Comprehensive Pharmacology Notes: Cardiovascular, Diuretics, and Men's Health

Diuretics: Potency, Mechanisms, and Clinical Applications

Loop Diuretics
- Mechanism of Action (MOA): These agents inhibit the sodium-potassium-chloride reabsorption pathway specifically in the thick ascending limb of the loop of Henle, leading to potent diuresis. They also block water reabsorption and promote the excretion of sodium and potassium.
- Drug Names: Furosemide, bumetanide, and torsemide.
- Adverse Effects:
  - Hypokalemia (K^+ < 3.5\,mEq/L) characterized by muscle weakness, cramps, fatigue, and cardiac arrhythmias.
  - Ototoxicity (risk increases with prolonged use or high doses, presenting as tinnitus).
  - Hypotension, hyponatremia, hyperglycemia, and hyperuricemia.
  - Hematologic effects (specific to torsemide): leukopenia, neutropenia, and thrombocytopenia.
  - Dehydration and hypovolemia.
- Nursing Considerations: Monitor cardiac rhythm and blood pressure ( $BP$ ). Assess intake and output ( $I\&O$ ); report if urine output is < 30\,ml/hour. Monitor daily weights and lung sounds. Administer in the morning to prevent nocturnal diuresis.
Thiazide Diuretics
- Mechanism of Action (MOA): These inhibit sodium-chloride reabsorption in the distal convoluted tubule, resulting in moderate diuresis and the excretion of sodium, potassium, and water.
- Drug Names: Hydrochlorothiazide ( $HCTZ$ ), chlorothiazide, and metolazone.
- Adverse Effects:
  - Hypokalemia, hyponatremia, and hypotension.
  - Hypercalcemia, hyperglycemia, hyperlipidemia, and hyperuricemia.
  - Dizziness (specifically noted for metolazone), photosensitivity, and thrombocytopenia.
- Contraindications: Should not be used if renal function is severely impaired (indicators: BUN > 20\,mg/dL, \text{creatinine} > 1.2\,mg/dL, or output < 30\,ml/hour).
- Nursing Considerations: Monitor for signs of elevated glucose, uric acid, and lipids. Instruct patients to take medication in the morning.
Potassium-Sparing Diuretics
- Mechanism of Action (MOA):
  - Spironolactone: Acts as an aldosterone antagonist.
  - Amiloride and Triamterene: Block the sodium-potassium exchange in the distal tubule and collecting duct.
  - Result: These promote the excretion of sodium and water while retaining potassium.
- Drug Names: Spironolactone, amiloride, and triamterene.
- Adverse Effects:
  - Hyperkalemia (K^+ > 5.0\,mEq/L) with symptoms including nausea, vomiting, diarrhea, chest pain, palpitations, and cardiac dysrhythmias.
  - Spironolactone-specific: Gynecomastia, impotence, and menstrual irregularities.
- Nursing Considerations: Check baseline vitals, serum potassium, and urine output before administration. Avoid during pregnancy. Advise patients to avoid potassium-rich foods.
Osmotic Diuretics
- Mechanism of Action (MOA): Mannitol increases plasma osmolality, pulling fluid from tissues into the bloodstream to be filtered by the kidneys. The drug remains within the nephron to exert an osmotic effect.
- Drug Name: Mannitol.
- Indications: Treatment of cerebral edema (to decrease intracranial pressure), glaucoma, and the induction of renal excretion for toxic substances.
- Adverse Effects: Fluid and electrolyte imbalances, pulmonary edema (due to fluid overload), and headache.
- Nursing Considerations: Perform lung sound assessments to check for dyspnea or crackles; monitor renal function and urine output.
Diuretic Interactions and Support
- Potassium Food Sources: Patients on potassium-depleting diuretics should consume green leafy vegetables, legumes, bananas, oranges, cantaloupe, dates, beans, lentils, dried fruits, potatoes, broccoli, green beans, squash, and sweet potatoes.
- Digoxin Interaction: Hypokalemia (caused by loop/thiazide diuretics) significantly increases the risk of digoxin toxicity. Serum potassium levels ( $3.5\text{--}5.0\,mEq/L$ ) must be monitored.

