In the Pharmaceutical world, dissolution is a profound quality control test. It is defined as the amount of solute or solid drug that is placed in a solution per unit time under standardized conditions of temperature, solvent composition and liquid or solid interface. In the dissolution testing process, solubility is the most important parameter to consider in achieving the desired effect. It is a challenge for most Scientists to develop most drugs due to their low aqueous solubility.
A drug needs to be in a solution state to be absorbed in the site of absorption. Hence Scientists have come up with different methods of increasing solubility of drugs, that range from modification of the drugs particle size and crystal formation to use of surfactant. The final drug product is a solution made up of purified water, co-solvents, surface-active agents, preservatives, sweeteners such as glucose and saccharin, viscosity modifiers, anti-oxidants, colors, flavors and buffers to regulate pH levels. It is therefore essential to ensure one has the proper equipment at hand.
The whole process requires a variety of apparatus to ensure a high quality product. The following is an outlined list of apparatus used in dissolution testing as per the guidelines of the United States Pharmacopeia:
a) Rotating Basket: This has a retaining capacity of about 500 to 4000 ml. It has 50 to 200 rpm and is used in the dissolution of immediate release, delayed release, chewable tablets, and delayed release suppositories, extended-release tablets and floating dosage form.
b) The Paddle: It has a rotating speed of 25 to 50 rpm and a 500 to 4000 ml capacity. It is used in the dissolution of immediate release, orally disintegrating tablets, chewable tablets, delayed and extended-release tablets and capsules as well as suspensions.
c) The Reciprocating Cylinder: It has a 6 to 35 rpm rotator speed and a 250 ml capacity. It is used for controlled release formulations, chewable tablets and for beads.
d) The Flow-Through Cell: It has a volume capacity of up to 3 liters per hour. It is used for drugs with low solubility API, for powders and granules and also for micro-particles and implants.
e) The Paddle over Disk: It has a 25 to 50 rpm rotator speed. It has a volume capacity of 500 to 4000 ml and is used for transdermal patches, for ointments, floaters and emulsions.
f) The Rotating Cylinder: It has a 25 to 50 rpm rotator speed. It has a 500 to 4000 ml volume capacity and is used for transdermal patches.
g) The Reciprocating Holder: It has a 30 rpm rotator speed and its medium volume capacity is variable. It is used for controlled release formulations, for pH profile and for small volumes.
The need for dissolution apparatus in the Pharmaceutical business cannot be emphasized enough. Oral ingestion of drugs is the most convenient means of drug administration due to its high compliance amongst users, its cost-effectiveness and its flexibility in accommodating the desired dosage. As a result, most drug manufacturing companies are more inclined to result in dissolution testing in the production of bioequivalent oral products.