Hydroxypropyl Cellulose
Hydroxypropyl Cellulose (HPC) is known as a coating agent, emulsifier, stabilizer, suspension agent, tablet binder, thickener, and viscosity-increasing agent. Hydroxypropyl Cellulose is one of the ingredients in Arvin Kala’s diverse product portfolio.
Description
Hydroxypropyl cellulose is an odorless, tasteless powder that ranges in color from white to slightly yellow.
Hydroxypropyl cellulose is extensively utilized in both oral and topical pharmaceutical formulations. In oral products, hydroxypropyl cellulose is mainly used in tablet formulations as a binder, film-coating agent, and extended-release matrix former.
Hydroxypropyl cellulose concentrations between 2 and 6% w/w can be used as a binder in both wet-granulation and dry, direct-compression tableting processes. Concentrations between 15 and 35% w/w are used to create tablets with extended drug release. The drug release rate increases as the viscosity of hydroxypropyl cellulose decreases. Adding an anionic surfactant increases the viscosity of hydroxypropyl cellulose, thereby reducing the drug release rate. Blends of hydroxypropyl cellulose with other cellulosic polymers are used to enhance wet granulation and tableting characteristics, as well as to achieve better control and manipulation of the drug release rate.
As an alternative to wet granulation, dry granulation and direct compression of hydroxypropyl cellulose formulations have shown acceptable tableting and flow characteristics for use in extended-release matrix tablets.
Typically, a 5% w/w solution of hydroxypropyl cellulose is used for film-coating tablets. Aqueous solutions containing hydroxypropyl cellulose with some methyl cellulose or ethanolic solutions have been utilized. Stearic acid or palmitic acid can be added to ethanolic hydroxypropyl cellulose solutions as plasticizers. However, environmental concerns have limited the use of ethanol in film-coating solutions. Low-substituted hydroxypropyl cellulose is used as a tablet disintegrant; refer to Hydroxypropyl Cellulose, Low-substituted for more details.
Hydroxypropyl cellulose is also utilized in microencapsulation processes and as a thickening agent. In topical formulations, it is used in transdermal patches and ophthalmic preparations.
Hydroxypropyl cellulose is also employed in cosmetics and food products as an emulsifier and stabilizer.
Stability and Storage Conditions
Hydroxypropyl cellulose powder is stable, but it becomes hygroscopic after drying.
Aqueous solutions of hydroxypropyl cellulose are stable at pH 6.0 to 8.0, with their viscosity remaining relatively unchanged. However, at low pH, these solutions may undergo acid hydrolysis, leading to chain scission and a reduction in viscosity. The rate of hydrolysis increases with higher temperatures and hydrogen ion concentration. At high pH, alkali-catalyzed oxidation can degrade the polymer, also resulting in decreased viscosity. This degradation can occur due to the presence of dissolved oxygen or oxidizing agents in the solution.
As the temperature increases, the viscosity of aqueous hydroxypropyl cellulose solutions gradually decreases until it suddenly drops around 45°C due to the limited solubility of the polymer. However, this process is reversible, and the original viscosity is restored upon cooling.
The high level of substitution in hydroxypropyl cellulose enhances its resistance to degradation by molds and bacteria. However, aqueous solutions can degrade under severe conditions, leading to a decrease in viscosity. Certain enzymes produced by microbial activity can break down hydroxypropyl cellulose in solution. Therefore, for prolonged storage, an antimicrobial preservative should be added to aqueous solutions. Solutions of hydroxypropyl cellulose in organic solvents generally do not require preservatives.
Ultraviolet light can degrade hydroxypropyl cellulose, causing aqueous solutions to slightly decrease in viscosity if exposed to light for several months.
Aqueous hydroxypropyl cellulose solutions achieve optimal stability when the pH is maintained between 6.0 and 8.0, and when the solution is shielded from light, heat, and microbial activity.
Store hydroxypropyl cellulose powder in a tightly sealed container in a cool, dry location.
Method of Manufacture
A purified form of cellulose is treated with sodium hydroxide to create a swollen alkali cellulose, which is more chemically reactive than untreated cellulose. This alkali cellulose is then reacted with propylene oxide at high temperature and pressure. The propylene oxide can attach to the cellulose via an ether linkage at the three reactive hydroxyl groups on each anhydroglucose unit of the cellulose chain. This etherification process results in hydroxypropyl substituent groups that are predominantly secondary hydroxyls. The secondary hydroxyl in the side chain can further react with propylene oxide, allowing for potential ‘chaining-out’. This results in the formation of side chains containing more than 1 mole of combined propylene oxide.
Safety
Hydroxypropyl cellulose is commonly utilized as an excipient in both oral and topical pharmaceutical formulations. Additionally, it is widely employed in cosmetics and food products.
Hydroxypropyl cellulose is generally considered to be a nontoxic and nonirritant substance. It is not absorbed from the gastrointestinal tract and is completely excreted in feces after oral administration in rats. It does not cause skin irritation or sensitization. However, its use as a solid ocular insert has occasionally been linked to discomfort or irritation, including hypersensitivity and eyelid edema. Adverse reactions to hydroxypropyl cellulose are uncommon. Nonetheless, there has been a report of a patient developing contact dermatitis from hydroxypropyl cellulose in a transdermal estradiol patch.
The WHO has established an acceptable daily intake for hydroxypropyl cellulose of up to 1500 mg/kg of body weight. Consuming hydroxypropyl cellulose in excess may result in a laxative effect.
Chemical-physical values
| Test Item | Unit | Specification |
|---|---|---|
|
APPEARANCE |
|
WHITE POWDER OR GRANULES |
|
HYDROXYPROPYL CONTENT |
%wt |
Min 60.0 &
Max 77.0
|
|
APPARENT VISCOSITY |
cp 2% IN WATER |
Min 150.0 &
Max 400.0
|
|
LOSSON DRYING |
%wt |
Max 5.0 |
|
RESIDUE ON IGNITION |
%wt |
Max 0.5 |
| Test Item | Unit | Specification |
|---|---|---|
|
PH |
|
Min 5.0 &
Max 8.0
|
|
HEAVY METALS |
ppm |
Max 20 |
|
LEAD |
ppm |
Max 10
|
|
CHLORIDES |
%wt |
Max 5.0 |
|
PARTICLE SIZE, Through 60 mesh |
|
In 100% |
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