Calcium Channel Blockers (CCBs)

Dihydropyridines
- Drug Names: Amlodipine (Norvasc), nifedipine (Procardia), felodipine (Plendil), and nicardipine (Cardene).
- MOA: Prevent calcium entry into vascular smooth muscle, causing potent vasodilation. This leads to decreased BP and decreased afterload with minimal effect on heart rate ( $HR$ ) or contractility.
- Indications: Hypertension, chronic stable angina, and vasospastic angina.
- Side Effects: Hypotension, reflex tachycardia, peripheral edema, headache, and gingival hyperplasia (requires daily gum inspection).
Nondihydropyridines
- Drug Names: Diltiazem (Cardizem) and verapamil (Calan).
- MOA: Prevent calcium entry into myocytes, resulting in decreased $HR$ , decreased contractility, and coronary/peripheral vasodilation.
- Indications: Hypertension, chronic stable angina, vasospastic angina, and antiarrhythmic use.
- Side Effects: Hypotension, bradycardia, AV heart block, and constipation.
Key Nursing Considerations for CCBs
- Contraindications: Use cautiously with heart failure due to negative inotropic effects; monitor closely if beta blockers have failed.
- Patient Teaching: Avoid grapefruit juice (risk of overdose). Rise slowly to mitigate orthostatic hypotension. Report dizziness, edema, or shortness of breath. Increase fiber intake for patients on verapamil or diltiazem.
- Monitoring: Obtain baseline $BP$ , pulse, liver, and kidney function tests.

ACE Inhibitors and Angiotensin II Receptor Blockers (ARBs)

ACE Inhibitors (-pril)
- Drug Names: Captopril (Capoten), benazepril (Lotensin), enalapril (Vasotec), fosinopril (Monopril), lisinopril (Prinivil), perindopril (Aceon), quinapril (Accupril), ramipril (Altace), and trandolapril (Mavik).
- MOA: Inhibits Angiotensin-Converting Enzyme ( $ACE$ ), preventing the conversion of Angiotensin I to Angiotensin II. This results in decreased vasoconstriction and decreased aldosterone secretion (reducing $BP$ , afterload, and preload). It also prevents the breakdown of bradykinin, a vasodilator.
- Adverse Effects: Dry, nonproductive cough (reversible); significant hypotension (especially with the first dose); fatigue, headache, mood changes, taste alterations, and hyperkalemia.
- Critical Safety: Angioedema is a potentially fatal adverse effect involving inflammation of the tongue, face, and lips leading to airway impairment.
Angiotensin II Receptor Blockers (ARBs) (-sartan)
- Drug Names: Valsartan (Diovan), losartan (Cozaar), irbesartan (Avapro), candesartan (Atacand), and olmesartan (Benicar).
- MOA: Block angiotensin II receptors directly, preventing vasoconstriction and aldosterone secretion.
- Adverse Effects: Similar to ACE inhibitors but without the dry cough (as they do not affect bradykinin). Includes hyperkalemia, hypotension, and airway impairment risks.
Comparative and Nursing Key Points
- First-dose Hypotension: Monitor closely after the initial dose, particularly in heart failure patients.
- Renoprotective/Cardioprotective: Both classes prevent ventricular remodeling post-MI and reduce proteinuria in diabetic nephropathy.
- Hyperkalemia: Both cause potassium resorption due to decreased aldosterone; monitor serum $K^+$ levels and avoid NSAIDs.
- Captopril Dosage: Typically administered $2\text{--}3$ times per day.
- Pregnancy: ARBs are Category D (contraindicated).

Beta-Adrenergic Antagonists (Beta Blockers)

Cardioselective ( $\beta_1$ -selective)
- Drug Names: Metoprolol (Lopressor, Toprol-XL), atenolol, bisoprolol, and carvedilol (noting carvedilol also has $\alpha_1$ blocking properties).
- MOA: Block $\beta_1$ receptors in cardiac tissue to decrease $HR$ , contractility, AV conduction, $BP$ , and myocardial oxygen demand.
Nonselective ( $\beta_1 + \beta_2$ )
- Drug Names: Propranolol (Inderal), carvedilol, nadolol, and timolol.
- MOA: Block both $\beta_1$ (cardiac) and $\beta_2$ (bronchial and vascular smooth muscle) receptors.
- Warning: $\beta_2$ blockade can cause severe bronchoconstriction, making these dangerous for patients with asthma or COPD.
Key Nursing Considerations
- Abrupt Withdrawal: Never stop abruptly; requires medical tapering to avoid rebound effects like increased angina, $BP$ , and $HR$ .
- Diabetes: These drugs can mask tachycardia and tremors, which are symptoms of hypoglycemia. Patients must monitor blood glucose closely.
- Mortality Benefit: Carvedilol, metoprolol succinate, and bisoprolol are proven to reduce death in heart failure ( $HF$ ) and post-MI patients with an $LVEF \le 40\%$ .
- Administration: Check $HR$ and $BP$ before giving; hold dose if parameters are too low. Report shortness of breath (edema/ $HF$ exacerbation).

