How are drugs developed to target specific areas (pain/allergies/disease). How do you translate scientific body knowledge into a drug that targets that area. And how do scientists determine cross reactions to other drugs or conditions. Do they have to test every combo?
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Drugs are chemicals that bind to a specific molecular target and usually block that target from doing the bad thing it was doing. The premise of a good drug is that it is specific and selective- meaning it binds very well to the thing you want it to, and not to anything else. This is easiest to accomplish when the target belongs to a different organism, like a bacteria or virus, and more difficult to do when it needs to bind to a target on a cell in the body. As the science gets better, we can replace older less specific drugs – think chemotherapy which targets rapidly dividing cells like cancer cells, but also other “normal” cells to a lesser extent, thus making you very sick, and is now being replaced with drugs that recognize specific molecules that cancer cells will have that normal cells do not, or immunotherapy, which elicit that immune system to recognize a cancer target and destroy it.
Most drugs target molecules called enzymes – which control a single interaction in the cell. Once you determine the enzyme that you need to inhibit, you can then chemically refine the drug to improve its selectivity so that it does not bind to other similar enzymes. For instance, aspirin inhibits the Cox2 enzyme, but it also inhibits the Cox1 enzyme. Ibuprofen and other newer NSAIDs target Cox2 and bind much less to Cox1 so they are more selective. They don’t inhibit Cox1 controlled blood clotting or stomach neutralization nearly as much as aspirin does, while still relieving inflammation from Cox2.
Most large pharmaceutical companies have multiple divisions, the basic chemistry and biology research to discover new drugs and refine them (R&D), up scaling production and modifying the format of the drug to be efficiently available and active biologically (Formulations and Pharmacokinetics) and testing in animals and humans for proper dosing, effectiveness and safety (Clinical Development). Smaller companies will do part of the soup to nuts, and partner with other companies to accomplish the rest. Clinical trials are extensive and very, very expensive (think hundreds of millions of dollars).
There are ways to determine many drug interactions just based on mechanisms of action, as well as how the drug is metabolized by the liver. The reason many prescriptions are labeled to to warn you not to eat grapefruit has to do with the fact that grapefruit has a big effect on the way the liver handles things, and it will cause an unwanted blood level of the drug. Most interactions are easy to predict, but others may not be, and will be added as the drug goes through clinical trials. The last stage of clinical development can last years, even after the drug is approved for general use, and if unexpected interactions crop up, they will be added to the database of the drug.
There is much, much more to it but I gave it my best shot!
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