Quinidine is an active substance that belongs to the group of antiarrhythmic drugs. It is used to treat certain heart rhythm disorders.
Medical use and application
Quinidine is an active substance that belongs to the group of antiarrhythmic drugs. It is used to treat certain cardiac arrhythmias. Quinidine, as an active ingredient in the antiarrhythmic group, helps treat various problems with the heart (for example, too fast and irregular heartbeat, atrial flutter, and atrial fibrillation). It is administered in a cardiac treatment whenever there is a need to lower a fast heartbeat or normalize an irregular heartbeat. The treatment of cardiac arrhythmias as well as the regulation of the heart rhythm is also carried out with drugs containing the active substance quinidine. Furthermore, quinidine can be used for cardioversion when it is not possible to perform electroshock therapy.
Pharmacologic action
Quinidine is a class 1 a antiarrhythmic agent. It blocks sodium channels in cardiac myocytes so that, because of the decreased sodium influx, the excitability of the myocardium decreases. In addition, the potassium outflow is inhibited by quinidine, so that the action potential is prolonged. In addition, quinidine exerts a vasodilatory effect, which lowers arterial blood pressure and thus relieves the heart and its muscles. The resulting muscle relaxation is particularly noticeable in the arms and legs of affected patients. The reduced excitability of the heart also makes the heart beat more slowly and more regularly. The active ingredient quinidine is absorbed very quickly by the human body. It is detectable in the patient’s blood after only about 15 minutes, at which time the symptoms are already noticeably reduced. In combination with a calcium channel blocker, quinidine also leads to better regulation of circulatory disturbances during cardiac stress.
Risks and side effects
Quinidine has been observed to have a negative effect on the gastrointestinal tract in a very large number of patients. This usually results in nausea, vomiting, and diarrhea. If an overdose of the active ingredient occurs, so-called quinidine poisoning can occur, which affects the central nervous system and can lead to visual disturbances, nystagmus or even damage to the optic nerve. Typical symptoms are hearing disorders (e.g. tinnitus) as well as headaches, dizziness or even confusion. In rare cases, the function of the liver can be disturbed by the active substance quinidine. If the patient has cardiac insufficiency (NYHA III and IV) or an excessively slow heartbeat, quinidine must not be taken. It is also not indicated if the patient has already had an overdose of cardiac glycosides or if there are conduction disorders of the heart. If the patient suffers from an excessive atrial beat rate, then after ample consideration by the attending physician, another antiarrhythmic agent should be used first. Sufficient experience with the use of quinidine in pregnancy is not available. However, there is a possibility of loss of the unborn child, so it should be taken only after weighing the risk-benefit of the attending physician. Since the active substance passes into breast milk, quinidine should not be taken during breastfeeding. Although no harmful effects are known for infants, it should also be weighed up here whether the benefit for the mother is greater than the risk for the infant. In children, the use has not yet been tested, so that in this case only the treating physician can decide whether the use of quinidine is necessary. If quinidine is taken together with other medicines, some interactions may occur, which may vary depending on the form of the medicine (e.g. tablet, injection). For example, if antihypertensive drugs are taken in higher doses, there is a risk of a negative effect on the heart. The effect of quinidine can also be increased as a result. If treatment with antibiotics or antifungal agents is required at the same time, the effect of quinidine may be reduced. If cardiac glycosides (e.g. digoxin or digitoxin) are also taken at the same time, quinidine may increase the effect of these agents.Due to the numerous interactions with other drugs, quinidine should therefore only ever be taken in consultation with the attending physician. Since the side effects of quinidine can sometimes be very severe, it is now only very rarely prescribed by doctors. In Germany, the active ingredient is generally available only on prescription.
