Gels are suspensions, in a
water medium, of insoluble drugs in hydrated form wherein the particle size
approaches or attains colloidal dimensions. In addition to the active ingredients,
gels may contain peppermint oil, glycerin, sorbitol, sucrose, saccharin and
various preservatives. This list of ingredients is not all-inclusive but is
based on information found in the monographs of official preparations.
Generally, if gels are left undisturbed for some time, they may become
semisolid or gelatinous, with some small amounts of water separating on
standing.
Preparations of Gels
1. Aluminum Hydroxide Gel, USP, BP
Other Names: Gelatum Alumini
Hydroxidi; Colloidal Aluminum Hydroxide; Alugel; Amphogel; Ce-lu-gel; Cremalin;
Fluagel; Hydroxal; Vanogel
Formula:
Ammonium Alum 800g
Sodium Carbonate 1000g
Purified Water, q.s. _________
To Make 2000ml
Preparation:
Dissolve the Sodium Carbonate
in 4000ml of hot water and filter. Dissolve ammonium alum in 2000ml of hot
water and filter in the carbonate solution with constant stirring. Then add
4000ml of hot water and remove all gas. Dilute to 80, 000ml of cold water.
Collect and wash the precipitate and suspend it in 2000ml of purified water
flavored with 0.01% of peppermint oil and preserve with 0.1% of sodium
benzoate. Homogenize the resulting gel.
The principal property desired
is a very fine particle size to achieve large surface and thus maximum
adsorption capacity.
The preparation may contain
peppermint oil, glycerin, sorbitol, sucrose saccharin, or other suitable,
flavors and it may contain suitable preservatives in a total amount of
exceeding 0.5%.
Uses: Antacid in the treatment of peptic ulcer. The compound is not
an adsorbent but reacts chemically to neutralize the gastric contents. It has
been used for intestinal toxemia, but more effective agents are available. The
major advantage of aluminum hydroxide is that no systemic alkalosis is
produced. The disadvantage would be constipation.
Dose: Usual, 10ml four times daily or more.
2. Dried Aluminum Hydroxide Gel, NF, BP
Other Name: Gelatum Alumini Hydroxidi Siccum
Preparation: It is prepared as described under aluminum hydroxide
gel, and dried at a low temperature until it has the required amount of Al2O3.
Dose: 390mg, the equivalent of 300mg of Al(OH)3, four
times a day.
3. Aluminum Phosphate Gel, NF
Other Names: Gelatum Alumini Phosphatis; Phosphagel
Preparation:
The gel may be prepared by
precipitation from a solution of aluminum chloride with a solution of sodium
phosphate. The particle size of the precipitate which is an important factor in
its absorption, is governed by several factors:
(a) The concentration of the
reactants.
(b) The temperature and pH
maintained during the process.
(c) The manner of addition of
reactants whether the sodium phosphate is added to the aluminum solution, or
the reverse. The soluble salts formed in the reaction are removed by washing
either by decantation with water, or by dialysis.
It may contain peppermint oil,
glycerin, sorbitol, sucrose, saccharin, or other suitable agents for flavoring
purposes. It may also contain sodium benzoate, benzoic acid, or other suitable
agents and in small amount not exceeding 0.5% as preservative.
Uses: Antacid. It has approximately half the neutralization
capacity of aluminum hydroxide gel but has the advantage over the latter of not
interfering with the adsorption of phosphate from the intestinal tract.
Dose: Usual, 15ml.
