In vitro-in vivo relationship for amorphous solid dispersions using a double membrane dissolution-permeation setup

The use of amorphous solid dispersions (ASDs) is one commonly applied formulation strategy to improve the oral bioavailability of poorly water-soluble drugs by overcoming dissolution rate and/or solubility limitations. While bioavailability enhancement of ASDs is well documented, it has often been a challenge to establish a predictive model describing in vitro-in vivo relationship (IVIVR). In this study, it is hypothesized that drug absorption might be overestimated by in vitro dissolution-permeation (D/P)-setups, when drug in suspension has the possibility of directly interacting with the permeation barrier. This is supported by the overprediction of drug absorption from neat crystalline efavirenz compared to four ASDs in a D/P-setup based on the parallel artificial membrane permeability assay (PAMPA). However, linear IVIVR (R² = 0.97) is established in a modified D/P-setup in which the addition of a hydrophilic PVDF-filter acts as a physical boundary between the donor compartment and the PAMPA-membrane. Based on microscopic visualization, the improved predictability of the modified D/P-setup is due to the avoidance of direct dissolution of drug particles in the lipid components of the PAMPA-membrane. In general, this principle might aid in providing a more reliable evaluation of formulations of poorly water-soluble drugs before initiating animal models.

Stability and intrinsic dissolution of vacuum compression molded amorphous solid dispersions of efavirenz

In this study, the stability and intrinsic dissolution of vacuum compression molded (VCM) amorphous solid dispersions (ASDs) of efavirenz (EFV) were investigated in relation to its solubility limits in seven polymers determined by the melting point depression (MPD) method. The extrapolated solubility limits of EFV at 22 °C ranged from 3 to 68% (w/w) with PVOH being the only polymer suggesting immiscibility with EFV according to both MPD and Hansen solubility parameters (HSPs). All ASDs with EFV loadings below or close to their calculated solubility limit did not show any signs of crystallization upon conditioning for 7 months at either 22 or 37 °C and 23 or 75% relative humidity. However, all ASDs with EFV loading above the solubility limit crystallized at high humidity, while the ASDs with cellulose derived carrier polymers proved kinetically stable at low humidity over 7 months. While the EFV intrinsic dissolution rates from the VCM ASDs were partly depending on the polymer dissolution rate, no correlation was observed between EFV matrix crystallization and its miscibility in the polymer. Altogether, the observations of the study underline the importance of combining preformulation miscibility determination and dissolution studies to rationally decide on both stability and viability of ASD formulations.

Separation and Quantitation of Alkylphosphocholines and Analogues of Different Liposome Formulations by HPTLC

High-performance thin-layer chromatographic (HPTLC) analysis of non UV-active phospholipids in biological matrixes is a common method for separation, detection, and quantitation. Liposomes containing new alkylphosphocholines and analogues with enhanced cytostatic activity had been prepared. The liposomal formulations were designed to enable the intravenous application of the alkylphosphocholines and analogues and to reduce dose-limiting toxicities observed after oral administration. For quality control the liposomes were analyzed by HPTLC for content of 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), cholesterol, alkylphosphocholines, and analogues and their related compounds (main degradation products). Due to the differences in lipophily of the compounds, different mobile phases were necessary to achieve separation. Automated Multiple Development was used to reduce the number of plates and to improve the selectivity and the capacity of the chromatographic system to separate the described alkylphosphocholines and analogues from DPPG and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine in one chromatographic system.

Rapid development of API nano-formulations from screening to production combining dual centrifugation and wet agitator bead milling

Various wet ball nanomilling-screening tools for poorly soluble APIs are available which differ in their milling principle, batch size and number of samples. Here, the transferability of results from screening (small to medium-scale) to pharmaceutical production (largescale) was investigated. Wet ball milling in a dual centrifuge (DC) (10-100 mg API, 40 samples in parallel) was used to identify stable nanoformulations. In addition different sized agitator bead mills were used for scale-up to industrial scales. DC-and small-scale agitator milling (AM) resulted in small and virtually identical API-particles. Additionally, similar API-particles were obtained using two different sized agitator bead mills (batch size 1.5 and 30 kg) and applying comparable specific grinding energies (SGE). The SGE used in the trials represents the grinding limit for this API-suspension. Using lower SGEs, AM results in larger API-particles. All used milling tools had no influence on the APIs crystal structure and wear of grinding media (Zr/Y) is low. The study confirmed the importance to choose the right formulation and process parameters, which positively affect grinding efficacy, particle size distribution and wear contamination. The excellent comparability of results obtained from DC-milling and AM significantly reduces the duration for successful and predictable formulation development.

