The effects of hardness on disintegration and dissolution characteristics of uncoated caffeine tablets made at eight different pressure levels were studied. The disintegration times were determined using the J.P. VIII procedure with disks and the dissolution rate measurements were performed with the U.S.P.XVIII procedure (U.S.P. method) and the J.P. VIII disintegration test apparatus (J.P. method). A good correlation between the hardness and the disintegration times was obtained. The dissolution rate constants were determined from the equation of Noyes & Whitney (1897) and a good correlation between the hardness and the dissolution rate constants was obtained. The hardness governed the dissolution over all the stages from tablet to the smallest particles after the breakage by disintegration. The dissolution rates of the J.P. method were greater than those of the U.S.P. method.

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The procedures (purification, developing solvent, medium) used in the original thinlayer bioautographic method of Donoho and Kline for the determination of monensin in chick tissues were modified to improve the recovery and sensitivity of the assay. Recoveries of monensin from fortified tissue samples were 92.9% from fat, 86.0% from liver and 104.4% from muscle. The assay sensitivity was improved to give a detection limit of 0.01ppm in fat and 0.0125ppm in other tissues. Feed containing monensin at 80, 100 or 120ppm was given to chicks for 9 weeks, and the residual levels of monensin in tissues were assayed. The residual levels of monensin at 0 hour after withdrawal were 0.057 to 0.110ppm in fat, none to 0.035ppm in muscle, none to 0.039ppm in liver and none to 0.014ppm in kidney. No detectable amount of monensin was found in fat at 48 hours or more after its withdrawal from the feed, or in liver, muscle and kidney at 24 hours or more after withdrawal. When monensin was given for seven days at significantly higher levels (300 and 600 ppm) than recommended, the tissue levels did not increase proportionally with the levels in the feed. The half-life of monensin disappearance from fat was estimated to be 3.4 to 4.0 hours.

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