Six-Month Toxicity Comparison of the Antituberculosis Drugs Aconiazide and Isoniazid in Fischer 344 Rats

Aconiazide, a hydrazone derivative of isoniazid, has been proposed for the treatment of tuberculosis. The toxicity of aconiazide was assessed by treating male and female Fischer 344 (F344) rats daily by gavage for 6 months at doses up to 400 mg/kg body wt. For comparison, the toxicity of isoniazid was determined following treatment in an identical manner at equimolar doses. Aconiazide resulted in only one death during the 6-month experiment, whereas isoniazid caused a significant increase in morbidity and mortality. Each drug induced significant dose-related decreases in body weight in both sexes, and isoniazid caused a significant decrease in liver weight in male rats. Isoniazid also induced centrilobular hepatic necrosis in male rats, a lesion not observed upon aconiazide treatment. Plasma drug levels were ≥10-fold greater in rats administered isoniazid as compared to aconiazide. The higher levels of free drug observed with isoniazid may contribute to greater toxicity of isoniazid compared to aconiazide.

A semiparametric approach to risk assessment for quantitative outcomes

Characterizing the dose-effect relationship and estimating acceptable exposure levels are the primary goals of quantitative risk assessment. A semiparametric approach is proposed for risk assessment with continuously measured or quantitative outcomes which has advantages over existing methods by requiring fewer assumptions. The approach is based on pairwise ranking between the response values in the control group and those in the exposed groups. The work generalizes the rank-based Wilcoxon-Mann-Whitney test, which for the two-group comparison is effectively a test of whether a response from the control group is different from (larger than) a response in an exposed group. We develop a regression framework that naturally extends this metric to model the dose effect in terms of a risk function. Parameters of the regression model can be estimated with standard software. However, inference requires an additional step to estimate the variance structure of the estimated parameters. An effective dose (ED) and associated lower confidence limit (LED) are easily calculated. The method is supported by a simulation study and is illustrated with a study on the effects of aconiazide. The method offers flexible modeling of the dose effect, and since it is rank-based, it is more resistant to outliers, nonconstant variance, and other departures from normality than previously described approaches.

High-performance liquid chromatographic analysis of the antituberculosis drugs aconiazide and isoniazid

Reversed-phase HPLC methods are described for determining the stability and concentration certification of the antituberculosis prodrug aconiazide (ACON) in aqueous dosing solution and for assessing the concentrations of ACON and isoniazid (INH) in plasma from ACON-treated male and female Fischer-344 rats. ACON was analyzed in plasma by direct injection; it was separated on a 250 x 4.6 mm I.D. 5 microns C18 column using a 40% aqueous methanol mobile phase containing 5 g/l ammonium formate, and detected at 313 nm. INH was determined in the plasma of treated rats after a two-step precipitation of plasma proteins; it was separated on a 250 mm x 4.6 mm I.D. 5 microns CN column, eluted with 5% aqueous isopropanol containing 5 g/l ammonium formate, and detected with an electrochemical detector at +0.8 V. These methods allow a simple, rapid, and reliable determination of ACON and INH in plasma down to 0.1 micrograms/ml.