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Chemical stability of an ester prodrug of a glycoprotein IIb/IIIa receptor antagonist in solid dosage forms.

DMP 754 is an ester prodrug of a glycoprotein IIb/IIIa receptor antagonist that undergoes ester and amidine hydrolysis in the presence of excipients. A means for the stabilization of DMP 754 was needed for the formulation of a stable drug product. Incorporation of a pH modifier in the formulation was used to control the microenvironment pH to coincide with that of maximum stability for DMP 754. Stability of tablets and capsules manufactured by (a) trituration process, (b) dry granulation process, and (c) wet granulation process was evaluated in HDPE bottles. Formulations manufactured by the dry and wet granulation processes contained disodium citrate as the pH modifier. Although aqueous wet granulation of a hydrolyzable drug is usually avoided, tablets and capsules manufactured by wet granulation were more stable in this case than those manufactured by the dry granulation process. This was attributed to the more uniform distribution of the pH modifier. Although the compression process resulted in enhanced degradation of the binary blend of DMP 754 and anhydrous lactose, tablets manufactured by the wet granulation process were more stable than capsules manufactured by the same process. Decreasing excipient-to-drug ratio enhanced the stability of tablets manufactured by the wet granulation process.

Amino Acids↗

Formulation and evaluation of a folic acid receptor-targeted oral vancomycin liposomal dosage form.

PURPOSE: To demonstrate utility of folic acid-coated liposomes for enhancing the delivery of a poorly absorbed glycopeptide, vancomycin. via the oral route. METHODS: Liposomes prepared as dehydration-rehydration vesicles (DRVs) containing vancomycin were optimized for encapsulation efficiency and stability. A folic acid-poly(ethylene oxide)-cholesterol construct was synthesized for adsorption at DRV surfaces. Liposomes were characterized by differential scanning calorimetry (DSC) and assessed in vitro in the Caco-2 cell model and in vivo in male Sprague-Dawley rats. Non-compartmental pharmacokinetic analysis of vancomycin was conducted after intravenous and oral administration of solution or liposome-encapsulated vancomycin with or without 0.05 mole ratio FA-PEO-Chol adsorbed at liposome surfaces. RESULTS: Optimal loading of vancomycin (32%) was achieved in DRVs of DSPC:Chol:DCP, 3:1:0.25 mole ratio (m.r.) after liposome extrusion. Liposomes released less than 40% of the entrapped drug after 2 hours incubation in simulated gastrointestinal (GI) fluid and simulated intestinal fluid containing a 10 mM bile salt cocktail. Incorporation of FA-PEO-Chol in liposomes increased drug leakage by 20% but resulted in a 5.7-fold increase in Caco-2 cell uptake of vancomycin. Liposomal delivery significantly increased the area under the curve of oral vancomycin resulting in a mean 3.9-fold and 12.5-fold increase in relative bioavailability for uncoated and FA-PEO-Chol-coated liposomes, respectively, compared with an oral solution. CONCLUSIONS: The design of FA-PEO-Chol-coated liposomes resulted in a dramatic increase in the oral delivery of a moderate-size glycopeptide in the rat compared with uncoated liposomes or oral solution. It is speculated that the cause of the observed effect was due to binding of liposome-surface folic acid to receptors in the GI tract with subsequent receptor-mediated endocytosis of entrapped vancomycin by enterocytes.

Algorithms↗

Dissolution testing as a prognostic tool for oral drug absorption: immediate release dosage forms.

Dissolution tests are used for many purposes in the pharmaceutical industry: in the development of new products, for quality control and, to assist with the determination of bioequivalence. Recent regulatory developments such as the Biopharmaceutics Classification Scheme have highlighted the importance of dissolution in the regulation of post-approval changes and introduced the possibility of substituting dissolution tests for clinical studies in some cases. Therefore, there is a need to develop dissolution tests that better predict the in vivo performance of drug products. This could be achieved if the conditions in the gastrointestinal tract were successfully reconstructed in vitro. The aims of this article are, first, to clarify under which circumstances dissolution testing can be prognostic for in vivo performance, and second, to present physiological data relevant to the design of dissolution tests, particularly with respect to the composition, volume, flow rates and mixing patterns of the fluids in the gastrointestinal tract. Finally, brief comments are made in regard to the composition of in vitro dissolution media as well as the hydrodynamics and duration of the test.

Administration, Oral↗

Liposomes dispersed within a thermosensitive gel: a new dosage form for ocular delivery of oligonucleotides.

