Weights & Sinkers
What are Weights and Sinkers?
The USP allows, as a variation to Apparatus 2, the use of a helix of non-reactive material as a ‘sinker’ for floating dosage units. Thin stainless steel wire (type 316) is commercially available for this purpose.
Capsule sinkers are commonly used when to keep the capsule or tablet at the bottom of the vessel or to help it sink in the first place. Few guidelines exist for these except that a few turns of wire can be used to sink the tablet.
Inevitably, home made sinkers tend not to be reproducible and so commercially available sinkers are quite popular. The choice of sinker will depend on the tablet or capsule. In general there are some guidelines that can be followed however:
- The sinker should ideally not touch the tablet as this can effect the dissolution rate. They are available in different sizes to accommodate most capsule/tablet dimensions.
- A minimum amount of weight is preferable, just enough to have the desired effect
- Coated sinkers can be used where there may be a reaction between steel and the tablet
- Basket type sinkers can be used but care should be taken that the outer coating of the tablet does not clog the mesh.
- Wire spirals should be as wide as practically possible to avoid clogging which will effect the dissolution rate.
Japanese Sinkers are specified by the JP and have strict dimensions.