So I had my 1st dose of a biologic yesterday. It was 1ml injected into my stomach. I only need to do this once every 8 weeks and it blocks a protein in my immune system from working. But wouldn’t it leave the body after a couple of days? How can it have such an everlasting effect?
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Biologics are different from “small molecule” drugs in that they are designed to look/function similar your body’s normal proteins. They can also be modified to enhance certain activities or increase stability.
The main ways your body processes small molecule drugs typically (not always) occurs in the gut, liver, and kidneys. Let’s look at these one by one.
Gut: you inject the biologic. Gut is bypassed.
Liver: the liver generally has the machinery to process and degrade small molecules via certain enzymes. Even though these enzymes can be relatively large, the action only occurs at a specific site. Think of a pair of scissors. Even though there are several parts, the cutting only occurs at a point in between the blades. But there is a size limit for both scissors and enzymes. For example, you wouldn’t cut down an oak tree with a pair of scissors, and these enzymes can’t break down large proteins.
Kidney: your kidneys actually help *reabsorb* proteins. You shouldn’t be peeing out proteins. If you are, something has gone wrong.
Proteins have a different breakdown and degradation process than regular small molecule drugs do. As such, IgG (one of the common forms of biologic medications) has a half-life of 10-21 days. This can be further extended by making certain changes to specific areas of the protein. But even assuming on the low end of that range, and using the 5 half-life rule for complete elimination of a drug, that’s 50 days until the biologic drug is fully removed from your body. This allows for extended dosing intervals and less frequent injections.
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