The Therapeutic Index

The dose of a drug required to produce a specified effect in 50% of the population is the median effective dose (ED50, Figure 5-4B). In preclinical studies of drugs, the median lethal dose (LD50) is determined in experimental animals. The LD50/ED50 ratio is an indication of the therapeutic index, which is a statement of how selective the drug is in producing its desired versus its adverse effects. In clinical studies, the dose, or preferably the concentration, of a drug required to produce toxic effects can be compared with the concentration required for therapeutic effects in the population to evaluate the clinical therapeutic index. Since pharmacodynamic variation in the population may be marked, the concentration or dose of drug required to produce a therapeutic effect in most of the population usually will overlap the concentration required to produce toxicity in some of the population, even though the drug's therapeutic index in an individual patient may be large. Also, the concentration-percent curves for efficacy and toxicity need not be parallel, adding yet another complexity to determination of the therapeutic index in patients. Finally, no drug produces a single effect, and the therapeutic index for a drug will vary depending on the effect being measured.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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