroscopy and by indirect ophthalmoscopy. MAIN OUTCOME MEASURES: Conjunctival inflammation, anterior chamber (AC) flare, cells and fibrin, vitreous haze and cells, iridal hyperemia, corneal clouding, lens opacities, and onset times. RESULTS: Intracamerally injected eyes frequently showed conjunctival congestion, AC cells and flare, iridal hyperemia, and fibrin within 6 hours. Up to 80% showed AC cells and flare at 9 hours, and up to 70% showed fibrin at 24 hours. These signs diminished within 48 hours. Fibrin and cells also were seen on the lens surface of most of the eyes. Intravitreally injected eyes showed no signs of inflammation within 24 hours, other than some conjunctival inflammation. After the 24-hour time point, in addition to some conjunctival inflammation, some other signs of inflammation were observed infrequently in the intravitreally injected eyes, including minor vitreous cell reaction in 2 eyes. Although there was 1 dispersive OVD-treated eye with cells and fibrin on the lens capsule at 48 hours, no aqueous cells or flare were seen in the AC of any intravitreally injected eyes at any time during the course of the study. CONCLUSIONS: The rabbit intravitreal assay, when limited to 72 hours, does not seem to have adequate sensitivity to detect endotoxin reliably in OVDs.

Thermogravimetry-mass spectrometry for carbon nanotube detection in complex mixtures.

In spite of the growth of the carbon nanotube (CNT) industry, there are no established analytical methods with which to detect or quantify CNTs in environmental matrices. Given that CNTs have relatively high thermal stabilities, we investigated the use of thermal techniques to isolate and quantify single wall carbon nanotubes (SWCNTs). Test materials included ten types of commercial SWCNTs, representative biological macromolecules (bovine serum albumin and methylcellulose), soot, natural coastal sediments, and SWCNT-amended sediments. Different SWCNTs exhibited widely diverse degradation temperatures, and thermal analytical methods may require SWCNT-type specific parameters. To improve quantification capabilities, evolved gases were monitored by mass spectrometry. SWCNTs produced diagnostic ion ratios reflective of their high carbon and low hydrogen and oxygen contents. Current detection limits are roughly 4 µg(SWCNT) per sample (e.g., 100 µg(SWCNT) g(-1)(sediment) and 40 mg sample), controlled by interfering ions associated with the instrument's non-airtight design. Although future modifications could improve this limitation, the current method is sufficient for quantifying SWCNTs in laboratories and industrial sites where SWCNTs are handled. Furthermore, the method shows promise to distinguish between incidental (e.g., soot) and engineered (e.g., SWCNTs) nanoparticles, which is not possible with current state-of-the-art techniques.

Absolute molecular weight determination of hypromellose acetate succinate by size exclusion chromatography: use of a multi angle laser light scattering detector and a mixed solvent.

Molecular weight distribution is an important quality attribute for hypromellose acetate succinate (HPMCAS), a pharmaceutical excipient used in spray-dried dispersions. Our previous study showed that neither relative nor universal calibration method of size exclusion chromatography (SEC) works for HPMCAS polymers. We here report our effort to develop a SEC method using a mass sensitive multi angle laser light scattering detector (MALLS) to determine molecular weight distributions of HPMCAS polymers. A solvent screen study reveals that a mixed solvent (60:40%, v/v 50mM NaH(2)PO(4) with 0.1M NaNO(3) buffer: acetonitrile, pH* 8.0) is the best for HPMCAS-LF and MF sub-classes. Use of a mixed solvent creates a challenging condition for the method that uses refractive index detector. Therefore, we thoroughly evaluated the method performance and robustness. The mean weight average molecular weight of a polyethylene oxide standard has a 95% confidence interval of (28,443-28,793) g/mol vs. 28,700g/mol from the Certificate of Analysis. The relative standard deviations of average molecular weights for all polymers are 3-6%. These results and the Design of Experiments study demonstrate that the method is accurate and robust.

Effect of source variation on drug release from HPMC tablets: linear regression modeling for prediction of drug release.

The aim of this study was to investigate the effect of source variation of hydroxypropyl methylcellulose (HPMC) raw material on prediction of drug release from HPMC matrix tablets. To achieve this objective, the flow ability (i.e., angle of repose and Carr's compressibility index) and apparent viscosity of HPMC from 3 sources was investigated to differentiate HPMC source variation. The physicochemical properties of drug and manufacturing process were also incorporated to develop the linear regression model for prediction of drug release. Specifically, the in vitro release of 18 formulations was determined according to a 2 × 3 × 3 full factorial design. Further regression analysis provided a quantitative relationship between the response and the studied independent variables. It was found that either apparent viscosity or Carr's compressibility index of HPMC powders combining with solubility and molecular weight of drug had significant impact on the release behavior of drug. The increased drug release was observed when a greater in drug solubility and a decrease in the molecular weight of drug were applied. Most importantly, this study has shown that the HPMC having low viscosity or high compressibility index resulted in an increase of drug release, especially in the case of poorly soluble drugs.

