Excipients are inactive ingredients used in pharmaceutical formulations to enhance the physical properties, stability, appearance, and patient acceptability of the final product.
In semisolid dosage forms, various types of excipients serve specific purposes:
1) Bases: Bases
provide the structure and consistency of the semisolid dosage form.
They can be lipophilic (e.g., petrolatum, lanolin) or hydrophilic (e.g., polyethylene glycols) and may be used in various combinations to create the desired formulation properties.
2) Gelling agents:
Gelling agents are used to form a three-dimensional network in gels, creating the characteristic semisolid consistency.
Examples of gelling agents include carbomers, hydroxyethyl cellulose, hydroxypropyl methylcellulose, and xanthan gum.
3) Emulsifying agents:
These agents help form stable emulsions in creams and certain ointments by reducing the interfacial tension between the oil and water phases.
Examples of emulsifying agents include polysorbates, glyceryl stearate, cetyl alcohol, and sorbitan esters.
4) Solvents:
Solvents are used to dissolve or disperse the drug and other excipients in the formulation.
They can be aqueous (e.g., water, glycerin) or non-aqueous (e.g., propylene glycol, ethanol) and may be used in varying ratios to achieve the desired solubility and stability of the drug.
5) Penetration enhancers:
These excipients improve the permeability of the drug through the skin, enhancing its absorption and bioavailability.
Examples of penetration enhancers include fatty acids (e.g., oleic acid), alcohols (e.g., ethanol, isopropanol), and surfactants (e.g., sodium lauryl sulfate).
6) Stabilizers:
Stabilizers help maintain the physical and chemical stability of the semisolid dosage form during storage and use.
They can include antioxidants (e.g., butylated hydroxytoluene), chelating agents (e.g., ethylenediaminetetraacetic acid), and pH adjusters (e.g., citric acid, sodium hydroxide).
7) Preservatives:
Preservatives are added to semisolid dosage forms, particularly those containing water, to prevent microbial growth and ensure product safety.
Examples of preservatives include parabens, benzalkonium chloride, and phenoxyethanol.
8) Thickeners:
Thickeners are used to increase the viscosity and consistency of semisolid dosage forms.
Examples of thickeners include colloidal silicon dioxide, carboxymethyl cellulose, and magnesium aluminum silicate.
9) Humectants:
These excipients help retain moisture in the formulation, preventing drying and improving the product's skin-moisturizing properties.
Examples of humectants include glycerin, propylene glycol, and sorbitol.
10) Coloring agents, fragrances, and flavors:
These excipients are added to semisolid dosage forms to enhance their appearance, aroma, and patient acceptability.
Examples include FD&C dyes, essential oils, and natural or artificial flavors.