PURPOSE: The main goal of this study was to develop an ocular controlled release formulation of a model oligonucleotide (pdT16), contained within liposomes dispersed within a thermosensitive gel composed by poloxamer 407. METHODS: The influence of the poloxamer concentration 2% or 27% on the stability of the liposomes (PC: CHOL and PC: CHOL: PEG-DSPE) was investigated. The in vitro release profiles of pdT16 from various poloxamer formulations (free pdT16 dispersed within 20% and 27% poloxamer gels, pdT16 encapsulated within liposomes dispersed within 20% and 27% poloxamer gels) were realized using a membrane-free release model. RESULTS: The dispersion of liposomes within a dilute 2% poloxamer solution resulted in a great leakage of pdT16 from liposomes. However, the destabilization effect of poloxamer was reduced when higher concentration (27%) was used. Poloxamer dissolution was found to control the release process of pdT16, whereas the dispersion of liposomes within 27% poloxamer gel was shown to slow down the diffusion of pdT16 out from the gel. CONCLUSIONS: The dispersion of liposomes within a 27% poloxamer gel presented an interesting system to control the release of a model oligonucleotide compare to a simple gel.

Drug Carriers↗

Influence of dosage form on the gastroenteropathy of flurbiprofen in the rat: evidence of shift in the toxicity site.

PURPOSE: Gastroduodenal and intestinal permeability were compared after single doses of sustained release and regular release flurbiprofen in the rat to assess possible site-specific formulation-dependent toxicity. METHODS: Pharmacokinetics was assessed and gastrointestinal permeability was evaluated using sucrose and 51Cr-EDTA as gastroduodenal and intestinal permeability probes, respectively. RESULTS: The two formulations demonstrated equal areas under the flurbiprofen concentration-time curve. The sustained release formulation peaked 2-3 h slower with 57-74% lower concentrations than regular release formulation. In comparison, the regular release powder induced greater gastroduodenal permeability while sustained release granules induced greater intestinal permeability. When S-flurbiprofen concentrations were plotted versus intestinal permeability, a linear relationship and an anti-clockwise hysteresis were obtained for regular and sustained release formulations, respectively. CONCLUSIONS: Sustained release formulations of flurbiprofen demonstrate reduced gastroduodenal permeability but shift the site of this side-effect to the more distal intestine.

Administration, Oral↗

In vitro dissolution profile of water-insoluble drug dosage forms in the presence of surfactants.

The determination of the in vitro release profile of water-insoluble drug products requires dissolution media different from those used for water-soluble drug products. Since the relevance of drug dissolution in organic solvents is questionable, we investigated the use of surfactants to determine the dissolution profiles of water-insoluble drug products. In most cases, the drug dissolution rate and extent increased as the surfactant concentration in the aqueous dissolution medium increased. Suitable dissolution profiles were obtained in the presence of sodium lauryl sulfate (SLS) for water-insoluble drug products, such as griseofulvin, carbamazepine, clofibrate, medroxyprogesterone, and cortisone acetate. These findings recommend the use of surfactants for determining the aqueous dissolution of water-insoluble drug products rather than adding organic solvents to the dissolution medium.

Capsules↗

In vitro-in vivo relationship of oral extended-release dosage forms.

PURPOSE: A method to establish the in vitro-in vivo relationship of oral extended-release products is proposed. METHODS: The approach utilizes incremental amounts of drug released and absorbed within defined time intervals, to construct a chi2 distributed variable for testing in vitro-in vivo similarity. RESULTS: A case study is used to demonstrate that the similarities between incremental values of in vivo absorbed and in vivo dissolved fractions are distinguishable for different dissolution profiles despite naturally significant linear correlations between cumulative in vivo absorbed and in vitro dissolved fractions (with different dissolution tests) of an oral extended-release product. CONCLUSIONS: The method enables investigators to compare different in vitro dissolution profiles of an oral extended-release product to find an optimized dissolution profile to be the surrogate of the in vivo release process of the product.

Absorption↗

Structure and behavior in hydrophilic matrix sustained release dosage forms: 4. Studies of water mobility and diffusion coefficients in the gel layer of HPMC tablets using NMR imaging.

PURPOSE: The purpose of this study was to characterise the water mobility in the gel layer of hydrating HPMC tablets. Water mobility in the gel layer of different HPMCs was studied. METHODS: NMR imaging, a non-invasive technique, has been used to measure the spatial distribution of self-diffusion coefficient (SDC) and T2 relaxation times across the gel layer. RESULTS: It has been shown that there is a water mobility gradient across the gel layer of HPMC tablets. Although SDC and T2 relaxation times in the outer parts of the gel layer approached that of free water, in the inner parts they decreased progressively. Water mobility and SDC in the gel layer of different HPMCs appeared to vary with degree of substitution of the polymer and the lowest values were obtained across the gel layer of K4M tablets. CONCLUSIONS: Water mobility varies across the gel layer of hydrating HPMC tablets and it is dependent on the degree of substitution of the polymer.