Release of theophylline and carbamazepine from matrix tablets--consequences of HPMC chemical heterogeneity.

The release of theophylline and carbamazepine from matrix tablets composed of microcrystalline cellulose, lactose and hydroxypropyl methylcellulose (HPMC) was studied. The aim was to investigate the effect of different substituent heterogeneities of HPMC on the drug release from matrix tablets composed of either 35% or 45% HPMC. The release of the poorly soluble carbamazepine was considerably affected by the HPMC heterogeneity, and the time difference at 80% drug release was more than 12h between the formulations of different HPMC batches. This was explained by slower polymer erosion of the heterogeneous HPMC and the fact that carbamazepine was mainly released by erosion. In addition, results from magnetic resonance imaging showed that the rate of water transport into the tablets was similar. This explained the comparable results of the release of the sparingly soluble theophylline from the two formulations even though the polymer erosion and the swelling of the tablets were considerably different. Thus, it can be concluded that the drug release was highly affected by the substituent heterogeneity, especially in the case of carbamazepine, which was released mainly by erosion.

The consequence of the chemical composition of HPMC in matrix tablets on the release behaviour of model drug substances having different solubility.

This study investigates the effect of the chemical heterogeneity of hydroxypropyl methylcellulose (HPMC) on the release of model drug substances from hydrophilic matrix tablets. The hypothesis was that the release of drug substances could be influenced by possible interactions with HPMC batches having different chemical heterogeneity. The cloud point of the most heterogeneous batch was more affected by the model drug substances, methylparaben and butylparaben, and most by butylparaben with the lowest solubility. The different clouding behaviour was explained by the heterogeneously substituted batches being more associative and the more lipophilic butylparaben being able to interact more efficiently with the hydrophobic HPMC transient crosslinks that formed. Interestingly, tablet compositions of the heterogeneously substituted HPMC batches released the more soluble methylparaben at lower rates than butylparaben. The explanation is that the hydrophobic HPMC interactions with butylparaben made the gel of the tablet less hydrated and more fragile and therefore more affected by erosional stresses. In contrast, drug release from compositions consisting of the more homogeneously substituted batches was affected to a minor extent by the drugs and was very robust within the experimental variations. The present study thus reveals that there can be variability in drug release depending on the lipophilicity of the drug and the substituent heterogeneity of the HPMC used.

[Preparation and in vitro release characteristics of pulsed-release tablets of Apocynum venetum].

OBJECTIVE: Using Apocynum venetum as a model drug to prepare pulsed-release tablets based on diffusion, swelling, osmotic pressure mechanism and to evaluate the release characteristics. METHOD: The pulsatile release tablets were prepared by film coating methods using HPMC E5 and Eudragit The effect of formulation on pulsatile release of A. venetum was investigated. RESULT: The pulsed-release tablet was prepared by a swelling layer coating which contains HPMC E5 and a controlled-release membrane containning Eudragit. The delayed release time of the tablets was (5.0 +/- 0.5) h. CONCLUSION: The pulsatile release characteristics of A. venetum pulsatile release tablets were confirmed in vitro.

The effect of sucrose and salts in combination on the drug release behaviour of an HPMC matrix.

Previous work has shown how high concentrations of sugars can accelerate drug release from hydroxypropyl methylcellulose (HPMC) matrices by suppressing polymer hydration. This study investigates the effects of combining sugar and salts, using sucrose, sodium chloride and trisodium citrate, soluble ingredients commonly found in foods. A factorial study showed that each solute suppressed HPMC solution sol-gel transition temperature (a sensitive measure of molecular hydration) independently, and their effects reflected their rank order in the Hofmeister series. In mixtures, the effects were purely additive, with no evidence of antagonism or synergy. In dissolution tests, both salts significantly reduced the threshold sugar concentration required to elicit an acceleration of drug release, and when used in combination, 0.15 M sodium chloride with 0.015 M trisodium citrate reduced the threshold sucrose concentration from 0.7 M to 0.35-0.4 M, a reduction of almost 50%. The results show that food salts can significantly reduce the concentration required for sugar effects on HPMC matrices, and this may be a factor to consider when interpreting their in vivo behaviour in the fed state.

Practical application to time indicator of a novel white film formed by interaction of calcium salts with hydroxypropyl methylcellulose.

We have found that a cast film forms a white film when an aqueous solution comprising hydroxypropyl methylcellulose (HPMC) and calcium salts such as calcium lactate pentahydrate (CLP) and calcium chloride (CaCl(2)) is used. In contrast, the obtained white film was transformed into a transparent film by the addition of purified water. The transformation time for the change from the white film to the transparent film was dependent on film thickness. The relationship between the transformation time and the film thickness was significantly correlated, and it was found that the white film could be adaptable as time indicator. The formation of a white film comprising HPMC and calcium salts was strongly dependent on temperature conditions. The objective of the present study is to investigate the mechanism of the formation of this white film because of the interaction between HPMC and calcium salts. The DSC and XRPD results indicate that the calcium salts affect the HPMC polymer phase in the cast film comprising HPMC and calcium salts. By carrying out attenuated total reflection Fourier transform infrared (ATR FT-IR) analysis, we found that the white film could be formed by the calcium salts affecting the region associated with the C-O-C, C-O, and CH(3) stretching of the HPMC polymer phase.

