Calcium alginate is an odorless or almost odorless, tasteless, white to pale yellowish-brown powder or fibers.
Alginato calcico; alginic acid, calcium salt; algin; CA33; calc algin; calcium polymannuronate; Calginate; E404; Kaltostat.
Chemical Name and CAS Registry Number: Calcium alginate [9005-35-0]
Empirical Formula and Molecular Weight
[(C6H7O6)2Ca] n: 195.16 (calculated) and 219.00 (actual, average) Each calcium ion binds with two alginate molecules. The molecular weight of 195.16 relates to one alginate molecule, and the equivalent of half a calcium ion, therefore n = 1=2. Calcium alginate is a polyuronide made up of a sequence of two hexuronic acid residues, namely D-mannuronic acid and L-guluronic acid.
The two sugars form blocks of up to 20 units along the chain, with the proportion of the blocks dependent on the species of seaweed and also the part of the seaweed used. The number and length of the blocks are important in determining the physical properties of the alginate produced; the number and sequence of the mannuronate and guluronate residues varies in the naturally occurring alginate. It has a typical macromolecular weight between 10 000 and 600 000.
Functional Category: Emulsifying agent; stabilizing agent; tablet disintegrant; thickening agent.
Applications in Pharmaceutical Formulation or Technology
In pharmaceutical formulations, calcium alginate and calciumsodium alginate have been used as tablet disintegrants. The use of a high concentration (10%) of calcium-sodium alginate has been reported to cause slight speckling of tablets.
A range of different types of delivery systems intended for oral administration have been investigated. These exploit the gelling properties of calcium alginate. Calcium alginate beads have been used to prepare floating dosage systems containing amoxicillin, furosemide, meloxicam, and barium sulfate, and as a means of providing a sustained or controlled-release action for sulindac, diclofenac, tiaramide, insulin and ampicillin.
The effect of citric acid in prolonging the gastric retention of calcium alginate floating dosage forms has been reported. Impregnating meloxicam in calcium alginate beads may reduce the risk of ulceration and mucosal inflammation following oral adminstration.
The use of calcium alginate beads, reinforced with chitosan, has been shown to slow the release of verapamil, and may be useful for the controlled release of protein drugs to the gastrointestinal tract. The bioadhesive properties, swelling and drug release of calcium alginate beads have also been investigated.
A series of studies investigating the production, formulation, and drug release from calcium alginate matrices for oral administration have been published. The release of diltiazem hydrochloride from a polyvinyl alcohol matrix was shown to be controlled by coating with a calcium alginate membrane; the drug release profile could be modified by increasing the coating thickness of the calcium alginate layer. The microencapsulation of live attenuated Bacillus Calmette–Gue´rin (BCG) cells within a calcium alginate matrix has also been reported.
It has been shown that a modified drug release can be obtained from calcium alginate microcapsules, pellets and microspheres. When biodegradable bone implants composed of calcium alginate spheres and containing gentamicin were introduced into the femur of rats, effective drug levels in bone and soft tissue were obtained for 30 days and 7 days, respectively.
The incorporation of radioactive particles into calcium alginate gels may be useful for the localized delivery of radiation therapy to a wide range of organs and tissues. Therapeutically, the gelling properties of calcium alginate are utilized in wound dressings in the treatment of leg ulcers, pressure sores, and other exuding wounds. These dressings are highly absorbent and are suitable for moderately or heavily exuding wounds.
Calcium alginate dressings also have hemostatic properties, with calcium ions being exchanged for sodium ions in the blood; this stimulates both platelet activation and whole blood coagulation. A mixed calcium–sodium salt of alginic acid is used as fibers in dressings or wound packing material.
Sterile powder consisting of a mixture of calcium and sodium alginates has been used in place of talc in glove powders. In foods, calcium alginate is used as an emulsifier, thickener, and stabilizer.
Method of Manufacture
Calcium alginate can be obtained from seaweed, mainly species of Laminaria. Solutions of sodium alginate interact with an ionized calcium salt, resulting in the instantaneous precipitation of insoluble calcium alginate, which can then be further processed. Introducing varying proportions of sodium ions during manufacture can produce products having different absorption rates.
Related Substances: Alginic acid; potassium alginate; sodium alginate; propylene glycol alginate.