Definition: Semi-solid dosage forms are dermatological preparations intended to apply externally on the skin to produce local or systemic effects e.g. ointments, creams, gels, and 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. Semisolids can adhere to the application surface for sufficiently long periods before they are washed off. This property helps prolong drug delivery at the application site. Novel semisolids are non-greasy since they are made up of water-washable bases. Hence, they cause less irritation to the skin and are superior to the conventional semisolid dosage form.
Ideal Properties of Semi-Solid Dosage Forms:
1. Physical Properties:
(a) They should have a smooth texture.
(b) They should be elegant.
(c) They should be non-dehydrating.
(d) They should be non-gritty.
(e) Semi-solid dosage forms possess non-greasy and non-staining property.
(f) They are non-hygroscopic.
2. Physiological Properties:
(a) They should be non-irritating.
(b) They should not alter skin functioning.
(c) They should be easily miscible with skin secretion.
(d) They should have a low sensitization effect.
3. Application Properties:
(a) They should be easily applicable with efficient drug release.
(b) They should possess high aqueous washability.
Types of Semi-solid dosage form:
Ointments: Ointments are semisolid preparations meant for external application to the skin or mucous membrane. They usually contain a medicament or medicaments dissolves, suspended, or emulsified in the base.
Creams: Creams are viscous emulsions of semisolid consistency intended for application to the skin or mucous membrane and o/w type and w/o type.
Pastes: Pastes are preparations that contain a large amount of finely powdered solids such as starch and zinc oxide. These are generally very thick and stiff.
Jellies: These are thin transparent or translucent, non-greasy preparations. They are similar to mucilages because they are prepared by using gums but they differ from mucilages in having jelly-like consistency.
Gels: These are jelly-like semisolid dispersions of a drug meant to be applied to the skin.
Suppositories: These are meant for insertion into the body cavities other than the mouth. They may be inserted into the rectum, vagina, or urethra.
Poultices: These are also known as cataplasms. They are soft viscous wet masses of solid substances.
Plasters: These are semi-solid masses applied to the skin to enable prolonged contact of the drug with the skin. or Substances intended for external application, made of such materials and consistency as to adhere to the skin and thereby attach as dressing.
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