4.2 Cardiovascular, Renal, and Endocrine Pharmacology
Key Takeaways
- Inhibition of the renin-angiotensin-aldosterone system with ACE inhibitors, ARBs, or ARNIs reduces cardiovascular and renal morbidity; switching from an ACE inhibitor to sacubitril/valsartan requires a mandatory 36-hour washout to prevent life-threatening angioedema.
- Dihydropyridine calcium channel blockers selectively dilate peripheral arterioles, whereas non-dihydropyridines (diltiazem, verapamil) exert negative chronotropic, dromotropic, and inotropic effects and are potent CYP3A4 inhibitors contraindicated in HFrEF.
- Loop diuretics (furosemide) block NKCC2 cotransporters in the thick ascending limb, causing calcium and magnesium wasting, whereas thiazides block NCCT cotransporters in the distal convoluted tubule and promote calcium retention.
- Diabetes Canada guidelines recommend SGLT2 inhibitors and GLP-1 receptor agonists with proven cardiorenal benefit for patients with type 2 diabetes and atherosclerotic cardiovascular disease, heart failure, or chronic kidney disease.
- Thionamide antithyroid therapy requires vigilantly monitoring for agranulocytosis; propylthiouracil (PTU) is preferred in the first trimester of pregnancy and thyroid storm due to peripheral T4-to-T3 conversion blockade, but carries higher fulminant hepatotoxicity risks compared to methimazole.
Last updated: August 2026
4.2 Cardiovascular, Renal, and Endocrine Pharmacology
Cardiovascular, renal, and metabolic disorders represent the highest-volume pharmacotherapeutic encounters in Canadian institutional and community pharmacy practice. Understanding molecular mechanisms, hemodynamic cascades, Canadian clinical practice guidelines (Hypertension Canada, CCS Heart Failure, Diabetes Canada), and toxicities is essential for candidate success on the PEBC Evaluating Examination.
1. Renin-Angiotensin-Aldosterone System (RAAS) and Vasodilator Pharmacology
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| RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM CASCADE |
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| [Angiotensinogen] (Liver)
| |
| v <--- Renin (Juxtaglomerular Cells: stimulated by low perfusion / beta-1)
| [Angiotensin I]
| |
| v <--- ACE / Kininase II (Inhibited by ACE Inhibitors) ===[X] Bradykinin Breakdown
| [Angiotensin II] (Cough / Angioedema)
| |
| +---> AT1 Receptor (Blocked by ARBs) ---> Vasoconstriction + Aldosterone Release
| +---> AT2 Receptor ---> Vasodilation + Antiproliferation
| |
| [Natriuretic Peptides: ANP, BNP] ===> Vasodilation + Natriuresis |
| |
| v <--- Neprilysin (Inhibited by Sacubitril) |
| [Inactive Fragments] |
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RAAS Inhibitor Classes and Clinical Mechanics
- Angiotensin-Converting Enzyme (ACE) Inhibitors (Ramipril, Perindopril, Enalapril): Inhibit ACE, preventing conversion of Ang I to Ang II, dilating the renal efferent arteriole (reducing intraglomerular pressure and proteinuria), and reducing systemic vascular resistance. Concurrently block kininase II, causing bradykinin accumulation, which mediates dry cough ($10-20%$) and rare, life-threatening angioedema.
- Angiotensin Receptor Blockers (ARBs: Candesartan, Valsartan, Telmisartan): Competitive antagonists at the $\text{AT}_1$ receptor. Provide equivalent blood pressure lowering and nephroprotection without increasing bradykinin, resulting in minimal cough or angioedema risk.
- Angiotensin Receptor-Neprilysin Inhibitors (ARNI: Sacubitril/Valsartan): Sacubitril prodrug inhibits neprilysin, elevating circulating natriuretic peptides (ANP, BNP, CNP), bradykinin, and adrenomedullin. Valsartan blocks $\text{AT}_1$ receptors. Indicated for Heart Failure with Reduced Ejection Fraction (HFrEF, CCS guidelines).
