- Semi Solid Dosage Forms
- Semi solid bases
- Semi solid requirements
- Semi solid Selection
Semi-solid dosage forms
• Semi solid dosage form contains the active drug ingredient and non-drugs excipients comprising the vehicle or formulation matrix.
• Example of semi solid dosage forms is ointment, pastes, cream, emulsion, gel & rigid foams.
• Their common property is ability to cling to the surface of application for reasonable time before being washed or worn off
• Their plastic theological behavior, allow them to retain their shape as well as to cling as a film until acted upon by an outside force causing deformation and flow.
• Their formulation is optimized for exhibiting the relevant bio pharmaceutical and pharmacokinetic characteristics of drugs.
• Most topical formulation are left open to the air after application but transdermal delivery systems are self contained closed system.
• Ointment Semi solid dosage forms :- Ointment are semi solid preparation with or without medicinal substance intended for external application to the skin or mucous membrane.
• These are used for emolliency or other quasi medicinal benefits.
• The ointment bases are used as vehicle to transfer drug into skin.
• Pastes :- are dispersion of high concentration of insoluble powdered substances (20 to 50% ) in a fatty or aqueous base.
• The fatty bases are less greasy as well as stiffer in consistency than ointment because of the large amount of powdered material present.
• These pastes adhere well to the skin and are of benefit in the treatment of chronic or lichenified lesions.
• Pastes provide a protective layer and when covered with suitable dressing prevent excoriation of the patient skin by scratching.
• Jellies :- are water soluble bases prepared from natural gums (such as tragacanth, pectin, alginates and boro glycerin ) or synthetic derivation of natural substance ( such as methyl cellulose and sodium carboxy methyl cellulose)
• Gels :- are usually clear transparent semi solid dosage forms containing the solubilized active substance e.g. gels formed with cellulose such as hydroxy propyl cellulose and hydroxy propyl methu cellulose.
• The number of raw material available for used in each route of administration are as follows
Skin>oral>parenteral
I. Factor influencing penetrations of drugs
• Factor associated with skin :-
A. Hydration of the horny layer :- increase hydration of horny layer is increase penetrations of drug.
B. Thickness of the horny layer :- horny layer thickness is increasing its decrease drug penetrations.
C. Other conditions like age, disease, injury etc. are also affected.
• Factor associated with the medicament :-
A. Solubility of the drug :- lipid soluble drug are easily penetrations.
B. Dissociation constants ( pKa) :- if the pKa value is increasing drug penetrations is decrease.
C. Particle size :- particle size is decrease it is increasing penetrations of molecules.
D. Crystal structure :- metastable form are rapidly penetrated.
• Factor associated with vehicle :-
A. Alterations of skin permeability :- organic solvent are increasing hydration of penetrations.
B. Penetrations of the epidermis :- Bases miscible with the sebum penetrate into the region of the skin in which sebum is found.
C. Hydration of stratum corneum :- An occlusive layer reduce evaporation of water from skin. Increasing hydration of the horny layer and therefore promotes penetration of medicament.
D. Contact with body surface :- sticky bases such as soft paraffin, paraffin ointment B.P.C, simple ointment B.P. etc. Adheres well to the skin but are difficult to apply evenly and remove completely.
• Semi solid bases :-
• The ointment base is the substance or part of an ointment preparation which serves as carrier or vehicle for the medicament.
• Ideal requirements of semi solid bases :-
1. Physical properties :-
• Smooth texture
• Elegant in appearance
• Non dehydrating
• Non gritty
• Non greasy and Non staining
• Non hygroscopic
2. Physiological properties :-
• Non irritating
• Do not alter membrane
• Miscible with skin secretion
• Have low sensitization index
3. Application properties :-
• Easily applicable with sufficient drug release
• Highly aqueous wash ability.
Selection of semi solid bases :-
1. Desired release rate of the drug substance from the ointment base.
2. Rate and extent of topical or percutaneous drug absorption.
3. Desirability of occlusion of moisture from skin.
4. Stability of the drug in the ointment base.
5. Effect of drug on the consistency of base.
6. Easy removal of base on washing.
7. Characteristics of the surface to which it is applied.
.png)
