What is a semi-solid dosage form?
The semi-solid dosage form is in the form of dermatological products of semisolid consistency which are applied on the skin for therapeutic or protective action. Semisolid dosage forms are intended for topical application in the form of ointments, creams, paste, and gels, etc.
These are applied on the skin and may be placed on the surface of the eye, or further used nasally, vaginally, or rectally. Mostly these preparations are used for the effects of the therapeutic agents which they contain. The non-medicated forms are used for their physical effects as protectants or lubricants.
Semi-solid dosage forms are those which are applied to the skin or accessible mucous membranes which tend to treat a pathological condition or provides protection against the harmful environment.
These are having properties to which cling to the skin or mucous membrane for a protracted duration of time to exert their therapeutic effect through protection.
|Semi-solid dosage forms||Ointments|
This is because of their plastic rheological behavior which allows semisolids to retain their shape and cling as a film until that acted upon by an outside force.
These are usually intended for localized drug delivery. These constitute a significant proportion of pharmaceutical dosage forms. These may be applied topically on the skin, cornea, rectal tissue, nasal mucosa, vagina, buccal tissue, urethral membrane, and external ear lining in different forms.
Ideal properties of semi-solid dosage form-
The ideal properties are which shows their physical, physiological, and application of the semisolid dosage forms are-
-These are having a smooth texture.
-These are elegant in appearance.
-These are non-dehydrating.
-These are non-gritty.
-These are non-greasy and also non- staining.
-These are non-hygroscopic.
-These do not alter the function of the mucous membranes or skin.
-These are miscible with skin secretion.
-These have a low sensitization index.
-These are non- irritating.
-These do not alter membrane or skin functioning with their effect.
-These are compoundable with skin secretion.
-These are easily applicable to efficient drug release.
-These are having a high aqueous washability.
You may read- Drug dosage form.
Classification of semi-solid dosage forms-
Semi solids dosage forms are including ointments, creams, pastes, gel, plasters and etc.
Ointments are soft hydrocarbon-based semisolid preparation which composed of fluid hydrocarbon. It meshed in a matrix of higher melting solid hydrocarbon petrolatum which exists in a tasteless, odorless, unctuous material with a melting range.
The main ingredients that forming the system are hydrocarbon and silicone oil which are generally poor solvents for most of the drugs, and likely setting a low limit on the drug delivery capabilities of the system.
These are the semi-solids greasy preparation that is used for application on the skin or mucosa. The base is usually anhydrous and containing medicaments in solution or suspension.
These are generally used for their properties are-
-Protection effect of lesions.
-Topical application of medications.
Types of ointments-
Unmedicated ointments- These are the ointments that do not contain any drug ingredients. These are used as emollients and protectants. For example- Petroleum jelly.
Medicated ointments- These are the ointments which are show local and systemic effects with active ingredients. Sub-types of medicated ointments–
Creams are the viscous semi-solid emulsion that is used for external use. These are usually containing a water-soluble base due to softer consistency and have lightweight in comparison to true ointments when applied to the skin, creams leave no visible evidence of their presence on the skin.
These are the semisolid emulsion with opaque appearance as contrasted with translucent ointments. These are consistency and rheological character depend on whether the cream is water in oil (w/o) or oil in water (o/w).
Types of Creams-
The creams are of two types-
–Aqueous creams– In aqueous creams, the emulsions are in oil in a water type (o/w). These are relatively non-greasy and further divided into three types depending on the type of emulsifying agent used for preparing them.
Anionic emulsifying wax creams are prepared by the fusion method. The wax and oily ingredients are melted together and cooled to about 600C. The water or aqueous solution is warmed to the same temperature and mixed with the oily mixture with constant stirring which is continued until cold.
Cationic emulsifying wax creams are made in the same way as anionic emulsifying wax creams. Cetostearyl alcohol and cetrimide are used to prepare creams.
Non-ionic emulsifying wax creams are prepared in the same way as anionic and cationic creams. These creams are prepared by using self-emulsifying monostearin, sorbitan ester, macrogol ester nonionic emulsifying wax, polysorbates, polyvinyl alcohols, and higher fatty alcohols.
–Oily creams– In oily creams, the emulsions are water in oil type (w/o). These creams are greasy. The oily creams are further divided into two types depending on the type of emulsifying agent used for preparing w/o emulsion.
