Antihyper and hypotensive drugs pharmacology
Reading File
Finding Sources
Finding Sources
Searching the Web
antihypertensive drugs pharmacology classes mechanisms 2025
Reading File
Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Finding Sources
Finding Sources
Finding Sources
Reading File
Searching PubMed
antihypertensive drug classes mechanisms hypertension management
I now have rich material from Katzung's Basic and Clinical Pharmacology and Goodman & Gilman's. Let me compile a comprehensive, well-organized answer.
Antihypertensive & Hypotensive Drugs - Pharmacology
Overview
Hypertension is defined as BP ≥130/80 mmHg (AHA/ACC) or ≥140/90 mmHg (ESC/European). It is the most common cardiovascular disease and the principal cause of stroke, a major risk factor for coronary artery disease, heart failure, and renal insufficiency. Antihypertensive drugs work through three main hemodynamic strategies:
- Reducing blood volume (lowers cardiac output and central venous pressure)
- Reducing cardiac output (reducing heart rate and stroke volume)
- Reducing systemic vascular resistance (arterial vasodilation)
Drug Classes at a Glance
| Class | Prototype | Primary Mechanism | Key Indication |
|---|---|---|---|
| Thiazide diuretics | Hydrochlorothiazide, Chlorthalidone | Volume reduction | First-line, elderly, isolated systolic HTN |
| ACE inhibitors | Captopril, Lisinopril, Enalapril | Block Ang I→II; raise bradykinin | Diabetes, CKD, HF, post-MI |
| ARBs | Losartan, Valsartan | Block AT1 receptor | ACE inhibitor cough intolerance |
| Calcium channel blockers | Amlodipine (DHP), Diltiazem (NDHP) | Block L-type Ca²⁺ channels | Angina, elderly, atherosclerosis |
| Beta-blockers | Metoprolol, Atenolol, Carvedilol | Block β1 (heart) ± β2 ± α1 | Post-MI, HF, angina, AF |
| Alpha-1 blockers | Prazosin, Doxazosin | Block vascular α1 receptors | Prostate hypertrophy + HTN |
| Central α2 agonists | Clonidine, Methyldopa | ↓ sympathetic outflow from CNS | Pregnancy (methyldopa) |
| Direct vasodilators | Hydralazine, Minoxidil | Open K⁺ channels / release NO | Resistant HTN, HF (hydralazine) |
| Nitroprusside | Sodium nitroprusside | Release NO → venous + arterial dilation | Hypertensive emergency (IV) |
| Aldosterone antagonists | Spironolactone, Eplerenone | Block mineralocorticoid receptor | HF, primary aldosteronism |
1. Diuretics
Thiazides & Thiazide-like (Hydrochlorothiazide, Chlorthalidone, Indapamide)
Mechanism: Inhibit Na⁺/Cl⁻ cotransporter (NCC) in the distal convoluted tubule → natriuresis → volume depletion → reduced cardiac output. Long-term: also reduce systemic vascular resistance by poorly understood mechanisms.
Key pharmacological points:
- Chlorthalidone has a half-life >24 h (vs. several hours for HCTZ) and provides more stable 24-hour BP reduction - meta-analyses confirm superiority over HCTZ
- Effective at low doses (12.5-25 mg/day); increasing beyond 25 mg/day does not improve BP control but increases adverse effects
- First-line agents for uncomplicated hypertension, especially in the elderly
Adverse effects: Hypokalemia, hyperuricemia, hyperglycemia, hyperlipidemia (dose-dependent). Hypokalemia is particularly dangerous in the elderly (arrhythmia risk) and in patients on digoxin.
Combining with ACE inhibitors/ARBs: Attenuates K⁺ wasting; this is a rational combination but must start at low doses due to markedly enhanced hypotensive effect.
Loop Diuretics (Furosemide, Bumetanide)
Used for severe hypertension with renal insufficiency (GFR <30 mL/min, where thiazides lose efficacy) or acute pulmonary edema.
