Drug dynamics and kinetics (Effectiveness and Safety) Text: London

PRACTICAL LESSON 4

Drug dynamics and kinetics (Effectiveness and Safety)

Text: London (Speaking) (2 hours)

4.1Effectiveness and Safety

The two goals of drug development are effec­tiveness (efficacy) and safety. Since all drugs can harm as well as help, safety is relative. The wider the margin of safety (therapeutic window)-the spread between the usual effective dose and a dose that produces severe or life-threatening side effects-the more useful the drug. If a drug's usual effective dose is also toxic, doctors aren't willing to use the drug except in serious situations in which there's no safer alternative.

The best drugs are both effective and, for the most part, safe. Penicillin is such a drug. Except in people who are allergic to it, penicillin is vir­tually nontoxic, even in large doses. On the other hand, barbiturates, which were commonly used as sleep aids, can interfere with breathing, disturb the heart rhythm, and even cause death if taken in excess. Newer sleep aids such as triazolam and temazepam have better safety margins.

Some drugs must be used despite their having a very narrow margin of safety. For example, war­farin, which is taken to prevent blood clotting, can cause bleeding. People who take warfarin need frequent checkups to see whether the drug is having too much or too little effect on blood clot­ting.

Clozapine is another example. This drug often helps people with schizophrenia when all other drugs have failed. But clozapine has a serious side effect: it can decrease the production of white blood cells needed to protect against infection. Because of this risk, people who take clozapine must have their blood tested frequently for as long as they take the drug.

When people know what to expect from a drug, both good and bad, they and their doctors can better judge how well the drug is working and whether potentially serious problems are developing. Anyone taking a drug shouldn’t hesitate to ask a doctor, nurse, or pharmacist to explain the goals of treatment, the types of adverse drug reaction and other problems that may arise, and the extent to which they can participate in the treatment plan to help ensure the best outcome. People should also keep their health care practitioners well informed about medical history, current medications, and any other relevant information.