Bioavailability of norfloxacin from PEG 6000 solid dispersion and cyclodextrin inclusion complexes in rabbits

Computational investigation on the host-guest inclusion process of norfloxacin into β-cyclodextrin

A theoretical (1)H NMR spectroscopy and thermodynamic analysis of the host-guest inclusion process involving the norfloxacin (NFX) into β-cyclodextrin (β-CD) was carried out. DFT structure and stabilization energies were obtained in both gas and aqueous phases. We could establish that the complex formation is enthalpy driven, and the hydrogen bonds established between NFX and β-CD play a major role in the complex stabilization. Besides, a theoretical (1)H NMR analysis has shown to be a supplementary proceeding to predict appropriately the inclusion mode of norfloxacin molecule into the β-CD. In this work, a theoretical study of the NFX@β-CD complex is reported for the first time, seeking a deep understanding of topology and thermodynamics of the inclusion complex formation. Graphical Abstract Topology, thermodynamic and (1)H NMR analysis of NFX@β-CD host-guest complexes.

Influence of β-cyclodextrin on the Properties of Norfloxacin Form A

Cyclodextrins are able to form host-guest complexes with hydrophobic molecules to result in the formation of inclusion complexes. The complex formation between norfloxacin form A and β-cyclodextrin was studied by exploring its structure affinity relationship in an aqueous solution and in the solid state. Kneading, freeze-drying, and physical mixture methods were employed to prepare solid complexes of norfloxacin and β-cyclodextrin. The solubility of norfloxacin significantly increased upon complexation with β-cyclodextrin as demonstrated by a solubility isotherm of the AL type along with the results of an intrinsic dissolution study. The complexes were also characterized in the solid stated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffractometry, scanning electron microscopy (SEM), and solid-state nuclear magnetic resonance (ssNMR) spectrometry. The thermal analysis showed that the thermal stability of the drug is enhanced in the presence of β-cyclodextrin. Finally, the microbiological studies showed that the complexes have better potency when compared with pure drug.

Analysis of amorphous solid dispersions using 2D solid-state NMR and (1)H T(1) relaxation measurements

Solid-state NMR (SSNMR) can provide detailed structural information about amorphous solid dispersions of pharmaceutical small molecules. In this study, the ability of SSNMR experiments based on dipolar correlation, spin diffusion, and relaxation measurements to characterize the structure of solid dispersions is explored. Observation of spin diffusion effects using the 2D (1)H-(13)C cross-polarization heteronuclear correlation (CP-HETCOR) experiment is shown to be a useful probe of association between the amorphous drug and polymer that is capable of directly proving glass solution formation. Dispersions of acetaminophen and indomethacin in different polymers are examined using this approach, as well as (1)H double-quantum correlation experiments to probe additional structural features. (1)H-(19)F CP-HETCOR serves a similar role for fluorinated drug molecules such as diflunisal in dispersions, providing a rapid means to prove the formation of a glass solution. Phase separation is detected using (13)C, (19)F, and (23)Na-detected (1)H T(1) experiments in crystalline and amorphous solid dispersions that contain small domains. (1)H T(1) measurements of amorphous nanosuspensions of trehalose and dextran illustrate the ability of SSNMR to detect domain size effects in dispersions that are not glass solutions via spin diffusion effects. Two previously unreported amorphous solid dispersions involving up to three components and containing voriconazole and telithromycin are analyzed using these experiments to demonstrate the general applicability of the approach.

Characterization of the molecular distribution of drugs in glassy solid dispersions at the nano-meter scale, using differential scanning calorimetry and gravimetric water vapour sorption techniques

The molecular distribution in fully amorphous solid dispersions consisting of poly(vinylpyrrolidone) (PVP)-diazepam and inulin-diazepam was studied. One glass transition temperature (T(g)), as determined by temperature modulated differential scanning calorimetry (TMDSC), was observed in PVP-diazepam solid dispersions prepared by fusion for all drug loads tested (10-80 wt.%). The T(g) of these solid dispersions gradually changed with composition and decreased from 177 degrees C for pure PVP to 46 degrees C for diazepam. These observations indicate that diazepam was dispersed in PVP on a molecular level. However, in PVP-diazepam solid dispersions prepared by freeze drying, two T(g)'s were observed for drug loads above 35 wt.% indicating phase separation. One T(g) indicated the presence of amorphous diazepam clusters, the other T(g) was attributed to a PVP-rich phase in which diazepam was dispersed on a molecular level. With both the value of the latter T(g) and the DeltaC(p) of the diazepam glass transition the concentrations of molecular dispersed diazepam could be calculated (27-35 wt.%). Both methods gave similar results. Water vapour sorption (DVS) experiments revealed that the PVP-matrix was hydrophobised by the incorporated diazepam. TMDSC and DVS results were used to estimate the size of diazepam clusters in freeze dried PVP-diazepam solid dispersions, which appeared to be in the nano-meter range. The inulin-diazepam solid dispersions prepared by spray freeze drying showed one T(g) for drug loads up to 35 wt.% indicating homogeneous distribution on a molecular level. However, this T(g) was independent of the drug load, which is unexpected because diazepam has a lower T(g) than inulin (46 and 155 degrees C, respectively). For higher drug loads, a T(g) of diazepam as well as a T(g) of the inulin-rich phase was observed, indicating the formation of amorphous diazepam clusters. From the DeltaC(p) of the diazepam glass transition the amount of molecularly dispersed diazepam was calculated (12-27 wt.%). In contrast to the PVP-diazepam solid dispersions, DVS-experiments revealed that inulin was not hydrophobised by diazepam. Consequently, the size of diazepam clusters could not be estimated. It was concluded that TMDSC enables characterization and quantification of the molecular distribution in amorphous solid dispersions. When the hygroscopicity of the carrier is reduced by the drug, DVS in combination with TMDSC can be used to estimate the size of amorphous drug clusters.

