Ointments are semisolid preparations intended for external application to the skin and mucus membranes. These are highly viscous liquids prepared for ease of application or extent of application such as local systemic effect.

Medicated topical formulations contain medicinal substances suspended in ointment or emulsion bases that may be classified as creams, gels, lotions, foam, paste and so on. The official definition of ointment in its present form was introduced in the USP XV in 1955, which broadly includes ‘petrolatum’, i.e. oleaginous bases; ‘emulsions bases’ (either water in oil or oil in water); and water-soluble bases known as ‘absorption bases’.

The properties of oleaginous and emulsion bases like creams and lotions vary, since each formulation is designed for specific pharmaceutical activity like antifungal, analgesic, moisturizing, hemostasis and other medicinal properties.

The USP classifies ointments into four general classes based on the property of ‘ointment base’ used to prepare semisolid solution. Some pharmacopeia also includes a fifth class of ointment. These are
(1)    Hydrocarbon bases (Oleaginous bases): This class includes white petrolatum, emollient, occlusive, non water-washable, hydrophobic and greasy solutions.
(2)    Absorption bases (Anhydrous base): This is a sub-class of oleaginous bases which includes hydrophilic petrolatum, emollient, occlusive, anhydrous and greasy bases.
(3)    Emulsion base (W/O type): This class includes lanolin, soap, cold cream, emollient, occlusive and greasy base, some absorb additional water.
(4)    Emulsion base (O/W type): This is second class of emulsion that are hydrophilic bases, water-washable, non-occlusive, non-greasy, which can be diluted with water.
(5)    Water-soluble bases: These contain hydrophilic solutes concentrated in water like polyethylene glycol (PEG), mucilage, usually anhydrous, lipid-free, water-soluble and washable bases.

Preparation of ointments has two major objectives – type of base vehicle (as discussed) and the bulk of quantity to be prepared. The principle objective of preparation is dispersion of base vehicle uniformly throughout with drug substance(s) finely dispersed or suspended such that they are easily absorbed in vehicle base.

The usual method of addition of the powdered drug material is to dissolve the medicinal substance in little quantity of base to form a concentrate and then dilute freshly prepared viscous liquid by addition of more base, and gentle mixing. This gives uniformly dispersed solute in the final ointment formulation.

Medicated creams and lotions are prepared by means of a two-phase heat system. The oil-phase ingredients and water-phase ingredients are prepared separately, followed by mixing in separate vessel. Mixing depends upon type of w/o or o/w emulsion. Safety of ointment formulation must be incorporated during manufacturing steps such that production and packaging steps are sterile and properly validated according to regulatory protocols.

Entry of toxins during production or packaging ointments may cause allergic reactions and skin inflammations. Allergic reactions may also result from lack of proper preservative in specific base component but this phenomenon is undermined from packaging point of view. The important aspects of safety of formulation that arise from packaging is the ease of application and dispensing of formulation while use. The packaging material and design must ensure safety from unwanted reactions, prolonged storage under optimal conditions, leak-proof design, ease of dispensing required quantity, and convenience of handling.  

Packaging and labelling of ointments
The principle aim of packaging is to provide a container that contains the product free from toxic chemical environment of moisture, dust, microbial contamination and unwanted reaction. Special packaging is accomplished through air-tight containers, special caps and seals, tins and cans that ensure freshness, sterility, cleanliness and prolonged life. Biological substances are usually inert to glass and plastic material therefore majority of packaging material includes COC (cyclic olefin co-polymers), different grades of thermoplastic and thermosetting plastics and glass containers. Some oleaginous hydrocarbon or other anhydrous formulations can be filled in composite materials prepared from aluminum, tin, cellulose and thermoplastic plastics.

Special packing features add convenience for use, reuse, opening, closing, and ease of disposal of packet. This is accomplished with the help of special designs for nozzles, lids, caps, corks, seals, stoppers, clamps, and pads. Packets can be prepared for dispensing single serving or bulk commodity but this is market regulated and design oriented rather subjected to choice of material for packaging. A barrier can be put in packaging where miscible substances are needed to supply or to ensure protection and sterility of each product during transport. Packaging is accomplished with the help of packaging and filling machines installed in the production line, which includes counting, weighing, forming and filling, bottling and sealing machines.

