Basket vs. Paddle Dissolution

In the pharmaceutical industry, ensuring that a tablet or capsule releases its active ingredient at the correct rate is a matter of patient safety. This process is measured through Dissolution Testing. If a drug dissolves too quickly, it could lead to toxicity; if it dissolves too slowly, the treatment may be ineffective.

To simulate the human stomach, scientists primarily use two apparatuses defined by the United States Pharmacopeia (USP): Apparatus 1 (Basket) and Apparatus 2 (Paddle). While both serve the same goal, their applications and mechanics differ significantly.

Why Dissolution Testing is Mandatory

Before any medication reaches the pharmacy shelf, it must undergo rigorous testing to verify its absorption profile. By controlling the rotation speed of the shaft and the temperature of the medium (typically $37^\circ C$ ), labs can predict how a drug will behave inside the body.

USP Apparatus 2: The Paddle Method

The Paddle method is perhaps the most common technique used for solid oral dosage forms like standard tablets.

How it Works:

The Blade: A rotating shaft is fitted with a metallic or coated blade (paddle) at the end, which acts as a stirrer.
The Process: The tablet is dropped into the dissolution vessel. Once it settles at the bottom, the paddle begins to rotate to agitate the medium.
The Sinker: Some tablets tend to float or stick to the sides of the glass vessel. In these cases, a sinker (made of non-reactive wire) is used to keep the tablet positioned directly beneath the rotating shaft.

Best Suited For:

Standard, non-coated tablets.
Disintegrating tablets.
Certain controlled-release formulations.

USP Apparatus 1: The Basket Method

The Basket method utilizes a different attachment at the end of the rotating shaft to hold the dosage form.

How it Works:

The Basket: A cylindrical basket made of non-reactive mesh is attached to the shaft.
The Process: The drug is placed inside the basket before the test begins. As the shaft rotates, the mesh allows the medium to flow in and the dissolved drug to move out into the vessel, creating a uniform solution.
Managing "Sticky" Drugs: The basket is ideal for tablets containing HPMC (Hydroxypropyl Methylcellulose) or other binders that swell and become "sticky" when wet. These tablets would otherwise stick to the bottom of the vessel in a paddle test, ruining the data.

Best Suited For:

Capsules (which naturally float).
Suppositories.
Sticky or swelling tablets.
Beads or multi-particulate formulations.

Key Differences at a Glance

Feature	Paddle Method (Apparatus 2)	Basket Method (Apparatus 1)
Apparatus Type	A vertical blade/stirrer.	A cylindrical mesh cage.
Sample Placement	Dropped directly into the vessel.	Placed inside the basket.
Floating Samples	Requires a sinker to keep the drug down.	Naturally contained within the mesh.
Common Use Case	Standard tablets.	Capsules and "sticky" swelling tablets.
Risk Factor	Tablet may stick to vessel walls.	Mesh pores can become clogged with particles.

Choosing the Right Method

The decision to use a paddle or a basket is not arbitrary; it depends entirely on the physical properties of the dosage form. Pharmaceutical scientists must choose the method that provides the most accurate and reproducible "sink conditions" to ensure the medication performs exactly as intended in the patient's system.