Z79.4 is used for Long term (current) use of insulin, and used to describe the encounter of a patient that is currently using insulin and has been accustomed to taking it for an extended period.
Z79.84 – is used for Long term (current) use of oral hypoglycemic drugs.
If a procedure was performed it must also be reported such as the injection. The code selection would depend on the type of medication or drug and if it was being used long term. If so, refer to the list of Z79 Long term (current) drug therapy codes to ensure the most specific code selection. Code Z79.4 should not be assigned if insulin is given temporarily to bring a type 2 patient’s blood sugar under control during an encounter.
Without more information on the medication, it would be hard to advise, I would refer you to Find-A-Code’s WK Drug database for additional information. Neither of the two above codes seem to fit this scenario.