Application of spectrofluorometry for evaluation of dry powder inhalers in vitro.

Andersen cascade impactor (ACI) is commonly used for the testing of pharmaceutical aerosols, which has to be coupled with an instrument for quantitative analysis of drug depositing on each stage of the ACI. This procedure consumes much time in operation. Therefore, this study was aimed at speeding up the process of drug analysis in aerosol formulations after obtaining samples from the ACI. From the results obtained, it was proved that the validated spectrofluorometric method was accurate and sensitive. It was capable of giving similar results to those we obtained from HPLC-UV analysis. There was no interference from the amount of lactose carrier incorporated in the formulation in the step of salbutamol analysis indicating specificity of the method. As a result, samples were analyzed without further separation. The detection limit was 0.1 microg/ml. Hence, spectrofluorometry can be used as a substitute method to HPLC-UV in determining the small quantity of salbutamol after aerosolization from dry powder aerosols. The present study suggests that spectrofluometry can be a rapid and efficient method in the pharmaceutical analysis of aerosols.

Stereoselective release behaviors of imprinted bead matrices.

In this work, the stereoselective release behaviors of "low"-swelling molecularly imprinted polymer (MIP) bead matrices in pressed-coat tablet type were studied. Either R-propranolol selective MIP or S-propranolol selective MIP was combined with excipients and racemic propranolol and fabricated into the matrix. Subsequently, the release of different propranolol enantiomers from the matrices was examined. Also, the microscopic structure of the hydrated "low"-swelling MIP matrix was determined using a cryogenic scanning electron microscope in order to compare with that of the hydrated "high"-swelling MIP matrix. In vitro release profiles of the "low"-swelling matrices showed a difference in the release of enantiomers, in that the non-template isomer was released faster than the template isomer. However, in the last phase of dissolution this difference reduced and later reversed, resulting at last in the type of specificity being similar to that obtained previously with "high"-swelling MIP matrices. In summary, MIP beads can be fashioned into matrices and incorporated into different formulations to regulate the resultant stereoselectivity. From the behaviors of stereoselective release observed in MIP matrices, we can conclude that the enantioselective-controlled delivery mechanism of MIPs via formulations depends on the relative affinity of the enantiomer for the template sites, as well as the nature of the polymer, such as hydrophobicity and swellability.

Enantioselective release of controlled delivery granules based on molecularly imprinted polymers.

The objectives of our study were two fold: to examine enantioselective release of controlled delivery granules based on molecularly imprinted polymers (MIPs) for various racemic drugs, including ibuprofen and ketoprofen (NSAIDs) and propranolol (beta-blockers); to evaluate the use of controlled delivery granules containing a combination of different MIPs for the multiple simultaneous enantioselective-controlled delivery of mixed racemic drugs. In this work, the MIP beads selective to S-Ibuprofen, S-ketoprofen, and R-propranolol were prepared using multistep swelling and thermal polymerization method. Afterward, the MIP beads were formulated with racemate of the chiral drugs and a binder and followed by granulation. Then, the enantioselective release of racemic drugs from the prepared MIP granules was investigated by an in vitro dissolution test using a chiral HPLC for assays of enantiomers. The influence of drug/polymer ratio and medium pH on the selective enantiomeric release of MIP granules was explored. Further, the release of the enantiomers of racemic ibuprofen and racemic ketoprofen from the granule containing two MIPs - S-ibuprofen MIP and S-ketoprofen MIP - was examined. The release profiles of both S-ibuprofen MIP granule and R-propranolol MIP granule exhibited differential release of enantiomers. Also, the findings indicated the stereoselective retardation of those controlled delivery granules as well as the influence of MIP formulation on enantioselective release mechanism. The enantioselective release of S-ibuprofen MIP granule and R-propranolol MIP granule appeared to depend on polymer loading and medium pH. In this case, the drug/polymer ratio of 1:25 showed the best enantioselective release with initial enantiomeric excess of 100%. On the other hand, the enantioselectivity of both granules was the greatest in buffer pH 7.4. Furthermore, the efficiency in enantioselective release of the combined MIP granule was higher than its relative single MIP granules, as a result of the cross-reactivities of the MIPs. In our study, controlled delivery granules based on MIPs demonstrated significant enantioselective release for several chiral drugs, and thus it may be developed as a tool to administer chiral pharmaceutical as a single enantiomer.

