I've just come across an interesting article about
returning to a biologic that worked in the past:https://www.gastroenterologyandhepatology.net/archives/november-2019/restarting-biologic-agents-after-a-drug-holiday/
I didn't know that thinking had moved on from the old advice that once you stop a biologic you can't return to it due to risk of producing antibodies.
In the article there's an interesting explanation of a possible reason for why we become unresponsive to biologics after a while:
DR: The reason that doctors can now have discussions with patients about
cycling back to a treatment that was tried previously is because of the theoretical concept that the inflammatory pathways in an active IBD patient may change based on the treatment and time. For example, if a doctor treats a patient with an anti–tumor necrosis factor (TNF) drug such as infliximab, and the patient responds and does well initially but then loses response, the presumption is that his or her inflammation may have been driven by TNF, and, therefore, the anti-TNF drug treats it. However, if the loss of response is not due to antidrug antibodies, it may be due to a change in mechanism, or what some doctors call mechanistic escape. That principle, in theory, means that the patient had a different inflammatory pathway become activated. This may occur because the human body has many collateral and backup systems. If one inflammatory pathway is blocked, and whatever is driving the patient’s Crohn’s disease or ulcerative colitis has not been addressed, the body will try to find a new pathway to keep driving the disease forward. When a new pathway becomes dominant, the patient loses response to the current treatment and the doctor tries a different therapy, and perhaps that works for a while, but at some point, the patient may lose response to the new therapy.
What we have started to see is that doctors can cycle back to the drug that the patient lost response to in the first place. Researchers have now demonstrated that this can be done safely in many patients as long as the loss of response was not due to antidrug antibodies. That is the one exception where it is not possible to go back to the original drug.