An NDC identifies a specific drug product and package listed with the FDA. A HCPCS code identifies a service, supply or drug for billing: Level I (CPT) covers procedures and services, and Level II covers drugs, supplies and equipment. Drugs given in a clinic are usually billed with a HCPCS Level II code and reported with their NDC.
Two different questions
An NDC answers "which product, from which labeler, in which package?". A HCPCS code answers "what was provided, and how much counts as one unit?". One HCPCS drug code usually covers every labeler's version of a drug, while each of those products has its own NDCs.
Who maintains them
Labelers list their products with the FDA, which publishes the NDC Directory. HCPCS Level I is the AMA's CPT code set. HCPCS Level II is maintained by CMS and updated quarterly.
Which HCPCS codes describe drugs
Most drug codes are J-codes. Drugs can also appear under Q-codes (often temporary codes), C-codes (used by hospital outpatient departments under Medicare's OPPS, including pass-through drugs), and some A- and S-codes. Vaccines are the main exception: they have CPT product codes (90xxx) rather than HCPCS Level II codes.
On a claim
The HCPCS code and its units go in the service line; the NDC, its unit qualifier and quantity go with the same line in N4 format. The administration service is a separate CPT line, such as an infusion or injection code.
Questions
Do pharmacy claims use HCPCS codes?
Generally no. Retail pharmacy claims (NCPDP) are billed by NDC. HCPCS drug codes are used on medical claims for drugs a clinician gives or supplies.