Medication reviews in patients with rheumatoid arthritis often uncover clinically significant drug therapy problems. Methotrexate toxicity, drug interactions, and therapeutic duplication are common issues that pharmacists must proactively identify. In this case-based review, we’ll walk through three high-yield drug therapy problems involving rheumatoid arthritis, methotrexate, omeprazole, cilostazol, and duplicate alpha-blocker therapy.
Rheumatoid Arthritis Case Summary
A 67-year-old male with a history of rheumatoid arthritis presents for routine follow-up. He reports increasing fatigue and recurrent mouth sores over the past few months. His rheumatoid arthritis is moderately controlled with methotrexate 20 mg weekly.
His medication list includes:
- Methotrexate 20 mg once weekly
- Omeprazole 40 mg daily
- Cilostazol 100 mg twice daily
- Doxazosin 8 mg daily
- Tamsulosin 0.4 mg daily
- Lisinopril 20 mg daily
- Atorvastatin 40 mg nightly
- Metformin 1000 mg twice daily
- Aspirin 81 mg daily
- Amlodipine 5 mg daily
- Acetaminophen as needed
Recent labs reveal:
- WBC 3.2 x10³/mm³
- Hemoglobin 10.6 g/dL
- MCV 104 fL
- Platelets 138 x10³/mm³
Let’s break down the key drug therapy problems.
Drug Therapy Problem #1: Missing Folic Acid with Methotrexate
Methotrexate is a cornerstone therapy for rheumatoid arthritis. However, it inhibits dihydrofolate reductase, interfering with folate metabolism and DNA synthesis. Without folic acid supplementation, patients are at a greater risk for:
- Macrocytic anemia
- Leukopenia
- Thrombocytopenia
- Stomatitis (mouth sores)
- Fatigue
This patient’s elevated MCV, anemia, leukopenia, fatigue, and mouth sores strongly suggest folate-related methotrexate toxicity. Folic acid supplementation (commonly 1 mg daily or 5–7 mg weekly) significantly reduces hematologic and mucosal adverse effects without compromising methotrexate efficacy in rheumatoid arthritis. If you see methotrexate without folic acid in rheumatoid arthritis, that should immediately trigger a red flag during medication review.
Drug Therapy Problem #2: Omeprazole–Cilostazol CYP2C19 Interaction
Cilostazol is metabolized by CYP3A4 and CYP2C19. Omeprazole is a moderate CYP2C19 inhibitor (excellent board exam nugget). When these medications are combined, cilostazol serum concentrations increase. Elevated levels raise the risk of:
- Headache
- Palpitations
- Hypotension
- Bleeding
When used with strong or moderate CYP2C19 inhibitors, the recommended cilostazol dose is reduced from 100 mg twice daily to 50 mg twice daily. This patient remains on full-dose cilostazol despite taking omeprazole 40 mg daily. Cilostazol has specific labeling recommending dose reduction with CYP2C19 inhibitors. This is not a “monitor and move on” situation — dose adjustment is recommended.
Drug Therapy Problem #3: Duplicate Alpha-1 Blocker Therapy
This patient is prescribed both doxazosin and tamsulosin. Both medications are alpha-1 adrenergic blockers. Although tamsulosin is more uroselective and doxazosin has greater systemic blood pressure effects, they share the same mechanism of action. Risks of duplicate alpha-blocker therapy include:
- Orthostatic hypotension
- Dizziness
- Syncope
- Falls
With a blood pressure of 116/64 mmHg, this patient is already well controlled. Continuing dual therapy increases fall risk without a clear benefit. Therapeutic duplication is one of the most common drug therapy problems found during comprehensive medication reviews. Always scan for medications within the same pharmacologic class.
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