Fremanezumab (Ajovy) was just approved by the FDA for the preventive treatment of migraine headaches. It is the second drug, following erenumab (Aimovig), with a similar mechanism of action. While erenumab blocks calcitonin gene-related peptide (CGRP) receptor, fremanezumab binds to the CGRP molecule and blocks its attachment to the CGRP receptor. Both are very effective in preventing migraine attacks and both, so far, appear to be very safe. Just like erenumab, it is approved for the prevention of migraines without regard to the frequency of attacks, unlike onabotulinumtoxinA (Botox), which is only approved for chronic migraines, which are defined as occurring on 15 or more days each month.
Here are some differences between the two drugs that we know of so far. Fremanezumab can be injected monthly or with a triple dose, every three months. Considering that one of my patients developed a rash from erenumab (no surprise there – any drug can cause an allergic reaction), I probably will start with a single shot once a month and then may give a triple dose every three months. The second difference is that constipation is not listed as a side effect of fremanezumab in the FDA-approved prescribing information, while it is listed as occurring in 3% of patients on erenumab. Since these drugs have a similar mode of action, I will not be surprised if fremanezumab also causes constipation in some patients. So far, only two of my patients (out of about 300) declined to continue erenumab because of constipation.
Erenumab is available only in an easy-to-use autoinjector pen, while fremanezumab comes only in a prefilled syringe. I suspect some patients will prefer to come into the office every three months to get their fremanezumab injections, rather than inject themselves, but the majority will self-inject it. One advantage of prefilled syringes is that a small test dose can be given before giving the entire amount. This is what I plan to do for my patient who developed a rash from erenumab.