Potassium-sparing (Spironolactone, Eplerenone, Amiloride)
- Spironolactone/Eplerenone: Aldosterone antagonists - valuable in heart failure (mortality benefit), primary aldosteronism, resistant hypertension
- Amiloride/Triamterene: Block ENaC channels in collecting duct; used to prevent thiazide-induced hypokalemia
2. ACE Inhibitors (ACEi)
Drugs: Captopril, Enalapril, Lisinopril, Ramipril, Benazepril, Fosinopril, Quinapril, Perindopril, Trandolapril
Mechanism: Inhibit peptidyl dipeptidase (angiotensin-converting enzyme), which:
- Prevents conversion of Angiotensin I → Angiotensin II (vasoconstrictor, aldosterone stimulator)
- Inhibits bradykinin degradation (bradykinin = potent vasodilator via NO and prostacyclin release)
Both actions contribute to the hypotensive effect - blocking the bradykinin receptor with icatibant blunts the BP-lowering effect of captopril.
Hemodynamic profile: Lower BP by decreasing peripheral vascular resistance. Cardiac output and heart rate are NOT significantly changed. No reflex tachycardia (baroreceptor resetting + enhanced parasympathetic tone).
Prodrugs: All except captopril and lisinopril are prodrugs (esterified forms) hydrolyzed primarily in the liver to active diacid forms (e.g., enalapril → enalaprilat). Enalaprilat is available IV for hypertensive emergencies.
Special renal effects: Decrease efferent arteriolar resistance → reduce intraglomerular pressure → reduce proteinuria → slow CKD progression. Recommended in diabetic nephropathy even without hypertension.
Other benefits: Reduce mortality in heart failure and post-MI. Reduce incident diabetes in high cardiovascular-risk patients.
Elimination: Most eliminated renally - dose reduce in renal insufficiency. Exceptions: fosinopril and moexipril have hepatic + renal elimination.
Adverse effects:
- Dry cough (most common, up to 15% - bradykinin-mediated, switch to ARB)
- Angioedema (rare but serious, contraindicated if history)
- Hyperkalemia (especially + K⁺-sparing diuretics/supplements - can be life-threatening)
- First-dose hypotension (especially volume-depleted patients)
- Teratogenicity (contraindicated in pregnancy - fetal renal dysgenesis)
- Acute renal failure in bilateral renal artery stenosis
3. Angiotensin Receptor Blockers (ARBs)
Drugs: Losartan, Valsartan, Irbesartan, Candesartan, Telmisartan, Olmesartan, Azilsartan
Mechanism: Selectively block the AT1 receptor, blocking all angiotensin II effects (vasoconstriction, aldosterone release, sympathetic facilitation, cellular hypertrophy) regardless of Ang II source (ACE-dependent or chymase-dependent).
Unlike ACEi: Do NOT raise bradykinin → no cough, lower risk of angioedema. The AT2 receptor (potentially beneficial, vasodilatory, antiproliferative) remains unopposed.
Indications: Identical to ACEi; preferred when ACEi cough is intolerable. Same renal protection in diabetic nephropathy.
Contraindications: Pregnancy (same as ACEi). Do NOT combine ACEi + ARB - increases adverse effects without additional BP benefit.
4. Calcium Channel Blockers (CCBs)
Dihydropyridines (DHPs): Amlodipine, Nifedipine, Felodipine, Nicardipine
Mechanism: Block L-type (voltage-gated) Ca²⁺ channels in vascular smooth muscle >> cardiac muscle → arteriolar vasodilation → reduce systemic vascular resistance
- Minimal cardiac depression at therapeutic doses (vascular selectivity)
- May cause reflex tachycardia, especially short-acting nifedipine (avoid short-acting forms)
- Amlodipine: long half-life (~36h), once daily, no abrupt withdrawal issues
Non-Dihydropyridines (NDHPs)
- Diltiazem: Moderate vascular + cardiac effects; reduce HR and AV conduction
- Verapamil: Primarily cardiac (negative chronotrope, dromotrope, inotrope); greatest cardiac depression of CCBs
NDHPs are contraindicated with beta-blockers due to risk of AV block and severe bradycardia.
