An Introduction to Medicinal Chemistry 5th Edition

Book Preface

The medicinal chemist attempts to design and synthesize a pharmaceutical agent that has a desired biological effect on the human body or some other living system. Such a compound could also be called a ‘drug’, but this is a word that many scientists dislike because society views the term with suspicion. With media headlines such as ‘Drugs Menace’ or ‘Drug Addiction Sweeps City Streets’, this is hardly surprising. However, it suggests that a distinction can be drawn between drugs that are used in medicine and drugs that are abused. Is this really true? Can we draw a neat line between ‘good drugs’ like penicillin and ‘bad drugs’ like heroin? If so, how do we define what is meant by a good or a bad drug in the first place? Where would we place a so-called social drug like cannabis in this divide? What about nicotine or alcohol?

The answers we get depend on who we ask. As far as the law is concerned, the dividing line is defined in black and white. As far as the party-going teenager is concerned, the law is an ass. As far as we are concerned, the questions are irrelevant. Trying to dividedrugs into two categories—safe or unsafe, good or bad—is futile and could even be dangerous.

First, let us consider the so-called ‘good’ drugs used in medicines. How ‘good’ are they? If a drug is to be truly ‘good’ it would have to do what it is meant to do, have no toxic or unwanted side eff ects, and be easy to take.

How many drugs fit these criteria?

The short answer is ‘none’. Th ere is no pharmaceutical compound on the market today that can completely satisfy all these conditions. Admittedly, some come quite close to the ideal. Penicillin, for example, has been one of the safest and most eff ective antibacterial agents ever discovered. Yet, it too has drawbacks. It cannot kill all known bacteria and, as the years have gone by, more and more bacterial strains have become resistant. Moreover, some individuals can experience severe allergic reactions to the compound.

Penicillin is a relatively safe drug, but there are some drugs that are distinctly dangerous. Morphine is one such example. It is an excellent analgesic, yet there are serious side eff ects, such as tolerance, respiratory depression, and addiction. It can even kill if taken in excess.

Barbiturates are also known to be dangerous. At Pearl Harbor, American casualties were given barbiturates as general anaesthetics before surgery. However, because of a poor understanding about how barbiturates are stored in the body, many patients received sudden and fatal overdoses. In fact, it is thought that more casualties died at the hands of the anaesthetists at Pearl Harbor than died of their wounds.

To conclude, the ‘good’ drugs are not as perfect as one might think. What about the ‘bad’ drugs then? Is there anything good that can be said about them? Surely there is nothing we can say in defence of the highly addictive drug known as heroin?

Well, let us look at the facts about heroin. It is one of the best painkillers we know. In fact, it was named heroin at the end of the nineteenth century because it was thought to be the ‘heroic’ drug that would banish pain for good. Heroin went on the market in 1898, but five years later the true nature of its addictive properties became evident and the drug was speedily withdrawn from general distribution. However, heroin is still used in medicine today—under strict control, of course. The drug is called diamorphine and it is the drug of choice for treating patients dying of cancer. Not only does diamorphine reduce pain to acceptable levels, it also produces a euphoric effect that helps to counter the depression faced by patients close to death. Can we really condemn a drug which does that as being all ‘bad’?

By now it should be evident that the division between good drugs and bad drugs is a woolly one and is not really relevant to our discussion of medicinal chemistry. All drugs have their good and bad points. Some have more good points than bad and vice versa, but, like people, they all have their own individual characteristics. So how are we to define a drug in general?