Dosage Form:Classification Part 2

According to route of administration,the second type of dosage forms are Topical Dosage Forms.

Topical Dosage Forms

Topical Dosage forms are defined as the the medication which are meant to be applied on the surface of the body externally.

Topical semi-solid dosage forms are normally presented in the form of creams, gels, ointments, or pastes. They contain one or more active ingredients dissolved or uniformly dispersed in a suitable base and any suitable excipients such as emulsifiers, viscosity-increasing agents, antimicrobial agents, antioxidants, or stabilizing agents. Preparations susceptible to the growth of microorganisms should contain a suitable antimicrobial agent in an appropriate concentration unless the preparations themselves have adequate antimicrobial properties. Assurance must be provided through product development studies that such excipients do not adversely affect either the stability of the final product or the availability of the active ingredient(s) at the site of action; there must be no incompatibility between any of the components of the dosage form.

It may be necessary for a topical semi-solid dosage form to be sterile, for example, when it is intended for use on large open wounds or severely injured skin.

Topical dosage form are further classified in to semi-solid dosage form and solid dosage form.
Semi-solid dosage form include :

OINTMENTS
CREAMS
GELS
PASTE
POULTICE
PLASTERS

Solid dosage forms include :

DUSTING POWDERS
OTHERS

Starting with;

(1)

OINTMENTS

Ointments are homogeneous, semi-solid preparations intended for external application to the skin or mucous membranes. They are used as emollients or for the application of active ingredients to the skin for protective, therapeutic, or prophylactic purposes and where a degree of occlusion is desired.

Ointments are formulated using hydrophobic, hydrophilic, or water-emulsifying bases to provide preparations that are immiscible, miscible, or emulsifiable with skin secretions. They can also be derived from hydrocarbon (fatty), absorption, water-removable, or water-soluble bases.

Hydrophobic ointments-

Hydrophobic (lipophilic) ointments are usually anhydrous and can absorb only small amounts of water. Typical bases used for their formulation are water-insoluble hydrocarbons such as hard, soft, and liquid paraffin, vegetable oil, animal fats, waxes, synthetic glycerides, and polyalkylsiloxanes.

Water-emulsifying ointments-

Water-emulsifying ointments can absorb large amounts of water. They typically consist of a hydrophobic fatty base in which a w/o agent, such as wool fat, wool alcohols, sorbitan esters, monoglycerides, or fatty alcohols can be incorporated to render them hydrophilic. They may also be w/o emulsions that allow additional quantities of aqueous solutions to be incorporated. Such ointments are used especially when formulating aqueous liquids or solutions.

Hydrophilic ointments-

Hydrophilic ointment bases are miscible with water. The bases are usually mixtures of liquid and solid polyethylene glycols (macrogols).

(2)

Creams

Creams are 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 the solids in the internal phase. Creams are intended for application to the skin or certain mucous membranes for protective, therapeutic, or prophylactic purposes, especially where an occlusive effect is not necessary. The term "cream" is most frequently used to describe soft, cosmetically acceptable types of preparations.

Generally, o/w creams are prepared at an elevated temperature and then cooled down to room temperature in order for the internal phase to solidify. The semi-solid form of a w/o cream is attributable to the character of the external phase

Hydrophobic creams (w/o)-

Hydrophobic creams are usually anhydrous and absorb only small amounts of water. They contain w/o emulsifying agents such as wool fat, sorbitan esters, and monoglycerides.

Hydrophilic creams (o/w)-

Hydrophilic creams contain bases that are miscible with water. They also contain o/w emulsifying agents such as sodium or triethanolamine soaps, sulfated fatty alcohols, and polysorbates combined, if necessary, with w/o emulsifying agents. These creams are essentially miscible with skin secretions.

(3)

Gel and Paste

Gels are usually homogeneous, clear, semi-solid preparations consisting of a liquid phase within a three-dimensional polymeric matrix with physical or sometimes chemical cross-linkage by means of suitable gelling agents.

Gels are applied to the skin or certain mucous membranes for protective, therapeutic, or prophylactic purposes.

Hydrophobic gels-

Hydrophobic gel (oleogel) bases usually consist of liquid paraffin with polyethylene or fatty oils gelled with colloidal silica or aluminium or zinc soaps.

Hydrophilic gels-

Hydrophilic gel (hydrogel) bases usually consist of water, glycerol, or propylene glycol gelled with suitable agents such as tragacanth, starch, cellulose derivatives, carboxyvinyl polymers, and magnesium aluminium silicates.

(4)

Poultice

Poultices are viscous pasty preparation applied to hot skin to reduce inflammation or to act as counter irritant.The material possesses the properties of heat-retention and absorption;due to the latter,they draw infected fluid from the tissue when used for boils.

Kaolin poultice is well known example of poultice,consisting of around 50% and 40% of glycerin.The Kaolin-Glycerin mixture has the qualities of good heat retention and absorption.

In preparation of KAOLIN Poultice,heavy kaolin is first sifted and dried at 100℃ to remove moisture.It is then mixed with boric acid and gradually triturated with glycerin to form a smooth paste.The paste is heated up to 120℃ to prevent decomposition of glycerine.

(5)

Dusting Powders