Anomalous dissolution behaviour of tablets prepared from sugar glass-based solid dispersions

In this study, anomalous dissolution behaviour of tablets consisting of sugar glass dispersions was investigated. The poorly aqueous soluble diazepam was used as a lipophilic model drug. The release of diazepam and sugar carrier was determined to study the mechanisms governing dissolution behaviour. The effect of carrier dissolution rate and drug load was tested with four different sugars, in the order of decreasing dissolution rates: sucrose, trehalose and two oligo-fructoses; inulinDP11 and inulinDP23 having a number average degree of polymerization (DP) of 11 and 23, respectively. Diazepam was incorporated in these sugar glasses in the amorphous state by means of freeze drying using water and tertiary butyl alcohol (TBA) as solvents. None of the tablets disintegrated during dissolution. Dissolution of 80% of the lipophilic drug within 20 min was found when diazepam and sugar dissolution profiles coincided. The sugar carrier and diazepam dissolved at the same rate, which was constant in time and fast. This condition was met for relatively slow dissolving carriers like the inulins or for low drug loads. For relatively fast dissolving carriers like sucrose or trehalose with high drug loads, release profiles of diazepam and sugar did not coincide: diazepam dissolved much more slowly than the sugars. In case of non-coinciding release profiles, diazepam release was split into three phases. During the first phase non-steady-state dissolution was observed: diazepam release accelerated and a drug rich layer consisting of crystalline diazepam was gradually formed. This first phase determined the further release of diazepam. During the second phase a steady-state release rate was reached: zero-order release was observed for both drug and carrier. During this phase, the remaining (non-crystallised) solid dispersion is dissolved without the further occurrence of crystallisation. The third phase, starting when all carrier is dissolved, involved the very slow dissolution of crystallised diazepam, which was present either as the skeleton of a tablet resulting in a zero-order release profile or as separate particles dispersed in the dissolution medium resulting in a first-order release. To understand the anomalous dissolution behaviour, a model is proposed. It describes the phenomena during dissolution of amorphous solid dispersion tablets and explains that fast dissolution is observed for low drug loads or slow dissolving carriers like inulin.

Drug-excipient interactions and their affect on absorption

Excipient(s) are traditionally thought of as inert but they can have a tremendous impact on the ultimate pharmacological availability of a drug substance when added to a formulation. The magnitude of this effect will depend on the characteristics of the drug and on the quantity and properties of the excipients. The aim of this article is to identify the various physicochemical and physiological processes that can be altered by drug-excipient interactions and to explore mechanisms by which they might occur. The regulatory implications of drug-excipient interactions will also be discussed.

Comparative dissolution studies for mefenamic acid-polyethylene glycol solid dispersion systems and tablets

The purpose of this study was to enhance the dissolution of mefenamic acid (MFA) through the formation of solid dispersion systems, and to compare the dissolution of the unformulated dispersions with those of formulated dispersions in tablets. Solid dispersions of MFA were prepared in polyethylene glycol 3350 (PEG) as a binary system, and PEG and Tween 20 (TW) as a ternary system by the melt method. The dispersions were characterized by dissolution, scanning electron microscopy, and powder x-ray diffraction studies. A decrease in MFA composition in the binary dispersion systems from 50 to 5% w/w resulted in a 50% increase in the dissolution rate during the period of study, and this was threefold higher than that of pure MFA. Incorporation of TW in the preparation of ternary dispersion systems resulted in a further increase in MFA dissolution. A sevenfold increase in MFA dissolution was observed when the ternary system composition was MFA/PEG/TW 4.7:93:2.3 (% w/w). Scanning electron microscopy and x-ray diffraction pictures showed an increase in size and decrease in crystallinity of the dispersions, respectively. Compression of the dispersions into tablets did not have any effect on the dissolution of the drug from the dispersions. Compression of pure MFA and Avicel PH 101, which was used as a diluent and disintegrant, resulted in a threefold increase in dissolution. However, the dissolution of the uncompressed mixture was identical to that of pure MFA. Thus, further processing of the solid dispersions into tablets did not decrease the rate of dissolution of the drug in the dispersions. This may be very important in the formulation of solid dispersions as tablets, which could lead to a reduction in the dose of practically water-insoluble drugs.