BAKTAR是否會造成高血鉀？

Baktar (Trimethoprim-sulfamethoxazole) 的life-threatening effect較容易發生在HIV、嗜中性球低下或對成分過敏患者。其中trimethoprim會抑制遠曲小管的Na⁺ channel，造成intracellular sodium濃度下降，進而降低Na⁺/K⁺ATPase function，導致滯留於血漿中的K⁺濃度上升。

Trimethoprim導致高血鉀的機轉與amiloride雷同，兩者在結構上也相似。

Trimethoprim ➝抑制➝ Na⁺ channel ➝➝ intracellular sodium concentration decrease ➝➝ serum potassium level increase

由於可能造成血鉀濃度上升，renal impairment或年紀大患者使用Baktar時若有並用會造成高血鉀的藥品，如spironolactone或ACEI、ARB、NSAIDs要留意血鉀濃度變化。

Risk factor

• High dosage (20 mg/kg/day of trimethoprim)
• Renal impairment (serum creatinine ≥ 1.2 mg/dl)
• Hypoaldosteronism
  1. Potassium-altering medications
  2. NSAIDs
  3. ACEI, ARB
  4. Potassium-sparing diuretics
• Older age

Prevention and management of baktar-induced hyperkalaemia

• Induction of high urine flow rates and enhanced sodium delivery to the distal nephron
  1. IV saline
  2. Loop diuretics (if volume-replete)
• 鹼化尿液 (goal: pH ≥ 7.5)
  1. sodium bicarbonate
  2. acetazolamide
• 劑量調整 (if renal impairment)
  1. Ccr < 30 ml/min, 減半
  2. Ccr < 15 ml/min, avoid
• 嚴重高血鉀&renal failure → 停用

References

• Uptodate.com. 2021. UpToDate. [online] Available at: <https://www.uptodate.com/contents/trimethoprim-sulfamethoxazole-an-overview?search=sulfamethoxazole%20trimethoprim&usage_type=default&source=search_result&selectedTitle=1~150&display_rank=1> [Accessed 20 July 2021].
• Perazella, M., 2000. Trimethoprim-Induced Hyperkalaemia. Drug Safety, 22(3), pp.227-236.