Jars, plastic tubes and small bottles of convenient size are usual packaging designs that contain ointments and thick emulsions like cream, gel and paste. Ointment jars and tubes can be made available from one-half ounces (12 grams) to 16-ounces (500 grams). Larger quantities are packed in bottles of appropriate size. A jar is a rigid cylindrical or spherical container with a wide mouth (opening). Jars can be made of glass, ceramic or plastic depending upon type of material handling, food, cosmetics or viscous chemical. Lid of an ointment jar can be straight sided screw-cap or simple cap with lock seal. Glass or plastic jars can be transparent, amber or opaque and available in wide variety of colours.

Metal or composition plastic tips are available with a variety of inner liners to assure a hermitical seal or dust-and air-tight closure. Lid liners are usually paper of plastic laminates or discs glued or otherwise fitted to the closure. Pourable liquids are easily packed in a bottle whereas jars are convenient for handling small to medium load quantity of sticky materials or thick materials having semi-solid consistency. Jars can be easily cleaned, sterilized, reused and recycled. Jars are often recycled according to the SPI recycling code for the material.

Ointments jars can be easily filled mechanically to somewhat less than capacity to minimize contact between the ointment and the cap or cap-liner. Ointment jars can be hand-filled by the pharmacists. This can be accomplished quite readily by skillful use of a flexible spatula. The spatula is forced across the ointment jar while depression that is aesthetically acceptable. Much of the same result can be accomplished by depressing the spatula into the center of the filled jar and gradually rotating the jar against the stationary spatula. A closure applied to the mouth of a jar can be a screw cap, lug cap, cork stopper, or other suitable means.

Ointment tube is a squeezable container made of tin, aluminum or plastic materials like polythene, polypropylene and other flexible heat-sealable plastics. Ointment tubes have an advantage over jars that product always remains isolated from external environment of dust, light and air. The use of fingers is minimized and precise amount of product can be dispensed for single use. Tube is ideal for oleaginous ointments and emulsions like toothpaste but not suitable for sticky formulations that require scrapping or reduce the actual amount of product dispensed from the container.

Depending on the expected shelf life, a number of factors should be considered in selecting an ointment tube, which include instability or incompatibility of active ingredient with metal-ion catalysis, leaching of color of ointment in plastic, presence or absence of internal tube linings (epoxy coatings), and type of nozzle for dispensing the product. A cylindrical tube is a hollow piece with round or oval profile, one end of the tube body is given nozzle shape and that can be closed by different caps while the other end is sealed. Prescription ointments can be conveniently filled in tubes and quantity can be prepared in bulk as compared to jars that are normally used for limited quantity of material.

A typical procedure for material insertion into tube is through compression filling machine or roller paper containing ointment. The ointment tube selected should be of adequate capacity and dimensions (length, diameter). Ointment tube sealing folds can be easily made by folding the tube over itself using a spatula blade. This flattens the tube and serves as folding point, which can be thermo-sealed. Alternatively, ointment tube clips can be fixed over the tube ends and clamped in place using pliers or a small vise.

The sole purpose of folding and clamping is to prevent leakage when routine-use pressure is applied. The fold dimensions are inexact; however, the individual folds on a one-ounce tube (12 grams) are approximately 1/8 to 3/16 inch. On larger scale, ointment-tube filling is accomplished using automatic equipment, which air cleans the tubes, fills, folds and crimps the end in one continuous operation. Some equipment stamp date of expiry and batch number onto the crimped surface. Plastic tubes are being used with increasing frequency for large scale manufacturing operations. From filling standpoint plastic tubes are handled much like metal tubes.

Labelling of jars and tubes is a minor difficulty unless compounded by unsightliness characteristic of ointment tubes during use. As a general rule label should be attached to itself i.e. it should completely encircle the tube or jar or lid of jar. In case of tube it should be affixed close to the neck end. Given the usual handling of ointment tubes by the patient, it is a good practice to dispense the tube in a hinged pasteboard box of convenient size.

The paperboard or corrugated box serves to hold and protect the ointment tube as well as carries the label. Box is identified with an inked-on prescription number so that both tubes and box are identified. On manufacturing scale tubes and jars are labeled in variety of ways. Proper labels may be used, labeling may be silk-screened onto plastic surfaces with details of manufacturer marketing company and other necessary batch details and barcodes.