CGRPs in Real World: Similar Efficacy, More AEs

Richard Mark Kirkner

June 19, 2020

The calcitonin gene–related peptide receptor monoclonal antibodies (CGRP mAbs) for treatment of migraine have gained wide acceptance since their approval in 2018, but a real-world study has reported adverse event rates higher than those the preapproval clinical trials reported and has found that patients who fail on one of the treatments are likely to fail again if they're switched to another.

At the virtual annual meeting of the American Headache Society, Larry Robbins, MD, assistant professor of neurology at Chicago Medical School, North Chicago, reported on the results of his postapproval study of 369 migraine patients taking one of the three approved CGRP mAbs. "If patients do not do well on one mAb, it is sometimes worthwhile to switch, but most patients do not do well from the second or third mAb as well," Dr. Robbins said in an interview. "In addition, there are numerous adverse effects that were not captured in the official phase 3 studies. Efficacy has held up well, but for a number of reasons, the true adverse event profile is often missed."

Assessing Efficacy and Adverse Events

In evaluating the efficacy of the three approved CGRP mAbs, Dr. Robbins used measures of degree of relief based on percentage decrease of symptoms versus baseline and the number of migraine days, combined with the number of moderate or severe headache days. Most of the patients kept calendars and were interviewed by two headache specialists. The study also utilized a 10-point visual analog scale and averaged relief over 3 months.

Of the patients on erenumab (n = 220), 10% described 95%-100% relief of symptoms, 24% reported 71%-100% relief, 34% described 31%-70% relief, and 43% experienced 0%-30% relief. Adverse events among this group included constipation (20%), nausea (7%), increased headache and fatigue (5% for each), and joint pain and depression (3% for each). Three patients on erenumab experienced unspecified serious adverse reactions.

In the fremanezumab group (n = 79), 8% described 95%-100% relief, 18% had 71%-100% relief, 33% experienced 31%-70% improvement, and 50% had 30% improvement or less. Adverse events in these patients included nausea, constipation, and depression (6% each); increased headache and muscle pain or cramps (5% each); rash, joint pain, anxiety, fatigue, or weight gain (4% for each ); and injection-site reactions, irritability, or alopecia (3% combined).

Patients taking galcanezumab (n = 70) reported the following outcomes: 3% had 95%-100% relief of symptoms, 14% had 71%-100% relief, 46% with 31%-70% relief, and 40% had 0%-30% relief. This group's adverse events included constipation (10%); depression and increased headache (6% for each); nausea, fatigue, or injection-site reactions (4% each ); and muscle pain or cramps, rash, anxiety, weight gain, or alopecia (3% each).

Dr. Robbins also assessed switching from one CGRP mAb to another for various reasons. "When the reason for switching was poor efficacy, only 27% of patients did well," he stated in the presentation. "If the reason was adverse events, 33% did well. When insurance/financial reasons alone were the reason, but efficacy was adequate, 58% did well after switching."

Overall, postapproval efficacy of the medications "held up well," Dr. Robbins noted. "Efficacy after 2 months somewhat predicted how patients would do after 6 months." Among the predictors of poor response his study identified were opioid use and moderate or severe refractory chronic migraine at baseline.

However, the rates of adverse events he reported were significantly greater than those reported in the clinical trials, Dr. Robbins said. He noted four reasons to explain this discrepancy: the trials did not use an 18-item supplemental checklist that he has advocated to identify patients at risk of side effects, the trials weren't powered for adverse events, patients in the trials tended to be less refractory than those in the clinic, and that adverse events tend to be underreported in trials.

"Adverse events become disaggregated, with the same descriptors used for an adverse event," Dr. Robbins said. "Examples include fatigue, somnolence, and tiredness; all may be 1%, while different patients are describing the same adverse event. It is possible to reaggregate the adverse events after the study, but this is fraught with error."

Uncovering Shortcomings in Clinical Trials

Emily Rubenstein Engel, MD, director of the Dalessio Headache Center at the Scripps Clinic in La Jolla, Calif., noted that Dr. Robbins' findings are significant for two reasons. "Dr. Robbins has uncovered a general flaw in clinical trials, whereby the lack of consistency of adverse event terminology as well as the lack of a standardized questionnaire format for adverse events can result in significant under-reporting of adverse events," she said.

"Specifically for the CGRPs," Dr. Engel continued, "he has raised awareness that this new class of medication, however promising from an efficacy standpoint, has side effects that are much more frequent and severe than seen in the initial clinical trials."

Dr. Robbins reported financial relationships with Allergan, Amgen and Teva. Dr. Engel has no financial relationships to disclose.

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