Tablets are oral dosage forms that are administrated orally. The dosage form enterprises of the active ingredient that has been compressed together with the excipients. Dissolution process involves the disintegration of the tablet into smaller particles to release the active pharmaceutical ingredient to the blood system. The excipients have different purposes, and they may have an influence on the ability of the tablet to disintegrate and dissolve. Binders such as starch hold the tablet together, thus, controlling the rate of release of the active pharmaceutical ingredient.
The process of tablet dissolution involves two steps. The first one involves the drug particles changing from the solid state to a solute state in the dissolution medium. Consequently, a thin stagnant film layer is formed around the drug particle. The second step is where the solutes move from the thin stagnant layer to the bulk of the dissolution medium.
Knowledge of the rate of dissolution of various tables serves different purposes in the formulation of these tablets and also in the quality control of these tablets. Modification of tablets dissolution can also be used in developing modified release tablets. Modified release tablets can help in improving the bioavailability of drugs in the blood because enhancing its efficacy.
The rate of drug release in-vivo can be determined by measuring the drug's concentration in plasma and urine. However, the in-vivo method of determining blood concentration is not accurate, and it has some challenges. The difficulties arising from the in-vivo method led to the introduction of the dissolution testing method using the in-vitro methods.
Dissolution Testing:
The primary objective of the dissolution testing is to determine the drug release features of an individual formulation. The in-vitro dissolution testing also ensures sufficient and reproducible bioavailability. The test gives an assurance that the active ingredient released from the table to the dissolution medium within a reasonable period.
The dissolution of the tablet in the dissolution medium depends on the size of the granules. Small granules have a large surface area; since they can easily absorb the dissolution medium to form a solution. The nature of excipients also used to determine the dissolution profile of the particular tablet. Disintegrants such as carboxymethyl cellulose facilitate tablet breakdown making the particles dissolve rapidly. The pH of fluids in the gastrointestinal tract also determines the rate of dissolution of tablets.
Other factors that affect the rate of tablet dissolution include those related to the physical-chemical properties of the active ingredient. The method of manufacture also influences the rate of dissolution of tablets.
Tablet dissolution testing instruments:
The apparatus used in testing tablet dissolution include at least six testing stations, stirrers, and a heating device to be used for heating the dissolution medium. The media volume for small dosage strengths should be between 900 ml or 500 ml. Increased sink conditions should have a media volume of 1000ml, two liters, or four liters. The media should have a buffer, commonly acetate with a pH of 4.1 to 5.5 is utilized. The paddle speed can be 50 rotations per minute, and it can go up to 100 rotations per minute. Temperatures should be within a range of 37 degrees centigrade (+/- 0.5). Sampling time points include 10, 15, 20, 20, 45, 60 minutes.
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