Concept:
DMARDs are drugs that slow the progression of rheumatoid arthritis and modify the disease process.
Step 1: Understanding DMARDs.
DMARDs reduce inflammation and immune-mediated joint damage over time. They are different from simple pain-relieving drugs.
Step 2: Checking methotrexate.
Methotrexate is a commonly used conventional DMARD.
Step 3: Checking cyclophosphamide and infliximab.
Cyclophosphamide is an immunosuppressant used in some autoimmune conditions.
Infliximab is a biological DMARD that blocks TNF-\(\alpha\).
Step 4: Checking ibuprofen.
Ibuprofen is an NSAID. It reduces pain and inflammation but does not modify the disease progression of rheumatoid arthritis.
Step 5: Final answer.
Therefore, ibuprofen is not a DMARD.
\[
\boxed{\text{Ibuprofen}}
\]