- Mandatory Safety Mandate: A 36-hour washout period is legally and clinically required when transitioning a patient from an ACE inhibitor to sacubitril/valsartan. Simultaneous neprilysin and ACE inhibition produces massive bradykinin surges and severe angioedema.
- Mineralocorticoid Receptor Antagonists (MRAs):
- Spironolactone: Non-selective MRA; also blocks androgen and progesterone receptors, predisposing to gynecomastia, breast tenderness, and menstrual irregularities.
- Eplerenone: Highly selective MRA with minimal endocrine side effects.
- Finerenone: Non-steroidal, selective MRA authorized to slow CKD progression and reduce cardiovascular events in type 2 diabetes.
- Electrolyte Hazard: All MRAs cause hyperkalemia; potassium and serum creatinine must be monitored within $1-2\text{ weeks}$ of initiation.
Vasodilators: Calcium Channel Blockers and Nitrates
| Drug Class | Representative Agents | Mechanism of Action | Hemodynamic / Clinical Effects | Adverse Effects & Pearls |
|---|---|---|---|---|
| Dihydropyridine CCBs | Amlodipine, Nifedipine XL, Felodipine | Selective block of vascular L-type $\text{Ca}^{2+}$ channels ($\text{Ca}_v1.2$) | Arteriolar vasodilation, $\downarrow$ SVR, no intrinsic negative inotropy | Peripheral dependent ankle edema (precapillary dilation), reflex tachycardia, flushing, headache |
| Non-Dihydropyridine CCBs | Diltiazem, Verapamil | Block L-type $\text{Ca}^{2+}$ channels in myocardium, SA node, and AV node | Negative chronotropy, negative dromotropy, negative inotropy | Bradycardia, AV block, constipation (verapamil relaxes colonic smooth muscle). Potent CYP3A4 and P-gp inhibitors. Contraindicated in HFrEF (LVEF $<40%$) |
| Organic Nitrates | Nitroglycerin, Isosorbide dinitrate/mononitrate | Bioactivated by mitochondrial ALDH-2 to release NO $\to \uparrow$ cGMP | Predominant venodilation $\to \downarrow$ preload, $\downarrow$ wall stress; coronary vasodilation | Nitrate tolerance avoided via daily $10-12\text{ hour}$ nitrate-free interval. Co-administration with PDE-5 inhibitors (sildenafil, tadalafil) is strictly contraindicated (fatal refractory hypotension) |
2. Renal Pharmacology and Diuretic Mechanisms
Diuretics modulate renal tubular electrolyte transporters, altering sodium excretion, intravascular volume, and systemic hemodynamics.
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| RENAL TUBULAR SITES OF DIURETIC ACTION |
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| 1. Proximal Convoluted Tubule: Carbonic Anhydrase Inhibitors (Acetazolamide) |
| - Blocks NaHCO3 reabsorption -> alkaline diuresis, metabolic acidosis |
| 2. Thick Ascending Limb Loop : Loop Diuretics (Furosemide, Bumetanide) |
| - Blocks NKCC2 cotransporter -> Ca2+ and Mg2+ wasting; abolishes medullary grad |
| 3. Distal Convoluted Tubule : Thiazides (Hydrochlorothiazide, Chlorthalidone) |
| - Blocks NCCT cotransporter -> Ca2+ retention; ineffective if eGFR <30 |
| 4. Cortical Collecting Duct : K+-Sparing Diuretics (Amiloride, Spironolactone) |
| - Blocks ENaC / Aldosterone -> K+ retention, metabolic acidosis |
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Diuretic Comparison Matrix
- Loop Diuretics (Furosemide, Bumetanide, Torsemide): Inhibit the luminal $\text{Na}^+/\text{K}^+/2\text{Cl}^-$ (NKCC2) symporter in the thick ascending limb of the loop of Henle. Abolish the hypertonic medullary interstitial gradient, providing potent natriuresis and diuresis. Promote urinary wasting of $\text{Na}^+, \text{K}^+, \text{Cl}^-, \text{Mg}^{2+}$, and $\text{Ca}^{2+}$ (used acutely in hypercalcemia). Adverse effects: Hypokalemic metabolic alkalosis, hypocalcemia, hypomagnesemia, hyperuricemia, and ototoxicity (dose-dependent, synergistic with aminoglycosides).