Indications:
- DHPs: Hypertension, angina (especially vasospastic), elderly patients, isolated systolic HTN, atherosclerosis
- NDHPs: Angina, supraventricular tachycardia/AF rate control
Adverse effects (DHPs): Peripheral edema (not diuretic-responsive, due to precapillary dilation), flushing, headache, reflex tachycardia
Adverse effects (NDHPs): Constipation (verapamil), bradycardia, AV block, negative inotropy
5. Beta-Blockers (β-Blockers)
Drugs:
- Selective β1 (cardioselective): Metoprolol, Atenolol, Bisoprolol, Nebivolol
- Non-selective (β1+β2): Propranolol, Nadolol, Timolol
- Mixed α/β blockers: Labetalol (α1+β1+β2), Carvedilol (α1+β1+β2 + antioxidant)
- Vasodilating β-blocker: Nebivolol (releases NO from endothelium)
Mechanism: Block β1-adrenergic receptors in the heart → decrease heart rate, decrease contractility, decrease cardiac output → lower BP. Also suppress renin release from juxtaglomerular cells.
Additional mechanisms over time: Peripheral vascular resistance decreases with chronic use (reset vascular adrenoreceptors).
Indications:
- Post-MI (reduce mortality, prevent reinfarction)
- Heart failure with reduced ejection fraction (bisoprolol, carvedilol, metoprolol succinate - titrate up slowly)
- Angina pectoris
- Atrial fibrillation (rate control)
- Hypertensive emergency (labetalol IV)
- Aortic aneurysm (reduce wall stress)
Contraindications/Cautions:
- Reactive airway disease / COPD (β2 blockade causes bronchoconstriction) - avoid non-selective; use cardioselective with caution
- AV block, sick sinus syndrome
- Acute decompensated heart failure (can initiate at stable stage)
- Peripheral artery disease (relative)
- Do not stop abruptly - rebound hypertension, angina, MI
Adverse effects: Fatigue, cold extremities, masking of hypoglycemia symptoms (dangerous in insulin-dependent diabetics), sexual dysfunction, bradycardia, hyperkalemia (via β2 block reducing cellular K⁺ uptake)
6. Alpha-1 Blockers (α1 Antagonists)
Drugs: Prazosin, Doxazosin, Terazosin
Mechanism: Competitively block α1-adrenergic receptors on arteriolar smooth muscle → vasodilation → reduced systemic vascular resistance
Key features:
- Useful in men with BPH (relax prostate/bladder neck smooth muscle)
- Metabolically favorable: reduce LDL, raise HDL, improve insulin sensitivity
- First-dose syncope is a significant risk - start at bedtime with low dose
- Long-term cardiovascular outcome data less favorable than thiazides or CCBs (ALLHAT trial: doxazosin arm stopped early - more heart failure events)
- Not recommended as first-line monotherapy for uncomplicated HTN
7. Central Sympatholytics
Central α2 Agonists: Clonidine, Methyldopa, Guanfacine, Tizanidine
Mechanism: Stimulate α2 receptors (and imidazoline receptors) in the brainstem (nucleus tractus solitarius, vasomotor center) → reduced sympathetic outflow → decrease in heart rate, cardiac output, and peripheral resistance
Clonidine:
- Available orally and as transdermal patch (weekly dosing improves compliance)
- Significant sedation and dry mouth (common)
- Rebound hypertension on abrupt withdrawal (especially with high doses) - taper slowly
Methyldopa:
- Prodrug: converted to α-methylnorepinephrine (false neurotransmitter) in the brain
- Drug of choice in pregnancy-associated hypertension (most safety data)
- Adverse effects: sedation, positive Coombs' test (hemolytic anemia - rare), hepatitis (rare), lupus-like syndrome
8. Direct Vasodilators
Hydralazine
Mechanism: Directly relaxes arteriolar smooth muscle (likely by activating K⁺ channels and/or interfering with intracellular Ca²⁺ release) → selective arteriolar dilation → reduced SVR
Key features:
- Causes reflex sympathetic activation → tachycardia, increased cardiac output (may worsen angina; combine with beta-blocker)
- Causes reflex sodium retention (combine with diuretic)
- Used in combination with isosorbide dinitrate in African American patients with HFrEF (A-HeFT trial)
