Source: http://www.fdalawblog.net/2013/08/an-fda-warning-letter-that-does-not-add-up-otc-drug-monograph-combination-products-with-conflicting/
Timestamp: 2019-04-19 22:33:43+00:00

Document:
When the time intervals or age limitations for administration of the individual ingredients differ, the directions for the combination product may not exceed any maximum dosage limits established for the individual ingredients in the applicable OTC drug monograph.
Similar statements appear in other OTC drug monographs at 21 C.F.R. § 333.160(d) (topical antimicrobial drug products), § 346.52(d) (anorectal drug products), § 347.60(d) (skin protectant drug products), § 349.79(d) ophthalmic drug products ), § 352.60(d) (sunscreen drug products), and § 358.760(d) (dandruff drug products).
What each regulation says in essence is that when the directions for use of an OTC combination drug product results in a conflict in time intervals, the directions should be written to ensure that the maximum dosage limits established under the applicable monograph for the individual ingredients are not exceeded.
Given all of this history, why then would FDA tell Sovereign that there is no way to write adequate directions for use for the combination cough/cold OTC drug products it contract manufacturers that would meet the dosing direction and dosage limit requirements for each individual active ingredient under the monograph? That’s the truly perplexing part of this story. Perhaps FDA made the statements in error and has not yet acted to correct them. If that’s the case, then the uncorrected Warning Letter sends the wrong – indeed, incorrect – message to the OTC drug industry. Or perhaps there’s more to the story and something is brewing at FDA. But if that were the case, then one might have expected to see more on the topic over the past 8 months. So we’re left scratching our heads.

References: § 333
 § 346
 § 347
 § 349
 § 352
 § 358