The FDA has just approved galcanezumab (Emgality), the third CGRP monoclonal antibody for the prophylactic treatment of migraines. It follows erenumab (Aimovig) and fremanezumab (Ajovy) and just like these two drugs it appears to be very safe and very effective for over 50% of patients.
Galcanezumab is also administered by a monthly subcutaneous injection. The initial dose is two 120 mg injections, followed by a single 120 mg injection every month. Similarly to erenumab, it comes in an autoinjector pen which is easy to self-administer. Fremanezumab is not available in an autoinjector pen but only in a small prefilled syringe, which may make some patients hesitant to use it, however injecting with a prefilled syringe is often less painful.
Galcanezumab and fremanezumab list as their only side effect injection site reaction, while erenumab also has the side effect of constipation. Erenumab was approved four months ago and at our Center we have already injected about 300 patients. Constipation is a problem for a small number of patients and in a couple of them it was severe enough that they stopped the injections.
Fremanezumab was approved only a couple of weeks ago and we’ve treated only about a dozen patients so far, so it is too early to tell if it will also cause constipation. After all, these three drugs are similar to each other in that they block the effect of calcitonin gene-related peptide (CGRP), a chemical released during a migraine attack. The only difference in the way they work is that erenumab blocks the CGRP receptor, where the CGRP molecule attaches itself, while the other two drugs block the actual CGRP molecule. It is possible that this difference in the mechanism of action is why erenumab is more likely to cause constipation.
We have also seen one patient who developed a rash about 5-6 days after being injected with erenumab, which resolved with a short course of prednisone.
All three manufacturers offer a free trial, in come cases for up to a year. Many insurers are starting to pay for these truly remarkable medications, although most require that the patient first tries and fails one or two inexpensive oral preventive medications. We’ve also encountered some insurers who will pay for either Botox or erenumab, but not for both. This is a problem for some of our patients who get partial relief from each treatment and almost complete relief when these two are combined. One strategy is to continue obtaining Botox through the insurance and getting one of the monoclonal antibodies through the free trial program.
One common question we get asked is how soon will the injection work. In some patients the relief begins in a couple of days, but we have also seen patients who improve only after 2 treatments. The large trials that led to the FDA approval suggest that each subsequent treatment will provide better relief than the previous one.
