Biomedical subjects

J M Sousa Lobo

Publications and source records attributed to J M Sousa Lobo.

4 recordsLinked to original sources

PubMed2003

Evaluation of mathematical models describing drug release from estradiol transdermal systems.

The in vitro release profiles of 13 patches of estradiol (from five marketed products) were determined by the paddle-over-disk method. The transdermal systems were membrane-controlled type or matrix diffusion-controlled type. The estradiol content of test aliquots of the dissolution medium was determined by HPLC. To analyze the release mechanism, several release models were tested such as zero order, first order, Higuchi, Weibull, Korsmeyer-Peppas, and Makoid-Banakar. The release profiles showed that the drug was released at a constant rate for three patches. The drug-release rate from the other 10 patches was not constant, and diminished with the square-root of time (Higuchi model).

Administration, Cutaneous↗

PubMed2001

Modeling and comparison of dissolution profiles.

Over recent years, drug release/dissolution from solid pharmaceutical dosage forms has been the subject of intense and profitable scientific developments. Whenever a new solid dosage form is developed or produced, it is necessary to ensure that drug dissolution occurs in an appropriate manner. The pharmaceutical industry and the registration authorities do focus, nowadays, on drug dissolution studies. The quantitative analysis of the values obtained in dissolution/release tests is easier when mathematical formulas that express the dissolution results as a function of some of the dosage forms characteristics are used. In some cases, these mathematic models are derived from the theoretical analysis of the occurring process. In most of the cases the theoretical concept does not exist and some empirical equations have proved to be more appropriate. Drug dissolution from solid dosage forms has been described by kinetic models in which the dissolved amount of drug (Q) is a function of the test time, t or Q=f(t). Some analytical definitions of the Q(t) function are commonly used, such as zero order, first order, Hixson-Crowell, Weibull, Higuchi, Baker-Lonsdale, Korsmeyer-Peppas and Hopfenberg models. Other release parameters, such as dissolution time (tx%), assay time (tx min), dissolution efficacy (ED), difference factor (f1), similarity factor (f2) and Rescigno index (xi1 and xi2) can be used to characterize drug dissolution/release profiles.

Chemistry, Pharmaceutical↗

PubMed2001

Influence of dissolution medium agitation on release profiles of sustained-release tablets.

Reaching nearly perfect sink conditions is very important in the determination of drug dissolution rates. Many times, the only factor that is taken into consideration in achieving sink conditions is the relation between the drug concentration and its solubility. The analytical conditions of the dissolution assay, as well as the dissolution apparatus, stirring speed, and nature and volume of the dissolution fluid may also influence the dissolution results. The main objective of this work was to study the influence of the stirring rate conditions and of the dissolution apparatus in the diltiazem hydrochloride release from tablets. Diltiazem hydrochloride sustained-release (SR) tablets were tested and the follow ing dissolution parameters were evaluated: t10%, t25%, t50%, dissolution time, mean dissolution time (MDT), and dissolution efficiency (DE) at t120, and at t360. To analyze the release mechanism, several release models were tested, such as Higuchi, zero order, first order, Baker-Lonsdale, Hixson-Crowell, Weibull, and Korsmeyer-Peppas. The similarities between two in vitro dissolution profiles were assessed by the similarity factor f2. The in vitro release kinetics of diltiazem hydrochloride sustained-release tablets were evaluated using the USP 2 (paddle) and USP 4 (flow-through) apparatus.

Algorithms↗

PubMed2001

Divisability of diltiazem matrix sustained-release tablets.

The objective of this work was to study the possibility of a solid sustained-release dosage form, like a tablet, be divided without changing its release characteristics. Diltiazem hydrochloride Sustained-Release (SR) tablets with a standard groove on one face, were tested and the following dissolution parameters were evaluated: t10%, t25%, and t50% dissolution time, and dissolution efficiency at t120, and at t360. To analyze the release mechanism, several release models were tested such as Higuchi, zero order, first order, Baker-Lonsdale, Hixson-Crowell, Weibull, and Korsmeyer-Peppas. The similarities between two in vitro dissolution profiles were assessed by the difference factor (f1), the similarity factor (f2) and the Rescigno index (xi(i)). The in vitro release kinetics of diltiazem hydrochloride tablets were evaluated using USP apparatus 4. Using a one-way ANOVA (a = 0.05), statistically significant differences were found for t10%, t25%, and t50% dissolution times with a constant and with a variable pH dissolution fluid. The variation coefficient for the divisibility assay (Portuguese Pharmacopoeia VI) was lower than the limit value of 10%. The diltiazem release rate from this pharmaceutical system was not constant, and diminished with the square root of time (Higuchi model) showing that the phenomenon controlling drug release was the diffusion occurring inside the swelled polymeric matrix. Diltiazem release rate was a function of the area in direct contact with the dissolution fluid and not of the pharmaceutical matrix volume. The results obtained permit us to conclude that the division, in this case, affects the drug release characteristics.

Analysis of Variance↗