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The authors investigated the release of isoniazid from repository tablets as related to form, processing technology, strength constant and storage for 5 years. On determining the diffusion coefficient (D), the initial dissolution rate (Vo) and the time required for the diffusion of the releasing medium to the middle of the tablet (t1/2), it was found that the difference in release rate between the flat and the biconvex tablets is small. Furthermore, it was stated that the three-layer tablets have very high D and Vo values and very low t1/2 values, for what reason they are unsuited for repository tablets of the composition under investigation. Moreover, it was found that an increase of the strength constant does not affect the D, t1/2 and Vo values, and that the release of isoniazid is retarded only in flat tablets with the highest strength constant. Storage exerts no effect on the drug release from these tablets. The industrial production of these tablets is under way.
Formulation studies have been conducted on an oxytetracycline dihydrate tablet formulation containing microcrystalline cellulose and alginic acid, wet granulated with polyvinylpyrrolidone (PVP) solution. A range of granule properties including size, strength packing and porosity, and tablet properties including breaking load, porosity, disintegration and dissolution have been measured. Increased compaction pressure decreased tablet porosity. The reproducibility of the above properties was determined by tests on nine standard batches of granules and tablets. An increased concentration of PVP in the binder solution decreased the rate of tablet dissolution. Although the volume of granulating solution apparently controlled the granule size, it did not significantly alter the tablet dissolution, when the amount of PVP was constant.
Using three brands of multiple-scored levodopa tablets, B.P. (500 mg) and one brand of sulphamethoxypyridazine tablets B.P. (500 mg) the weight and content uniformity of the subdivisions has been examined. It is shown that quartering of such tablets can result in subunits which do not conform to recognized standards of weight uniformity, and in some instances content uniformity may be questionable. The homogeneity of distribution of active constituent between tablets has been determined and compared with that within tablets (between quarters of individual tablets). Statistical evaluation of the results is presented.
Three poorly soluble drugs (chloramphenicol, phenacetin and prednisolone) were compressed into tablets of 10% drug content on a physical testing instrument at three different compression pressures. The dissolution profiles were determined by a modification of the U.S.P. method for drug suspensions, granules before compression, disintegrated and intact tablets. By comparison of the dissolution rates for disintegrated tablets with those for granules before compression, or suspensions, it is possible to separate the change in particle size during compression from the pressure-dependent dissolution behaviour of intact tablets. A comparative measurement of dissolution for disintegrated tablets with that for granules provides a useful method for elucidating the particle bonding or cleavage within the tablet during compression.
The authors study the blood levels of DPA after ingestion of the drug in the usual tablet form and after ingestion of an enteric coated tablet with delayed intestinal absorption. They emphasize the fast and very variable absorption of the drug in the usual tablet form which makes necessary the administration of several doses each day. They find a slower absorption from the enteric coated tablet resulting incumulative effects. This form allows an easier administration schedule (one dose in the morning and one dose in the evening). Moreover, the blood levels show less variation during a twenty-four-hour period. Undoubtedly, this new form is an improvement in comparison with the usual tablet.
The effect of tablet porosity, surface roughness and film thickness on the adhesion of hydroxypropyl methyl cellulose films to placebo tablet substrates have been studied using a specially designed tensile tester (Fisher & Rowe, 4976). There were direct relations between measured adhesion and tablet porosity and also surface roughness and tablet porosity. The effect of film thickness on the measured adhesion is complex with an initial decrease with thicknesses up to 35 micron and then a gradual increase with thicknesses up to 140 micron dut to differences in the strees distribution within the film during testing. A knowledge of these effects is necessary if results from various sources are to be compared. The findings illustrate the potential capability of the extrapolation of measured adhesion results to zero porosity and zero thickness values in order to obtain a measure of the true or intrinsic adhesion at any film/tablet interface without the confusing elements of tablet porosity, surface roughness and residual stresses in the film.
