Variance comparison as a tool in clinical pharmacology: an example with two loop diuretics.

Comparison of variances can be usefUl in assessing the regularity of drug effects. In order to compare the variances of the saluretic effects of piretanide and frusemide, two loop diuretics with different bioavailabilities, a double-blind cross-over study was carried out in 34 normal volunteers. The diuretics were given in randomized order, with an interval of 7 days, in single equipotent doses (frusemide 6.25 mg and piretanide 1.0 mg chosen from previous results) adjusted by body weight. The dispersion of individual values (comparison of variances from paired measures) for Na+, Cl- and Ca++ excretion, urine osmolality and excretion of the drugs, was significantly smaller for piretanide than for frusemide. It is concluded that the saluretic effect of a single dose of piretanide varies less than that of an equipotent dose of frusemide. The methodology may be useful in trials of drugs for which regularity of effect is important.