USP Dissolution Apparatus Types, Noyes-Whitney Equation

Apparatus 1

Name: Basket

Primary Use: Capsules, floating tablets, suppositories.

Apparatus 2

Name: Paddle

Primary Use: Most common. Standard tablets.

Apparatus 3

Name: Reciprocating Cylinder

Primary Use: Extended-release dosage forms, chewable tablets.

Apparatus 4

Name: Flow-Through Cell

Primary Use: Low-solubility drugs, implants, microparticles.

Apparatus 5

Name: Paddle over Disk

Primary Use: Transdermal patches.

Apparatus 6

Name: Cylinder

Primary Use: Transdermal patches.

Apparatus 7

Name: Reciprocating Holder

Primary Use: Transdermal patches, osmotic pumps.

dC / dt

Rate of dissolution

D

Diffusion coefficient of the drug

A

Surface area of the drug particles

Cs

Saturation solubility of the drug in the diffusion layer

Cb

Concentration of the drug in the bulk fluid

h

Thickness of the stagnant diffusion layer

decrease the particle size

To increase the dissolution rate of a poorly soluble drug, a manufacturer will primarily ‘blank’ (micronization)

Surface Area (A)

Reducing particle size massively increases the total ‘blank’, driving up the dissolution rate.