This is just a diagram of Drug Inactivation. Here is a classical picture of A macrolide. It's very similar to erythromycin. When it's intact, it's active but it could be phosphorylated in this position. So you get the phosphate added. When it's got that, it's inactive. It's no longer active in the microbe that it's directed at. Same thing down here, you've got a break in the bond by an esterase. Now that ring is opened, it's no longer active. That's also true of penicillin. When you have a beta lactamase, there is a similar type of bond that's critical. It gets broken and your compound is inactive.

Target modification. Ribosome changes; even though the drug gets in, it can't bind to the ribosome. This mechanism commonly has methyl groups added to the ribosome. Drugs can't bind to the ribosome. The organism is no longer susceptible to the agent.

Efflux. The drug gets in. Can't stay in long enough to do its job. It's pumped out very fast. We're finding this more often now. Even in Gram positive agents where it wasn't so obvious such as Strep. pneumoniae. Strep. pneumoniae, for instance, doesn't alter its cell wall or anything. This appears to be a common case with macrolides. It's pumping it out. It's not destroying the macrolide. The macrolide just never gets in or if it gets in, it's pumped out too rapidly to be effective.

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