Dose Response and Selective Toxicity
Potency and Efficacy
• potency – refers to the amount of drug that must be given to obtain a particular response
• efficacy – refers to the maximal response that can be obtained with the drug → more important
Which drug is more potent?
→ Ais more potent
Which drug has greater efficacy?
→ B has more efficacy
Dose Response frequency dist = log
• as dose increases so does the response dose curve
◦ variability in the response between individuals
◦ variability between drugs.
• therapeutic dose must be less than the toxic dose
◦ ex: chemotherapy – toxicity at therapeutic doses
Therapeutic Index TD50/ED50
• the higher the number the lower the probability that the
drug will cause an adverse effect.
• chose 50% where curve is change quickly and linearly
• therapeutic window: ~90% response with little adverse
effects Selective Toxicity
→ Harm to one organism w/out harming some other kind.
ex: antibiotics, antifungal chemotherapy
• need to have insecticides and fungicides
• weed killer without harming the crop
• kill a parasite without harming the host (human) lice, helminths, bacterial infections, cancer
• selective accumulation of a herbicide, ex: sulphuric acid.
• early theories of disease suggested that the body was overcome by evil spirits and that
treatment was designed to drive off evil spirits, burning of sulphur, blood letting.
• Pasteur and Koch demonstrated that certain disease were caused by microbes
• this lead to search for new treatments
• most scientists were of the opinion that it would be impossible to find agents that are selectively
toxic to a micro-organism
• Paul Ehrlich did not share this view
• he noted that dyes were selectively accumulated by certain tissues
• he argued that by designing the correct drug it would bind to parasites selectively
• if it bound to parasites but not human cells, human cell would not be injured by the compound.