A patient with CKD 4 or 5 has Swelling, Hypertension, and Needs a Water Pill. What is the Best Option?
Chlorthalidone is a useful diuretic, or water pill, and blood pressure therapy. However, when the kidneys worsen and the patient approaches stages 4 and 5 CKD, the usefulness decreases and an alternative diuretic needs to be considered.
Kidney providers have many classes of water pills they can use to treat patients. Depending on the situation, we may prefer one type of diuretic over another. The following graphic shows a picture of a kidney filter and where along that filter the different classes of water pills work:
For simplicity, we will focus on the loop diuretics, which work at the loop of Henle, see above, and the thiazide diuretics which work at the distal convoluted tubule. Why do specialists commonly switch from highly effective thiazides like hydrochlorothiazide and chlorthalidone to loop diuretics like furosemide when a patient reaches stages 4 or 5 chronic kidney disease (CKD)? One main reason is the thiazides become less effective in stages 4-5. The loop diuretics work better in advanced chronic kidney disease. So, we switch. Note the effect on salt or Na reabsorption seen at different parts of the kidney filter. The loop of Henle reabsorbs 25-30% of the salt whereas the distal convoluted tubule reabsorbs only 5-10% of the salt. When the kidney filter is working to remove fluid from the body, the loop handles more work than the distal convoluted tubule. Both classes of diuretics block salt uptake, and water follows the salt. Since loop diuretics involve more salt, furosemide or Lasix are more powerful than the thiazide diuretics, hydrochlorothiazide and chlorthalidone.
Interestingly, kidney providers sometimes combine the two classes of water pills together to get double the diuretic effect when a patient has diuretic resistance. You may see that.
Loop diuretics can lower blood pressure just like thiazide diuretics. They work better when patients have CKD 4 or 5. We usually add loop diuretics to ACE inhibitors like lisinopril or ARBs like losartan. We usually write furosemide or Lasix twice daily. There are other loop diuretics out there that we can write once a day. It requires much expertise and skill to balance the risk of sudden kidney injury and the benefit of the right dose of the water pill. Kidney doctors work closely with cardiologists and primary providers to make sure the kind and dose of medication is correct.
So in summary, when your primary provider or cardiologist consults nephrology to assist with fluid management in CKD 4 or 5, you may see a change in your water pill prescriptions. The change is normal and considers the GFR, the stage of CKD, the blood pressure levels, the amount of swelling, and more. You may require more frequent blood draws during this time as well to make sure the kidney function stays stable during this change.