Carl T. Olson

Stagewise, adaptive dose allocation for quantal response dose-response studies

A principal design objective of many dose-response studies is to estimate extreme percentiles of a dose-response distribution, e.g., the ED95 dose for a particular drug therapy, as precisely as feasible using the smallest number of experimental subjects possible. Such a design requirement necessitates that allocation of subjects to drug doses be carried out in a stagewise fashion to maximize the information obtained from each subsequent experimental observation in light of what has previously been determined. This paper describes and illustrates specialized methods and associated computer programs to evaluate, on a stagewise basis, the anticipated relative sensitivities of alternative experimental plans in the case of dichotomous responses. Following each stage of experimentation, the current estimates of the dose-response distribution parameters, as well as the uncertainties in these estimates, are updated and are used to assign subjects to experimental dose levels for the next stage of testing. Competing dose allocations are compared with respect to anticipated improvement in estimation precision. The adoption of such a stagewise dose allocation strategy is illustrated by example.

Stagewise, group sequential experimental designs for quantal responses. one-sample and two-sample comparisons.

The use of stagewise, group sequential experimental designs with dichotomous responses in toxicity or drug screening programs is discussed. Such designs represent a compromise between the standard, fixed sample size designs and fully sequential designs. Stagewise group sequential designs place specified numbers of animals on test at each stage, up to a maximum number of stages. The greatest increases in sample size efficiency occur with small numbers of stages, particularly when going from one stage to two. Two-stage designs can result in a 15 to 20 percent reduction in average sample size. Five-stage designs can result in a 30 to 40 percent reduction in average sample size, with no appreciable decrease in Type 1 error or power. Examples of the efficiencies that arose in actual screening programs are given. This paper demonstrates that the routine use of stagewise, group sequential designs in standardized screening protocols can result in substantial savings in animal use with virtually no sacrifice of statistical sensitivity.

Statistical Analysis of Dose-Response Experiments by Maximum Likelihood Analysis and Iteratively Reweighted Nonlinear Least Squares Regression Techniques:

Dose-response studies often form integral parts of pharmacological investigations of drug activity and efficacy and of toxicological investigations of drug and chemical safety. Standardized dose-response study protocols, statistical models, model fitting techniques, and computer programs are widely available for such applications. Many studies however, require nonstandard models and model fitting procedures to adequately describe the resulting data. Maximum likelihood analysis can accommodate a wide variety of model structures in a unified manner. This presentation illustrates how general purpose nonlinear regression analysis routines, such as those that are available in SAS or in BMDP, can be used to obtain maximum likelihood model solutions and associated error analyses for nonstandard model fitting situations. This reduces the need for special purpose computer programs for individual modeling applications. Methodological considerations in the application of nonlinear regression modeling procedures to maximum likelihood estimation are discussed. The methodology is illustrated with several modeling situations.

Metabolism of nephrotoxic cis- and trans-decalin in Fischer-344 rats

The cis- and trans-decalin stereoisomers have found many uses as solvents and fuel components. The metabolism of the decalin isomers in male and female Fischer-344 rats and the effects of the decalins on renal damage were evaluated. Only male rats had kidney damage. Metabolism of cis-decalin yielded cis,trans-1-decalol and cis,cis-2-decalol in the urine of both sexes, with the male also producing cis,cis-1-decalol. The urinary metabolites of trans-decalin included trans,cis-2-decalol in both male and female rats and trans,trans-1-decalol in males. Extracts of kidney homogenates from male rats, but not from females, dosed with cis- and trans-decalin yielded cis-2-decalone and trans-2-decalone, respectively. A single male rat treated with trans-decalin produced no 2-decalone in the kidney extract and also showed no renal damage.

The metabolism of n-octane in Fischer 344 rats

The urinary metabolites of n-octane in Fischer 344 rats given the hydrocarbon by gavage included 2-octanol, 3-octanol, 5-oxohexanoic acid, and 6-oxoheptanoic acid. The sex of the animals influenced the relative amounts of metabolites formed. Analyses were performed by gas-liquid chromatography (GC) and gas-liquid chromatography/mass spectrometry (GC/MS). This is the first reported finding of keto acids in hydrocarbon oxidative metabolism. No kidney damage was found as a result of n-octane dosing although the 2,2,4-trimethylpentane (iso-octane) isomer does cause kidney lesions in male rats.