- Thiazide and Thiazide-Like Diuretics (Hydrochlorothiazide, Chlorthalidone, Indapamide, Metolazone): Inhibit the $\text{Na}^+/\text{Cl}^-$ (NCCT) cotransporter in the distal convoluted tubule. Promote calcium reabsorption via basolateral $\text{Na}^+/\text{Ca}^{2+}$ exchange (beneficial in osteopenia/osteoporosis and calcium nephrolithiasis). Adverse effects: Hypokalemia, hyponatremia, hypercalcemia, hyperuricemia (precipitating gout), and hyperglycemia. Ineffective as monotherapy when $\text{eGFR} < 30\text{ mL/min/1.73 m}^2$ (except indapamide and metolazone).
- Potassium-Sparing Diuretics (Amiloride, Triamterene): Directly block Epithelial Sodium Channels (ENaC) in principal cells of the late distal tubule and cortical collecting duct, preventing $\text{Na}^+$ reabsorption and decreasing the lumen-negative transepithelial potential that drives $\text{K}^+$ and $\text{H}^+$ secretion.
3. Antiarrhythmic Pharmacology (Vaughan Williams Classification)
Antiarrhythmic drugs modify cardiac ion channels and action potential dynamics:
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| VAUGHAN WILLIAMS ANTIARRHYTHMIC CLASSIFICATION |
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| Class Ia : Moderate Na+ block + K+ block (Procainamide, Quinidine, Disopyramide) |
| -> Prolongs QRS and APD / QT; intermediate dissociation kinetics |
| Class Ib : Fast Na+ block (Lidocaine, Mexiletine) |
| -> Shortens APD; binds ischemic/depolarized tissue; zero QT prolongation |
| Class Ic : Potent Na+ block (Flecainide, Propafenone) |
| -> Marked QRS widening, no effect on APD; contraindicated post-MI (CAST) |
| Class II : Beta-Adrenoceptor Antagonists (Metoprolol, Bisoprolol, Esmolol) |
| Class III: K+ Channel Blockers (Amiodarone, Dronedarone, Sotalol) |
| -> Prolongs APD / QT; Torsades de Pointes risk (low with amiodarone) |
| Class IV : Non-Dihydropyridine CCBs (Verapamil, Diltiazem) |
| Class V : Adenosine (A1 agonist, converts PSVT), Digoxin, Ivabradine (If blocker) |
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- Flecainide and Propafenone (Class Ic): Exhibit slow dissociation kinetics from open $\text{Na}^+$ channels. In the Cardiac Arrhythmia Suppression Trial (CAST), Class Ic agents increased mortality in patients with prior myocardial infarction or structural heart disease; they are strictly contraindicated in structural/ischemic heart disease.
- Amiodarone (Class III): Exhibits Class I, II, III, and IV actions. Contains iodine ($37%$ by weight) and has a prolonged elimination half-life ($t_{1/2} \approx 40-60\text{ days}$). Displays low proarrhythmic Torsades de Pointes risk compared to other Class III agents, but carries multisystem toxicities:
- Pulmonary Toxicity: Chronic interstitial pneumonitis/fibrosis (requires baseline chest X-ray and pulmonary function tests).
- Thyroid Dysfunction: Amiodarone-Induced Hypothyroidism (AIH) or Amiodarone-Induced Thyrotoxicosis (AIT Type 1 vs Type 2; requires baseline and periodic TSH).
- Hepatic & Ocular: Elevated AST/ALT, corneal microdeposits (vortex keratopathy), optic neuropathy.
- Dermatologic: Photosensitivity and slate blue-gray skin discoloration.
- Drug Interactions: Potent inhibitor of CYP3A4, CYP2C9, and P-gp; doubles plasma concentrations of digoxin and warfarin (empirically reduce doses by $50%$).
