Analytical methods (isolation, TLC, UV-spectroscopic and preferably fluorimetric determination) of [1-(p-chlorobenzoyl)-5-methoxy-2-methylindole-3-acetoxy] acetic acid (acemetacin, TV 1322, Rantudil), its analogues, hydrolysis-products and metabolites from biological material are described. 2. Stability is also dealt with. Hydrolysis of the p-chlorobenzoyl group results in strongly fluorescing compounds and can be used in determination of acemetacin, indometacin and derivatives 3. Proof is given that in in vitro studies, such as e.g. Mizushima's protein turbidity test or the test for inhibition of prostaglandin-synthetase, only intact acemetacin (and none of its potential break-down products) is present and is active. 4. In in vitro studies, such as the inhibition of total complement and of the increase in activity of serum sulfhydryl groups, acemetacin and a series of its salts proved to be at least as effective as indometacin. 5. In comparing protein binding, acemetacin, like indometacin, is found to bind strongly to albumin. The portion of free, non-protein bound acemetacin, which thus remains available for the pharmacological action, is found to be approx. 60% higher than the corresponding portion of free indometacin.
