Topical Dosage Forms—Semisolids

Conventional Topical Dosage Forms (Semisolids) includes

1. Ointments
2. Creams
3. Jellies
4. Pastes
5. Others: Poultices (Cataplasms), Powders, Dressings, Plasters, nails etc

Ointments

Ointments as semisolid preparations intended for external application to the skin or mucous membranes for protection (calamine, ZnO, TiO2, Silicones) or emollient effect.

In an ointment base, Medicament is dissolved, suspended or emulsified.

Types of ointments:

1. According to penetration

• Epidermic ointment: These ointments are intended to produce their action on the surface of the skin and produce local effect,they are not absorbed. • They acts as protectives, antiseptics and parasiticides.
• Endodermic ointment: These ointments are intended to release the medicaments that penetrate into the skin. They are partially absorbed and acts as emollients, stimulants and local irritants.
• Diadermic ointment: These ointments are intended to release the medicaments that pass through the skin and produce systemic effects (absorb & produce systemic effect)

2. According to therapeutic use:

Antibiotic, Antifungal, Anti-inflammatory, Anti-pruritic, Counter irritant, keratolytic ointment etc

3. Type of ointments

1. Water-soluble ointment
2. Water-insoluble ointment

Types of ointment base:

The base should not produce irritation or sensitisation of the skin, nor should it retard wound healing; it should be smooth, inert, odourless or almost odourless, physically and chemically stable and compatible with the skin and with incorporated medicaments. .Four general classes of ointment bases:

Ointments may contain suitable auxiliary substances such as antioxidants, stabilisers, thickeners and emulsifiers and, when the base might support the growth of microbial contaminants, suitable antimicrobial preservatives.

1.   Hydrocarbon (Oleaginous) Bases

• Liquid petrolatum gelled by the addition of polyethylene.
• Hydrocarbon bases, being occlusive, increase skin hydration by re ducing the rate of loss of surface  water.  Bases  of  this  kind  may  be  used  solely  for  such  a  skin -moisturizing  or emollient effect. Skin hydration, on the othe r hand, may increase drug activity.
• Petrolatum used as an ointment base has a high degree of compatibility with a variety of medicaments.
• Vegetable fixed oils or animal fats. Bases of this type include lard, benzoinated lard, olive oil, cottonseed oil, and ot her oils. Such bases are emollient but generally requi re addition of antioxidants and othe r preservatives. Not used now.
• Gelled (by polyethylene) mineral oil vehicle (Plastibase)
• Disadvantage –
  • Greasiness. The greasy or oily material may stain clothing and i s difficult to remove.
  • Greasiness also interfere with skin function (sweat&heat)
• Stability or drug activity might be superior in a hydrocarbon stability or drug activity might be superior in a hydrocarbon base & percutane ous absorption may be superi or when using a hydrocarbon base; but  patient acceptability is diminished because of the greasy nature of the base

2.   Absorption Bases

Absorption bases are hydrophilic, anhydrous materials/substances or hydrous bases that have the ability to absorb additional water.

(i) Anhydrous bases, which absorb water to become water-in-oil (W/O) emulsions;

• Hydrophilic petrolatum USP is an anhydrous absorption base . Its W/O emulsifying property is conferred by the inclusion of cholesterol.
• Eg. Wool fat (anhydroud lanolin), absorbed water 50 % of its wt (obtained wool of sheep)

(ii) Hydrous base are W/O emulsions, which have the ability to absorb additional water

Eg hydrous wool fat(lanolin) insoluble in water -30% water; Bee wax (white and yellow)- honeycomb of bee wax

Absorption bases  impart excellent emolliency and a degree of occlusiveness on application

3.   Water–Removable (Water-Washable) Bases or emulsion base (O/W emulsion bases)

• most commonly used type of ointment base (creams are 0/w emulsion)
• Emulsion bases are washable and are removed easily from skin or clothing. Emulsion bases can be diluted with water
• Cream like consistency
• Prepared from emulsifying wax, white soft paraffin & liquid paraffin

Vanishing cream is an o/w emulsion that contains a large percentage of water as well as a humectant (e.g., sorbitol, glycerin, or propylene glycol) that retards the surface evaporation of water.

4.   Water–Soluble Bases

• Water-soluble bases are the polyethylene glycols (PEGs -carbowaxes)
• PEGs are relatively inert, nonvolatile, water-soluble or wate r-miscible liquids
• Polyethylene  glycol   400  is   a  liquid  superficially  similar  to  propylene  glycol,  while polyethylene glycol 6000 is a waxy solid.
• Tragacanth, gelatin, cellolose derivatives etc used as water soluble base
• Water solubility of the polyethylene glycol bases may be attractive, but the glycol(s) may be irritating to traumatize d tissue

Praparation of ointment

Ointment preparation or manufacture depends on the type of vehicle and the quantity to be prepared. The main objective is to disperse/incorporation the drug uniformly throughout the base.

1.   Incorporation of the drug by Trituration:

The components of the ointment are mixed together by various means until a uniform preparation has been attained. – On a small scale, the pharmacist may mix the components of an ointment in a mortar with a pestle, or a spatula and an ointment slab may be used to rub the ingredients together.

2.   Fusion:

Highest MP –should be melted first to avoid overheating.

By the fusion method, all or some of the components of an ointment are combined by being melted together and cooled with constant stirring until congealed. Those components not melted are generally added to the congealing mixture as it is being cooled and stirred.  Naturally, heat-labile substances and any volatile components are added last when the temperature of the mixture is low enough not to cause decomposition of volatilization of the components.

3.   Chemical reaction:- iodine ointment

4.   Emulsification: heat base @70 degrees centigrade

5. Preparation of semi-solid/ointments at Industrial

• Triple roller mill
• Colloidal mill (mixing + size reduction both)

• Uses: Ointments are mainly used as propective or emollient action.

Poultices (Cataplasms)

• Poultices, or cataplasms, represent one of the most ancient classes of pharmaceutical preparations. A poultice is a soft, moist mass of meal, herbs, seed, etc., usually applied hot in a cloth. The consistency is gruel-like, which is probably the origin of the word poultice.
• Cataplasms were intended to localize infectious material in the body or to act as counterirritants. The materials tended to be absorptive, which, together with heat, accounts for their popularity.
• Eg. Kaolin Poultice

Evalaution of Ointments

1. Uniformity of weight/ Content uniformity test
2. Penetration
3. Rate of release of Drug
4. Absorption of medicament into blood stream
5. Irritant effect
6. Spreadability