Log-dosage probit

Although the LD 0 can be obtained from a log dosage-probit line by graphic estimation, bioassay data need to be subjected to probit analysis to obtain a more reliable value. This analysis will provide, in addition to the LD50, parameters such as the X2 value (for testing the heterogeneity of discrepancies between observed and expected numbers), 95% fiducial limits to the... 

Figure 5.12 Log dosage-probit line for the progeny of the R x S cross expected from a single recessive genetic system.

Tsukamoto, M., The log dosage-probit mortality curve in genetic research of insecticide resistance in insecticides, Botyu-Kagaku (Scientific Pest Control), 28, 91,1963. 

Figure 2 shows the standard dosage-mortality lines for 7-hexachlorocyclohexane (line 4), parathion (line C), and p,p -DDT (line F) plotted according to the probit-log dosage procedure of Bliss (1). Line B is the corresponding dosage-mortality line resulting when... 

FIGURE 5.8. Examples of probit-log dosage response curves illustrating differences in slope curves and the relationship between the slope, LD50, and LD0i. 

The concentration of choice for mode of action studies is the lowest drug concentration which inhibits growth entirely. This can either be estimated by extrapolation of the probit-transformed log dosage response correlation or by determination of the MIC, ie. minimal inhibitory concentration, by the method of serial twofold dilution of drug-containing medium in test tubes, inoculation of these media and visual observation of growth after incubation overnight. 

Ideally, to correlate dose and effect, an increase in dosage should increase the extent or severity of effects. Verification requires testing of a variety of dose levels of the substance under identical test conditions and comparing the observed effects. Based on these test data the dose/effects curve is modeled using one or more of the accepted models such as probit, log probit, or Mantel-Bryant. Once a dose/effect relationship is established and modeled by a series of mathematical expressions, it is then possible to estimate whether the dose to which a population is exposed is likely to result in measurable effects. When the dose/effect relationship has been defined for a human population, this is obvi-... 

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