Nifedipine is a medicine used to lower blood pressure, the effect of which is based on the inhibition of the influx of calcium into the muscle cells of the smooth muscles. The active ingredient belongs to the group of calcium antagonists of the 1,4-dihydropyridine type. The drug that used to be frequently used for high blood pressure has largely lost its importance due to its short duration of action and some side effects.
What is nifedipine?
Nifedipine belongs to the group of dihydropyridines. The representatives of this class of active ingredients lower blood pressure by inhibiting the influx of calcium into the calcium channels of the smooth muscles. The active ingredient nifedipine is regarded as the lead substance for one of the three structural types of calcium channel blockers.These are the antihypertensive drugs of the nifedipine type. The other two calcium channel blockers belong to the phenylalkylamines (verapamil type) and the benzothiazepines (diltiazem type).
The mechanisms of action of these three types differ. The dihydropyridines ensure vasodilation, while the phenylalkylamines lower the heart rate and the benzothiazepines combine both mechanisms.
Nifedipine is a water-insoluble, yellowish powder. The substance is also very sensitive to light. In the liver, the active ingredient is broken down very quickly by the enzyme CYP3A4 and is therefore subject to a considerable restriction in bioavailability due to a high first-pass metabolism.
Pharmacological effect
The effect of nifedipine is based on the inhibition of the influx of calcium into the cells of the vascular smooth muscles through the calcium channels. Nifedipine thus acts as a calcium channel blocker. The influx of calcium ions into the muscle cells changes the electrical tension and the muscles are subject to contraction. With regard to the vascular muscles, this means a narrowing of the blood vessels with an increase in blood pressure.
This calcium influx is part of the normal regulatory system within the bloodstream. However, if there is essential hypertension (high blood pressure) or other diseases that are based on circulatory disorders, only an expansion and relaxation of the blood vessels can normalize the blood pressure. This relaxation of the vascular muscles is achieved by inhibiting the influx of calcium into the vascular muscle cells.
Nifedipine only inhibits the L-type calcium channels. The L-type calcium channel is voltage-dependent and is located in the cell membrane of the T-tubules of muscle cells. The influx of calcium ions into the cytoplasm of the muscle cells is controlled by the depolarization of the cell membrane via the activation of the ryanodine receptor. Since the ryanodine receptor is closely related to the dihydropyridine receptor, dihydropyridines can stop the influx of calcium into the cell. Since the channel is deactivated slowly, it is known as longlasting or L channel.
Nifedipine mainly affects the vascular muscle cells, but not the heart muscle cells. However, the organism tries to counteract a drop in blood pressure within the framework of the regulatory mechanisms. This can lead to side effects that can be dangerous if the circulatory system is unstable.
Medical application & use
Because of its antihypertensive effect, nifedipine is used for essential high blood pressure, hypertensive emergencies, Raynaud's syndrome and stable angina pectoris. This drug is also often used in cases of premature labor. It can also be used in creams for anal fissures. The creams contain 0.2 percent nifedipine.
Essential high blood pressure, also called essential hypertension, exists for no apparent cause. Nifedipine helps here by relaxing the vascular muscles. In a hypertensive emergency, severe high blood pressure suddenly occurs, which can even damage internal organs. In this threatening condition, blood pressure must be lowered quickly to avoid further damage. Nifedipine is best suited for this.
The hypertensive crisis, a preliminary stage of the hypertensive emergency, manifests itself in angina pectoris, dizziness, breathing difficulties, nosebleeds, confusional states up to coma, urinary behavior and visual disturbances.
Raynaud's syndrome, on the other hand, is an arterial circulatory disorder in the fingers. The fingertips are white and cold because their blood flow is disturbed by the cramping of the vascular muscles. The use of nifedipine has proven itself in Raynaud's syndrome. Nifedipine can also be used to treat stable angina pectoris.
In order to achieve a lasting effect, nifedipine is now administered in retard form. The slow release of nifedipine is guaranteed with the prolonged-release tablets, so that new active ingredients are always available after the rapid decline in effectiveness due to the first-pass effelt.
Risks & side effects
In the past, nifedipine was mainly used to lower blood pressure. In the meantime, however, nifedipine has lost its outstanding importance, as on the one hand it only works for a short time in the sustained-release form due to the first-pass mechanism and on the other hand its side effects and contraindications have been recognized more and more.
The active ingredient only works to relax the vascular muscles and has no significant influence on the heart rate. However, the strong surge in the drug leads to a rapid drop in blood pressure, which provokes counter-reactions in the body. For example, nifedipine is contraindicated in unstable angina pectoris, as reflex tachycardia develops, which in this condition can be life-threatening.
Today calcium antagonists of the second generation are often used, which are stored in the membranes due to their solubility in fat and thus released more slowly. The lower exposure to these drugs also reduces the risk of reflex tachycardia.
In addition to unstable angina pectoris, nifedipine is also contraindicated for heart attacks, high-grade aortic valve stenoses, states of shock or when certain medications such as rifampicin are given.
Common side effects when taking nifedipine are headache, flushing, and general weakness. Abdominal pain, flatulence, constipation, nervousness, anorexia, sweating, muscle cramps, fever, polyuria or visual disturbances are less common. Reflex tachycardia is also one of the rarer side effects.
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