Chemical Phenomena↗

Pharmacokinetics of oral extended-release dosage forms. I. Release kinetics, concentration, and absorbed fraction.

In this study, we derive pharmacokinetic models for oral extended-release (OER) drug products with defined in vivo release kinetics (IVRK) and a compartmental system. Fitting the model to clinical data, we were able to examine the correlation between released and absorbed fractions. Furthermore, we found that absorbed fractions of OER products can be expressed by absorption rate and release duration only. The expression is unchanged in different compartmental systems with the same IVRK, implying that the IVRK drives the pharmacokinetic system of an OER product. The apparent absorption rate constant of an OER product can be estimated by solving an implicit equation using observed concentrations. We also propose a new method for calculating absorbed fractions, which is more accurate than Loo-Riegelman method. Ultimately, these methods may permit optimally designed OER products.

Absorption↗

Diffusion in HPMC gels. II. Prediction of drug release rates from hydrophilic matrix extended-release dosage forms.

PURPOSE: A mathematical model is described for the prediction of the relative change in drug release rate as a function of formulation composition for HPMC-based extended-release (ER) tablets of adinazolam mesylate and alprazolam. METHODS: The model is based on the equation derived by Higuchi for the diffusional release of soluble drugs from polymeric matrices and on our recent measurements of the concentration dependency of adinazolam diffusivity in dilute HPMC gels and solutions. The assumptions made in applying the model include (i) that diffusion is the sole mechanism of drug release (i.e. swelling kinetics are ignored), and (ii) that the surface area-to-volume ratio and concentrations of adinazolam, lactose and HPMC in the gel layer are proportional to that of the dry tablet. RESULTS: Reasonable correlations were obtained between the experimental drug release rate ratios and the predicted drug release rate ratios for ER adinazolam mesylate (R2 = 0.82) and low-dose (0.5 mg) ER alprazolam tablets (R2 = 0.87). The predictive power for a 6-fold higher dose of ER alprazolam tablets was not as good (R2 = 0.52). CONCLUSIONS: These results are consistent with previous knowledge of the release mechanisms of these formulations. ER adinazolam mesylate and ER alprazolam 0.5 mg exhibit primarily a diffusion controlled release mechanism, while ER alprazolam 3 mg deviates from pure diffusional release. The limitations of the model are discussed and point to the need for continued study of the swelling kinetics of matrix ER systems.

Benzodiazepines↗

Radiolabeling of intact dosage forms by neutron activation: effects on in vitro performance.

Compressed tablets containing various quantities of stable isotopes of Ba, Er, and Sm for use in neutron activation studies were evaluated for the effect of stable isotope incorporation on tablet hardness and disintegration times. At concentrations likely to be used in scintigraphic studies employing neutron activation as a radiolabeling method, no significant effect on in vitro parameters were observed. While the incorporation of stable isotopes influenced tablet hardness to a greater degree than disintegration time, irradiation of tablets in a neutron flux of 4.4 x 10(13) n/cm2 sec had a direct effect on tablet disintegration time. Thus, future neutron activation studies should focus on minimizing the amount of stable isotope to be incorporated with the formulation while using the shortest feasible irradiation time.

Barium Radioisotopes↗

In situ determination of delavirdine mesylate particle size in solid oral dosage forms.

PURPOSE: The in-situ particle size of delavirdine mesylate in dry mix and tablets was determined. METHODS: Optical microscopy and fluorescence microscopy combined with image analysis were used for qualitative and quantitative measurements. RESULTS: Using optical microscopy, it was demonstrated qualitatively that fragmentation of the large drug particles was occurring during tablet compression. Quantitative comparisons between dry mix and tablet samples showed that in the dry mix, drug particles remain intact, with particle lengths exceeding 200 microm. In the tablets, no particles longer than 100 microm had been observed. Analysis of multiple tablet lots revealed consistent in-situ drug particle size distributions, regardless of the original bulk drug particle size. CONCLUSIONS: Bulk drug particle size of delavirdine mesylate is not predictive of the particle size in the tablet due to fragmentation of particles during compression. Optical and fluorescence microscopy are valuable tools for probing in-situ particle size in complex matrices.

Administration, Oral↗

Solid-state nuclear magnetic resonance (NMR) spectra of pharmaceutical dosage forms.

