Respected Sir/Madam,



I have a question regarding calculation of LD50 (Lethal Dose) and IC50 (50%
inhibitory concentration) of an antimicrobial experiment.



I have used a compound isolated from a plant and observed its effect on the
fungus *Fusarium oxysporum* by the food poisoning method. Solutions of the
compound at concentrations of 0, 50, 100, 150, 200 and 250痢/ ml were added
to sterilized medium in Petri dish (9cm dia.) and after transferring the
mycelia of fungal strains, the dishes were incubated in the dark. When the
mycelium of fungi reached the edges of the control (0痢/ ml) dishes, the
antifungal indices were calculated. Each test was repeated three times and
the average was calculated. The formula to calculate antifungal index (AI)
was



AI % = (1- Da / Db) * 100

Where Da = diameter of growth zone in experiment (cm); Db = diameter of
growth zone in control (cm).



The results are as follows



Concentration (痢/ ml)

0

50

100

150

200

250

AI% (average of 3 replicates)

0

10

21.59

33.89

47.96

59.93















I have the Version 2.3.1 (2006-06-01) of R loaded in my computer and want to
calculate LD50 and if possible IC50 values with the data. I have checked the
Help menu---Manuals in PDF---An introduction to R. There is an example of
calculating LD50 in Chapter 11, page no. 63.

But I cannot fit my data in the model珦ome error messages are coming.



Please suggest some functions on R or the method by which I can do the
calculations. I am not at all used to programming language so a detailed
solution would be very much helpful.



Thanking you in anticipation.

Sincerely yours.


-- 
Dipjyoti Chakraborty
C/o Dr Adinpunya Mitra
Natural Products Biotechnology Lab
Agriculture & Food Technology Depart.
IIT-KGP
Kharagpur-721 302-India

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