Sodium biological variability

The synthetic preparations used are the sodium salts of the natural isomers of the thyroid hormones. Levothyroxine sodium (L-T, synthroid, levoxyl, levothroid, unithroid, others) is available in tablets in a variety of doses and as a lyophilized powder for injection. L-T has a narrow therapeutic index, and the FDA has mandated demonstration of bioequivalence for brand and generic preparations by the various producers. Liothyronine sodium (L-Tft is available in tablets (cytomel) and in an injectable form (triostat). A mixture of L-T and L-T is marketed as liotrix (thyroiar). Desiccated thyroid preparations, derived from whole animal thyroids and containing both T and T have highly variable biologic activity and are much less desirable. 

Residual chlorine in a water sample will destroy the biological population and may prevent an accurate determination of bacteria in the sample, unless the chlorine is destroyed at the time of sample collection. Therefore, if a sample from a halogenated water supply is taken, 1.0 ml of 10% solution of sodium thiosulfate should be added to the 11 sample bottle, before sterilization in the field service unit. This reagent should neutralize 15mgl residual chlorine in the sample, and should show no effect upon variability or growth. 

Many studies have been published on the use of various enhancers for the rectal absorption. They increase the absorption of an active substance by enhancing the membrane permeation, rather than increasing the solubility. Published examples of absorption enhancers are capric acid and sodium caprate, lauric acid and sodium laurate, sodium salicylate and sodium cholate. These enhancers however give an unpredictable and strongly variable improvement of the biological availability [5b]. Nevertheless they sometimes lead to a licensed medicine sodium caprate is already in use in a suppository product available in Japan [7]. 

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