Developing new drugs is vital to being able to treat many medical problems. However drug development is a lengthy process, taking up to 15 years and can cost in the region of £450 million (approximately $800 million). How does the drug discovery process work, and why does it cost so much?
Medical Needs: Necessity is the Mother of Invention
Drug discovery begins by identifying a medical need. This portion of the process tends to focus on diseases that affect the developed world, to allow pharmaceutical companies to get a return on their sizable investment. Next, the company must work to understand the mechanism of the disease in order to identify a suitable drug target.
Using appropriate analytical tests, labs can screen compounds to determine whether they interact with the target in question. For example, high-throughput screening is an automated approach that can test tens of thousands of compounds to find a lead. A ‘lead compound’ has the desired pharmacological property and is the starting point for drug design.
From Lead Compound into a Drug
Researchers then carry out structure-activity relationship studies to determine how the lead compound interacts with its target, and to identify the functional groups responsible for this biological activity. The lab must retain these groups, but can alter other areas of the compound. This allows them to produce new compounds with improved properties – such as being more selective, which results in fewer side effects and being easier (and therefore cheaper) to synthesize.
As well as optimizing the interaction between the lead compound and the target, it is also important to look at how the body processes the compound (known as pharmacokinetics). We break pharmacokinetics into five main categories: Absorption (how the drug is taken up by the body), distribution (how the drug reaches its target), metabolism (how the body breaks the drug down), excretion (how the drug is removed from the body) and toxicity (harm the drug can cause to healthy tissue).
Once a lab finds that a lead compound has the desired biological effect and a suitable pharmacokinetic profile and confirms that the new compound offers advantages over existing therapies, it can enter clinical trials. Only about 1-5 compounds will make it to phase I studies from the tens of thousands of compounds initially screened.
Drug Development Stages: Clinical Studies
Phase I studies determine how well patients tolerate the drug. Phase II studies determine whether the drug has the desired pharmacological effect to treat the disease, as well as continuing to test its pharmacokinetic profile and toxicity in humans. Researchers can also work out the dosing regimen during this phase. About 1-2 drugs will reach this point out of tens of thousands that go through initial screening. Phase III studies test patients taking the drug against those on a placebo to determine whether the drug has the desired pharmacological effect, and also whether it really does offer advantages over existing therapies.
Drug Approval Process: Finish Lines are Few and Far Between
Once a compound has made it through all these stages, manufacturers can then market the compound and prescribe it as a drug, although they will continue to monitor it for long term safety, any rare side effects not picked up in clinical trials, and its efficiency. Drugs have been withdrawn at this stage because of serious side effects or lack of biological activity resulting in poor treatment outcome. New drug discovery really is a challenging process.
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Hopkins, A.L, Groom, C.R and Alex, A. Ligand efficiency – A useful metric for lead selection. (2004). Drug Discovery Today. Accessed November 17, 2013.
Rawlins, M. D. Cutting the cost of drug development? (2004). Nature Reviews Drug Discovery. Accessed November 17, 2013.
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