SUPPLEMENTARY INFORMATION:

FDA initially approved NDA 010401 for MYSOLINE (primidone) suspension, 250 mg/5 mL, on July 5, 1956. In 2001, MYSOLINE (primidone) suspension, 250 mg/5 mL, was discontinued after antimicrobial effectiveness testing raised concerns about potential microbial contamination, in particular with Pseudomonas aeruginosa. In the Federal Register of January 2, 2026 (91 FR 148), FDA determined that MYSOLINE (primidone) suspension, 250 mg/5 mL, was withdrawn from sale for reasons of safety or effectiveness. FDA noted that, as a scientific matter, before MYSOLINE (primidone) suspension, 250 mg/5 mL, could be considered for reintroduction to the market, a reformulation would be required including establishment of preservative content acceptance criteria and correlation with passing antimicrobial effectiveness testing results. FDA stated that the NDA holder for MYSOLINE (primidone) suspension, 250 mg/5 mL, would have to demonstrate the safety and effectiveness of the reformulated product. FDA further stated that, at that time, no new formulation had been approved for MYSOLINE (primidone) suspension, 250 mg/5 mL.

On June 12, 2026, FDA asked FHTA whether it intended to reformulate MYSOLINE (primidone) suspension, 250 mg/5 mL, to establish preservative content acceptance criteria and correlation with passing antimicrobial effectiveness testing results, or whether FHTA would agree to waive the opportunity for hearing and permit FDA to withdraw approval of NDA 010401 under 21 CFR 314.150(d) (§ 314.150(d)). FDA referred to its determination that MYSOLINE (primidone) suspension, 250 mg/5 mL, was withdrawn from sale for reasons of safety or effectiveness in connection with concerns regarding potential microbial contamination, in particular with Pseudomonas aeruginosa. On June 22, 2026, FHTA responded that it was not seeking a hearing and agreed to withdrawal of NDA 010401 pursuant to § 314.150(d).

For the reasons discussed above, which FHTA does not dispute in its response, and in accordance with FHTA's response, approval of NDA 010401 for MYSOLINE (primidone) suspension, 250 mg/5 mL, and all amendments and supplements thereto, is withdrawn under § 314.150(d). Distribution of MYSOLINE (primidone) suspension, 250 mg/5 mL, into interstate commerce without an approved application is illegal and subject to regulatory action (see sections 505(a) and 301(d) of the Federal Food, Drug, and Cosmetic Act (21 U.S.C. 355(a) and 331(d)).

91 FR 61408