What is the benefit of drugs with short half lives vs long half lives

In My Humble Opinion
1

In many classes of drugs there are drugs with short half lives and drugs with long half lives.

Prozac has a half life of 5 days. Paxil has a half life of 21 hours.

Xanax is about 12 hours, Valium is 2 days.

I know drugs with a long half life are good if you need to taper off an addictive drug. People physically addicted to benzos are switched to valium and tapered. People addicted to SSRIs are switched to Prozac and tapered. People addicted to opiates are switched to buprenorphine or methadone.

So one benefit of long half life drugs is the ability to taper off addictive classes of medications.

For other drugs it means they can be dosed more sporadically. With testosterone injections, or injections of anti-psychotics, a long half life drug would need to be injected less often.

So theres at least 2 benefits from long half life drugs

  • They make them easier to taper off if the drug is addictive
  • They can be dosed less often

So what are the benefits of shorter half life drugs?

My impression is there are benefits like, if its a new drug and it doesn’t agree with you, its out of your system quickly. Or if its a drug with toxic effects or lots of interactions with other drugs, its out of your system more quickly.

But what are the pros and cons of long half life vs short half life drugs in the same class of medication?

2

Some drugs might keep you awake longer than you want. So if you want to sleep you need a short half-life.

I have ADHD and I prefer Ritalin and Adderall over Vyvanse for this reason.

3

Not an expert, but I expect one advantage of long half life drugs is that it allows for a more even dosage over time. As opposed to drugs with a short duration, which normally consist of a spike when applied in which they are a higher dose than desired, followed by a longer period when they are understrength.

4

Of course, don’t forget that there are many different factors that determine how “good” a drug is, and you can’t just design a custom drug that has exactly all the parameters you want. Maybe there are two drugs known for some condition, and one has a higher rate of success, and the more successful one just happens to have a short half life.

5

Thats a good point. I really wish they would release the S-isomer of modafinil. The R-isomer is available as armodafinil, but it has a 15 hour half life. Meanwhile the S-isomer only has a 4 hour half life, which means if you take it in the morning its 95% gone by bedtime.

6

D isomer. (Nitpick)

I have some recollection that there was an advantage to have high short spikes of some antibiotics (like penicillin l) but I don’t remember why.