Indirect-Acting Anti-Adrenergic and Vasodilators

Centrally Acting Alpha-2 Agonists
- Drug Names: Clonidine (Catapres) and Methyldopa.
- MOA: Stimulate central alpha-2 receptors to decrease sympathetic outflow, resulting in decreased $BP$ and vascular resistance.
- Indications: Hypertension (not first-line) and opioid withdrawal. Methyldopa is the drug of choice for hypertension in pregnancy.
- Adverse Effects: Orthostatic hypotension, fatigue, dizziness, sedation, bradycardia, and edema. Clonidine is associated with xerostomia (dry mouth).
- Dosage Forms: Clonidine transdermal patches are changed every $7$ days.
Direct-Acting Vasodilators
- Hydralazine (Apresoline): Direct arterial vasodilation. Used for essential hypertension and $HF$ (specifically in Black patients when combined with isosorbide dinitrate, known as BiDil). Adverse effects: Hypotension, headache, and B6 deficiency.
- Minoxidil: Direct arterial vasodilation for severe hypertension refractory to other drugs. Adverse effects: T-wave changes, pericardial effusion/tamponade, and hypertrichosis (hair growth).
- Sodium Nitroprusside (Nitropress): Potent arterial and venous vasodilator used for hypertensive emergencies and acute decompensated heart failure ( $ADHF$ ). Adverse effects: Severe hypotension, cyanide/thiocyanate toxicity, and platelet inhibition.

Cardiac Glycoside: Digoxin (Lanoxin)

Mechanism of Action (MOA): Inhibits the sodium-potassium ATPase pump, increasing intracellular calcium. This produces a positive inotropic effect (increased contractility) and negative chronotropic/dromotropic effects (decreased $HR$ and AV conduction velocity).
Indications: Heart failure, atrial fibrillation, and atrial flutter.
Therapeutic Profile: Narrow therapeutic index ( $0.5\text{--}2\,ng/mL$ ).
Administration Protocol:
- Measure apical pulse for $1$ full minute (at the $5^{th}$ intercostal space).
- Hold dose if HR < 60\,bpm or > 100\,bpm.
- Verify potassium and magnesium levels (hypokalemia/hypomagnesemia increase toxicity risk).
- IV infusion: Undiluted at $0.25\,mg/min$ . Avoid IM (painful, erratic absorption).
Digoxin Toxicity:
- Early S/S: Anorexia, nausea, vomiting, bradycardia, headache, dizziness, and confusion.
- Late S/S: Visual disturbances (blurred vision, yellow-green halos).
- Antidote: Digoxin immune Fab (Digibind).
Patient Teaching: Avoid high-fiber foods (decreases absorption). Do not skip doses.

Adrenergic Agonists and Extravasation

Sympathomimetic Profiles:
- Epinephrine: Nonselective ( $\alpha_1, \alpha_2, \beta_1, \beta_2$ ). Causes vasoconstriction, increased $HR$ , and bronchodilation.
- Norepinephrine (Levophed): Nonselective ( $\alpha_1, \alpha_2, \beta_1$ ). Potent vasoconstrictor used to increase $BP$ and cardiac contraction.
- Dopamine: Dose-dependent. Low dose = renal vasodilation; Moderate = $\beta_1$ (increased cardiac output); High = $\alpha_1$ (vasoconstriction).
- Dobutamine: $\beta_1$ -selective. Increases contractility and cardiac output.
- Phenylephrine: $\alpha_1$ -selective vasoconstrictor to increase $BP$ .
Extravasation Management:
- Definition: Leakage of vesicant medications (vasopressors) into surrounding tissue.
- Consequence: Tissue ischemia and necrosis, potentially leading to limb loss.
- Treatment: Phentolamine (alpha blocker) must be administered quickly to reverse vasoconstriction and restore blood flow.

Men's Health Pharmacology

Benign Prostatic Hyperplasia (BPH)
- Alpha-1 Adrenergic Blockers: Tamsulosin (Flomax), alfuzosin, doxazosin, prazosin, and silodosin. They relax smooth muscle in the prostate and bladder neck to increase urine flow but do not reduce prostate size. Administer at bedtime; monitor for orthostatic hypotension.
- 5-Alpha Reductase Inhibitors: Finasteride (Proscar) and dutasteride. These block the conversion of testosterone to $DHT$ , resulting in decreased prostate size.
- Safety: Finasteride is Category X; pregnant women must not handle crushed or broken tablets.
Erectile Dysfunction (ED)
- PDE-5 Inhibitors: Sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). They inhibit phosphodiesterase-5 to increase blood flow to the corpus cavernosum.
- Major Contraindication: Use with nitrates (e.g., nitroglycerin) is strictly prohibited due to the risk of life-threatening hypotension.
- Side Effects: Priapism (erection over $4$ hours - emergency), blue-green vision, and sudden hearing loss.
Testosterone Replacement
- Pregnancy Category: Category X (causes fetal virilization).
- Adverse Effects: Acne, gynecomastia, fluid retention, hypertension, hepatic injury, increased aggression, and virilization in women.