Dimethyl fumarate delayed-release capsules may decrease lymphocyte counts. In the MS placebo-controlled trials, mean lymphocyte counts decreased by approximately 30% during the first year of treatment with dimethyl fumarate delayed-release capsules and then remained stable. Four weeks after stopping dimethyl fumarate delayed-release capsules, mean lymphocyte counts increased but did not return to baseline. Six percent (6%) of dimethyl fumarate delayed-release capsules patients and <1% of placebo patients experienced lymphocyte counts <0.5x10
9/L (lower limit of normal 0.91x10
9/L). The incidence of infections (60% vs 58%) and serious infections (2% vs 2%) was similar in patients treated with dimethyl fumarate delayed-release capsules or placebo, respectively. There was no increased incidence of serious infections observed in patients with lymphocyte counts <0.8x10
9/L or
<0.5x10
9/L in controlled trials, although one patient in an extension study developed PML in the setting of prolonged lymphopenia (lymphocyte counts predominantly <0.5x10
9/L for 3.5 years)
[see Warnings and Precautions (
5.2)].
In controlled and uncontrolled clinical trials, 2% of patients experienced prolonged, severe lymphopenia, (defined as lymphocyte counts <0.5 x 10
9/L for at least six months); in this group of patients, the majority of lymphocyte counts remained <0.5x10
9/L with continued therapy. In these patients with prolonged, severe lymphopenia, the median time for lymphocyte counts to return to normal after discontinuing dimethyl fumarate delayed-release capsules was 96.0 weeks.
In these controlled and uncontrolled clinical studies, among patients who did not experience prolonged, severe lymphopenia during treatment, the median times for lymphocyte counts to return to normal after discontinuing dimethyl fumarate delayed-release capsules were as follows:
• 4.3 weeks in patients with mild lymphopenia (lymphocyte count ≥0.8x10
9/L) at discontinuation,
• 10.0 weeks in patients with moderate lymphopenia (lymphocyte count 0.5 to <0.8x10
9/L) at discontinuation, and
• 16.7 weeks in patients with severe lymphopenia (lymphocyte count <0.5x10
9/L) at discontinuation.
Dimethyl fumarate delayed-release capsules have not been studied in patients with pre-existing low lymphocyte counts.
Obtain a CBC, including lymphocyte count, before initiating treatment with dimethyl fumarate delayed-release capsules, 6 months after starting treatment, and then every 6 to 12 months thereafter, and as clinically indicated. Consider interruption of dimethyl fumarate delayed-release capsules in patients with lymphocyte counts less than 0.5 x 10
9/L persisting for more than six months. Given the potential for delayed recovery of lymphocyte counts, continue to obtain lymphocyte counts until their recovery if dimethyl fumarate delayed-release capsules are discontinued or interrupted due to lymphopenia. Consider withholding treatment from patients with serious infections until resolution. Decisions about whether or not to restart dimethyl fumarate delayed-release capsules should be individualized based on clinical circumstances.