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Response to Methacholine

Methacholine, also marketed under the brand name of Provocholine, is a medicine used to determine whether a patient has asthma. The drug is a bronchoconstrictor, meaning that it tightens the airways. A patient's response to methacholine can tell doctors whether she has a type of asthma that would not be detected in a regular examination.

  1. Methacholine Challenge

    • The process of using methacholine to detect asthma is called a methacholine challenge. The doctor gives the patient several doses of methacholine by inhalation. Each one is progressively stronger. The doctor measures how much breath the patient can expel in one second. According to RX List, if the patient's ability to expel air is reduced by less than 14%, the asthma test result is negative.

    Side Effects

    • Methacholine can have a number of side effects, including headache, irritation of the throat, itching and a feeling of lightheadedness. If methacholine is given by mouth or injection instead of inhalation, vomiting, nausea, pain under the sternum, low blood pressure and fainting may occur. Some patients may experience heart block, a condition where the heart stops conducting normal electrical impulses.

    Age

    • Doctors have not yet determined the safety or effectiveness of methacholine in children under the age of five. However, the American Journal of Respiratory and Critical Care Medicine reports that young rabbits are more strongly affected than mature rabbits. Immature animals showed a greater increase in breathing resistance from methacholine--950% compared to 380%--possibly because their smaller airways contain more smooth muscle. This suggests that methacholine should be used with extreme care in children.

    Counterindications

    • Patients with conditions that may be adversely affected by a bronchoconstrictor should be treated with extreme care. These conditions include heart and cardiovascular disease when accompanied by slow heart rate, thyroid disease, peptic ulcer disease, epilepsy and urinary tract obstruction. Methacholine should be used only when its diagnostic benefits are greater than the patient's risk.

    Warning

    • Methacholine is meant to help diagnose asthma, but it does not help cure or treat it. It should never be used as a therapeutic agent. Diagnosis with methacholine can have serious side effects, including severe respiratory problems, and should always be done under the supervision of an experienced doctor. If problems occur, immediately administer a bronchodilator to clear the airways.

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