PT
● MODULE 09 / 20
Renal Drugs, Fluids & Electrolytes
Locate nephron drug targets and predict changes in volume, potassium, calcium and acid-base balance.
Quick revision ↓ Medical Dictionary
FULL CHAPTER EXPLANATION
Deep Learning — Module 09
Read this section in sequence. It moves from drug targets to therapeutic effects, adverse reactions and safe use.
01
Diuretics along the nephron
Acetazolamide inhibits carbonic anhydrase, reducing proximal bicarbonate reabsorption. Loop diuretics such as furosemide inhibit the Na-K-2Cl cotransporter in the thick ascending limb and produce powerful natriuresis. Thiazides inhibit the sodium-chloride cotransporter in the distal convoluted tubule. Their different sites explain differences in efficacy, electrolyte effects and use. Diuresis treats volume or pressure problems in selected contexts; it does not repair every cause of kidney injury.
02
Potassium and calcium consequences
Loop and thiazide diuretics can increase distal sodium delivery and potassium loss. Loop agents increase urinary calcium loss, whereas thiazides generally reduce it. Spironolactone and eplerenone block mineralocorticoid receptors; amiloride blocks epithelial sodium channels. These potassium-sparing agents can cause hyperkalemia, especially when combined with renin-angiotensin inhibitors or impaired renal function. Spironolactone also has endocrine adverse effects, including gynecomastia.
03
Osmotic agents and water handling
Mannitol increases tubular osmotic load but can initially expand extracellular volume and is inappropriate in some fluid-overloaded or anuric states. Desmopressin stimulates V2-mediated water retention and is useful in central diabetes insipidus; excess effect can cause dilutional hyponatremia. Vasopressin antagonists increase free-water excretion in selected monitored indications. Distinguish solute removal from water removal, because serum sodium reflects water relative to exchangeable solute rather than total body sodium alone.
04
Acid-base and electrolyte medicines
Acetazolamide can produce a normal-anion-gap metabolic acidosis through bicarbonate loss. Loop and thiazide therapy can promote metabolic alkalosis in appropriate settings. Potassium supplementation requires knowledge of renal function and ongoing losses. In severe hyperkalemia, intravenous calcium stabilizes cardiac membranes but does not lower serum potassium; insulin shifts potassium intracellularly while definitive removal requires another strategy. These are mechanisms for supervised care, not a substitute for emergency assessment and monitoring.
05
Monitoring and fluid reasoning
Before changing a diuretic, assess perfusion, edema, blood pressure, renal function and electrolytes. Excess fluid removal may worsen hypotension or renal perfusion, while inadequate removal leaves congestion. Rapid correction of chronic sodium disturbances can cause neurological injury, so correction is protocol-driven. The teaching task is to identify whether the problem is excess total-body fluid, reduced effective circulation, a free-water imbalance or an electrolyte deficit, rather than treating every abnormal sodium result with the same fluid.
High-Yield Revision
- Loops increase calcium excretion; thiazides usually reduce it.
- Potassium-sparing does not mean electrolyte-neutral.
- Calcium protects the heart in hyperkalemia but does not remove potassium.
Common Exam & Concept Pitfalls
- Do not infer intravascular volume solely from visible edema.
- Serum sodium concentration is not a direct measure of total body sodium.
Sources & Further Reading
Curriculum scope checked 23 September 2026. These original study notes summarize established principles; current institutional guidance and product information govern clinical use. Faculty review is pending.
RAHBAR study structure: target → drug action → therapeutic use → adverse effects → monitoring. Use institutional curriculum and faculty guidance for local sequencing, practical requirements and assessment specifications.