Efficacies of Atropine/2-PAM and Atropine/HI-6 in Treating Monkeys Intoxicated with Organophosphonate Nerve Agents

The efficacies of atropine (ATR)/ 2-PAM and ATRl HI-6 in treating male rhesus monkeys injected with the neurotoxic organophosphonate (OP) agents GA, GB, GD, GF, or VX were compared. Experiments were conducted using no more than 8 monkeys per OP and treatment regimen. Doses were selected using a modified up-and-down experimental design, challenging one monkey per day per OP and treatment. Results were used to approximate the median lethal dose (MLD) for groups of treated monkeys or monkeys given only a vehicle following challenge with an OP. Mortality and signs of intoxication with each treatment were statistically compared. Doses of 2-PAM (25.7 mgl kg) or HI-6 (50 mgl kg) and atropine (0.4 mg free base! kg) were given in a single intramuscular (IM) injection 1 min following challenge with an OP. Strong and well-defined relationships between agent dose and 10-h lethality were observed in untreated animals. The 10-h IM OP MLDs for untreated monkeys were estimated to be 80, 43, 8.0, 22, and 7.4 μg/kg for GA, GB, GD, GF, and VX, respectively. No statistical differences w ere found between AT Rl 2-PAM and AT Rl HI-6 treatment efficacies in preventing lethality for any of the OPs. Both oxime combinations appear to provide protection against a 2 × 10-h MLD of GA, GF, or VX; only

Metabolism and nephrotoxicity of tetralin in male Fischer 344 rats

Tetralin, a component of fuels, solvents, and varnishes, is metabolized in male Fischer 344 rats to 1-tetralol, 2-tetralol, 2-hydroxyl-1-tetralone, 4-hydroxyl-1-tetralone, 1,2-tetralindiol, and 1,4-tetralindiol. Rats treated with tetralin demonstrated the classic lesions of hydrocarbon-induced nephropathy.

Neuromuscular Effects of Low Level Exposures to Sarin, Pyridostigmine, Deet, and Chlorpyrifos

A study is being initiated to investigate subtle neurobehavioral effects and neuropathology in rats due to exposure to combinations of low levels of Sarin (GB), N,N-diethyl-m-toluamide (DEET), chlorpyrifos (CPF), and pyridostigmine bromide (PB). A similar study is being initiated in rhesus monkeys to investigate neurophysiologic effects and neuromuscular pathology due to exposure to a combination of GB, DEET, CPF, and PB, along with vaccination with botulinum toxoid. A description of these studies is presented.

Efficacy of Tacrine as a Nerve Agent Pretreatment

Tacrine (THA) was evaluated in vitro and in vivo as a pretreatment for nerve agent intoxication. In vitro experiments showed that the primary effect of THA was direct inhibition of purified fetal bovine serum acetylcholinesterase (AChE) with a slight effect on slowing the aging rate of nerve agent-inhibited AChE. THA produced significant behavioral effects at doses above 1.7 mg/kg, i.m., in the mouse and 3.4 mg/kg, i.m., in the guinea pig. At the no observable effect level (NOEL) for mice (1.7 mg/kg), THA was effective (P < or = 0.05) in reducing tabun- and soman-, but not sarin-induced lethality in mice. Experiments in the guinea pig showed that at the NOEL (3.4 mg/kg, i.m.) THA was not effective in decreasing lethality due to soman exposure. Since there was significant overlap between pharmacologically effective doses of THA and those which produce behavioral toxicity, THA was not considered a suitable pretreatment for nerve agent intoxication.

The metabolism of 2,3,4-trimethylpentane in male fischer-344 rats

The urinary metabolites of the potent nephrotoxic hydrocarbon 2,3,4-trimethylpentane (2,3,4-TMP) given Fischer-344 male rats by gavage included 1-hydroxy-2,3,4-trimethylpentane, 2,3,4-trimethyl-1-pentanoic acid and 2,3,4-trimethyl-5-hydroxy-1-pentanoic acid. Analyses were performed by gas-liquid chromatography (GC) and gas-liquid chromatography/mass spectrometry (GC/MS). A comparison of the urinary metabolites of 2,3,4-TMP with those of 2,2,4-trimethylpentane (2,2,4-TMP) showed that more monocarboxylic acid was produced with 2,3,4-TMP.