A trial was made to study the possibility of preparing high-quality therapeutic tablets by direct compression of the solidified drugcarrier melt via solid dispersion technique. Paracetamol-mannitol, amylobarbitone-urea and caffeine-nicotinamide systems were investigated. Phase diagrams of the first two systems were found to be of the simple eutectic type, while that of the third system was a peritectic type. Solubility studies were also carried out. Dissolution rate studies showed that the fused mannitol/paracetamol (80:20), urea/amylobarbitone (80:20) and nicotinamide/caffeine (50:50 and 70:30) solid dispersions exhibited better rates of dissolution than those of the pure drugs. Comparative studies were carried on with tablets prepared by direct compression of the drug-carrier solidified melt exhibiting the highest dissolution rate and by slugging the pure drug and the drug-carrier physical mixture of corresponding composition. The physical properties and dissolution rate data showed the superiority of the tablets prepared by the solid dispersion technique. The drug release from these tablets was 4.5, 7.6 and 3.7 times greater than that from tablets prepared from pure paracetamol, amylobarbitone and caffeine respectively.
Stable and pharmaceutically elegant sublingual nitroglycerin tablets were formulated using povidone to retard volatilization of the drug. Formulation and processing variables were investigated to produce an acceptable product. A blend of two grades of povidone, of different degrees of cross-linkage and water solubility, provided stable tablets which exhibited rapid disintegration. Directly compressed sublingual tablets made in this study retained over 80% of the initial nitroglycerin when exposed to the atmosphere at room temperature for 2 months. The direct compression tablets are of good appearance and low friability, and the formulation is readily compressed without problems. An interesting relationship among the hardness, disintegration time, and compaction pressure is described.
Eight dissolution methods (beaker, rotating basket, oscillating basket, solubility simulator, rotating flask, and column) were evaluated using 21 commercial film-coated chloramphenicol (I) tablets and a nondisintegrating benzoic acid (II) tablet. The relative agitating intensities obtained from different dissolution methods were compared through the relative zero-order nondisintegrating tablet dissolution rate constants. Correlation coefficients between I dissolution rate parameters (lag time, T20, T50, and T80) were determined. Significant correlation was observed for the lag time among seven methods, and all pairwise regression lines passed through zero except one. The regression line slopes reflected the relative destructive force intensities produced by each dissolution method on the coated I tablet films. The seven dissolution methods could be classified into two main groups according to correlations of four dissolution rate parameters. The classification criterion agreed well with that based on the agitation method. However, dissolution methods may not be interchangeable even though they belong to the same dissolution method group.
The bioavailability of a rapidly dissolving tablet of theophylline and three brands of standard aminophylline tablets was estimated in a four way cross-over study involving 8 healthy adult volunteers. The relative extent of bioavailability as assessed by the measurement of the total area under the plasma concentration time curves showed no difference between the products (P greater than 0.05). Computed estimates of the rate of drug absorption were similar for all 4 products tested. The results indicate that the rapidly dissolving tablet offers no advantage in respect to rate and extent of absorption over conventional aminophylline tablets.
The wet mixing time has been shown to influence the properties of an oxytetracycline dihydrate tablet formulation, wet granulated with PVP solution. Increased time of wet mixing produced larger, stronger and more dense granules, which compressed into tablets with longer disintegration and dissolution times. Decreased drug particle size aggravated these trends. A decrease in drug particle size also produced larger, stronger and more dense granules. Above an oxytetracycline mean particle diameter of about 6 mum, the tablet dissolution was satisfactory. As the oxytetracycline particle size was decreased further, however, the distintegration and dissolution of the corresponding tablets was markedly slower.
1 Plasma prednisolone levels have been compared following the administration of enteric-coated prednisolone to fasted and non-fasted subjects. The effect on plasma levels of altering the formulation of the enteric-coating has also been studied. 2 The presence of food in the stomach at the time of administration does not affect the absorption of enteric-coated prednisolone tablets. 3 There was considerable inter-subject variation in plasma prednisolone levels after administration of shellac based enteric-coated tablets. However, plasma levels were more consistent when a preparation whose formulation was based upon cellulose acetate phthalate (CAP) was given. 4 It is concluded that the pattern of absorption and plasma prednisolone levels depend on the formulation of the enteric coating. The bioavailability of the CAP based preparation is similar to that of plain prednisolone.
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