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Wednesday, April 1, 2015

Magmas



Magmas are aqueous suspensions of insoluble inorganic drugs. They differ from gels in that the suspended particles are larger. Magmas are thick and viscous, and so there is no necessity of suspending agents except for Dihydroxyaluminum Aminoacetate Magma which contains suspending agents in addition to suitable preservatives and flavoring agents.


Magmas may be prepared by:
(1) Simple Hydration
(2)  Chemical Reactions


Examples:

(a) Bentonite Magma – It is prepared by simple hydration – sprinkling the parent substance on hot purified water.

(b) Magnesia Magma – It is prepared by hydration of calcined magnesia or by chemical reaction between sodium hydroxide and magnesium sulfate.

(c) Bismuth Magma – It is prepared by reacting bismuth nitrate with ammonium carbonate not by the process of simple solution with mixing but by previously reacting bismuth subnitrate with nitric acid and official ammonium carbonate with diluted ammonia solution and then mixing the resulting two solutions.

If the insoluble substance is freshly precipitated by mixing hot, dilute solutions, there is only slight sedimentation on standing. This characteristic of magmas is sometimes enhanced by passing the product through a colloid mill.

A great majority of magmas are intended for oral use. All magmas must bear a “Shake Well” label. Freezing should be avoided.


Preparations of Magmas


(1) Bentonite Magma, USP

Other Name: Magma Bentoniti

Formula:
Bentonite                           50g
Purified water,  q.s.       ________
           To make                1000ml

Preparation:
To make 800ml of heated purified water, sprinkle upon it the bentonite, in portions allowing each portion to become thoroughly wetted without stirring. Allow to stand with occasional stirring for 24 hours. Stir until a uniform magma is obtained. Add sufficient quantity of purified water to make 1000ml and mix.

It may also be prepared by mechanical means, such as by the use of a blender. Place about 500ml of purified water in the blender, and while the machine is running, add the bentonite. Add purified water to make up to 1000ml or up to the operating capacity of the blender. Blend the mixture for 5 to 10 minutes; add purified water to make 1000ml and mix.

Use: As suspending agent for insoluble medicaments.


(2) Bismuth Magma, NF

Other Names: Magma Bismuthi; Milk of Bismuth; Bismuth Cream.

Formula:
Bismuth Subnitrate                     80g
Nitric Acid                                120ml
Ammonium Carbonate               10g
Strong Ammonium Solution
Purified Water, each q.s.        _______
               To make                    1000ml

Preparation:
Add the bismuth subnitrate to 60ml of purified water mixed with 60ml of nitric acid in a suitable container, agitate and warm gently until solution is effected. Pour this solution with constant stirring, into 5000ml of purified water containing 60ml of nitric acid. Dilute 160ml of strong ammonia solution with 4300ml of purified water in a glazed or glass vessel of at least 12,000ml capacity. Dissolve the ammonium carbonate in this solution. Pour the bismuth solution quickly into it with constant stirring. If the mixture is not distinctly alkaline add sufficient diluted ammonia solution to make it so and allow it to stand until the precipitate has settled. Pour or siphon off the supernatant liquid and wash the precipitate twice with purified water by decantation. Transfer the magma to a strainer of close texture (to provide continuous washing with purified water) the outlet being elevated to prevent the surface of the magma from becoming dry. Allow the operation to proceed until the washings cease to yield a pink color with phenolphthalein test solution. Drain the moist magma, transfer it to a graduated vessel, add sufficient quantity of purified water to make the product measure 1000ml and mix thoroughly.

The above method may be varied provided the product meets the requirements of the National Formulary.

Uses: Astringent, adsorbent and protective in the treatment of diarrheas and intestinal inflammation and ulceration.


(3) Milk of Magnesia, USP, BP

Other Names: Magma Magnesiae; Magnesium Hydroxide Mixture; Cream of Magnesia; Magnesia Magma USP XVI.

Definition: It is a suspension of magnesium hydroxide containing 7 – 8.5% of Mg(OH)2.

No Formula is given by the present USP as there are various satisfactory methods of preparation and any one of these may be used if the finished product conforms to the official specification.

Former Formula and Preparation:

Formula:
Magnesium Sulfate        300g
Sodium Hydroxide         100g
Purified Water,  q.s.


Preparation:
Dissolve the magnesium in sufficient quantity of purified water to make 650ml in a vessel of about 500ml capacity and heat to boiling. Dissolve the sodium hydroxide in sufficient quantity of purified water to make 1000ml. Add this slowly to the boiling solution of magnesium sulfate and continue the boiling for 30 minutes. Transfer the mixture to a cylindrical container of not less than 5000ml capacity and fill with hot purified water. Allow to stand until the precipitate subsides and remove the supernatant liquid. Wash repeatedly with hot purified water until all the sulfates have been practically eliminated as shown by testing the supernatant liquid with Barium Chloride T.S. Concentrate the mixture by evaporation until it contains not less than 7% of magnesium hydroxide.

Uses: Non-systemic gastric antacid and mild cathartic. When use routinely as antacid, the cathartic effect may be minimized by the occasional used of calcium carbonate.

Dose: 5 – 30ml usual antacid, 5ml four times a day.

Note: Purified water is used in the precipitation because the slightest trace of iron will cause discoloration. If the water available is free from iron and otherwise suitable, or if it has been heated to boiling with powdered magnesium carbonate (5 g in each 1000ml) and then filtered, purified water will not be necessary.

Cork stoppers should be protected by dipping them in melted paraffin otherwise the Milk darkens due to the action of the tannin in the cork. The product should be protected from freezing, as this alters the colloidal gel, and therw will be a formation of more dense precipitate and a clear stratum will separate on top.
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