Sterol creams are water in oil (w/o) type emulsions in which wool fat or wool alcohol is used as an emulsifying agent.
Soap creams are water in oil (w/o) emulsions in which the emulsifying agents used are triethanolamine soap, calcium soap or borax soap. Emulsions containing soaps of liquid fatty acids are made without heat.
Pastes that are semi-solid dosage form preparation intended for external application to the skin. These are generally very thick and stiff. These do not melt at ordinary temperature and thus forms a protective coating over the site of application. These are mainly used as antiseptic protectives or soothing dressings which are often spread on lint before being applied.
These are combines into three agents- oil, water, and powder. These are the ointments in which a powder is suspended. For powder base, they may be for anhydrous (liquid or soft paraffin) and for water-soluble (glycerol and mucilage) are used.
Poultices are soft, viscous met masses of solid substances that are applied to the skin for their fermentation action in order to provide relief from pain or reduce inflammation, or to act as a counter-irritant. These are also called cataplasms. These are used to prepare in ancient times to drain infectious material from the diseased tissues. Now today, these are considered to be outdated preparation and hardly prescribed by the physician or prepared by a pharmacist.
Heavy kaolin is commonly included in the formula for preparing poultice because these act as a carrier of heat. These are applied to the affected part after heating it in a dish with occasional stirring until the heat is tolerated on the back of the hand. The melted poultice is spread as a thick film on a dressing material and applied as hot as the patient can bear it to the affected area.
Jellies which are transparent or translucent non-greasy, a semisolid dosage form used for external application to the skin or mucous membrane. These are maybe prepared from natural gums, such as tragacanth, pectin, sodium alginates, or synthetic derivatives of natural substances, such as methylcellulose and sodium carboxymethyl cellulose. These are similar to mucilages in having jelly-like consistency.
Types of jellies-
There are three types of jellies are-
Medicated jellies– Medicated jellies are chiefly used on mucous membranes and skin for their spermicidal, local anesthetics, and antiseptics properties. It contains sufficient water. After evaporation of water, jellies provide local cooling effects and the residual film gives protection. For example- ephedrine sulfate jelly is used as a vasoconstrictor to arrest the bleeding of the nose. This containing phenylmercuric nitrate is used as a spermicidal contraceptive.
Lubricating jellies– Lubricating jellies are used for the lubrication of diagnostic equipment such as surgical gloves, cystoscopes, finger stalls, catheters, rectal thermometers, etc. These should be thin, transparent, and water-soluble. These should be sterile because they are used as lubricants for articles to be inserted into sterile regions of the body such as urinary bleeder, etc.
Miscellaneous jellies– Miscellaneous jellies are meant for-
–Patch testing– These are used as a vehicle for allergens that are applied to the skin to check sensitivity. When drying, the residual film is formed which helps to keep separate the patches and avoid confusing results.
Electro–cardiography– These are applied to the electrode to reduce the electrical resistance between the patient’s skin and the electrode. These contain sodium chloride, pumice powder, and glycerin. Sodium chloride is a good conductor of electricity where glycerin acts as a humectant.
Gels are the semi-solid dosage forms of at least two constituents, consisting of a condensed mass enclosing and interpenetrated by a liquid. These are transparent to opaque semisolids containing a high ratio of solvent to gelling agent merge or entangle to form a three-dimensional colloidal structure.
These are produced jelly-like consistency by the addition of a gelling agent. These are prepared for administration by various routes for eyes, nose, vaginal and rectum, etc. In the formulation of gels tragacanth, pectin, agar natural gums are used.
These are used to achieve optimal cutaneous and percutaneous drug delivery. These are having the property to avoid enzymatic activity and drug interaction with food and drinks. These are applied over the skin for slow and prolonged absorption.
Types of gels-
–Hydrogels are the network of polymers chain that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. These are highly absorbent which contain over 90% water, natural or synthetic polymeric networks.
These are also possessing a degree of flexibility that very similar to natural tissue, due to their significant water content. These are common including ingredients polyvinyl alcohol, sodium polyacrylate, acrylate polymers, and copolymers with an abundance of hydrophilic groups.
