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Biomedical subjects

J M Newton

Publications and source records attributed to J M Newton.

At least 19 recordsLinked to original sources
PubMed1992

Stomach outline visualization in gastrointestinal transit studies using scintigraphy.

A major disadvantage of gamma scintigraphy in gastrointestinal transit studies is the inability to provide adequate delineation of anatomical details. As an aid to the important requirement of outlining the stomach to ensure accurate quantification of the time at which material empties from this organ, a new technique is described, using short half-life 81mKr gas to provide clearer identification of the stomach outline and position.

Gastrointestinal Transit↗
PubMed1991

Effects of compaction variables on porosity and material tensile strength of convex-faced aspirin tablets.

The porosity and tensile strength of convex-faced aspirin tablets formed under a compaction pressure in the range 40-320 MPa and at punch velocities in the range 0.008 to 500 mm s-1 have been determined. The material tensile strength, sigma f, was calculated from the observed fracture load, Ps, using the equation of Pitt et al (1988): sigma f = 10 Ps/pi D2(2.84 t/D - 0.126 t/W + 3.15 W/D + 0.01)-1 where D is the tablet diameter, t is the overall tablet thickness and W is the central cylinder thickness. Tablets formed at lower compaction pressures had a higher porosity and lower tensile strength than those formed at higher compaction pressures. Tablets of face curvature ratio (D/R) in the range 0.25-0.67 and a normalized cylinder length (W/D) of 0.2 had the optimum tensile strength. (R is the radius of curvature of the tablet face.) Tablets formed at high compaction rates were significantly weaker than those formed at lower compaction rates.

Aspirin↗
PubMed1979

The release of a model low-dose drug (riboflavine) from hard gelatin capsule formulations.

The in vitro release of a model low dose drug, riboflavine, from hard gelatin capsules, formulated with a range of diluents, in the absence and presence of magnesium stearate (0.5, 1.0 and 2.0% w/w), has been assessed by a dissolution technique. Comparison of the values of the time for 50% of the drug content of the capsule to appear in solution T50, by analysis of variance, indicated that the type of diluent significantly influenced the drug release. Irrespective of the magnesium stearate content, the diluents could be ranked in the following order of effectiveness: Primojel greater than sodium bicarbonate greater than Avicel congruent to Dri-flo starch congruent to lactose greater than Emcompress congruent to kaolin greater than starch. Correction of the T50 values for possible adsorption of riboflavine onto the water insoluble diluents, using experimentally determined adsorption isotherms, altered the relative order of effectiveness of the diluents to Primojel greater than sodium bicarbonate greater than kaolin congruent to lactose greater than Avicel congruent to Dri-flo starch greater than Emcompress greater than starch. Comparison of the urinary excretion of riboflavine, after administration of capsule formulations containing lactose, Emcompress or kaolin as the diluent, to volunteers, suggests that the dissolution results not corrected for adsorption provide a better indication of the in vivo performance of the formulations.

Capsules↗
PubMed1979

The mechanical strength of film-coated tablets.

The mechanical strength of film-coated tablets has been assessed using the diametral compression test. The results show that the influence of the film is more complex than that suggested by Stern (1976). The film may increase the breaking load of the core itself by acting as a padding material during the test and also by filling in surface irregularities. The film may also have enough intrinsic strength and elasticity to hold the core together once it has broken. The maximum breaking load to completely fracture the coated tablet is related to film properties, but the relation is not a simple one.

Hardness↗
PubMed1979

Spectrophotometric determination of caffeine in coffee products: collaborative study.

An ultraviolet (UV) spectrophotometric method for determining caffeine in regular and decaffeinated coffee products has been studied collaboratively. Nine laboratories participated in this study which compares the proposed UV method with the official AOAC micro Bailey-Andrew method. Caffeine content was determined on as-is basis on 8 samples of green, roasted, and soluble coffees. The coefficients of variation for the proposed method ranged from 2.02 to 6.98% for the 8 samples studied. The results agreed well with those from the Bailey-Andrew Method. The method was adopted as official first action.

Caffeine↗
PubMed1977

The in vitro bioavailability of various drugs formulated as hard gelatin capsules.

A factorially designed experiment has been carried out to study the influence of various additives on the in vitro release of drug from hard gelatin capsules. Analysis of variance confirms previous findings that, although the main factors of diluent type, diluent concentration, the absence and presence of both magnesium stearate and sodium lauryl sulphate, were highly significant, the existence of interactions between the factors prevented exact quantitative prediction of the influence of each factor. There appears however, to be a strong indication that the in vitro drug release of capsule formulations (y), expressed as the % of the drug content of the capsule which dissolves, can be related to the solubility of the drug (cs) by the expression y = 21-2 log cs + 31.2.

Biological Availability↗
PubMed1977

The influence of additives on the presentation of a drug in hard gelatin capsules.

The influence of the concentration of lactose, magnesium stearate and sodium lauryl sulphate in the in vitro dissolution and the drug content of hard gelatin capsules filled under conditions which result in a maximum tapped bulk density, has been evaluated by a factorially-designed experiment. The 3 factors have a significant effect on both drug release and capsule filling. Interactions between the 3 factors, however, limit the exact quantification of the magnitude of their influence by a simple linear model. A quadratic relation, when only 2 factors are considered, can be used to provide a prediction of the influence of these factors. The relations between 2 factors are demonstrated as contours of equal in vitro drug release and equal drug content of capsule, at constant concentrations of the third factor. The contours show the important influence of lactose concentration drug release and capsule filling, and the large changes in response which can occur by the addition of a third factor. They also provide a clear guide to the formulation of hard gelatin capsules.

Capsules↗