4. Endocrine Pharmacology: Diabetes Mellitus (Diabetes Canada Guidelines)
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| DIABETES CANADA TYPE 2 PHARMACOTHERAPY ALGORITHM |
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| FIRST-LINE: Healthy Behavior Interventions + Metformin (unless contraindicated) |
| |
| IF CLINICAL ASCVD, HEART FAILURE, OR CKD PRESENT (Independent of Baseline A1C): |
| +---> Clinical ASCVD : SGLT2i (Empagliflozin) or GLP-1 RA (Liraglutide, Semaglutide)|
| +---> Heart Failure : SGLT2i (Dapagliflozin, Empagliflozin with proven HF benefit)|
| +---> CKD (eGFR/ACR) : SGLT2i (Canagliflozin, Dapagliflozin, Empagliflozin) |
| |
| OTHER SECOND-LINE (Glycemic Control Focus): |
| - DPP-4i (Sitagliptin, Linagliptin) | - GLP-1 RA | - SGLT2i |
| - Gliclazide (Sulfonylurea) | - Basal Insulin | - Pioglitazone (TZD) |
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Non-Insulin Antihyperglycemic Agents Matrix
| Drug Class | Mechanism of Action | HbA1c Reduction | Weight Effect | Hypoglycemia Risk | Key Clinical Pearls & Safety Warnings |
|---|---|---|---|---|---|
| Biguanides (Metformin) | Activates AMPK $\to \downarrow$ hepatic gluconeogenesis, $\uparrow$ peripheral glucose uptake | $1.0-1.5%$ | Neutral / Mild loss | Negligible | First-line agent. Contraindicated if $\text{eGFR} < 30\text{ mL/min/1.73 m}^2$ due to lactic acidosis risk; reduce dose if $\text{eGFR} < 45$. Hold prior to iodinated contrast. Causes vitamin B12 deficiency. |
| SGLT2 Inhibitors (Empagliflozin, Dapagliflozin, Canagliflozin) | Blocks SGLT2 in renal proximal tubule $\to$ blocks $90%$ glucose reabsorption $\to$ glucosuria | $0.5-0.8%$ | Loss ($2-3\text{ kg}$) | Negligible | Proven reduction in MACE, CV death, HF hospitalization, and CKD progression. Adverse effects: Mycotic genital infections, volume depletion/orthostasis, euglycemic DKA (euDKA) (hold $3\text{ days}$ prior to elective surgery/acute illness). |
| GLP-1 Receptor Agonists (Semaglutide, Liraglutide, Dulaglutide) | Incretin mimetic: glucose-dependent insulin secretion, $\downarrow$ glucagon, delays gastric emptying | $1.0-1.8%$ | Significant loss ($4-10+\text{ kg}$) | Negligible | Proven ASCVD benefit. Contraindications: Personal/family history of Medullary Thyroid Carcinoma (MTC) or MEN-2; history of pancreatitis. Delays oral drug absorption. |
| DPP-4 Inhibitors (Sitagliptin, Linagliptin, Saxagliptin) | Inhibits DPP-4 enzyme, prolonging endogenous active GLP-1 and GIP incretin hormones | $0.5-0.7%$ | Neutral | Negligible | Well tolerated. Linagliptin requires no renal dose adjustment. Saxagliptin carries an increased risk of heart failure hospitalizations. Rare acute pancreatitis. |
| Sulfonylureas (Gliclazide, Glimepiride, Glyburide) | Binds SUR1 on pancreatic $\beta$-cell $K_{\text{ATP}}$ channels $\to$ channel closure $\to$ depolarization $\to \uparrow$ insulin exocytosis | $0.8-1.2%$ | Gain | High | Gliclazide preferred over glyburide. Glyburide has active metabolites that accumulate in renal impairment, causing severe prolonged hypoglycemia. |
| Thiazolidinediones (Pioglitazone, Rosiglitazone) | PPAR-$\gamma$ nuclear receptor agonist $\to \uparrow$ insulin sensitivity in muscle/adipose | $0.8-1.2%$ | Gain | Negligible | Fluid retention and peripheral edema; contraindicated in NYHA Class III/IV Heart Failure. Increased fracture risk in females; bladder cancer warning (pioglitazone). |
Insulin Formulations and Pharmacokinetics
