Biological effectiveness, in goldfish, of some p-substituted acetanilides alone and in the presence of poloxamers.

The death times of goldfish have been measured in aqueous solutions containing different concentrations of p-substituted acetanilides alone or in the presence of poloxamers. Plots of reciprocal death time versus concentration were linear with a positive concentration intercept, the minimum effective concentration (MEC). The MEC values were directly related to the pi value (hydrophobic-lipophilic constant) of the functional group on the acetanilide indicating that activity is directly related to lipophilicity. Slopes of reciprocal death time versus drug concentration were linearly related to pi values but there was no direct dependence. The presence of poloxamers in aqueous acetanilide solutions reduced the goldfish death time. The effect of the poloxamers is believed to be one of rendering the goldfish membrane more permeable to drugs.