The error occurred in July, the Government Pharmaceutical Organisation (GPO) said.
The drugs were then distributed to seven state-owned hospitals in five provinces in the country, newly appointed managing director Suwach Siasiriwattana was quoted as saying by the Bangkok Post today.
Isosorbide dinitrate, used to treat congestive heart failure, was packed into packaging for amlodopine which is used to treat hypertension, he said.
As a result, five patients were prescribed the wrong drugs.
There were no reports of any adverse impacts on the patients, the report said.