Monograph: |
Guar Gum
A gum obtained from the ground endosperms of the seeds of Cyamopsis tetragonolobus (=C. psoraloides] (Leguminosae). Guar Galactomannan (Ph. Eur.) is described as a yellowish-white powder. It is soluble in cold and hot water; practically insoluble in organic solvents. Its main components are polysaccharides composed of D-galactose and D-mannose at molecular ratios of 1:1.4 to 1:2. The molecules consist of a linear main chain of p-(l->4)-glycosidically linked man-nopyranoses and single a-( 1-Β»6)-glycosidically linked ga-lactopyranoses.
Guar Gum (USNF 18) is a similar substance but slightly differently described. It is characterised as consisting chiefly of a high-molecular-weight hydrocolloidai polysaccharide. a ga-lactomannan, composed of galactan and mannan units combined through glycosidic linkages. It is a white to yellowish-white almost odourless powder, dispersible in hot or cold water to form a colloidal solution.
Adverse Effects and Precautions
Guar gum can cause gastro-intestinal disturbance with flatulence, diarrhoea, or nausea, particularly at the start of treatment.
because guar gum swells on contact with liquid it should always be washed down carefully with water and should not be taken immediately before going to bed. It should not be used in patients with oesophageal disease or intestinal obstruction.
Interactions
Guar gum may retard the absorption of other drugs given concomitantly; where this is likely to pose a problem the other drug should be taken at least an hour before administration of guar gum.
Uses and Administration
Guar gum is used in diabetes mellitus as an adjunct to treatment with diet, insulin, or oral hypoglycaemics since it is considered to reduce both postprandial and fasting blood-glucose concentrations. It is given with or immediately before meals in doses of 5 g usually three times daily. Adverse gastro-intestinal effects may be decreased by initial administration of 5 g once daily. Each dose of guar gum granules should be taken stirred in about 200 mL of a cold drink. Alternatively it can be sprinkled over or mixed with food which must be taken accompanied by about 200 mL of fluid. Guar gum has also been incorporated into various foods. Guar gum is also used to slow gastric emptying in some patients with the dumping syndrome. It is being investigated in the treatment of hyperlip-idaemias.
Guar gum is also used as a thickening and suspending agent, and as a tablet binder.
Guar gum is an example of a soluble fibre: wheat bran is an insoluble fibre. On contact with water it forms a highly viscous gel, the viscosity of which varies with such factors as its plant source or the form in which it is administered. Fibres such as guar gum reduce postprandial and fasting blood-glucose concentrations as well as plasma-insulin concentrations in healthy subjects and diabetic patients. Bran has little effect on glucose and insulin concentrations.' Possible mechanisms for these effects of guar gum include a delay in gastric emptying. decreased small-bowel motility, decreased glucose absorption resulting from increased viscosity of the contents of the gastro-inteslinal tract or inhibition of gastro-intestinal hormones. Guar gum also lowers serum total cholesterol and low-density-lipoprotein (LDL) cholesterol concentrations: high-density-lipoprotein (HDL) cholesterol and triglyceride concentrations appear to be unaffected. The most likely mechanism is binding of bile acids, reducing their enterohe-patic circulation in a similar way to bile-acid sequestrants. Reductions in fasting and postprandial blood-glucose concentrations and in glycosylated haemoglobin have been demonstrated in both type 1 and type 2 diabetics, but they have generally been small. Many studies have examined the effect of a high-fibre diet on diabetic control but have often used unspecified mixtures of soluble and insoluble fibres. Interpretation of these studies is further complicated by variations in the diet (such as carbohydrate and fat content), the effect of the diet on body weight. and the method of food preparation. Most studies have shown some improvement, albeit modest, in glycaemic control and lipid values' but there have been a few studies showing either no change or deterioration in blood-glucose concentrations. While it might be possible to prepare a palatable preparation of guar gum. gastro-intesti-nal effects can be a problem but can generally be ameliorated by gradual introduction.1 Advantages of natural dietary fibres may reside in the simultaneous reduction in ingestion of saturated fats or quickly digested carbohydrate.' For further discussion of high-fibre diets see Bran. When used alone in patients with hypercholesterolaemia guar gum has generally produced a modest reduction in plasma-cholesterol and LDL-cholestero] concentrations although some studies have been unable to demonstrate an effect. A few studies have suggested that the cholesterol-lowering effect is attenuated after 8 to 12 weeks of treatment but a long-term study observed a 17% decrease in total serum cholesterol that was maintained for 24 months. Preliminary studies have shown further reductions in cholesterol and LDL-cholesterol concentrations on addition of guar gum to therapy with other lipid regulating drugs. There have been suggestions that guar gum reduces appetite by promoting a feeling of fullness, but studies have not demonstrated a consistent reduction in body weight. Products containing guar gum have, however, been promoted as slimming aids. Their use cannot be advocated because of the risk of tablets swelling before reaching the stomach and causing oesophageal obstruction.
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