Argon laser trabeculoplasty in a residency program

The following article discusses the outcome of 60 eyes with various forms of glaucoma undergoing resident-performed argon laser trabeculoplasty (ALT). The majority (46/60) of eyes had primary open-angle glaucoma. Decrease in intraocular pressure (IOP) was not as great as reported in the literature. Our results suggest that initially treating 180 degrees of the angle is associated with improved overall results. ALT has proved to be a safe and effective alternative to conventional surgery for glaucoma in a residency training setting.

Adjustment of precompression force to reduce mixing-time dependence of tablet tensile strength

The dependence of tablet tensile strength on lubricant mixing time, pre- and main compression pressure was measured with microcrystalline cellulose, dicalcium phosphate dihydrate and starch 1500 on a rotary tablet machine. Loss of tablet tensile strength arising from lubricant overmixing can be substantially reduced in the case of microcrystalline cellulose by adjustment of pre- and main compression. This facility may be used in addition to or instead of reducing mixing time, or displacing lubricant by adding extra formulation components.

Effect of slugging pressure on the properties of granules and tablets prepared from potassium phenethicillin

The mechanism of preparing compacts by precompression has been investigated. The influence of slugging pressure on the bulk and tapped density, particle size distribution and the surface area of precompressed granules has been examined. The slugged granules have been tableted and the effect of compaction force on the weight uniformity, friability, crushing strength, disintegration time, dissolution rate and internal surface area of the tablets has been studied. The results show that the granules obtained from 15.9 mm slugs manufactured at low compaction forces (e.g. 49 MNm-2) had a lower bulk density, higher friability and larger surface area than those made at higher compaction pressures (e.g. 196 MNm-2). The lighter granules compacted into stronger tablets over a range of compaction forces and the effect was attributed to greater intergranular bonding caused by increased plastic flow.

Effect of variation in compaction force on properties of six direct compression tablet formulations

The effect of variation in compaction force on six direct compression tablet matrixes was investigated. An instrumented tablet press allowed direct measurement of applied and ejection forces. Hardness, apparent tablet density, and disintegration times also were determined. The disintegration time of spray-dried lactose tablets was essentially independent of compaction force. However, in the other systems investigated, the properties studied showed varying types of dependence on compaction pressure. A direct compression formula was developed and exhibits a decrease in disintegration time as compaction force is increased.

Effect of disintegrant type upon the relationship between compressional pressure and dissolution efficiency

Four tablet disintegrants: a relatively insoluble sodium carboxymethyl cellulose, casein formaldehyde, calcium carboxymethyl cellulose and a cross-linked polyvinylpyrrolidone have been evaluated. Three widely used disintegrants, sodium carboxymethyl cellulose, sodium starch glycolate and a cation exchange resin were included for comparison. The effect of compressional pressure on the disintegration and dissolution behaviours of a soluble and an insoluble system containing different disintegrants were examined. The results show that disintegrant type can have a pronounced effect upon the relationship between compressional pressure and dissolution efficiency. The significance of this relationship is discussed in terms of the properties of disintegrants and the differing mechanisms by which they act.

Water-sorption properties of tablet disintegrants

The water-sorption properties of four tablet disintegrants, starch, sodium carboxymethylcellulose, sodium starch glycolate, and a cation-exchange resin, were examined in the form of powders and in compressed tablets prepared from calcium phosphate dibasic dihydrate. Dissolution properties of the tablets compare well to the water-sorption properties. The effect of storage in the presence of water vapor upon tablets containing the various disintegrants was evaluated in terms of tablet hardness and disintegration time. Differences in the effects produced in the various tablet formulations can be related to the differing mechanisms whereby the disintegrants effect tablet rupture. Photomicrographic data support the conclusions drawn from the water-sorption, disintegration, and dissolution studies. Sodium starch glycolate and the cation-exchange resin merit careful consideration by formulators using calcium phosphate dibasic dihydrate or similar direct compression matrixes.

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.

Disintegration properties of calcium phosphate dibasic dihydrate tablets

The effect of compressional force on the disintegration time of tablets prepared from calcium phosphate dibasic dihydrate containing various tablet disintegrants was examined. The results show that effects of compressional force on disintegration time are of two types. The first type is that of insoluble disintegrants, e.g., starch and a cation-exchange resin, where the disintegration time initially shows a dramatic decrease. After this decrease, a further increase in compressional force appears to have no effect on the disintegration time. The second type is that of soluble disintegrants, e.g., calcium sodium alginate, sodium carboxymethylcellulose, and sodium staarch glycolate, where variation in compressional force has very little effect on the disintegration time. These results are discussed in terms of the differing mechanism whereby these substances act as disintegrants.