Antihypertensive Drugs
Here's a nifty chart with all the drugs, mechanisms, pathways, examples, and ways to remember them.
"Minoxidil = Mino-wider" – Minoxidil makes arteries wider, "widens like a minnow swimming in wide water".
"Nitroprusside = Nitro-speed" – Nitroprusside acts quickly (speedy NO release) to relax vessels.
| Drug Class | Mechanism of Action | Pathway Details | Memory Tip | Examples |
|---|---|---|---|---|
| α1-agonists | Activates α1 receptors on blood vessels, leading to the activation of the Gq-GPCR pathway | Gq-GPCR Pathway: Activation of α1 receptors triggers the Gq protein, which activates phospholipase C (PLC). PLC converts PIP2 into IP3 and DAG. IP3 causes calcium release from the sarcoplasmic reticulum, leading to smooth muscle contraction and vasoconstriction. | "α1 = tighten" – α1 agonists tighten (constrict) blood vessels. Think of "α1" as "alpha = strong, tight". | Phenylephrine (selective), norepinephrine (nonselective) |
| Nondihydropyridine Calcium Channel Blockers | Blocks L-type calcium channels in heart muscle and blood vessels | L-type Calcium Channels: These channels are critical for calcium influx during the plateau phase of the cardiac action potential. Calcium influx is necessary for myocyte contraction. By blocking these channels, these drugs reduce intracellular calcium levels, leading to reduced myocardial contractility (negative inotropic effect), slower heart rate (negative chronotropic effect), and vasodilation (relaxation of blood vessels). | "Non-DHP = heart and vessels" – Non-DHP blocks both heart (non-specific) and vessels. Think "non-DHP = no fast heart". | Verapamil, diltiazem |
| Dihydropyridine Calcium Channel Blockers | Blocks L-type calcium channels mainly in blood vessels | L-type Calcium Channels: In vascular smooth muscle, L-type channels are essential for calcium influx, which triggers muscle contraction. Blocking these channels in blood vessels leads to vasodilation (widening of vessels), particularly in arteries, lowering afterload and reducing blood pressure. Dihydropyridines have a greater affinity for vascular smooth muscle than for the heart. | "DHP = Dilate" – Dihydropyridines mainly dilate blood vessels. "DHP = Dilates Happy Pipes". | Nifedipine, amlodipine, felodipine |
| Phosphodiesterase-3 (PDE-3) Inhibitors | Inhibits PDE-3 enzyme, leading to increased cAMP levels in heart and blood vessels |
PDE-3 Enzyme: PDE-3 is an enzyme that degrades cAMP in cardiac and smooth muscle cells. cAMP is a key regulator of heart contractility and smooth muscle relaxation. By inhibiting PDE-3, these drugs increase cAMP levels, which enhances calcium influx during heart muscle contraction (increasing the force of contraction, positive inotropic effect) and promotes vasodilation in blood vessels.
|
"PDE = Pump, Dilate, Energize" – PDE inhibitors make the heart pump harder and dilate vessels. | Milrinone, cilostazol |
| Nitric Oxide (NO) | NO activates guanylate cyclase, increasing cGMP levels in vascular smooth muscle | NO and cGMP Pathway: Nitric oxide (NO) diffuses into vascular smooth muscle cells and activates guanylate cyclase, which increases the production of cGMP. cGMP reduces intracellular calcium levels by activating protein kinase G (PKG), which in turn leads to smooth muscle relaxation and vasodilation. NO is a key mediator in the endothelium-derived relaxation of blood vessels. | "NO = No tension" – Nitric oxide relaxes vessels, "NO" for "No pressure". | Nitroglycerin, isosorbide dinitrate, sodium nitroprusside |
| Hydralazine | Directly relaxes arterial smooth muscle by an unclear mechanism | Direct Vasodilator: Hydralazine’s exact mechanism isn’t fully understood, but it is believed to reduce intracellular calcium levels and/or alter calcium sensitivity in vascular smooth muscle, leading to direct relaxation of arterioles (small arteries). This effect primarily reduces afterload (the resistance the heart has to pump against). | "Hydralazine = hydrant relaxes pressure" – Hydralazine opens up arteries like a fire hydrant. | Hydralazine |
| Minoxidil | Opens potassium channels in smooth muscle cells, causing hyperpolarization and muscle relaxation | Potassium Channel Opener: Minoxidil opens ATP-sensitive potassium channels in vascular smooth muscle, leading to hyperpolarization (making the inside of the cell more negative) and preventing calcium influx. This results in smooth muscle relaxation and vasodilation, primarily in arteries. | Minoxidil | |
| Nitroprusside | Releases NO directly into the bloodstream, leading to increased cGMP and vasodilation | Direct NO Donor: Sodium nitroprusside breaks down in the bloodstream to release NO, which activates guanylate cyclase and increases cGMP in vascular smooth muscle. This leads to rapid and potent vasodilation of both arteries and veins, reducing both preload and afterload. | Sodium nitroprusside | |
| Sildenafil | Inhibits PDE-5 enzyme, leading to increased cGMP levels in pulmonary and corpus cavernosum vessels | PDE-5 Enzyme: PDE-5 specifically degrades cGMP in the smooth muscle of the corpus cavernosum (penis) and pulmonary arteries. By inhibiting PDE-5, sildenafil increases cGMP levels, causing vasodilation in these areas. It is used to treat erectile dysfunction and pulmonary hypertension. | "Sildenafil = Fill and expand" – Sildenafil helps fill blood vessels (erection) by expanding them. | Sildenafil (Viagra) |
Summary:
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α1-agonists: Tighten blood vessels through calcium release (Gq-GPCR pathway).
- Memory Tip: "α1 = tighten"
- Examples: Phenylephrine, norepinephrine
-
Nondihydropyridine Calcium Channel Blockers: Slow the heart and relax vessels by blocking calcium (L-type channels).
- Memory Tip: "Non-DHP = no fast heart"
- Examples: Verapamil, diltiazem
-
Dihydropyridine Calcium Channel Blockers: Primarily relax blood vessels (L-type channels).
- Memory Tip: "DHP = Dilate Happy Pipes"
- Examples: Nifedipine, amlodipine, felodipine
-
PDE-3 Inhibitors: Increase heart strength and relax vessels by boosting cAMP.
- Memory Tip: "PDE = Pump, Dilate, Energize"
- Examples: Milrinone, cilostazol
-
Nitric Oxide (NO): Relaxes vessels by increasing cGMP (guanylate cyclase).
- Memory Tip: "NO = No tension"
- Examples: Nitroglycerin, isosorbide dinitrate, sodium nitroprusside
-
Hydralazine: Directly relaxes arterial muscles, lowering afterload.
- Memory Tip: "Hydralazine = hydrant relaxes pressure"
- Examples: Hydralazine
-
Minoxidil: Opens potassium channels, leading to vessel relaxation.
- Memory Tip: "Minoxidil = Mino-wider"
- Examples: Minoxidil
-
Nitroprusside: Quickly relaxes vessels by directly releasing NO.
- Memory Tip: "Nitroprusside = Nitro-speed"
- Examples: Sodium nitroprusside
-
Sildenafil: Expands specific vessels by increasing cGMP (PDE-5 inhibitor).
- Memory Tip: "Sildenafil = Fill and expand"
- Examples: Sildenafil (Viagra)