Z79.631 Long term (current) use of antimetabolite agent

Billable ICD-10-CM code, FY2026. Exempt from present-on-admission (POA) reporting.

Applicable to

• Long term (current) use of 5-fluorouracil
• Long term (current) use of 6-mercaptopurine
• Long term (current) use of cytarabine
• Long term (current) use of methotrexate

Applies from Z79 Long term (current) drug therapy

Includes

• long term (current) drug use for prophylactic purposes

Excludes2 (not included here)

• drug abuse and dependence (F11-F19)
• drug use complicating pregnancy, childbirth, and the puerperium (O99.32-)

Code also

• any therapeutic drug level monitoring (Z51.81)

Applies from Z79.6 Long term (current) use of immunomodulators and immunosuppressants

Excludes2 (not included here)

• long term (current) use of steroids (Z79.5-)
• long term (current) use of agents affecting estrogen receptors and estrogen levels (Z79.81-)

MS-DRG index

Defines the logic of DRG(s) 949-950 in MDC 23.

Medicare Code Edits (MCE v43.1 (April 2026))

• Unacceptable principal diagnosis: These codes describe a circumstance which influences care but is not a current illness or injury, or capture only an underlying condition, and are unacceptable as principal diagnosis.

Code annotations containing back-references to Z79.631

Back-references to Z79

• Code Also: Z51.81 Encounter for therapeutic drug level monitoring ("any long-term (current) drug therapy (Z79.-)")
• Type 2 Excludes: Z92.2 Personal history of drug therapy ("long term (current) drug therapy (Z79.-)")

Diagnosis Index entries for Z79.631

• Long-term (current) (prophylactic) drug therapy (use of) › 5-fluorouracil
• Long-term (current) (prophylactic) drug therapy (use of) › 6-mercaptopurine
• Long-term (current) (prophylactic) drug therapy (use of) › antimetabolite agent
• Long-term (current) (prophylactic) drug therapy (use of) › cytarabine

Nearby codes

• Z79.622 Long term (current) use of Janus kinase inhibitor
• Z79.623 Long term (current) use of mammalian target of rapamycin (mTOR) inhibitor
• Z79.624 Long term (current) use of inhibitors of nucleotide synthesis
• Z79.63 Long term (current) use of chemotherapeutic agent
• Z79.630 Long term (current) use of alkylating agent
• Z79.631 Long term (current) use of antimetabolite agent (this code)
• Z79.632 Long term (current) use of antitumor antibiotic
• Z79.633 Long term (current) use of mitotic inhibitor
• Z79.634 Long term (current) use of topoisomerase inhibitor
• Z79.64 Long term (current) use of myelosuppressive agent
• Z79.69 Long term (current) use of other immunomodulators and immunosuppressants