A First Report of HCTZ and Dicyclomine Induced Uncharacteristic Contraction Alkalosis.

Background: Contraction alkalosis is characterized by low serum sodium and chloride and high serum carbon dioxide and bicarbonate levels. Case Report: A 28-year-old Caucasian active-duty male with a history of autosomal dominant polycystic kidney disease and diarrhea-predominant Irritable Bowel Syndrome (D-IBS) presented to his primary care provider (PCP) with elevated blood pressure (136/96 mmHg), was diagnosed with stage-2 hypertension, and started oral HCTZ (25 mg/day). His medications included dicyclomine (10 mg oral three times daily). Subsequently, (Visit 1), his blood pressure was 130/91 mmHg and he was started on telmisartan (20 mg/day). At Visit 2, 4 weeks later, his blood pressure improved (121/73 mmHg); however, blood chemistry revealed elevated serum CO2 (32 mEq/L) and chloride (94 mmol/L). Four days later, the patient presented to the Emergency Department with dyspnea and swallowing difficulty. The patient returned to his PCP 3 days later complaining of cough, congestion, vomiting, and mild dyspnea, blood pressure of 124/84 mmHg. Two months later, sudden onset of projectile vomiting and abdominal pain while running was reported, resolved by rehydration and a single oral dose of prochlorperazine 25 mg. Three months later, (Visit 3), he complained of lightheadedness and cloudy judgment, suggesting contraction alkalosis. HCTZ was discontinued and telmisartan was increased to 20 mg twice daily. A follow-up blood chemistry panel 2 weeks later revealed serum chloride and CO2 levels within normal limits and blood pressure under 130/80 mmHg. Conclusion: This is the first known report of contraction alkalosis driven by drug-drug interaction between dicyclomine and HCTZ.