Starch is a naturally occurring polysaccharide polymeric material that is widely present in cytoplasm of the plant cells found in fruit, root, pedicle, and leaves as the principal form of the carbohydrate reserve. It occurs as an odourless and tasteless, fine, white to off-white powder.
When examined microscopically, it consists of very small spherical or ovoid granules/ grains whose size and shape are characteristic for each botanical variety. The low cost of starch, its biodegradability and renewability have made it a suitable candidate for developing sustainable raw materials for pharmaceutical industries. However, due to the limitations of native starches, some special starch products, e.g., pregelatinized starch, Sodium carboxymethyl starch etc., were introduced. This article discusses the various pharmaceutical applications of native starch.
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Starch is one of the most commonly used disintegrants for immediate release tablet dosage forms at concentrations of 3–25% w/w (optimum concentration of 15%). The disintegration ability of native starch is due to wicking and restoration of deformed starch particles on contact with aqueous fluid. Some newer sources of starch have been chemically, physically or enzymatically modified to enhance their disintegrant properties e.g. carboxymethyl starch (CMS) which possesses high swelling capacity (absorb an amount of water 23 times its initial weight) combined with a high rate of water permeation.
Starch becomes an integral part of a formula during manufacture when added in the range of 5–80% w/w to achieve standardized triturates of colourants, potent drugs/ low dose Active Pharmaceutical Ingredients (APIs) and herbal extracts thus facilitating effective handling and subsequent mixing/ blending processes during manufacture. This is due to its desirable intrinsic properties such as absence of risky interactions with most common APIs and excipients, absence of physiological and pharmacological activities as well as consistent physicochemical and functional properties.
Considering the weight uniformity required by the pharmacopoeias, it thus becomes evident that controlling or enhancing the flow properties of powders/granules through the feed mechanisms using glidants is of paramount importance. Starch has been widely used for this purpose because of its additional use as disintegrant. It reduces inter-particulate friction when used at concentrations of 2–10% w/w to improve powder and granule flow, especially when using dried starches.
Modified starches (e.g., cross-linked high amylose corn starch) have been used as functional ingredients in sustained release formulations to maintain therapeutic concentration of drugs for extended periods of time. They are mainly used as microspheres or hydrogels and their use has been attributed to their improved functionality – its gel-forming ability, biodegradability, and biocompatibility.
Starches are used as antiadherent and lubricant at a concentration of 3–10% w/w during tablets and capsules production. The antiadherent properties of starch prevent the sticking of compressed powders/granules to punch faces and the die wall or in the case of encapsulation, prevents sticking to the powder mix to the dosators and tamping pins of encapsulates. Starch also reduces friction by interposing an intermediate layer between the tablet constituents and the die wall during compression and ejection processes.
Read Also: Preformulation Studies: Drug-Excipient Compatibility Studies pharmaceutical applications of native starch
In tablet formulations, starch prepared to gel (freshly prepared starch paste) by heat treatment of the starch dispersion in water is used at a concentration of 3–20% w/w (usually 5–10%, depending on the starch type) as a binder for wet granulation. This provides the necessary binding force that holds the powder particles together to form the required agglomerates. The quantity of the freshly prepared starch paste used should be determined by optimization studies, using parameters such as tablet friability and hardness, disintegration time, and drug dissolution rate. This also serves to ensure a uniform distribution and controllable release of the APIs.
Starch, particularly the fine powders of rice and wheat starch, is used as a base in topical preparations for its absorbency of liquids. Starch paste is used in ointment formulations, usually in the presence of higher ratios of glycerin.
The film-forming property of starch can be attributed to the amylose component of starch. Scientific investigations suggest that this property can be improved by combining starch with other polymers such as chitosan, microcrystalline cellulose, flax cellulose nanocrystals etc. A blend of starch and chitosan blend exhibit a good film-forming property which is attributed to hydrogen bond formation between the functional group (amino and hydroxyl groups) present on the backbone of the two component. Edible film is produced by combining cornstarch and microcrystalline cellulose in the absence or presence of plasticizers. Also, starch-based nanocomposite film is obtained from a blend of plasticized starch and flax cellulose nanocrystals. pharmaceutical applications of native starch
As an alternative to the use of metals and ceramics in TE, biodegradable polymers such as starch, collagen, fibrinogen, chitosan, hyaluronic acid (HA), poly(hydroxybutyrate), poly(a-hydroxy acids), poly(e-caprolactone), poly(propylene fumarates), poly(carbonates), poly-(phosphazenes) and poly(anhydrides) are believed to be the ideal materials for bone TE. Starch-based biodegradable polymers (SBBP), when used in bone tissue engineering scaffolds, can provide immediate structural support as a result of its good mechanical properties. It also allows for increased degradation time (producing non-toxic degradation products) and consequently expanded porosity as cellular integration increases, which is optimal for bone tissue engineering.
Natural and modified starches are now used in the development and formulation of plasma volume expanders. Examples include acetylated starch (e.g., acetyl starch) and hydroxyethyl starch which are now used to prevent shock following heavy blood loss resulting from surgery, trauma etc.
Starch appears to be useful adjuncts to standard ORS in the treatment of cholera/ diarrhoea in children. It promotes fluid and electrolyte absorption and may add additional energy without increasing the osmotic load and also shorten the recovery period from diarrheal disease. A typical example of starch used for this purpose is rice starch. Others include modified tapioca starch and plantain starch.
Starch particularly, potato starch has been used to produce artificial red blood cells with good oxygen-carrying capacity. It was prepared by encapsulating haemoglobin (Hb) with long-chain fatty acid grafted potato starch by self-assembly.
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