Pharm 101: Hydrochlorothiazide

Class

Thiazide diuretic

Pharmacodynamics

• Inhibit Na/Cl co-transporter in distal convoluted tubule
• Reduces NaCl reabsorption form luminal side of epithelial cells
• Leads to increased NaCl excretion and diuresis
• Enhanced Ca reabsorption (passive)

Pharmacokinetics

• Duration of action 8-12 hours
• Secreted by organic acid secretory system in proximal tubule
  • Compete with uric acid secretion by same system

Clinical uses

• Hypertension
• Heart failure
• Nephrolithiasis due to idiopathic hypercalciuria
• Nephrogenic diabetes insipidus

Adverse effects

• Dehydration/hypovolaemia
• Hypokalaemic metabolic alkalosis (similiar to loop diuretics)
• Hyperglycaemia
• Unmask hypercalcaemia due to other causes
• Hyperlipidaemia
• Hyponatraemia
• Hyperuricaemia

Precautions/contraindications

• Drug interactions:
  • Increased plasma Lithium level
  • NSAIDs can reduce effects

Further reading

• Buttner R. Pharm 101: Furosemide. LITFL
• Buttner R. Pharm 101: Acetazolamide. LITFL

References

• Katzung BG. Basic and Clinical Pharmacology. 14e. 2018: 836-837, 840