This is an outsider’s view of what drug repurposing is about.
When a drug is approved by the FDA, it is approved for a specific purpose. When an FDA-approved drug is used safely for a purpose other than for what it was approved, that is referred to as using it off-label. If a drug is proven effective for a new purpose, then it has been repurposed (aka repositioned). I think it will be FDA approved for that new purpose only if someone stands to profit handsomely from it, which is not the case for generic drugs.
There is some in-between territory—for example, when something is TGA-labeled. My impression of that term is that the TGA (Therapeutic Goods Administration) is like the FDA (Food and Drug Administration) but in Australia and whose goals are to help ensure therapies are available to people rather than to administer them into the ground. (Side note: In Japan, the regulatory agency is the PMDA: Pharmaceuticals and Medical Devices Agency.)
Here’s an example of off-label usage: amitriptyline is a tricyclic antidepressant that was found to be effective at reducing migraine frequency in many people. It’s not that antidepressants in general are considered good migraine preventatives; it’s just that amitriptyline was found to reduce the frequency of migraines in many people regardless of depression. It’s TGA-labeled for this purpose but not FDA-approved.
How do drugs get repurposed like this? Testers must test them on humans in rigorous, double-blind studies.
All drugs have side effects and risks, but many FDA-approved drugs are considered so safe that they become part of the smorgasbord of drugs that can be considered available to anyone, with and without the disease that was the original target. In other words, you don’t need to be depressed to take an antidepressant. As such, there will often be hundreds of trials looking for additional purposes of already successful drugs.
Jumping the gun
My impression of this repurposing quest is that it has expanded to clinical trials for new drugs that have no approved purpose yet, where only the safety has been evaluated. Clinical trials go in five phases: zero through four. The early phases are for evaluating safety, tolerability, and side effects. As soon as that work is done, others can swoop in and start testing for a variety of purposes, even before the drug is fully evaluated for its original intended purpose.
Also, drug testing outside of the U.S. is often years ahead of the U.S., presumably because the rules are more lenient. For example, loratadine was FDA-approved in 1993 and went OTC (over the counter) in 2002. However, it was available in Europe in 1988 and available there OTC in 1990.
I, nonhuman
Here’s another twist. Researchers might test FDA-approved drugs on animals, with the goal being to identify promising areas of further studies on humans but where the safety of the animals (e.g., worms, fruit flies, etc.) is not a concern. This is the focus of my next article, but I wanted to back up and take a detour through this area first.
Trials and tribulations
The following website provides “information on publicly and privately supported clinical studies on a wide range of diseases and conditions.”
A major weakness of the site is that it rarely contains study results. I think that no pharmaceutical company wants to make results readily accessible, especially if they are bad. If the results are bad, they like to act as if nothing ever happened. If the results are not bad, they like to control the narrative via time-sensitive press releases, not by modifying the clinical trials database.
I have used the website to explore a little bit of what’s going on with the search for finding new purposes for existing drugs. For example:
Varenicline (Chantix)
https://clinicaltrials.gov/search?term=varenicline (369 matches)
https://clinicaltrials.gov/search?term=varenicline+and+sca (1 match)
This drug (a nicotinic agonist, meaning it’s similar to nicotine) is fairly well-known in SCA3 circles, because the results were that ataxia symptoms improved:
https://www.ncbi.nlm.nih.gov/pubmed/22323747
However, it’s not a very popular SCA3 drug because few people are willing to take a newfangled drug with many side effects just for some possible symptom relief.
Lithium has been around since the 1800s. So why not see what effect it has on various diseases?
https://clinicaltrials.gov/search?term=lithium (473 matches)
https://clinicaltrials.gov/search?term=lithium+and+sca (4 matches)
Here’s a drug that’s used for some with ALS (amyotrophic lateral sclerosis), a disease somewhat symptomatically similar to SCA but that can progress about a hundred times faster:
Riluzole
https://clinicaltrials.gov/search?term=riluzole (116 matches)
https://clinicaltrials.gov/search?term=riluzole+and+sca (4 matches)
https://clinicaltrials.gov/search?term=riluzole+and+sclerosis (72 matches)
[Sarcasm alert] And why not test some dietary supplements? I mean, if people are buying it at Whole Foods, why not inject it directly into your bloodstream and see what happens?
Trehalose
https://clinicaltrials.gov/search?term=trehalose (44 matches)
Others
https://clinicaltrials.gov/search?term=garlic (84 matches)
https://clinicaltrials.gov/search?term=turmeric (192 matches)
https://clinicaltrials.gov/search?term=CBD (824 matches)
https://clinicaltrials.gov/search?term=cannabis (1192 matches)
Addendum
2017-04-20: Two examples of drug repurposing around neurodegeneration: trazodone and dibenzoylmethane (DBM).
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