DOSAGE FORMDosage forms are drug products in the form that they areavailable in the market (1) They are usually with an inactive components or excipients in aparticular way and configuration and together with the active ingredient formulatedinto a particular dose.
(1)TYPES OF DOSAGE FORMDepending on the method or route of administration, dosage forms come inseveral types. Types include the oral, ophthalmic, inhalation, parenteral, topical and suppository.These types can come or be manufactured in liquid, solid, gas and semisolid dosage forms. (1)(16) SEMI-SOLIDDOSAGE FORMSemisolidsconstitute a significant proportion of pharmaceutical dosage forms. They mostlyserve as a means for drugs to be delivered topically by way of the skin,cornea, nasal mucosa, vagina, buccal tissue, rectal tissue, urethral membrane,and external ear lining.
(17) Asemisolid dosage form has numerous advantages when it comes to easyapplication, rapid formulation, and ability to topically deliver a wide varietyof drug molecules. (17) (18)Semisolids are available as a wide range of dosage forms, each having uniquecharacteristics.Semisolid dosage forms are normally presented in the form ofcreams, gels, ointments, or pastes. (2)(18) They contain one or more active ingredients dissolved oruniformly dispersed in a suitable base and any suitable excipients such asemulsifiers, viscosity increasing agents, antimicrobial agents, antioxidants,or stabilizing agents. (2) (17) (18)It comprises of a body of product which is applied to skin or accessiblemucous membrane to alleviate or treat a pathological condition or otherprotection against harmful environmentSSPDF are required to be smooth in texture, elegant in appearance,non-dehydrating, non-gritty and greasy, non-staining, non-hygroscopic product,with a non-irritating effect on applied surface, good miscibility with surfacesecretion and do not alter the membrane function of surface. (19)Ointments, cream, pastes and gel products falls under the semi-solidpharmaceutical dosage form (19)Selecting an appropriatebase for semi-solid depends on a number of factors, the therapeutic effect tobe established, the nature of the active ingredient at the intended site ofaction, the desired shelf-life of the semi-solid and the supposed conditions inwhich the product will be exposed.
In many cases, a compromise has to be madein order to achieve the required stability. For example, drugs that hydrolyserapidly are more stable in hydrophobic bases than in water containing bases,even though they may be more effective in later. (20) The type of base requiredshould be considered and a non-irritating or bases capable of sensitizing theskin should be avoided. It must also not cause injury or delay healing.The base should neitherirritate nor sensitize the skin, nor should it delay wound healing. It shouldbe smooth, inert, odourless, physically and chemically stable, and compatiblewith both the skin and active ingredient(s) to be incorporated. It shouldnormally be of such a consistency that it spread and softens easily when stressis applied.
A wide range of rawmaterials is available for the preparation of a semisolid dosage form. Apartfrom the usual pharmaceutical ingredients such as preservatives, antioxidants,and solubilizers, the basic constituents of a semisolid dosage form are uniqueto its composition. The choice of suitable raw materials for a formulationdevelopment is made on the basis of the drug delivery requirements.
TYPESOF SEMI-SOLID DOSAGE FORMOintment: Ointmentsare homogenous, semi-solid preparations intended for external application tothe skin or mucous membrane. They are used as emollients or for the applicationof active ingredients to the skin for protective, therapeutic, or prophylacticpurpose and where a degree of occlusion is desired.Hydrophobicointments: Hydrophobic(lipophilic) ointments are usually anhydrous and can absorb only small amountsof water.
Typical bases used for their formulation are water-insolublehydrocarbons such as hard, soft and liquid paraffin, vegetable oil, animalfats, waxes, synthetic glycerides and polyalkylsiloxanes.Water-emulsifyingointments: Water-emulsifyingointments can absorb large amounts of water. They typically consist of ahydrophobic fatty base in which a w/o agent, such as wool fat, wool alcohols,sorbitan esters, mono glycerides, or fatty alcohols can be incorporated torender them hydrophilic. They may also be w/o emulsions that allow additionalquantities of aqueous solutions to be incorporated. Such ointments are usedespecially when formulating aqueous liquids or solutions.Hydrophilicointments: Hydrophilic ointmentbases are miscible with water. The bases are usually mixture of liquid and solid polyethyleneglycols (macrogols) 1.
Creams: Creamsare homogeneous, semi-solid preparations consisting of opaque emulsion systems.Their consistency and rheological properties depend on the type of emulsion,either water-in-oil (w/o) or oil-in –water (o/w), and on the nature of thesolids in the internal phase. Creams are intended for the application to theskin or certain mucous membranes for protective, therapeutic, or prophylacticpurposes, especially where an occlusive effect is not necessary.Gels: Gels are usually homogeneous, clear,semi-solid preparations consisting of a liquid phase within a three-dimensionalpolymeric matrix with physical or sometimes chemical cross-linkage by means ofsuitable gelling agents.Hydrophobic gels: Hydrophobicgel (oleogel) bases usually consist of liquid paraffin with polyethylene orfatty oils gelled with colloidal silica or aluminium or zinc soaps.Hydrophilic gels: Hydrophilicgels (hydrogel) bases usually consist of water, glycerol, or propylene glycolgelled with suitable agents such as tragacanth, starch, cellulose derivatives,carboxyvinyl polymers, and magnesium aluminium silicates.Pastes: Pastesare homogeneous, semi-solid preparations containing high concentrations ofinsoluble powdered substances (usually not less than 20%) dispersed in asuitable base. The pastes are usually less greasy, more absorptive, and stifferin consistency than ointments because of the large quantity of powderedingredients present.
Some pastes consist of a single phase, such as hydratedpectin, and others consist of a thick, rigid material that does not flow atbody temperature. The pastes should adhere well to the skin. In many cases theyform a protective film that controls the evaporation of water.Poultices: A poultice is an ancient form of topicalmedication also known as a cataplasma. It is a soft mass of vegetableconstituents or clay, usually heated before application. Kaolin poultice BP isprepared by mixing and heating dried, heavy kaolin and boric acid withglycerin. After cooling, the aromatic substances are incorporated withstirring. The product is spread on a dressing and applied hot to the skin.
Advantage of semi-solid dosageform:It is used externallyDrastic reduction in the side effect probabilityLocal actionFirst pass gut and hepatic metabolism is avoided.Patient compliance is increased, the drugtermination is problematic cases is facilitated as compared with other routesof drug administration.Disadvantages of semi-soliddosage form:There is no dosage accuracy in this type of dosageformThe base which is used in the semi-solid dosageform can be easily oxidized.If we go out after using semi-solid dosage formproblems can occur.
In general, semisoliddosage forms are complex formulations having complex structural elements whichconsist of Excipients. Excipients An excipient is a substance formulated alongsidethe active ingredient in preparing a pharmaceutical product.When it comes to drugs, most of the attention goes to the activepharmaceutical ingredient. But typically the vast majority of what is in atablet, capsule, semi-solid or liquid is not the active ingredient.
A drug isformulated with many other compounds called excipients which play an essentialrole in delivering the active ingredient to the patient.Excipients are intended to impact specific property to the product.Excipients are usually pharmacologically inactive and of reasonablecompatibility with final product and product container closure system. Types of excipientsAnti-adherentsreduce the adhesion between the powder or granules and the punch surface thus preventingsticking of the tablet to punches by offering a non-sticky surface. Theyare also used to help protect drugs from sticking to each other and the packageor container. The most commonly used is magnesium stearate.Binders