Hydralazine is a drug that has a vasodilator effect. It is used to treat heart failure as well as hypertension during pregnancy.
What is hydralazine?
Hydralazine belongs to the group of vasodilators. These are vasodilating agents that are used to lower high blood pressure. In Europe, however, the related dihydralazine is more commonly used. The World Health Organization (WHO) has placed hydralazine on the list of essential medicines. Hydralazine is usually administered as a combination preparation under the trade names TRI-Normin or Pertenso, and in the USA as the monopreparation Apresoline. The active ingredient is also known as dihydralazinum or 1-hydralazinylphthalazine. The basic chemical structure of the drug consists of two benzene rings, forming an aromatic molecule.
Pharmacological action
Due to the fact that hydralazine is one of the drugs that promote blood circulation, it causes immediate relaxation of the vascular muscles. This applies primarily to the small arteries. Hydralazine thus ensures a general widening of the blood vessels, which in turn results in the lowering of high blood pressure (hypertension). In addition, the active ingredient has the property of lowering vascular resistance within the kidneys and brain. This effect also relieves high blood pressure. In the context of long-term therapy, blood flow to the kidneys can be ensured in this way. However, it is important to ensure that the performance of the heart and the cardioactive properties of the hormone adrenaline are not impaired by hydralazine. Thus, the blood pressure-lowering effect of the vasodilator can lead to an increase in the heartbeat volume as well as the heart rate. However, it is possible to counteract this reflex by administering beta-blockers. Like other drugs that have a vasodilator effect, hydralazine can decrease urine volume. For this reason, the drug is well suited as a combination agent for beta-blockers and diuretic preparations. A similar effect to hydralazine is seen with the related drug dihydralazine. Hydralazine has a high absorption capacity in the intestine. However, its bioavailability is only 25 to 30 percent, which is due to the hepatic first-pass effect. The duration of the antihypertensive effect of the drug is approximately five to six hours. The maximum plasma level occurs after 30 to 120 minutes. Hydralazine is largely broken down by the liver. Excretion of metabolites occurs along with unchanged hydralazine via the kidneys.
Medical use and application
Hydralazine is used to treat high blood pressure, and the drug is used almost exclusively as a combination preparation. The most important areas of use are severe heart failure and hypertension during pregnancy. In the course of pregnancy, however, hydralazine is no longer considered the drug of first choice for severe hypertension. Medicine now considers the drugs labetalol and nifedipine to be more effective. Hydralazine is administered in the form of tablets. It is important to keep them at room temperature and protect them from light. Another administration option is injection solutions, which should also be stored at room temperature. In addition, the solution should not be allowed to cool.
Risks and side effects
The use of hydralazine may be associated with unpleasant side effects. However, these effects do not automatically manifest in every patient. In most cases, affected individuals suffer from gastrointestinal problems such as constipation, lack of appetite, diarrhea, nausea and vomiting, dizziness, drop in blood pressure, nasal congestion, or water retention in the body. In rare cases, you may also experience sensitivity disorders such as cold sensations, tingling or numbness, migraine-like headaches, urinary bladder disorders, muscle tremors, muscle cramps, an inflamed liver, fatigue, allergic reactions such as skin rash or itching, depression, anxiety, and erectile dysfunction. At the beginning of hydralazine therapy, an increased pulse, palpitations, and chest tightness occur with a rapid increase in the dose, which is due to the dilation of the blood vessels and the lowering of blood pressure.Prolonged use may cause muscle pain, rheumatic joint pain and fever in patients suffering from chronic renal impairment. Hydralazine should not be used if there is hypersensitivity to the drug or dihydralazine. The same applies if the patient suffers from a blockage of his heart valves, a pathological aortic bulge or butterfly lichen (lupus erythematosus). The drug must also not be administered if there is a pathological enlargement of the heart muscle. If there is cardiac insufficiency or chest discomfort (angina pectoris), it is advisable to administer beta-blockers at the same time. In case of circulatory disorders in the brain or advanced renal or hepatic weakness, a careful decision of the physician on the treatment is required. Hydralazine should not be administered during breastfeeding. If administration must nevertheless be made, breast-feeding should be stopped beforehand. There is a risk of drug interactions due to the simultaneous administration of hydralazine and other medications. For example, taking neuroleptics or tricyclic antidepressants at the same time as alcohol increases the blood pressure-lowering effect of the vasodilator. Doctors therefore recommend abstaining from alcoholic beverages during treatment. If simultaneous therapy with hydralazine and psychotropic drugs such as MAO inhibitors takes place, there is a risk of a drop in blood glucose, so that careful monitoring must be carried out. This also applies to treatment with the antihypertensive agent diazoxide, as this can cause a precarious drop in blood pressure. A strong sedative effect is possible with simultaneous use of sedatives or narcotics as well as sleeping pills, so the respective doses must be adjusted accordingly.
