#1636 Treatment of Tolvaptan related polyuria with bendroflumethiazide for ADPKD: Does it really work?
Authors: Ahn Noella , Baptiste Tara , Wong Alisa , Gale Daniel P 
Published: May 2024

Abstract

Background and Aims
Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease worldwide and accounts for 10% of patients on renal replacement therapy. Currently, the arginine vasopressin (AVP) V2 receptor antagonist Tolvaptan is the only available treatment for ADPKD which slows cyst formation and thus the progression of kidney disease by inducing AVP resistance. However, its aquaretic side effects can be debilitating and is the most common reason for medication discontinuation. Thiazides such as bendroflumethiazide are natriuresis-promoting diuretics through their action on the sodium-chloride channel in the distal convoluted tubule that are widely used to treat polyuria in inherited AVP deficiency or resistance. However, there is limited information about their effect in patients treated with Tolvaptan. The aim of this observational study is to review the impact on patients’ quality of life by using a low dose bendroflumethiazide with Tolvaptan in patients with ADPKD who are suffering from Tolvaptan induced aquaretic side effects.

Method
Details of all patients with ADPKD who are on Tolvaptan with or without bendroflumethiazide who are currently attending the polycystic kidney disease (PKD) clinic at Royal Free London NHS Foundation Trust were obtained, and their medications reviewed. Patients who have previously been or were currently on bendroflumethiazide to enable them to continue Tolvaptan therapy were identified. Information about the impact of bendroflumethiazide on their quality of life and their aquaretic side effects were obtained via phone call. If they discontinued bendroflumethiazide, the reason for this was explored. In addition, eGFR, sodium, potassium, and calcium at the time of bendroflumethiazide initiation as well as at three, six, nine and twelve months post bendroflumethiazide initiation were obtained.

Results
Out of 136 patients receiving Tolvaptan for treatment of ADPKD at our centre, eight (5.8%) were prescribed bendroflumethiazide for treatment of their aquaretic side effects from Tolvaptan. Two of these eight patients (25%) stopped bendroflumethiazide due to adverse reactions. The remaining six patients (75%) remained on the medication, and all reported significant subjective improvement in their symptoms of polyuria, nocturia and in their overall quality of life. Two of the six patients (33.3%) that remained on bendroflumethiazide had also subsequently increased their Tolvaptan dose. No electrolyte disturbances were noted after initiation of bendroflumethiazide.

Conclusion
Using bendroflumethiazide appears to improve the quality of life through reduction of polyuria and nocturia in patients suffering from Tolvaptan-induced aquaretic side effects with some patients subsequently able to increase their Tolvaptan dose by taking bendroflumethiazide which might result in augmented therapeutic benefit of Tolvaptan. Further placebo-controlled randomised studies with longitudinal will be needed to determine the true benefit-disbenefit balance of thiazide therapy in patients taking tolvaptan, especially to determine whether there is a negative effect on efficacy of tolvaptan on the underlying ADPKD. However, based on our small observational study, the number of patients needed to determine whether bendroflumethiazide improves the tolerability and medication adherence in patients who are debilitated by the aquaretic side effects of Tolvaptan would be small.