AssessmentsCalcium channel blockers
Calcium channel blockers
USMLE® Step 1 style questions USMLE
A 70-year-old Caucasian man comes to the office for a routine medical check-up. He has not seen a physician for many years because he considers himself to be in good health. His pulse is 74/minute and his blood pressure is 170/100 mm Hg. At this point, the patient is diagnosed with hypertension and is started on antihypertensive medication. During a follow-up visit to the office, a few months after, the patient’s blood pressure is 135/80 mm Hg. However, the physical examination is remarkable for bilateral, symmetrical pitting edema. Which of the following drugs was mostly likely prescribed and caused the edema in this patient?
Content Reviewers:Yifan Xiao, MD
Calcium entry blockers, or calcium channel blockers - CCBs for short - are vasodilators, or medications that promote dilation of blood vessels.
Now, by definition, blood pressure is the force that blood exerts on the walls of blood vessels and it’s basically what keeps blood flowing and perfusing tissues to deliver oxygen and nutrients.
Hypertension happens when this pressure is higher than it should be. In most cases, the cause is unknown.
But basically, we can do a number of things to help lower the blood pressure.
In other words, diminish the amount of blood that exerts force upon the same area.
Or, we can vasodilate the peripheral blood vessels, therefore increasing the area for the same amount of liquid that exerts force.
Generally, the underlying cause is the presence of atheromatous plaques in the coronary arteries which decreases the blood flow to the heart.
So, to help diminish the symptoms, it’s important to decrease the oxygen demand of the heart, again by decreasing heart rate or myocardial contractility; and increasing the oxygen supply by vasodilating the coronary arteries.
Now, let’s look at how calcium channels affect heart function.
These action potentials start automatically when sodium channels slowly let in a stream of sodium ions, which causes the membrane potential of the pacemaker cells to become more positive.
When this reaches the threshold membrane potential, it’s the cue for voltage-gated calcium channels to open, allowing a large influx of calcium ions, which depolarizes it further.
Then, these calcium channels close and potassium channels open to let potassium out of the cell, so the membrane potential goes back down, or repolarizes.
Now, each cycle of depolarization and repolarization represents a single heartbeat, so how fast this process repeats in one minute determines the heart rate.
Okay, so now let’s look at the cardiac muscle and vascular smooth muscle contraction, which also depends on calcium.
Voltage-gated calcium channels in the membrane of the muscle cell open when they receive an action potential and this allows calcium ions to flow into the cell from the extracellular space.
The extracellular calcium causes the release of intracellular calcium ions stored in the sarcoplasmic reticulum.
All these calcium ions then bind to troponin regulatory proteins, which change shape and release the thin filaments in the muscle fiber.
This allows the thin filament to bind to the thick filament, eventually leading to muscle contraction.
In the heart, this means greater myocardial contractility. In blood vessels, this means vasoconstriction.
Okay, so calcium channel blockers, as the name suggests, block voltage-gated calcium channels.
These medications act mainly on the smooth muscles of the blood vessels.
So, let’s start with the dihydropyridines, which are mainly used to treat hypertension.
They preferentially exert their effects on arterial smooth muscle, and nifedipine is the prototype of this class.
Besides treating hypertension, dihydropyridines are also commonly used to treat other disorders.
Since they can also dilate coronary arteries, they are effective for preventing angina.
They can treat Raynaud Phenomenon, a disease caused by vasoconstriction of the arteries in the tips of fingers, causing them to turn white, then blue, and finally red.
- "Katzung & Trevor's Pharmacology Examination and Board Review,12th Edition" McGraw-Hill Education / Medical (2018)
- "Rang and Dale's Pharmacology" Elsevier (2019)
- "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education / Medical (2017)
- "Hurst's the Heart, 14th Edition: Two Volume Set" McGraw-Hill Education / Medical (2017)
- "Amlodipine: an overview of its pharmacodynamic and pharmacokinetic properties" Clin Cardiol (1994)
- "Calcium Channel Blockers" The Journal of Clinical Hypertension (2011)
- "Calcium channel blockers for primary and secondary Raynaud's phenomenon" Cochrane Database of Systematic Reviews (2017)