Drugs Acting on the Renal System and Urinary Tract

Vocabulary practice flashcards covering renal physiology, diuretic classes, urinary tract anti-infectives, antispasmodics, analgesics, bladder protectants, and treatments for benign prostatic hyperplasia.

Nephron

The functional unit of the kidneys; approximately $25\%$ of the total number of nephrons are required to maintain healthy renal function.

Filtration (Renal)

The passage of fluid and small blood components through the glomerulus, filtering approximately $125\,\text{mL}$ of fluid per minute.

Secretion (Renal)

The active movement of substances from the blood into the renal tubule via transport systems to remove electrolytes, certain drugs, drug metabolites, and uric acid, as well as hydrogen ions for acid-base maintenance.

Reabsorption (Renal)

The movement of substances such as vitamins, glucose, electrolytes, sodium bicarbonate, and chloride from the renal tubule back into the vascular system to sustain physiological balances.

Detrusor Muscle

The smooth muscle of the urinary bladder that expels urine upon contraction; it is controlled by the sympathetic system for urine storage and the parasympathetic system for bladder emptying.

Diuretics

A therapeutic class of medications that increase urine volume excreted by the kidneys; indicated for heart failure, pulmonary edema, liver disease, hypertension, and elevated intraocular pressure.

Thiazide and Thiazidelike Diuretics

Mild, sodium-rich diuretics (e.g., chlorothiazide, hydrochlorothiazide, metolazone) that block the chloride pump in the renal tubule, preventing sodium and chloride reabsorption into the vascular system.

Loop Diuretics

Potent diuretics (e.g., furosemide, torsemide, bumetanide, ethacrynic acid) that block the chloride pump in the ascending loop of Henle, resulting in decreased sodium and chloride reabsorption, copious urine output, and hypertonic intravascular fluid.

Ototoxicity

An inner ear-damaging adverse effect specifically associated with loop diuretic administration.

Carbonic Anhydrase Inhibitors

Medications (e.g., acetazolamide, dichlorphenamide, methazolamide) that block carbonic anhydrase, resulting in increased urinary excretion of sodium and bicarbonate and decreased aqueous humor secretion to lower intraocular pressure in glaucoma.

Potassium-Sparing Diuretics

Aldosterone antagonists (e.g., spironolactone, triamterene, amiloride) that block aldosterone receptors in the distal tubule to induce sodium and water excretion while conserving potassium; drug of choice for hyperaldosteronism.

Mannitol

An osmotic diuretic composed of a large non-reabsorbable sugar that pulls fluid into the renal tubules without sodium loss; used to lower elevated intraocular pressure (IOP) and intracranial pressure (ICP), but contraindicated in heart failure.

Vasopressin Receptor Antagonists

Aquaretic agents (e.g., conivaptan, tolvaptan) that block antidiuretic hormone (ADH) actions to facilitate free water excretion without sodium removal, raising serum sodium levels in hyponatremic patients.

Tolvaptan Boxed Warning

A specific Black Box Warning alerting clinicians to the risk of severe liver injury.

Fluid Rebound

A physiological response triggered by significant water depletion or decreased fluid intake, leading to compensatory release of antidiuretic hormone (ADH) and activation of the renin-angiotensin-aldosterone system (RAAS) to conserve fluid.

Fosfomycin

A single-dose antibiotic indicated for urinary tract infections; suitable for use during pregnancy but frequently causes unpleasant gastrointestinal adverse effects.

Nitrofurantoin

A urinary tract antibiotic whose absorption improves when ingested with food; must be avoided in the first trimester of pregnancy due to congenital anomaly risks and at term due to hemolytic anemia in neonates.

Trimethoprim-Sulfamethoxazole

A combination antibacterial agent requiring screening for sulfa allergies; contraindicated during the first trimester due to congenital abnormalities and associated with newborn jaundice risk.

Methenamine

A urinary tract anti-infective that acts as a urinary acidifying agent to suppress bacterial proliferation.

Anticholinergic Antispasmodics

Urinary antispasmodic agents (e.g., oxybutynin, tolterodine) that block parasympathetic input to suppress urinary overactivity and relax detrusor and bladder smooth muscle.

Mirabegron

A urinary tract antispasmodic that stimulates sympathetic receptors within the bladder to induce relaxation of the detrusor muscle.

Phenazopyridine

An azo dye that exerts a topical analgesic action directly on the urinary tract mucosa to treat dysuria, urgency, and burning; causes harmless reddish-orange discoloration of urine and is restricted to $2\,\text{days}$ of use.

Pentosan Polysulfate Sodium

A bladder protectant possessing heparinlike properties that adheres to the mucosal wall to shield it from irritating urinary solutes; carries bleeding risks and requires baseline and $6\,\text{months}$ follow-up eye exams for ocular changes.

Alpha-1 Receptor Blockers (for BPH)

Adrenergic antagonists (e.g., doxazosin, tamsulosin, terazosin) that block alpha-1 receptors, causing venous and arteriolar dilation while relaxing sympathetic tone in the bladder neck and prostate.

5-Alpha Reductase Inhibitors

Antiandrogenic agents (e.g., finasteride, dutasteride) that block the conversion of testosterone into dihydrotestosterone (DHT) to inhibit prostate growth; requires avoiding blood donation and pregnancy conception for $6\,\text{months}$ following therapy.