\textbf{Ultra-Rapid / Rapid (Aspart, Lispro, Glulisine)} &: \text{Onset } 10-15\text{ min}, \text{Peak } 1-2\text{ h}, \text{Duration } 3-5\text{ h (Bolus / Prandial)} \\ \textbf{Short-Acting Regular (Humulin R, Novolin Toronto)} &: \text{Onset } 30-60\text{ min}, \text{Peak } 2-4\text{ h}, \text{Duration } 6-8\text{ h (IV Infusions in DKA)} \\ \textbf{Intermediate (NPH)} &: \text{Onset } 1-3\text{ h}, \text{Peak } 4-8\text{ h}, \text{Duration } 12-18\text{ h (Turbid suspension)} \\ \textbf{Long-Acting Basal (Glargine U100/U300, Detemir, Degludec)} &: \text{Onset } 1-2\text{ h}, \text{Peakless}, \text{Duration } 24-42+\text{ h (Degludec } t_{1/2} \approx 25\text{ h)} \end{aligned}$$ --- ## 5. Thyroid and Adrenal Pharmacotherapy ### Thyroid Pharmacotherapy: Hypothyroidism and Thyrotoxicosis - **Levothyroxine ($T_4$)**: Synthetic thyroxine, converted peripherally to active triiodothyronine ($T_3$) by $5'$-deiodinase. Half-life is $7\text{ days}$; steady-state requires $6-8\text{ weeks}$. Narrow therapeutic index drug. Take once daily in the morning on an empty stomach with a full glass of water, $\ge 30-60\text{ minutes}$ before breakfast. Avoid co-administration within $4\text{ hours}$ of calcium, iron, magnesium, or bile acid sequestrants. - **Thionamides (Methimazole vs. Propylthiouracil [PTU])**: - Inhibit thyroid peroxidase (TPO), blocking iodine organification and iodotyrosine coupling. - **Propylthiouracil (PTU)** also inhibits peripheral $5'$-deiodinase conversion of $T_4 \to T_3$. - **Methimazole** is first-line due to once-daily dosing and lower hepatotoxicity. - **PTU Indications**: Preferred during the **first trimester of pregnancy** (methimazole causes embryopathy: aplasia cutis, choanal atresia) and in **thyroid storm** (due to peripheral $T_4 \to T_3$ inhibition). PTU carries a black-box warning for fulminant **hepatic failure**. - **Agranulocytosis**: Rare ($0.2-0.5\%$) life-threatening complication of both thionamides. Patients presenting with fever, chills, or sore throat must stop the drug immediately and obtain an urgent CBC with differential.Test Your Knowledge
A 62-year-old patient with Heart Failure with Reduced Ejection Fraction (HFrEF, LVEF 28%) is being optimized on guideline-directed medical therapy. The cardiologist prescribes sacubitril/valsartan to replace ramipril 10 mg daily. Which instruction regarding the transition is critical to prevent a life-threatening adverse reaction?
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Test Your Knowledge
A 54-year-old patient with type 2 diabetes managed on metformin and empagliflozin presents to the emergency department with nausea, vomiting, tachypnea, and severe fatigue 48 hours following elective laparoscopic cholecystectomy. Laboratory analysis demonstrates an arterial pH of 7.22, serum bicarbonate of 11 mmol/L, serum beta-hydroxybutyrate of 4.8 mmol/L, and a blood glucose of 8.2 mmol/L. What physiological mechanism explains this patient's clinical state?
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Test Your Knowledge
A 68-year-old patient with hypertension is prescribed chlorthalidone 25 mg daily. Compared to loop diuretics such as furosemide, which metabolic and electrolyte pattern is uniquely characteristic of thiazide and thiazide-like diuretics?
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Test Your Knowledge
A 28-year-old woman in her sixth week of pregnancy is diagnosed with severe Graves' disease thyrotoxicosis. Which statement accurately reflects Canadian clinical guidelines regarding thionamide antithyroid drug selection and safety monitoring?
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