From the FDA Drug Label
Avoid coadministration of sulfamethoxazole and trimethoprim with drugs that are substrates of CYP2C8 and 2C9 or OCT2 Table 1: Drug Interactions with Sulfamethoxazole and Trimethoprim Drug(s) Recommendation Comments Diuretics Avoid concurrent use In elderly patients concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombocytopenia with purpura has been reported
The interaction between Amlodipine (calcium channel blocker) and Hydrochlorothiazide (HCTZ) (diuretic) when started on Trimethoprim/Sulfamethoxazole (Bactrim) (antibiotic) is that concurrent use of diuretics, such as HCTZ, with Trimethoprim/Sulfamethoxazole should be avoided, especially in elderly patients, due to an increased risk of thrombocytopenia with purpura.
- Key points:
- Avoid concurrent use of diuretics and Trimethoprim/Sulfamethoxazole
- Increased risk of thrombocytopenia with purpura in elderly patients
- Monitor patients closely when coadministering these drugs 1
From the Research
I strongly recommend monitoring blood pressure and electrolyte levels closely when taking amlodipine with hydrochlorothiazide (HCTZ) while starting Bactrim (sulfamethoxazole-trimethoprim), as this combination requires caution due to potential interactions that may impact morbidity, mortality, and quality of life. The potential interactions between these medications can lead to unpredictable electrolyte changes and enhanced blood pressure-lowering effects, potentially causing excessive hypotension 2.
Potential Interactions and Risks
- Bactrim may increase potassium levels, while HCTZ tends to decrease them, potentially offsetting each other but creating unpredictable electrolyte changes.
- Bactrim can enhance the blood pressure-lowering effects of amlodipine, possibly causing excessive hypotension.
- Elderly patients or those with kidney problems should be particularly vigilant as they face higher risks of adverse effects from these medication interactions.
Monitoring and Precautions
- Watch for symptoms like dizziness, lightheadedness, or unusual fatigue, especially during the first few days of Bactrim therapy.
- Stay well-hydrated and contact your healthcare provider immediately if you experience severe dizziness, fainting, or irregular heartbeat.
- Routine blood tests to monitor kidney function and electrolytes are advisable during this combination therapy, as supported by studies on the efficacy and safety of combination therapies involving amlodipine and HCTZ 3, 4.
Evidence-Based Recommendations
The most recent and highest quality study on the topic of combination antihypertensive therapy, including amlodipine and HCTZ, suggests that close monitoring of blood pressure and electrolyte levels is crucial when initiating or adjusting these medications, especially in combination with other drugs like Bactrim 5. Therefore, prioritizing the monitoring of these parameters and being cautious of potential interactions is essential for minimizing risks and optimizing patient outcomes.