Autonomic Nervous Systems
Which is a muscarinic receptor-blocking drug that is administered by inhalation to cause bronchodilation for patients with COPD? (LQ)
a. Ipratropium, a quaternary antimuscarinic drug, is FDA-approved for use as an inhaled bronchodilator for COPD. (It is used, but not FDA-approved for, some cases of asthma.) Albuterol certainly is an inhaled bronchodilator for asthma or COPD, but it works, of course, as a β2-adrenergic agonist.
b. Diphenhydramine has bronchodilator activity (by blocking both histamine H1 and muscarinic receptors), but it is not given by inhalation; moreover, for ambulatory patients with asthma the mucus-thickening effects of muscarinic receptor blockade can do more harm than good.
c. Pancuronium is a curare-like skeletal neuromuscular blocker (nicotinic/skeletal muscle competitive antagonist of ACh). Pilocarpine is a muscarinic agonist, used mainly for causing miosis in patients with angle-closure glaucoma. It will cause bronchoconstriction— an effect that may be harmful for patients with COPD and certainly would be harmful for asthmatics.
d. A wide variety of clinical conditions are treated with antimuscarinic drugs. Dicyclomine hydrochloride and methscopolamine bromide are used to reduce GI motility, although side effects—dryness of the mouth, loss of visual accommodation, and difficulty in urination—may limit their acceptance by patients.
e. Cyclopentolate hydrochloride is used in ophthalmology for its mydriatic and cycloplegic properties during refraction of the eye. Trihexyphenidyl hydrochloride is one of the important antimuscarinic compounds used in the treatment of parkinsonism.
f. For bronchodilation in patients with bronchial asthma and other bronchospastic diseases, ipratropium bromide is used by inhalation. Systemic adverse reactions are low because the actions are largely confined to the mouth and airways.