–Xerogels are an open network formed by the removal of all swelling agents from a gel. These are usually retained high porosity and enormous surface area, along with a very small pore size of 1-10nm.
–Organogels are the non-crystalline, non-glassy thermoreversible, or thermoplastic solid material composed of a liquid organic phase entrapped in a three-dimensionally cross-linked network.
The liquid for organogels is an organic solvent, mineral oil, or vegetable oils, etc.
Plasters are semisolid dosage forms in adhesive masses spread on a backing of paper, fabric, moleskin, or plastic for administration at the site. The adhesive materials are in rubber base or in synthetic resin. These are consisting of the protective liner, drug-containing layer, and backing layer.
These are applied to the skin to provide prolonged contact at the site. These are used to afford protection and mechanical support at the site. These help to bring the medication into close contact with the surface of the skin.
Types of plasters-
Adhesive plasters are also called sticking plaster. These are used for small injuries dressing not serious enough to require a full-size bandage. These are used to protect the cuts from friction, bacteria, damage, and dirt.
Sometimes these are having antiseptic properties. The additional function of adhesive is to hold the two cut ends of the skin together to make the healing process faster.
Medicated plasters are provided effect at the site of application. These can be cut in size to conform to the surface of the site that to be covered. Among the few plasters in use, today is salicylic acid plaster used on the toes for the removal of corns.
The horny or keratoid layers of skin are removed by the keratolytic action by salicylic acid. The concentration of salicylic acid in commercial corn plasters in the range of 10% to 40% is used.
Ingredients used for the preparation of semi-solid dosage form-
|Active pharmaceutical ingredients|
Bases – Bases are the most important ingredient which is used in the formulation of semisolid dosage forms. Ointments base do not merely act as the carriers of the medicaments, but these also control the extent of absorption of medicament incorporated in them.
Bases are inert, non-irritating and non-sensitizing, and compatible with skin pH and the drug. These are pharmaceutically elegant and possess good stability.
Types of bases-
Preservatives– Some bases, although, resist the microbial attack but because of their high water content, these are requiring an anti-microbial preservative. These are commonly used preservative which includes-
-Phenyl mercuric nitrate
Antioxidant– Oxygen is a highly reactive atom that is capable of becoming a part of potentially damaging molecules that commonly called free radicals. These free radicals are capable of attacking the healthy cells of the body, that are causing them to lose their structure and function. To prevent, an antioxidant is added are–
Gelling agents– These form a gel that dissolves in a liquid phase as a colloid mixture that forms a weakly cohesive internal structure. These are the organic hydrocolloids or hydrophilic inorganic substances that are- tragacanth, sodium alginate, pectin, gelatin, cellulose derivatives.
Permeation enhancers– In permeation enhancers the skin can act as a barrier. These actions with the introduction of various penetration enhancers, and penetration of the drug through the skin can be improved. For example- Oleic Acid.
Emulsifier– An emulsifier or emulgent is a substance that stabilizes an emulsion by increasing its kinetic stability. It must reduce surface tension for proper emulsification. These are preventing coalescence and have the ability to increase the viscosity at low concentrations.
Humectants– Humectant is hygroscopic substances which are used to increase the solubility of the active ingredient to elevate its skin penetration. These are often a molecule with several hydrophilic groups, where most often hydroxyl groups. These are also used to elevate the hydration of the skin. The examples are–
-Poly Ethylene glycol
Buffers– Buffers are added for various purposes such as compatibility with skin, drug solubility, and drug stability also. Buffers are influenced by the ionization of drugs. The example of buffers is-
Advantages of semi-solid dosage form-
-These are used externally
-These are the probability that can reduce the side effects.
-These are avoided by the first-pass gut and hepatic metabolism.
-These are having local action and Site-specific action of the drug on the affected area.
-These are convenient for unconscious patients or patients having difficulty with oral administration.
-These are suitable dosage forms for bitter drugs.
-These are more stable than liquid dosage forms.
Disadvantages of semi-solid dosage form-
-These do not have dosage accuracy.
-The base of the semi-solid dosage form can be easily oxidized.
– These may cause staining.
-These are bulky to handle.
-The application with a finger may cause contamination.
-These are physio-chemically less stable than solid dosage forms.
-These may cause irritation or allergy to some patients