Quote Originally Posted by RICHARD View Post
Please explain that sentence.

I am sitting here, stunned.

And give me an example-I'm stripping my brain thinking about this.

Stunned? It's medical fact. Not like it's my opnion, or anything.

To echo ES, I don't understand how you don't know this if you indeed worked in a medical environment, but I'll explain it for you anyway.

Pathogens, bacteria in particular, undergo mutation in a number of their population. The change in their genotype may give them an immunity to the effects of a drug. Most of the time, it doesn't. But sometimes it does.

Under normal circumstances, i.e. without the presence of drugs, the typical strains and the mutated, resitant organism live alongside each other, in the ileum, for example. The strains compete with one another to survive. In these conditions, the resistant organism have no advantage over the typical strains, and it is highly likely that the resistant organism will die out. Thus, it's resistant gene is lost.

However, introduce a drug into the environment. All the typical strains are destroyed, but the resistant organism remains. It now has no competition and is able to reproduce quite happily, each of it's daughter cells carrying this saving grace gene. The drug administered is rendered useless against the pathogen. The pathogen spreads to other people and now we have nothing effective to fight it.

That is how natural selection works - a change in the environment favouring a particular genotype, causing extinction and evolution.

The more drugs that are being exposed to the pathogens, the better conditons we are providing for much more dangerous strains. Plus, many bacteria are able to exchange genetic information via plasmids, or indeed their own DNA, to other species of pathogen, so the resistance genes are not limited to only one condition.

An example? Staphylococcus aureus! S.Aureus is present in your respiratory system and on the surface of your skin right now. Occasionally, it will cause a mild throat infection. At first, we treated it with penicillin, as pencillin was the wonder, cure-all drug at that time. Before long, penicillin no longer worked. At that time, no one really knew why.

Then this condition was treated with methicillin. It was oversubscribed as people wanted to keep popping these pills everytime they felt a bit hoarse. So we get methicillin-resistant staphyloccocus aureus. The first MRSA.

So then we're in a bit of trouble, and combat MRSA with vancomycin. We can't find anything else to administer but vancomycin. The inevitable happens. Now the most dangerous form of MRSA is Multiple Resistant Staphylococcus aureus.

So, again, it is practically and morally wrong to oversubscribe drugs.