Solid-state 13C NMR spectra of tablets or capsules of prednisolone, enalapril maleate, lovastatin, simvastatin, ibuprofen, flurbiprofen, mefenamic acid, indomethacin, diflunisal, sulindac, and piroxicam were obtained in the CP/MAS mode at 50 MHz. These studies show that (1) solid-state NMR spectroscopy can detect the active ingredients in low-dose tablets and capsules; (2) the use of interrupted decoupling often results in suppression of resonances due to excipients, thereby allowing better detection of resonances from the drug; and (3) the technique permits discrimination between two prednisolone polymorphs present in tablets obtained from various manufacturers even though the tablets contain only approximately 5% (w/w) of the drug.

Anti-Inflammatory Agents, Non-Steroidal↗

Transforming growth factor-alpha (TGF-alpha) in a semisolid dosage form: preservative and vehicle selection.

The selection of an ideal semisolid vehicle for growth factors presents a challenge. Some antimicrobial agents are known to delay wound healing. The objective of this investigation was to identify appropriate preservatives and vehicles for TGF-alpha. Criteria for acceptance are noninterference with the mitogenic activity of TGF-alpha as well as adequate product preservation. Vehicles considered were o/w creams, ointments, and a gel. Combinations of six preservatives were tested. Selection was determined using both microbial preservative challenge and TGF-alpha mitogenic assay. In the former, 10 species of microorganisms were inoculated into formulation samples. At selected time intervals, it was determined whether colonies decreased, increased, or remained constant. In the mitogenic assay, samples of either preservatives or formulation prototypes were introduced to TGF-alpha-stimulated fibroblast cell cultures. Mitogenesis was determined by measuring 3H-dThd uptake into newly synthesized DNA. As preservatives, sorbic acid and quaternium-15 appear to satisfy both selection criteria. A thermosetting gel appears most promising as vehicle.

Cell Division↗

Near infrared transmittance analysis for the assay of solid pharmaceutical dosage forms.

The recent commercial availability of near infrared spectrometric instruments for the transmittance analysis of solids makes it possible to analyse solid drugs in their finished form. Application of the method to the control of the assay of the active ingredient in diphenhydramine tablets gave results comparable to those obtained in reflectance mode with whole and milled tablets.

Diphenhydramine↗

Bioavailability studies of oral dosage forms containing levodopa and carbidopa using column-switching chromatography followed by electrochemical detection.

A reliable multi-dimensional column chromatographic method employing amperometric detection using a carbon fibre microelectrode procedure was used for monitoring the plasma profiles and to evaluate the pharmacokinetics and bioavailability of levodopa (L-dopa) and carbidopa (C-dopa), after ingestion of oral formulations containing these drugs. The peak currents obtained for the different analytes were directly proportional to the analyte over the concentration range 0.02-4 micrograms ml-1. Using this method, the minimum detectable concentration was estimated to be 5 and 8 ng ml-1 for L-dopa and C-dopa, respectively. Recovery studies ranged from 93.83 to 89.76%, with a relative standard deviation of less than 7%. The study was carried out in two separate weeks on five healthy non-patient fasted male/female volunteers in the age range 20-37 years and weighing between 60 kg and 78 kg. The pharmacokinetic profile of two controlled-release products containing both L-dopa and C-dopa (Sinemet CR3 and CR4) was compared on the one hand and Sinemet conventional tablets on the other. The pharmacokinetic parameters, peak concentration (Cmax), the time taken to obtain this level (Tmax), elimination half-time T1/2, elimination rate constant (Kel), plasma level ratio, fluctuation index (FI) and the area under the time-concentration curve (AUC0-8), were investigated for each individual formulation. A comparison of the uptake of L-dopa from the conventional formulation showed that L-dopa entered the plasma and achieved peak levels higher than that of the controlled release formulations. However, it showed a much higher fluctuation index and the plasma concentrations were more stable with the controlled release formulations. The data also indicated a very low accumulation of both levodopa and carbidopa following repeated administration of the drugs, which was consistent with their relatively short half-lives (less than 2 h). In contrast, the half-life for the metabolite 3-orthomethyl dopa (3-OMD) is in the order of 13 h. As a result, there was an extensive accumulation of 3-OMD and its levels were significantly higher than those of levodopa or carbidopa upon repeated administration. Urine recoveries of the three analytes over one 8 h dosing interval showed that the majority of the excreted levodopa and carbidopa was recovered during the first 4 h, and there is proportionally greater excretion of the carbidopa dose than the levodopa dose.

Adult↗