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Atropine is derived from the Atropa belladonna plant and its relatives, which are members of the potentially deadly nightshade family. The effects of atropine on the heart depend on the dosage that is administered. At lower dosages, the drug slows the heart. Higher dosages of atropine cause the heart rate to increase, and an overdose might be fatal.
One of the effects of atropine on the heart, the slowing of the heart rate at low dosages, occurs through central vagal stimulation. The parasympathetic vagus nerve serves to lower the heart rate. Atropine allows the sympathetic nerve to increase its dominance over the parasympathetic. This leads to a temporary rise in the patient's acetylcholine levels; acetylcholines are the primary neurotransmitters for the parasympathetic nerves.
Increased dosages result in reduced vagal tone and a higher heart rate. An overdose of atropine results in falling arterial pressure and the inability of the heart to pump sufficient blood throughout the body. Other potential effects of atropine on the heart include ventricular fibrillation and tachycardia.
Physicians prescribe atropine for a variety of reasons. The drug helps reduce spasms, so it is sometimes ordered for patients who have colitis, peptic ulcers or diverticulitis. Other uses of atropine include the treatment of colic, spastic bladder syndrome and irritable bowel syndrome. Atropine also can be used to treat certain poisonings.
Patients who have Parkinson's disease and take atropine might receive relief from the sweating and extreme salivation that are caused by their condition because the drug slows secretions. This effect makes the drug useful for certain patients who need to control the production of mucus in the lungs or sinuses. Atropine is sometimes used before surgery to reduce acid production and during surgery to regulate the patient's heartbeat. Emergency medical personnel might also administer atropine to resuscitate cardiac arrest patients. Many professionals have ceased using the drug for that purpose, however, because conclusive proof of the effectiveness of atropine on the heart for cardiac arrest was lacking as of late 2011.
In addition to injectable solutions administered by a healthcare professional, ophthalmic drops and ointments might be prescribed for the patient to use at home. Normally, atropine ophthalmic solutions are used before an eye examination or to treat uveitis. The doctor might also prescribe atropine pills. If a patient miss a dose, whether it is a pill or an eye solution, he or she should take the missed dose as soon as possible, as long as the next dose is not imminent. Patients should never double up on a dose; instead, they should return to their normal schedule.
Regardless of the delivery method, one of the risks of atropine is that the body might absorb more than it can diffuse efficiently. Symptoms that an overdose might have occurred include an irregular or racing heart, dizziness, confusion and blurred vision. The patient's skin might be dry and hot, and he or she might have difficulty swallowing or might complain of a headache. Nausea, with or without vomiting, can occur, or the patient might experience a seizure. A patient who experiences any of these symptoms while taking atropine should receive immediate medical care.