When used to treat asthma and allergic reactions, anticholinergic medications function as bronchodilators – opening constricted airways and loosening mucus in the respiratory tract. The medication is effective at treating both allergic reactions and asthma attacks, but may be used for a number of other conditions as well, such as Parkinson’s disease and irritable bowel syndrome.

Anticholinergics work by interfering with acetylcholine – a chemical that plays an important role in the autonomic nervous system (ANS). The ANS is responsible for many types of involuntary reactions, including heartbeat, blood pressure and some mucus secretion and muscle responses. Cholinergics are parts of the nervous system that use acetylcholine as a neurotransmitter. They use acetylcholine to pass signals from motor nerves to muscle fibers, causing the muscles to contract. Anticholinergics work by interfering with this process.

Anticholinergics are delivered to problem areas in an aerosol form. This allows the medication to have an impact on a specific area of the body and greatly reduces the number of side effects experienced with the medication. The medication is usually inhaled through one of the following:

• Inhaler. Portable aerosol device that delivers medication directly to the lungs.
  
  
• Nasal spray. Small bottle that is used to deliver medication into the nasal passages in the form of a fine mist.
  
  
• Nebulizer. Motorized device that uses pressurized air to aerosolize medication into a fine mist, making it easy to breath deep into the lungs.
  

When the muscles lining the airway are irritated they begin to spasm or constrict. This type of response, which often occurs during an allergic reaction or asthma attack, often leads to shortness of breath or difficulty breathing. When anticholinergics are inhaled deep into the lungs (through an inhaler or nebulizer), they are very effective at relaxing the constricted muscles in the airways. They accomplish this by blocking the effects of acetylcholine, which is a neuromuscular transmitter that prompts the muscles to tighten. Opening up the airways makes breathing easier and decreases wheezing.

Anticholinergics also block acetylcholine at the mucous membranes, reducing the amount of mucus produced in the respiratory tract. This allows an individual to expel mucus more easily and further improve their lung function.

Some inhaled anticholinergics are taken through a nasal spray. This form of treatment is useful only for clearing up symptoms in the nasal area (nasal spray medicines do not generally penetrate to the lungs). By blocking the actions of acetylcholine that stimulate secretions, anticholinergics are able to reduce the amount of mucus secreted by the mucous membranes in the nose and sinuses.  For this reason, anticholinergic nasal sprays are often used to treat a runny nose – a common hay fever (allergic rhinitis) symptom. Anticholinergic nasal spray treatments, however, are not effective at treating nasal congestion, sneezing or postnasal drip.

Anticholinergics usually work to stop asthma symptoms within 15 minutes, whereas short-acting bronchodilators (beta agonists) begin working almost immediately. As a result, most physicians do not recommend anticholinergics alone as an asthma rescue medication. However, the effects of anticholinergics last longer than beta-agonist treatments – usually for 3 to 4 hours. For this reason, anticholinergics are often combined with beta-agonists to offer both a quick response rate and long duration of effect.