Evaluation of stereoselective dissolution of racemic salbutamol matrices prepared with commonly used excipients and 1H-NMR study.

The purpose of this work was to examine the in vitro enantioselective dissolution of salbutamol from matrix tablets containing various chiral excipients, such as gamma cyclodextrin (gamma-CD), heptakis (2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD), sulfobutyl-beta-cyclodextrin (SBE-beta-CD), hydroxypropylmethylcellulose (HPMC), and egg albumin. In this study, two types of tablets were prepared; the coated tablet contained the complex of racemic salbutamol and cyclodextrin (gamma-CD, DM-beta-CD, and SBE-beta-CD), and the uncoated tablet was composed of the drug with either HPMC or egg albumin. Subsequently, these formulations were evaluated for enantioselective release. The results revealed that the formulations containing either SBE-beta-CD, HPMC, or egg albumin had no enantioselective release, while the formulation with DM-beta-CD gave slightly different release of the two enantiomers at the end of the dissolution profile. The formulation containing gamma-CD provided significant stereoselectivity throughout the dissolution profile. The release of the eutomer R-salbutamol was higher than that of the distomer S-salbutamol from the gamma-CD tablet. In addition, the enantioselective interaction for the gamma-CD inclusion complex was investigated by 1H-NMR (nuclear magnetic resonance) spectroscopy and gave evidence to support the enantioselectivity obtained on dissolution.

Cyclodextrin as a potential drug carrier in salbutamol dry powder aerosols: the in-vitro deposition and toxicity studies of the complexes.

This research was carried out to develop a new carrier in dry powder aerosols. Two types of cyclodextrin were chosen; gamma cyclodextrin (GCD) and dimethyl-beta-cyclodextrin (DMCD) as carriers in dry powder formulations. Salbutamol was used as a model drug and a control formulation containing lactose and the drug was included. A twin-stage impinger (TSI) was used to evaluate in delivery efficiency of those dry powder formulations. The toxicity of cyclodextrin complexes was investigated in the rat by monitoring blood urea nitrogen (BUN) and urinary creatinine, as well as determining haemolysis of human red blood cells. The release of salbutamol from dry powder formulations was also studied over a period of time. From the results obtained, it was found that the formulation containing GCD-enhanced drug delivery to the lower stage of the TSI (deposition = 65%) much greater than that of both formulations containing DMCD (50%) and the control formulation (40%) (P<0.05). After injecting the GCD complex BUN and creatinine levels in rats were similar to those obtained in the control while those receiving DMCD complex had higher BUN and creatinine. The haemolysis of red blood cells incubated with the DMCD complex was higher than that obtained in the GCD complex. The drug release in both formulations containing GCD and DMCD was fast (over 70% was released in 5 min) and nearly all the drug was released within 30 min. It can be concluded that GCD and DMCD are able to promote salbutamol delivery in dry powder inhaler compared to a formulation containing lactose. In addition, GCD is relatively safe in the rat if the amount of GCD in the formulation is similar to this experiment.

Evaluation of matrices containing molecularly imprinted polymers in the enantioselective-controlled delivery of beta-blockers.

Granules and beads of methacrylic acid (MAA) and granules of N-acryloyl-alanine polymer (NAA) were produced using ethylene glycol dimethacrylate as cross-linking monomer either by bulk (in the case of granules) or suspension (in the case of beads) polymerization. Either R- or S-propranolol, were used as an imprint molecule, acting as a template, with a view to conferring enantioselectivity of release upon the polymer. The molecularly imprinted polymers (MIPs) or nonMIPs (control) were formulated with racemic propranolol and other excipients and compressed to form matrix tablets. Enantioselective release of propranolol in vitro was monitored using a stereoselective HPLC assay. The influence of the method of polymer synthesis, drug: polymer ratio, pH and temperature on the release of the two enantiomers was determined. Stereoselectivity of release was identified in tablets containing either MAA or NAA granules or MAA beads, with the latter showing the greatest differences between enantiomers. Release of the enantiomer used as the print was always faster than the release of the nonprint enantiomer. In the case of S-propranolol-MIP bead matrices composed of MAA, greater differences in the release of enantiomers could be promoted by increasing the polymer: drug ratio of the tablet. Differences in the release rate of the two propranolol enantiomers was still apparent as the pH was varied between 3 and 7.4 and when the temperature was decreased from 37 to 25 degrees C. S-Propranolol-MIP bead matrices demonstrated cross-reactivities of stereoselective dissolution for enantiomers of pindolol and oxprenolol, both of which have structural similarities to the imprint molecule. It is concluded that polymers of this type may have great potential in controlling, via means of formulation, the release of drug eutomer whilst enhancing retention of distomer in the dosage form.