Physical properties of whey protein--hydroxypropylmethylcellulose blend edible films.

The formations of glycerol (Gly)-plasticized whey protein isolate (WPI)-hydroxypropylmethylcellulose (HPMC) films, blended using different combinations and at different conditions, were investigated. The resulting WPI: Gly-HPMC films were analyzed for mechanical properties, oxygen permeability (OP), and water solubility. Differences due to HPMC quantity and blend method were determined via SAS software. While WPI: Gly and HPMC films were transparent, blend films were translucent, indicating some degree of immiscibility and/or WPI-HPMC aggregated domains in the blend films. WPI: Gly-HPMC films were stronger than WPI: Gly films and more flexible and stretchable than HPMC films, with films becoming stiffer, stronger, and less stretchable as the concentration of HPMC increased. However, WPI: Gly-HPMC blended films maintained the same low OP of WPI: Gly films, significantly lower than the OP of HPMC films. Comparison of mechanical properties and OP of films made by heat-denaturing WPI before and after blending with HPMC did not indicate any difference in degree of cross-linking between the methods, while solubility data indicated otherwise. Overall, while adding HPMC to WPI: Gly films had a large effect on the flexibility, strength, stretchability, and water solubility of the film polymeric network, results indicated that HPMC had no effect on OP through the polymer network. WPI-HPMC blend films had a desirable combination of mechanical and oxygen barrier properties, reflecting the combination of hydrogen-bonding, hydrophobic interactions, and disulfide bond cross-linking in the blended polymer network.

Hydroxypropyl methylcellulose acetate succinate: potential drug-excipient incompatibility.

The stability of hydroxypropyl methylcellulose acetate succinate (HPMC-AS) and its potential incompatibility with active pharmaceutical ingredients (API) carrying hydroxyl group(s) were investigated in this research. HPMC-AS may undergo hydrolysis under harsh processing conditions with the generation of succinic acid and acetic acid, which can form ester bond(s) with the hydroxyl group(s) in API. In this case, the hot-melt extrusion (HME) product prepared from HPMC-AS and our model compound (compound A) was tested after heating at 140 degrees C up to 5 h. The succinate esters of compound A and its epimer were found in the product, suggesting potential drug-excipient incompatibility during formulation development. In addition, dyphylline was also tested with HPMC-AS and the potential incompatibility was further confirmed.

Morphological imaging of single methylcellulose chains and their thermoresponsive assembly on a highly oriented pyrolytic graphite surface.

Individual methylcellulose (MC) chains and their thermoresponsive assembly were successfully visualized on a highly oriented pyrolytic graphite (HOPG) surface by atomic force microscopy (AFM). Momentary contact of a dilute MC solution at 4 degrees C onto the HOPG substrate permitted clear imaging of individual MC chains having a molecular thickness of ca. 0.5 nm and a hexagonal orientation. By increasing the solution temperature from 4 to 80 degrees C, it was possible to bring about significant changes in the MC nanomorphology from stretched molecular chains to disordered massive aggregates. It was presumed that the hydrophobic interaction between the MC chains and the HOPG pi-conjugated system led to the successful visualization of thermally responsive changes in the MC conformations. These results imply that HOPG substrates could be used for clear nanoimaging of cellulosic polymers and other structural polysaccharides.

Determination of methylcellulose and hydroxypropyl methylcellulose food gums in food and food products: collaborative study.

A collaborative study was performed to determine the reproducibility of a method for the determination of methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) in food. These widely used food gums possess unusual solubility characteristics and cannot accurately be determined by existing dietary fiber methods. The new method uses the enzyme-digestion procedure of AOAC Official Method 991.43. Digestate solutions must be refrigerated to fully hydrate MC or HPMC. The chilled solutions are filtered and analyzed by size-exclusion liquid chromatography. Collaborating laboratories received 28 samples containing MC or HPMC in the range of 0-100%. The sample set included blind duplicates of 5 food matrixes (bread, milk, fish, potato, and powdered juice drink). Cochran and Grubbs tests were used to eliminate outliers. For food samples containing MC, values for within-laboratory precision, repeatability relative standard deviation (RSDr), ranged from 4.2 to 16%, and values for among-laboratories precision, reproducibility relative standard deviation (RSDR), ranged from 11 to 20%. For HPMC samples, RSDr values ranged from 6.4 to 27%, and RSDR values ranged from 17 to 39%. Recoveries of MC and HPMC from the food matrixes ranged from 78 to 101%. These results show acceptable precision and reproducibility for the determination of MC and HPMC, for which no Official AOAC Methods exist. It is recommended that this method be adopted as AOAC Official First Action.