21 CFR §516.137

1. (a)Within 90 days after the filing of a request for a determination of eligibility for indexing based on § 516.129(c)(7)(i), or 180 days for a request based on § 516.129(c)(7)(ii), FDA shall grant or deny the request, and notify the requestor of FDA's decision in writing.
2. (b)If FDA denies the request, FDA shall provide due notice and an opportunity for an informal conference as described in § 516.123 regarding its decision. A decision of FDA to deny a request for determination of eligibility for indexing following an informal conference shall constitute final agency action subject to judicial review.