Studies on the disposition of antipyrine, aminopyrine, and phenacetin using plasma, saliva, and urine.

In normal male subjects, the half-lives of antipyrine, aminopyrine, or phenacetin were not significantly different from the half-lives of each drug in saliva. Apparent volumes of distribution (aVd) in plasma and saliva differed by the extent to which each drug has been reported to bind to plasma proteins. Thus, the aVd of antipyrine in plasma and saliva was similar; there were significant differences in aVd for aminopyrine; even greater differences were observed for penacetin. The expression (see article) equals the fraction of the drug bound to plasma proteins. Rates of appearance in the urine of metabolites of antipyrine and aminopyrine were measured. General equations were used to show the relationship between half-life for elimination of the parent drug from the body and rate of excretion of metabolites. There were significant correlations between the half-life for elimination of antipyrine from the body and the half-life for production of 4-OH antipyrine (r equal 0.90), as well as between the plasma half-life of aminopyrine and the half-life of 4-aminoantipyrine (r equal 0.95). No significant correlation was observed in the same individual between the plasma half-lives of antipyrine and phenacetin (r equal 0.05, p greater than 0.05), of aminopyrine and phenacetin (r equal 0.11, p greater than 0.05), or of antipyrine and aminopyrine (r equal 0.50, p greater than 0.05).