## Metabolic Side Effects of Thiazide Diuretics **Key Point:** Thiazide diuretics (hydrochlorothiazide, chlorthalidone, indapamide) characteristically cause hyperuricemia and hyperglycemia due to specific renal and metabolic mechanisms. ## Mechanism of Hyperuricemia 1. **Decreased renal clearance of uric acid**: Thiazides compete with uric acid for secretion in the proximal tubule 2. **Volume depletion** → increased proximal tubule reabsorption of urate 3. **Result**: Serum uric acid rises, precipitating gout in susceptible patients ## Mechanism of Hyperglycemia 1. **Hypokalemia-induced insulin dysfunction**: Thiazides cause K⁺ depletion 2. **Impaired insulin secretion**: Low K⁺ reduces pancreatic β-cell insulin release 3. **Insulin resistance**: Metabolic effects of hypokalemia 4. **Result**: Fasting and postprandial glucose rise ## Metabolic Side Effects Comparison | Diuretic Class | Hyperuricemia | Hyperglycemia | Hypokalemia | Hyponatremia | | --- | --- | --- | --- | --- | | Thiazides | **Yes** | **Yes** | Yes | Possible | | Loop diuretics | Yes (mild) | Yes (mild) | Severe | Possible | | K⁺-sparing | No | No | **No** | Rare | | Osmotic | No | No | No | Yes | **High-Yield:** Thiazides are contraindicated or used with caution in patients with: - Gout or hyperuricemia - Diabetes mellitus - Severe hypokalemia **Clinical Pearl:** The hyperglycemic effect of thiazides is dose-dependent and more pronounced at higher doses (e.g., HCTZ > 25 mg/day). Chlorthalidone and indapamide have similar metabolic effects. **Mnemonic:** **THUG** = Thiazides cause **H**yperuricemia, **U**remia (renal dysfunction), **G**lucose elevation (hyperglycemia).
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