Determination of time course of tablet disintegration II: Method using continuous functions

Effect of Porosity on Strength Distribution of Microcrystalline Cellulose

Fracture strength of pharmaceutical compacts varies even for nominally identical samples, which directly affects compaction, comminution, and tablet dosage forms. However, the relationships between porosity and mechanical behavior of compacts are not clear. Here, the effects of porosity on fracture strength and fracture statistics of microcrystalline cellulose compacts were investigated through diametral compression tests. Weibull modulus, a key parameter in Weibull statistics, was observed to decrease with increasing porosity from 17 to 56 vol.%, based on eight sets of compacts at different porosity levels, each set containing ∼ 50 samples, a total of 407 tests. Normal distribution fits better to fracture data for porosity less than 20 vol.%, whereas Weibull distribution is a better fit in the limit of highest porosity. Weibull moduli from 840 unique finite element simulations of isotropic porous materials were compared to experimental Weibull moduli from this research and results on various pharmaceutical materials. Deviations from Weibull statistics are observed. The effect of porosity on fracture strength can be described by a recently proposed micromechanics-based formula.

Formulation and optimization of sustained release Stavudine microspheres using response surface methodology

The aim of the current study was to formulate and optimize the formulation on the basis of in vitro performance of microsphere. A 3² full factorial design was employed to study the effect of independent variables, polymer-to-drug ratio (X₁) and stirring speed (X₂), on dependent variables, encapsulation efficiency, particle size, and time to 80% drug release. The best batch exhibited a high entrapment efficiency of 70% and mean particle size 290 μm. The drug release was also sustained for more than 12 hours. The study helped in finding the optimum formulation with excellent sustained drug release.

Formulation and evaluation of mucoadhesive glipizide microspheres

The purpose of this research was to formulate and systematically evaluate in vitro and in vivo performances of mucoadhesive microspheres of glipizide. Glipizide microspheres containing chitosan were prepared by simple emulsification phase separation technique using glutaraldehyde as a cross-linking agent. Results of preliminary trials indicate that volume of cross-linking agent, time for cross-linking, polymer-to-drug ratio, and speed of rotation affected characteristics of microspheres. Microspheres were discrete, spherical, and free flowing. The microspheres exhibited good mucoadhesive property in the in vitro wash-off test and also showed a high percentage drug entrapment efficiency. A 3(2) full factorial design was employed to study the effect of independent variables, polymer-to-drug ratio (X(1) ), and stirring speed (X(2) ) on dependent variables percentage mucoadhesion, t(80), drug entrapment efficiency, and swelling index. The best batch exhibited a high drug entrapment efficiency of 75% and a swelling index of 1.42; percentage mucoadhesion after 1 hour was 78%. The drug release was also sustained for more than 12 hours. The polymer-to-drug ratio had a more significant effect on the dependent variables. In vivo testing of the mucoadhesive microspheres to albino Wistar rats demonstrated significant hypoglycemic effect of glipizide.

Formulation optimization of controlled release diclofenac sodium microspheres using factorial design

Diclofenac sodium is an ideal candidate for incorporation in a controlled release device to diminish its adverse effects after oral administration. Microspheres were prepared by using sodium alginate as a polymer and CaCl2 as a cross-linking agent. In this investigation, 3(3) full factorial design was used to investigate the joint influence of the three variables: the stirring speed (X1), concentration of CaCl2 (X2) and % of heavy liquid paraffin in a blend of heavy and light liquid paraffin in the dispersion medium (X3) on the time of 80% drug dissolution (t80). Potential variables such as concentration of sodium alginate and drug: sodium alginate ratio were kept constant in the experimental design. A statistical model with significant interaction terms is derived to predict t80. The results of multiple linear regression analysis and F-statistics revealed that for obtaining controlled drug release, the microspheres should be prepared using relatively lower stirring speed, higher concentration of CaCl2 and higher percentage of heavy liquid paraffin in the dispersion medium. The X1X2 and X2X3 interactions were found to be statistically significant in nature. A response surface plot is presented to show the effects of X1, X2 and X3 on t80. The drug was released by diffusion of anomalous type. A model was validated for accurate prediction of drug release profile. Acceptable batches were identified in the experimental design with constraints on percentage drug released in 1, 6 and 8 h.

Pharmacokinetic modelling of the plasma concentration-time profile of the vitamin retinyl palmitate following intramuscular administration

Seven healthy male volunteers (21-24 y) received by the ventro-gluteal route a single dose of 100,000 I.U. of the vitamin retinyl palmitate (RP) in a water-miscible preparation (W) and 5 weeks later the same dose in an oily solution (S). After administration of W median (range) peak plasma concentrations of 5.6 (4.4-8.7). 10(3) micrograms l-1 were reached after 12 h and high levels persisted for another 50 h. At 144 h levels were still, by a factor 3, higher than baseline. Plasma levels of RP after S remained close to baseline (20-50 micrograms.l-1) suggesting negligibly low bioavailability. The plasma level profile of RP after W could well be described by use of a one-compartment model with Weibull-type absorption and Michaelis-Menten elimination. The median (range) absolute bio-availability (estimates of lower limits) was 42 (32-52) per cent.

Dissolution of a soluble drug substance from vinyl polymer matrices

It was shown that vinyl polymers form good bases for in vitro sustained-release matrices, and that the character of the release curves is basically in line with their pH-solubility profiles. For a flow cell, the release curves may be approximated by the equation: In (m/m0) = - K(t -ti), where m is the amount not dissolved, m0 is the initial drug content, K is a dissolution constant, t is time, and ti is a lag time. Furthermore, it was shown that K is a function of tablet hardness (H) and polymer content (Q, percent). This functionality is well represented by the equation: In K = alpha H + gamma ln Q + epsilon, where alpha, gamma, and epsilon are polymer-dependent parameters. Matrix erosion is represented by an exponential decay: (p/p0) = exp(-Dt + a), where p is the amount not eroded, p0 is the initial weight, D is an erosion constant, and a is a soluble polymer-dependent parameter. In the case of these soluble polymers, K is not solely a function of D.

Simple methods for estimating percent disintegrated--time data

Two techniques are described for the treatment of dissolution rates to estimate the percent disintegrated--time data for tablets and capsules. The first is an extension of an equation derived previously with the assumption of first-order disintegration and dissolution processes; whereas, the second involves the determination of the rate constant from the terminal segment of the curve and the use of numerical derivatives according to a disintegration kinetics-independent approach. The dissolution data of six commercial tablet and capsule formulations were treated according to the described techniques. Good agreement was found between the percent disintegrated--time data estimated by the second approach for an acetaminophen tablet and those obtained by a well-established model where a Weibull function was employed.

Concentration profile for the dissolution of drug tablets undergoing simultaneous degradation

An empirical approach to the concentration-time history of a dissolving drug has resulted in a cube-root equation in which the characteristic constant of the equation embodies the important physical variables of the system. This expression has been used to study the dissolution of a drug that degrades simultaneously in the test solution. An alternative representation of the dissolution process is first-order kinetics. These two approaches are compared by fitting the experimental data of the dissolution of digoxin and melphalan tablets in various media, and a new method for the proper analysis of data for the dissolution of tablets that simultaneously degrade in the test solution is presented.