Nanofibers resulting from cooperative electrostatic and hydrophobic interactions between peptides and polyelectrolytes of opposite charge

We investigated whether cationic peptides that contain hydrophobic side chains were able to stabilize themselves via hydrophobic interactions between neighboring peptide molecules upon electrostatic binding to oppositely charged polyelectrolytes. The interaction mechanism was examined through a model system consisting of the anionic polyelectrolyte alginate and the cationic decapeptide ozarelix. The interaction resulted in the formation of highly ordered complexes that were noticeable upon visual inspection. These complexes were then investigated by microscopic techniques and shown to exhibit a branched network structure. Cryogenic-temperature transmission electron microscopy (cryo-TEM) and negative staining TEM revealed that the molecular interactions between alginate and ozarelix led to the formation of nanofibers. The rodlike nanofibers had a diameter distribution of 4-8 nm. Isothermal titration calorimetry was used to determine the thermodynamic parameters of the alginate-ozarelix interaction. The binding constant was found to be on the order of 10(6) M(-1), indicating a high binding affinity. The interaction of the peptide with the polyelectrolyte triggered profound changes in the conformation of ozarelix, which was confirmed by UV spectroscopy and circular dichroism. On the basis of these experimental results, a theoretical modeling study of the alginate-ozarelix interaction was conducted to gain a better molecular-level understanding of the complex structure. It revealed that, upon binding of ozarelix to alginate, new intermolecular and intramolecular aromatic interactions between the ozarelix molecules occurred. These interactions changed the conformation of the peptide, a modification in which the aromatic side chains played a major role. Our results indicate that the cationic peptides interact with the polyanions via electrostatic interactions, but are additionally stabilized via hydrophobic interactions. This binding mode may serve as a powerful tool to extend the duration of drug release in hydrogel drug delivery systems.

Development and validation of a HPLC method for routine quantification of the decapeptide Cetrorelix in liposome dispersions

The development and validation of an HPLC method for the quantification of the decapeptide Cetrorelix (acetyl-D-2-naphthylalanyl-D-4-chlorphenylalanyl-D-3-pyridylalanyl-seryl-tyrosyl-D-citrullyl-leucyl-arginyl-prolyl-d-alaninamide), a potent antagonist of the luteinising hormone-releasing hormone in liposome dispersions is described. An isocratic reversed phase method with UV-detection appeared most appropriate. Several detergents were tried to disrupt liposomes. Furthermore, detergents turned out to be useful, because they minimised unwanted loss of Cetrorelix due to adsorption to the vial surfaces. Triton X-100 was found most effective, while sodium cholate led to quantification problems. In the presence of 2.5% Triton X-100 calibration curves with a high degree of linearity were achieved in the desired range of 0.2-10 microg/ml. The limits of detection and quantification of Cetrorelix were calculated from the peak-to-noise ratio to be 11 and 37 ng/ml, respectively. The repeatability of the method in presence of phospholipid and Triton was good with relative standard deviations (R.S.D.) ranging from 0.8% (at 0.05 microg/ml) to 1.5% (at 0.2 microg/ml). The presence of liposomes at phospholipid contents of up to 0.25mg/ml did not significantly affect the slope or linearity of the calibration curve, nor the peak-to-noise ratio.

Adsorption of the decapeptide Cetrorelix depends both on the composition of dissolution medium and the type of solid surface

High performance liquid chromatography (HPLC) analysis of increasing amounts of the decapeptide Cetrorelix, a potent antagonist of the luteinising hormone-releasing hormone, in distilled water resulted in a poor and variable response when solutions of low concentration (0.2-4microg/ml) were analysed. Rinsing experiments revealed loss of analyte due to adsorption to the vial surfaces as the main reason for this. The adsorption of Cetrorelix was found to follow a Langmuir isotherm reaching a plateau at 0.4microg/cm(2) and to be influenced by both the dissolution medium and the type of vial used. The adsorption tendency of Cetrorelix was reduced by: (a) a more lipophilic solvent (ethanol), (b) a more acidic pH (acetic acid) inducing repulsive charges (c) a micellar solution of various tensides. With all of these media the HPLC response was higher (up to five times) and less variable. Adsorption of Cetrorelix to solid surfaces decreased in the rank order: glass > polypropylene = polyethylene > poly-(tetrafluoroethylene), with considerable differences between the glass vials of various suppliers.

Separation and quantitation of alkylphosphocholines and analogues of different liposome formulations by HPTLC

High-performance thin-layer chromatographic (HPTLC) analysis of non UV-active phospholipids in biological matrixes is a common method for separation, detection, and quantitation. Liposomes containing new alkylphosphocholines and analogues with enhanced cytostatic activity had been prepared. The liposomal formulations were designed to enable the intravenous application of the alkylphosphocholines and analogues and to reduce dose-limiting toxicities observed after oral administration. For quality control the liposomes were analyzed by HPTLC for content of 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), cholesterol, alkylphosphocholines, and analogues and their related compounds (main degradation products). Due to the differences in lipophily of the compounds, different mobile phases were necessary to achieve separation. Automated Multiple Development was used to reduce the number of plates and to improve the selectivity and the capacity of the chromatographic system to separate the described alkylphosphocholines and analogues from DPPG and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine in one chromatographic system.