Disintegrants are materials that are added to tablet and hard gelatin capsule formulations to aid in the breakup of a tablet or granules after oral administration. Disintegrant rapidly takes up water and breaks apart the formulation into smaller fragments upon contact with an aqueous environment thus making the drug available for dissolution over a larger surface area.
The mechanism of disintegrant action may include wicking, swelling, or structure recovery. It is likely that the disintegrant exhibits more than one type of mechanism. A disintegrant may be added intragranularly prior to wet granulation or extragranularly prior to lubrication or included in both ways. In direct compression of tablet, disintegrants are added prior to lubrication to facilitate the breakup of the tablet formulation.
Types of disintegants
Starch is one of the oldest disintegrants used in a solid dosage form. As a disintegrant, it is used at the concentration range of 3–25% w/w in a formulation. Typically, 10–15% w/w is needed to get good disintegrant action. At high concentrations, they can negatively impact the tablet hardness. In addition, starches used at high concentrations can cause issues of flow and compactability. Moreover, intragranular starch is not good as a disintegrant. Therefore, they have been largely replaced by modified starches and other superdisintegrants that can take up water faster even at low concentrations.
Pregelatinized starch at 5–10% w/w concentration is used as disintegrant. They mainly act through swelling mechanism and are more effective extragranularly.
Sodium Starch Glycolate (SSG)
Sodium starch glycolate (SSG) is the sodium salt of carboxymethyl ether of starch or of a cross-linked carboxymethyl ether of starch. Carboxymethylation (degree of substitution) induces hydrophilicity by disrupting hydrogen bonding and allowing water access to the molecule. Cross-linking reduces the water-soluble fraction and gel formation that also reduces viscosity in water.
The disintegrant efficiency has been inversely correlated to its levels of cross-linking. Since carboxymethylation and cross-linking have opposing effects on water solubility, water access, and viscosity, a balance between the two is important to ensure optimal performance. The mechanism of its disintegrant action has been attributed to its high rate of water uptake and rapid swelling property.
It is cross-linked homopolymer of 1-vinyl-2-pyrrolidone. As a disintegrant, it is used at a concentration of 2–5% w/w. It is water-insoluble material but has a high wicking tendency, causing it to take up water. In addition, structure recovery can disrupt tablet integrity by generating more pores. It swells without gelling and this property is advantageous for developing orally disintegrating tablets and in cases where gelling can delay dissolution.
Being nonionic in nature, the disintegrant action is independent of pH of the media and is a potential choice of disintegrant for cationic drugs. Coarse particles of cross-linked PVP have better disintegrant efficiency. In the case of insoluble fillers, crospovidone with higher porosity showed faster disintegration than disintegrant with lower porosity. Disintegration force decreased with decrease in porosity and particle size. For tablets containing insoluble system, liquid uptake, settling volume, and disintegration force are critical for dissolution.
Croscarmellose Sodium (CCS)
Croscarmellose sodium (CCS) is a cross-linked polymer of carboxymethylcellulose sodium. The carboxymethyl groups that substitute the hydroxyl groups determine the degree of substitution. Sodium chloride and sodium glycolate are by-products of the cross-linking reaction. It is used at a concentration of 0.5–5% w/w as a disintegrant both in wet granulated and direct compression systems.
It is insoluble in water but hydrophilic and rapidly takes up water and swells. Carboxymethyl substitution increases the swelling ability of CCS, with basic substituents in CCS having a greater tendency to swell than acidic substituents. The swelling ability of CCS is also adversely impacted at lower pH due to conversion of carboxymethyl sodium to its less hydrophilic free form. Particle size of CCS can impact disintegrant action with larger particles of CCS having a greater tendency to swell