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.
