21 CFR §516.153

1. (a)Within 180 days after the filing of a request for addition of a new animal drug to the index, FDA shall grant or deny the request and notify the requestor of FDA's decision in writing.
2. (b)If FDA denies the request for addition of a new animal drug to the index, FDA shall provide due notice and an opportunity for an informal conference as described in § 516.123. A decision of FDA to deny a request to index a new animal drug following an informal conference shall constitute final agency action subject to judicial review.