PASTE

Differences between pastes and ointments;

(i)     Pastes generally contains a large amount (50%) of finely powdered solids. So they are often stiffer than ointments.

(ii)   When applied to the skin pastes adhere well, forming a thick coating protects and soothes inflamed and raw surfaces and minimizes the damage done by scratching in itchy conditions such as chronic eczema. it is comparatively easy to confine pastes to the diseased  areas whereas ointments, which are usually less viscous, tend to spread on to healthy skin, and this may result in sensitivity reactions if the preparations contain a powerful medicament such as dithranol.

(iii) Because of the powder contents pastes are porous; hence, perspiration can escape. Since the powders absorbs exudate, pastes with hydrocarbon base are less macerating than ointments with a similar base.

(iv) They are less greasy than ointments but since their efficacy depends on maintaining a thick surface layer they are far from attractive cosmetically.

(v)   Most of the pastes are unsuitable for treating scalp conditions because they are difficult to remove from the hair.

BASES OF PASTES:

1. Hydrocarbon base:

Soft paraffin and liquid paraffin are commonly used bases for the preparation of paste.

Name of the preparation	Active ingredients	Base	Use
1.      Compound Zinc Paste B.P. 2.      Compound Zinc & Salicylic acid Paste B.P. (Lassar’s Paste) 3.      Coal tar paste 4.      Dithranol paste compound 5.      Aluminium paste B.P.C.       (Baltimore Paste)	Zinc oxide Zinc oxide & Salicylic acid Coal tar Dithranol Aluminium oxide	Soft paraffin Soft paraffin Soft paraffin Soft paraffin Liquid paraffin	Eczema, psoriasis. Eczema, psoriasis. Eczema Ring worm or psoriasis Protectant

2. Water miscible base:

Name of the preparation	Base	Use
1.      Resorcinol & sulfur Paste B.P.C. 2.      Zinc & Coal tar Paste 3.      Magnesium sulfate paste B.P.C. (Morison’s paste) 4.      Titanium dioxide paste B.P.C.	Emulsifying ointment Emulsifying wax Magnesium sulfate -45% Phenol in glycerol Suspension of TiO2, ZnO, light kaolin and red Fe2O3 in glycerol + water.	Dandruff, and are easily removable from the hair. Eczema Used to treat boils, because of their powerful osmotic effect of the salt and the glycerol. Absorbs exudates from weeping skin conditions.

3. Water soluble bases

Water soluble bases are prepared from mixtures of high and low molecular weight polyethylene glycols (or macrogols).

Name of the preparation	Base	Use
1.      Water soluble dental pastes 2.      Triamcinolone Dental paste B.P.C.	Neomycin sulfate Triamcinolone acetonide in an adhesive paste (NaCMC, pectin, + gelatin)	Sterilizing infected root canal Anti-inflammatory

METHODS OF PREPARATION:

Like ointment, pastes are prepared by trituration and fusion methods. Trituration method is used when the base is liquid or semisolid.

Fusion method is used when the base is semisolid and/or solid in nature.

Preparation 1.

Name:              Compound Zinc Paste

Formula           Zinc oxide, finely sifted                      25 g

                        Starch, finely sifted                 25 g

                        White soft paraffin                  50 g

Type of preparation: Paste with semi-solid base prepared by fusion and trituration.

Procedure;

(a)    Zinc oxide and starch powder are passed through No. 180 sieve.

(b)   Soft paraffin is melted on a water bath.

(c)    The required amount of powder is taken in a warm mortar, triturated with little melted base until smooth. Gradually rest of the base is added and mixed until cold.

Preparation 2.

Name:              Zinc and Coal tar Paste B.P.C.

Formula:         Zinc oxide, finely sifted

                        Coal tar

                        Emulsifying wax

                        Starch

                        Yellow soft paraffin.

Type of preparation: Paste with semi-solid base prepared by fusion.

Procedure:

Method-I

(a)    Emulsifying wax is melted in a tared dish (70⁰C).

(b)   The coal tar is weighed in the dish. Stirred to mix.

Soft paraffin is melted in a separate dish (70⁰C) and about half is added to the tar-wax mixture; stirred well. Remainder is added; stirred again until homogeneous.

Allowed to cool at about (30⁰C) and zinc oxide (previously passed through 180 mesh) and starch, in small amount with constant stirring. Stirred until cold.

Method-II

Wax and paraffin melted together, mixed well and stirred until just setting. Powders are mixed on a slightly warm tile and the tar is incorporated. This method eliminates the risk of over heating.