How to Make Dispersible Tablets

Dispersible tablets are designed to disperse in water, forming a homogeneous dispersion that can be easily swallowed. This makes them ideal for patients who have difficulty swallowing conventional tablets, such as children and the elderly. Making dispersible tablets involves careful formulation and processing to ensure rapid breakdown and smooth dispersion in liquid.

Understanding Dispersible Tablets

Unlike effervescent tablets which dissolve with fizzing, dispersible tablets break down into small particles when added to water, forming a suspension or dispersion. The key characteristics are rapid dispersion and ease of swallowing.

Key Components of Dispersible Tablet Formulations

Achieving fast and uniform dispersion requires specific ingredients:

• Active Pharmaceutical Ingredient (API): The medicinal compound. For dispersible tablets, the API is often in a finely divided form to aid dispersion.
• Superdisintegrants: These are crucial for rapid breakdown. They work by swelling or wicking water into the tablet matrix. Common examples include Crospovidone, Croscarmellose Sodium, and Sodium Starch Glycolate.
• Fillers/Diluents: Provide bulk to the tablet. Examples include Lactose, Microcrystalline Cellulose, Mannitol.
• Binders: Hold the tablet together but must not impede dispersion. Examples are Povidone, Hydroxypropyl Cellulose, and Hydroxypropyl Methylcellulose (HPMC), often used in wet granulation processes.
• Pharmaceutically Acceptable Clay: As mentioned in the reference, certain clays can be used. Clays like bentonite or kaolin can act as binders or potentially aid in the dispersibility or suspension characteristics. The reference highlights their use in a preferred method.
• Sweeteners and Flavors: Essential for palatability, especially for pediatric or geriatric formulations.
• Lubricants: Reduce friction during tableting (e.g., Magnesium Stearate).
• Glidants: Improve powder flow (e.g., Colloidal Silicon Dioxide).

Manufacturing Methods

Dispersible tablets can be made using standard tablet manufacturing techniques, adapted for dispersibility requirements. Common methods include:

1. Direct Compression: Simpler, fewer steps, suitable for APIs with good flow and compressibility. Requires excipients with excellent properties, including effective superdisintegrants.
2. Granulation:
   • Wet Granulation: Involves adding a liquid binder to a powder mixture to form granules. This improves flow and compressibility but requires drying. The reference describes a process starting with moistening, indicative of a wet granulation approach.
   • Dry Granulation (Roller Compaction or Sluggin): Powders are compressed into large slugs or sheets which are then milled into granules. Suitable for moisture-sensitive or heat-sensitive materials.

A Preferred Manufacturing Method (Based on Reference)

The provided reference describes a method, preferably comprising steps that align with a wet granulation process, utilizing a pharmaceutically acceptable clay:

• a) Dry Mixing: The process begins by mixing the active compound in dry finely divided form with an effective amount of a pharmaceutically acceptable clay, optionally adding one or more pharmaceutical carriers or excipients. This initial step ensures uniform distribution of the API and clay with other necessary dry ingredients like fillers or a portion of the superdisintegrant.
• b) Wet Massing: Following the dry mix, the reference indicates adding a sufficient amount of a pharmaceutically acceptable liquid to moisten... This step, often involving water or an organic solvent containing a binder, causes the powder particles to aggregate, forming a wet mass. The extent of moistening is crucial to form suitable granules.

This wet mass would then typically undergo further steps in a standard wet granulation process, including:

• Granulation: Breaking the wet mass into smaller granules using screens or choppers.
• Drying: Removing the liquid used for moistening, often in a fluid bed dryer or oven, until a target moisture content is reached.
• Milling/Sizing: Breaking dried granules into a specific size range to improve flow and compressibility.
• Lubrication and Final Mixing: Adding lubricants, glidants, and often the remaining portion of the superdisintegrant and other external phase excipients (like flavors, sweeteners) to the dried granules.
• Compression: Compressing the final blend into tablets using a tablet press.

This method, particularly employing clay and wet granulation as described, can be effective in producing granules that compress well while formulating a tablet designed for rapid dispersion once wetted.

Quality Control for Dispersible Tablets

After manufacturing, dispersible tablets are tested to ensure they meet specific pharmacopoeial standards (e.g., USP, Ph. Eur.). Key tests include:

• Dispersion Time: The time it takes for the tablet to disperse in a specified volume of water (usually 150 mL) at a set temperature (usually 15-25°C). Pharmacopoeial limits typically require dispersion within 3 minutes.
• Fineness of Dispersion: The dispersion is passed through a sieve (usually 710 µm or 750 µm). A minimal amount of particles should remain on the sieve, ensuring the dispersion is smooth enough to swallow easily.
• Uniformity of Dosage Units: Ensuring each tablet contains the correct amount of API.
• Friability and Hardness: While needing to disperse easily, the tablet must be robust enough to withstand handling and packaging.

Summary of the Process Steps

While variations exist, a common sequence, incorporating the referenced method, involves:

By following these steps and carefully selecting excipients, including the specified clay and superdisintegrants, pharmaceutical manufacturers can successfully produce high-quality dispersible tablets that offer a convenient dosing option.