Pharmaceutical semisolids are medicinal topicals intended for surface application either on the skin or mucous membrane.They include Ointments, Pastes, Creams, Emulsions, Gels & Rigid Foams. Their common property is to cling to the surface of their application for reasonable duration before they are washed or worn off. The adhesion is due to their plastic Rheological behavior.
Ointments are Semisolid preparations intended for external application to the skin or mucous membrane. Ointments contain medicament or a mixture of medicaments usually dissolved or dispersed in a suitable base.The type of ointment base used as a vehicle for drug is selected for optimum delivery of the drug & also to contribute emolliency or other quasi-medicinal qualities.
The USP recognizes four general classes of ointments:
1. Hydrocarbon Bases
2. Absorption Bases
3. Water Removable Bases
4. Water-Soluble Bases
Hydrocarbon Bases: e.g. white petrolatum, white ointment
Also referred to as oleaginous bases, hydrocarbon bases are occlusive & emollient in nature.They are non-water washable, hydrophobic & greasy,thus increase skin hydration by reducing the rate of loss of surface moisture.
Hydrocarbon bases are usually petrolatum per se or petrolatum modified by waxes or liquid petrolatum to change viscosity charcteristics.Petrolatum has a high degree of compatibility with a variety of medicaments and provide optimum stability such as antibiotics.
Absorption Bases: e.g. Lanolin, Cold cream
Absorption bases are hydrophilic, anhydrous materials that have the ability to absorb additional water.They may be anhydrous or W/O emulsions.They are emollient & occlusive as well.
Water-Removable Bases: e.g. Hydrophilic ointments
They are the most commonly used type of bases being water washable & miscible.These bases contain O/W emulsifiers which may be anionic, cationic or non-ionic in nature.
Water-Soluble Bases: e.g. Polyethylene glycol ointment
These are water miscible bases ,developed from polyethylene glycols. They are non-occlusive & non-greasy which are easily removed by washing.They mix readily with the skin secretions.
Preparation of ointments
Ointment preparation and manufacture depends upon the type of vehicle and the quantity to be prepared. The objective is the same I.e. to disperse a finely subdivided or dissolved drug throughout the vehicle.Normally the drug material is finely powdered before being dispersed.
Pilot-plant or small-scale production equipment is essential in developing a manufacturing procedure for a production-size batch.Mixing and stirring operations are critical in ointment production . In laboratory mixing, aeration can easily be prevented and also there is good maneuverability and control of the mixing action.These problems occur in the large scale industry manufacturing if semisolids where high speed agitation can cause aeration of the product n slowing the speed may not provide a satisfactory dosage form.
Methods & Machines used
Incorporation by Levigation
Small quantities such as 1 to several oz. Can be prepared by using spatula and ointment tile.The finely powdered drug is levigated thoroughly with a small quantity of base to form a concentrate.this concentrate is diluted geometrically with the remainder of the base.If the medicament is water soluble it is first dissolved in water & then incorporated into the base. But large quantities cannot be prepared by employing ointment tile & spatula. Mechanical mixers are used in large scale production of ointments which include Hobart mixers, Pony mixers & other types.
-The drug substance is finely divided.
-It is then added slowly or sifted into the base/vehicle which is present in a rotating mixer.
-Ointment is mixed until it reaches uniformity.
-The finished product may then be processed through a roller mill to ensure complete dispersion & reduce any aggregates.
The above mentioned procedure may be modified by preparing and milling a concentrate of the drug in a portion of the base.This concentrate is then dispersed in the balance of the vehicle, using a mixer of desirable size.Occasionally the base may be melted for easier handling and dispersion.the base us slowly cooled and continuous agitation is done to maintain dispersion.
Hobart Mixer For Pharmaceutical Ointments
Pony mixer for Pharmaceutical Ointments
Triple Roller Mill For Pharmaceutical Ointments
Packaging and Labeling
Ointments are either packed in ointment jars or collapsible metal or plastic tubes of appropriate size.
usually available in a size of 50-500 g. Straight sided screw-cap jars of glass or plastic are available. Clear amber or opaque glass is used as well as white opaque plastic,usually high density polyethylene.tops are usually metal or plastic. Inner liners of paper or plastic are laminated or disc-glued to ensure dust and air-tight enclosure.
Ointments are either mechanically or hand-filled to somewhat a little less capacity to avoid contact with the cap and cap-liner.
Tubes used are made up of aluminum ,tin or plastic (polyethylene, polypropylene).They have obvious advantage over jars as the use of finger is minimized and contact with dust light and air is limited.
A number of factors must be considered while selecting the appropriate material for ointment tube. Metal tubes present a possibility of metal-ion catalyzed instability while plastic tubes become stained by migration of color from the dosage form into the plastic side walls of the tube.The suitability of ointment containers should be verified by adequate testing prior to use.
In industries, ointment filling is accomplished by using automatic equipment that air cleans the tubes ,fills, folds and crimps the end in one continuous operation.Plastic tubes are being more frequently used in industries. They are handled much like metal tubes except for the end step which involves heat sealing instead of folding the end.
Labeling of ointment containers
It is good practice to dispense the tube in a vial or hinged paste-box of proper size.It will not only carry the tube but also serve to carry the label.In industries labeling may be silk screened onto the plastic surfaces.Expiation dates and code lot numbers may be stamped on as a part of the tube-crimping procedure.