Compressible starch

Like many other herbal extracts, valerian extract is very hygroscopic. Inclusion into tablets raises stability issues. Coatings reduce moisture absorption but often lead to tablet explosion or visual deterioration (black specs). Tablets formulated with 250 mg valerian extract, spray-dried lactose, and compressible starch were... 

A number of starch modifications are used in pharmaceutical applications. Pregelatinized or compressible starch has been chemically or mechanically processed to rupture all or part of the granules in water. It is then dried to yield an excipient material suitable for direct-compression formulations. Sterilizable maize starch contains magnesium oxide (not greater than 2.2%) and has been chemically or physically treated to prevent gelatinization on exposure to moisture or steam sterilization. Soluble starch results when potato or maize starch has been chemically treated to destroy the gelatinizing ability of starch. 

Wurster DE, Peck GE, Kildsig DO. A comparison of the moisture adsorption-desorption properties of corn starch, USP, and directly compressible starch. Drug Dev Ind Pharm 1982 8 343-354. 

Manudhane KS, Contractor AM, Kim HY, Shangraw RE Tableting properties of a directly compressible starch. / Pharm Set 1969 58 616-620. 

David and Augsburger (63) studied the decay of compressional forces for a variety of excipients, compressed with flat-faced punches on a Stokes rotary press. They found that initial compressive force could be subject to a fairly rapid decay and that this rate was dependent on the deformation behavior of the excipient for the materials studied, they found that maximum loss in compression force was for compressible starch and MCC, which was followed by compressible sugar and DCP. This was attributed to differences in the extent of plastic flow. The decay curves were analyzed using the Maxwell model of viscoelastic behavior. Maxwell model implies first order decay of compression force. 

Materials that act as disintegration agents with poor flow characteristics Microcrystalline cellulose Directly compressible starch Probably the most widely used direct compression excipients. Excellent compactibility at low pressures, high dilution capacity. 

Free-flowing materials that do not disintegrate Dibasic calcium phosphate dihydrate Excellent flow properties. Very brittle material, and is best used in combination with microcrystalline cellulose or directly compressible starch. 

Ghdants are needed to faciUtate the flow of granulation from the hopper. Lubricants ensure the release of the compressed mass from the punch surfaces and the release/ejection of the tablet from the die. Combinations of siUcas, com starch, talc (qv), magnesium stearate, and high molecular weight poly(ethylene glycols) are used. Most lubricants are hydrophobic and may slow down disintegration and dmg dissolution. 

Compressed yeast is also sold in supermarkets in 18-g and 56-g packages. Since this product contains approximately 10% added starch to increase its shelf life, it has a lower protein content and fermentative activity than the compressed yeast sold to bakeries. 

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

Fig. 17 Effect of starch content of granules on dissolution rate of salicylic acid contained in compressed tablets. Q, 5% . 10% x, 20% starch in granules. (From Ref. 22.).

Starch is often cited as a filler, but it is more commonly used in its dry state as a disintegrating agent. However, modified starches such as StaRx 1500 and National 1551 (partially hydrolyzed, or pregelatinized starch) are marketed for direct compression and appear to offer the advantage of substantial mechanical strength and rapid drug release. 

Fig. 17 Effect of powder bed height, piston height, and compression force on plug ejection force in an instrumented Zanasi LZ-64 automatic capsule-filling machine (pregelatinized starch lubricated with 0.005% magnesium stearate). Note that the first point of each curve is precompression. Piston height (mm) , 15 -jlf, 14 , 13 , 12. Powder bed height (mm) heavy line, 30 light line, 50. (From Ref. 51.)...

Shortly after a mixture of the four ingredients had been compressed into tablets, incandescence and an explosion occurred. This may have been caused by interaction of the oxidant and starch, accelerated by the acid salt, but may also have involved dichlorine monoxide liberated by the same salt. 

Star-branched butyl rubber, 4 437-438 copolymers, 4 445-446 Starch(es), 4 703-704, 20 452-453 as blood substitute, 4 111-112 cationic, 18 114-115 in cereal grains, 26 271-274 in cocoa shell from roasted beans, 6 357t compression effects in centrifuges, 5 513 depolymerization, 4 712 in ethanol fermentation, 10 534—535 etherified, 20 563 as a flocculant, 11 627 high-amylose, 26 288 Mark-Houwink parameters for, 20 558t modified and unmodified, 12 52-53 in paper manufacture, 18 122-123 performance criteria in cosmetic use, 7 860t... 

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