- Used in severe hypertension in pregnancy (IV)
Adverse effects: Drug-induced lupus (slow acetylators at high doses >200 mg/day), reflex tachycardia, headache, flushing, sodium retention
Minoxidil
Mechanism: Potassium channel opener (K-ATP channels) → arteriolar smooth muscle hyperpolarization → vasodilation
- More powerful than hydralazine; reserved for refractory hypertension
- Always combine with beta-blocker + loop diuretic (reflex tachycardia + severe fluid retention)
- Hypertrichosis (hair growth) - basis for topical use in alopecia
9. Drugs for Hypertensive Emergencies
| Drug | Route | Mechanism | Notes |
|---|---|---|---|
| Sodium nitroprusside | IV infusion | Releases NO → venous + arteriolar dilation | Fastest onset; risk of cyanide toxicity (thiocyanate) with prolonged use |
| Nicardipine | IV | L-type CCB (DHP) | Preferred for perioperative HTN emergency |
| Labetalol | IV bolus/infusion | α1 + β1/β2 blockade | Preferred in aortic dissection, stroke, pregnancy |
| Clevidipine | IV | Ultra-short-acting DHP CCB | Rapid titration, arteriolar |
| Hydralazine | IV/IM | Direct vasodilator | Preferred in pregnancy |
| Esmolol | IV | Ultra-short-acting β1 blocker | Aortic dissection, periop tachycardia |
| Fenoldopam | IV | Dopamine D1 agonist | Renal vasodilation, useful in renal impairment |
| Phentolamine | IV | Non-selective α blocker | Pheochromocytoma crisis |
10. Hypotensive Drugs (for Acute Hypotension / Shock)
These raise BP by increasing SVR and/or cardiac output:
| Drug | Class | Mechanism | Use |
|---|---|---|---|
| Norepinephrine | Vasopressor | α1 >> β1 agonist | Septic shock (first-line) |
| Epinephrine | Vasopressor | α1 + β1 + β2 agonist | Anaphylaxis, cardiac arrest |
| Vasopressin | ADH analog | V1 receptor → vasoconstriction | Septic shock (adjunct) |
| Dopamine | Catecholamine | D1 (low dose) → β1 (mod) → α1 (high) | Cardiogenic shock |
| Dobutamine | Inotrope | β1 >> β2 agonist | Cardiogenic shock (low SVR, low CO) |
| Phenylephrine | Pure α1 agonist | Vasoconstriction | Spinal hypotension, reflex bradycardia situations |
| Midodrine | α1 agonist (oral) | Peripheral vasoconstriction | Orthostatic hypotension |
| Fludrocortisone | Mineralocorticoid | Volume expansion | Autonomic neuropathy, orthostatic HTN |
First-Line Drug Selection by Clinical Context
Based on current AHA/ACC and ESC guidelines (Goodman & Gilman's, p.1411-1413):
| Condition | Preferred Drug(s) |
|---|---|
| Uncomplicated HTN | ACEI/ARB, CCB, or thiazide diuretic |
| Diabetes mellitus | ACEI or ARB (especially with proteinuria) |
| CKD / Proteinuria | ACEI or ARB |
| Heart failure (HFrEF) | ACEI/ARB/ARNI, BB, diuretics, MRA |
| Post-MI | ACEI/ARB, BB |
| Angina pectoris | BB, CCB |
| Coronary artery disease | ACEI/ARB, BB |
| AF rate control | BB, diltiazem, verapamil |
| Left ventricular hypertrophy | ACEI, ARB, CCB |
| Isolated systolic HTN | ACEI/ARB, CCB, thiazide |
| Aortic aneurysm | BB |
| BPH + HTN | α1 blocker |
| Pregnancy | Methyldopa, labetalol, nifedipine, hydralazine |
| Pheochromocytoma | α blockade first (phenoxybenzamine), then β |
Pharmacokinetic Principles
- Choose agents with long half-lives or controlled-release formulations for once-daily dosing (better compliance, more stable 24-h BP)
- Aim for trough-to-peak effect ratio >50% to ensure adequate BP control between doses
- Dose-reduce renally-cleared ACEi in CKD (except fosinopril, moexipril - dual elimination)
- Combination therapy is usually more effective and better tolerated than high-dose monotherapy; rational combinations include ACEI/ARB + CCB, ACEI/ARB + thiazide
- Do NOT combine ACEI + ARB (no added benefit, more adverse effects); Do NOT combine NDPHP CCB + BB (AV block risk)
Sources: Katzung's Basic and Clinical Pharmacology, 16th Ed., pp. 278, 1655 | Goodman & Gilman's The Pharmacological Basis of Therapeutics, pp. 755, 1020-1035, 1411-1429
This is a shared conversation. Sign in to Orris to start your own chat.