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Alginic acid (algine, alginate) is a viscous gum that is abundant in the cell walls of brown algae. more...

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Structure

Chemically, it is a linear copolymer with homopolymeric blocks of (1-4)-linked ß-D-mannuronate (M) and its C-5 epimer α-L-guluronate (G) residues, respectively, covalently linked together in different sequences or blocks.

The monomers can appear in homopolymeric blocks of consecutive G-residues (G-blocks), consecutive M-residues (M-blocks), alternating M and G-residues (MG-blocks) or randomly organized blocks. The relative amount of each block type varies both with the origin of the alginate. Alternating blocks form the most flexible chains and are more soluble at lower pH than the other blocks. G-blocks form stiff chain elements, and two G-blocks of more than 6 residues each form stable cross-linked junctions with divalent cations (e.g. Ca2+, Ba2+, Sr2+ among others) leading to a three-dimensional gel network. At low pH, protonized alginates will form acidic gels. In these gels, it is mostly the homopolymeric blocks that form the junctions, where the stability of the gel is determined by the relative content of G-blocks.

Forms

Commercial varieties of alginate are extracted from seaweed, including the giant kelp Macrocystis pyrifera, Ascophyllum Nodosum and various types of Laminaria.

Alginate absorbs water quickly, which makes it useful as an additive in dehydrated products such as slimming aids, and in the manufacture of paper and textiles. It is also used for waterproofing and fireproofing fabrics, for thickening drinks, ice cream and cosmetics, and as a detoxifier that can absorb poisonous metals from the blood. Alginate is also produced by certain bacteria, notably Azotobacter species. Attempts to produce bacterial alginate have not yet been commercially successful.

Alginate ranges from white to yellowish brown, and takes filamentous, grainy, granular, and powdered forms. It is insoluble in water and organic solvents, and dissolves slowly in basic solutions of sodium carbonate, sodium hydroxide and trisodium phosphate.

Uses

Purified forms of alginate are used in antacid preparations such as Gaviscon®, Bisodol®, Asilone®, and Boots Own® tablets. Alginate is used extensivly as a mold-making material in dentistry and prosthetics, and in textiles. It is also used in the food industry, for thickening soups and jellies. Calcium alginate is used in burn dressings that promote healing and can be removed painlessly.

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New Guidelines on GER in Children Expected This Summer - Brief Article - Statistical Data Included
From Family Pratice News, 1/15/00 by Miriam E. Tucker

CHARLESTON, S.C. -- New guidelines that will help primary care physicians manage infants and children with gastroesophageal reflux will be released this summer, Dr. Robert Baker said at a pediatric meeting sponsored by the Medical University of South Carolina.

The evidence-based guidelines, developed by a committee from the North American Society for Pediatric Gastroenterology and Nutrition, are scheduled to be published in August 2000 in the Journal of Pediatric Gastroenterology and Nutrition. The guidelines will address both diagnosis and treatment of GER in infants and children up to 18 years of age, said Dr. Baker, a member of the committee.

The committee, made up of five pediatric gastroenterologists and three general pediatricians (two of whom are also epidemiologists), based the guidelines on their review of 354 articles on diagnosis, treatment, and complications of GER, published from 1966 to the present. In areas where evidence was insufficient, expert opinion is given.

Algorithms are included for five common presenting symptoms of GER in infants: recurrent vomiting, vomiting and poor weight gain, vomiting and excessive crying, acute life-threatening events, and persistent reactive airway disease. For older children, three algorithms address GER presenting with chronic heartburn, dysphagia, or asthma.

Other presentations of GER, including the infant with dysphagia, infants with recurrent stridor or hoarseness, and the older child with hoarseness, are also addressed in the document, said Dr. Baker, codirector of pediatric gastroenterology and nutrition at the university.

For the apparently well infant with GER, the algorithm advises physicians to begin with a history and physical exam to look for "red flags" such as forceful vomiting or fever, and for complications of GER such as aspiration, poor weight gain, or bloody stools. If any are present, another appropriate algorithm should be used.

If the infant's GER is uncomplicated--just a "happy spitter"--no tests are needed, and the parents should be reassured. Thickened formula, which can decrease the number of vomiting episodes, can be considered, although there is not much literature to support its use.

Hypoallergenic formula can also be tried, but there is really no evidence that formula plays a role inmost cases of infantile GER, Dr. Baker said.

Although there is good evidence that the prone sleeping position reduces acid exposure, it is not recommended for most cases of GER in infants because of its association with sudden infant death syndrome.

Propulsid (cisapride) may be useful, but an electrocardiogram must be done prior to use. Other prokinetic agents should not be used in infants, he advised.

If the GER does not resolve by 24 months of age, the child should be referred to a pediatric gastroenterologist. Various diagnostic tests, including esophagogastroduodenoscopy and biopsy, pH probe, and upper GI x-rays should be considered at this point.

In the older child with chronic heartburn, management includes lifestyle modifications such as avoidance of chocolate, caffeine, and carbonated beverages, educating parents not to smoke around the child, and consideration of treatment with an acid suppressor.

Antacids such as Mylanta or Maalox have been shown to be effective in some children in studies done prior to the availability of acid suppressors and prokinetics for children.

More recent European data suggest that alginic acid is highly effective in reducing GER symptoms in children. Gaviscon is the only product sold in the United States that contains alginic acid, but the Gaviscon formula sold in this country contains much less alginic acid than does the European version, Dr. Baker said.

Although not approved for pediatric use, [histamine.sub.2]-receptor agonists like ranitidine and famotidine and proton pump inhibitors like omeprazole have been shown effective in treating esophagitis in children, Dr. Baker said.

If the child's symptoms don't resolve after 2 weeks of acid suppression, or if the child returns soon after stopping the medication, a proton pump inhibitor is the next pharmacologic agent to try. If that fails to alleviate the symptoms, a pediatric gastroenterology consult is advised and esophagogastroduodenoscopy with biopsy is suggested.

Surgery is the last resort for these patients, he said.

COPYRIGHT 2000 International Medical News Group
COPYRIGHT 2001 Gale Group

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