Differential permeation of propranolol enantiomers across human skin in vitro from formulations containing an enantioselective excipient.

This work tested the hypothesis that a stereospecific topical formulation could be used to engineer differential permeation rates for each enantiomer of an applied racemate across human skin in vitro. Racemic and enantiomerically pure R or S propranolol HCI were formulated with cellulose tris(3,5-dimethyl phenyl carbamate) (CDMPC) and applied to excised human skin using side-by-side Franz-type diffusion cells. When the pure enantiomers were used, there was a marked difference between the penetration rates of R and S propranolol (flux ratio: 2.06; P = 0.04). When racemic propranolol was used, the difference was reduced, although still statistically significant (flux ratio: 1.2; P = 0.08), particularly in view of the differential activities of the two enantiomers. Control experiments, in which no CDMPC was present, produced equal permeation rates. The results can be rationalised in terms of differential adsorption onto CDMPC within the vehicle, whereby S-propranolol is preferentially bound relative to R-propranolol. This causes an imbalance in the apparent donor phase concentrations that (in accordance with Fickian diffusion laws and thermodynamic activity) gives rise to differences in permeation rates. The diminished differential observed when the racemate was used, rather than individual enantiomers, is less easily rationalised. In this work, it was the permeation of the eutomer (S-propranolol) that was retarded, although the general principle of stereoselectively retarded skin permeation has been established.

Chiral determination of various adrenergic drugs by thin-layer chromatography using molecularly imprinted chiral stationary phases prepared with alpha-agonists.

Thin-layer chromatography (TLC) based on molecularly imprinted polymers (MIPs) of alpha-agonists as chiral stationary phases was applied to the determination of enantiomers of various adrenergic drugs including alpha- and beta-agonists and beta-antagonists (beta-blockers). In this study, three MIPs imprinted with (+)-ephedrine, (+)-pseudoephedrine and (+)-norephedrine plus a non-imprinted polymer (non-MIP) were prepared, processed and coated on a glass support as thin layers. then enantiomeric determination of adrenergic drugs was carried out by development of their racemates on the TLC plates, using established conditions. From the results, the racemates of the compounds used as print molecules were well separated into two isomers on the MIP-plates, except on the plate based on MIP of (+)-norephedrine. Most adrenergic drugs structurally related to print molecules were completely resolved into two spots with the MIP plates. In general the retention of (+)-isomers (or 1S-isomers) was greater than that of (-)-isomers (or 1R-isomers), indicating the stereoselectivity of the MIPs with the former isomers. Moreover, the role between the chemical structures of the analytes with chiral recognition of the MIPs has been investigated. The proposed method enables rapid determination of enantiomers and screening of large numbers for optical purity of adrenergic drugs.

Direct enantioseparation of adrenergic drugs via thin-layer chromatography using molecularly imprinted polymers.

Molecularly imprinted polymers (MIPs) of (-)-pseudoephedrine and (-)-norephedrine were prepared to use as chiral stationary phases (CSPs) in thin layer chromatography (TLC). The resolution of the enantiomers of adrenergic drugs, including pseudoephedrine, ephedrine, norephedrine, and epinephrine were investigated on these CSPs. In preparation of MIPs, two monomers: (1) methacrylic acid and (2) itaconic acid were employed as functional monomers. Mobile phase system of either methanol or acetonitrile was used and the effects of acetic acid content of the mobile phases were also investigated. The best resolution was achieved for enantioseparation of norephedrine on plates based on MIP of (-)-norephedrine using itaconic acid as functional monomer (alpha = 5.1) in mobile phase 1% acetic acid in methanol. Moreover, these MIPs were able to resolve the racemates of compounds whose structures corresponded to print molecule. The results obtained showed that TLC based on MIPs could succeed the direct separation of enantiomers of adrenergic drugs as a method of separation. The method offers a rapid, sensitive and reliable method for quality control of optically active compounds.