Particle size of drugs and its relationship to absorption and activity

Physical characterization of erythromycin: anhydrate, monohydrate, and dihydrate crystalline solids

Hot-stage microscopy, thermoanalytical methods, and X-ray powder diffraction were used to demonstrate that crystalline erythromycin dihydrate converts to the crystalline anhydrate via a noncrystalline intermediate. X-ray powder diffraction, IR spectral, thermogravimetric, and differential thermal analyses were used to characterize the monohydrate material. The flow interrupt technique, a procedure recently developed to deal with low surface area samples, was employed successfully in obtaining isotherms and specific surface areas for the monohydrate and anhydrate. The relative dissolution rates of the various hydrates were determined in an aqueous solution (0.01 M phosphate buffer, pH 7.5) at 37 degrees. The results showed a significant difference in the dissolution rate of the dihydrate compared to the monohydrate and anhydrate.

Effect of a second solubilizate on the partition coefficient of drugs in micellar solution and their permeation rate across an artificial membrane

The distribution of a solubilizate between micelles and the aqueous phase does not obey a simple partition law when a second solubilizate species is present. Alterations of the apparent partition coefficient cannot be explained in terms of a simple displacement mechanism, following the interaction of both solubilizates with the same site of the micelle. A non linear increase in solubilizate association to micelles following an increase in surfactant concentration is observed in the presence of a second solubilizate. A depression in the cloud point temperature follows the addition of a second species and is such that cannot be interpreted as a simple additive effect. Alteration of the apparent partition coefficient in a miscellar solution has an effect on the permeation rate of the solubilizate across an artificial membrane. Biopharmaceutical implications are discussed.

Bioavailability and generic prescribing

Although oral drug bioinequivalence has been attributed to a number of causes (excipients, dosage form, variation in dissolution time, and aging) less is known about bioavailability problems of topical medications in ophthalmology. Factors that can alter drug absorption from solutions (pH, partition coefficient, container impurities, contact time, etc.) are noted, and cases in which bioavailability problems should be considered as causes of therapeutic failure are discussed. Various attitudes representing pharmaceutical companies, the federal government, pharmacists, consumers and physicians toward the related problems of bioinequivalence and generic prescribing are examined. Techniques for in vivo and in vitro drug testing and for establishing uniform conditions of drug manufacture and storage can contribute to identification and minimization of bioavailability problems. A rational program based on a combination of such techniques could, ultimately, lead to establishment of the terms "generic equivalency" and "therapeutic equivalency" as synonymous.

Effect of compaction on particle size

Compressed tablets were prepared on a hydraulic press at several different compaction pressures by a standardized technique, using aspirin, dicalcium phosphate dihydrate, calcium phosphato-carbonate, alumina, and microcrystalline cellulose. All tablets except microcrystalline cellulose contained a cation-exchange resin as disintegrant. The particle-size spectra of the disintegrating compacts were evaluated using a particle-size counter or an air jet sieve. It is shown that compacts made from different materials but of the same initial particle-size spectra disintegrate to give particles of a considerably different size. Determination of the change in particle size produced by the compaction process provides useful insight into the nature of the compaction process.

Hydrolysis of fatty acid esters of acetaminophen in buffered pancreatic lipase systmes I

A series of fatty acid esters of acetaminophen were prepared beginning with acetate, the propionate, and all even-numbered fatty acids and going through the octadecanoate. The enzymatic hydrolysis of all derivatives was studied in vitro with varying amounts of lipase assed to the hydrolysis mixtures. Under the conditions of the in vitro hydrolysis, it was observed that all derivatives were hydrolyzed more readily in an aqueous medium at pH 7.8. A positive relationship was seen between the hydrolysis rates and the concentration of lipase at this pH. There was a negative relationship between the chain length of the acyl moiety and the corresponding hydrolysis rates. The short chain esters were hydrolyzed at rates many times more rapid than the long chain esters. The intermediate chain-lenght ester, p-acetamidophenyl decanoate, p-acetamidophenyl laurate, and p-acetamidophenyl myristate, were hydrolyzed at intermedediate time periods extending over 12 hr, approaching completion at 97.5, 87.5, and 80.5%, respectively, when 18 Wilson units of lipase was used in each milliliter of hydrolysis mixture. The longer chain esters, p-acetamidophenyl palmitate and p-acetamidophenyl stearate, were hydrolyzed to the extent of 16 and 8%, respectively, over 12 hr under the same in vitro conditions.

The particle-size of sulphadiazine produced by a solvent-change method

The factors affecting the particle-size of sulphadiazine produced by a solvent-change method of crystallization have been studied. The most important variables appear to be the degree of turbulence in the pipeline mixer used for the crystallization process, and the concentration of drug in the dimethylformamide injection solution. Mechanisms which can account for these, and other features of this crystallization method, are presented.