Description: Antimuscarinic agents, or muscarinic receptor antagonists, are anticholinergic drugs that competitively inhibit the muscarinic acetylcholine receptor. They are used in the treatment of a number of conditions including irritable bowel syndrome, motion sickness, asthma, peptic ulcers, for extrapyramidal symptoms of antipsychotics, COPD, urinary incontinence and Parkinson’s disease.
Drugs in this class include the following examples, all with anticholinergic side effects:
Ipratropium Side Effects
Ipratropium (brand name Atrovent) is used in the treatment of asthma. Its side effects include:
- Skin rash
- Pruritus (itching)
- Urinary tract infection
- COPD exacerbation
- Dyspnea (difficulty breathing)
- Upper respiratory tract infection
- Dry mouth
- Back pain
- Influenza like symptoms
(Atrovent drug label as reported by the U.S. Food and Drug Administration).
Diphenhydramine Side Effects
Diphenhydramine is an antihistamine also used in the treatment of extrapyramidal symptoms as a result of typical and atypical antipsychotics. Side effects include:
- Dry mouth
- Tachycardia (increased heart rate)
- Hypotension (low blood pressure)
- Diplopia (double vision)
- Dry eyes
(Diphenhydramine drug label as reported by the FDA).
Procyclidine Side Effects
Procyclidine (Kemadrin) is used in the treatment of drug-induced parkinsonism and Parkinson’s disease. It is associated with a number of side effects including:
- Blurred vision
- Dry mouth
(Kemadrin drug label as reported by the FDA)
Understand Your Risk for Side Effects with the Rxight® Genetic Test
Many patients do not develop side effects when taking antimuscarinics, although side effect frequency varies between individual drugs. Other patients will, however, develop multiple and often severe side effects that may result in drug cessation. This interpatient variability is in part explained by pharmacogenetics. Variation in the genomes of the patients can change how a patient interacts with a drug. “Polymorphisms” (individual variants) in genes that code for enzymes and receptors that interact with antimuscarinics are usually the culprits.
Identifying polymorphisms is therefore important for clinical decision-making. A doctor may, given a patient’s genomic profile and known polymorphisms, change a patient’s medications or reduce the starting dose. This can reduce the probability of developing side effects when taking antimuscarinics. Unfortunately, most healthcare providers do not provide genomic screening routinely. Therefore most patients do not know which polymorphisms they hold and thus what drugs may cause side effects or not be beneficial.
How Does Pharmacogenetic Testing Work?
The Rxight® pharmacogenetic test helps guide prescribers in finding a safe and effective dose based on a patient’s unique genetically modulated metabolism. It is based specifically in sequencing a number of genes that interact with hundreds of clinically relevant medications across dozens of pharmacological classes, including antimuscarinics. With a simple cheek swab of your DNA at a participating pharmacy, our labs will analyze your genome, flagging medications which may pose risks or be ineffective for you. That way, prescribers can avoid trial and error and instead find the right dose for you or an alternative drug – preferably before treatment begins.
Contributors to this Article:
Michael Sapko, MD, PhD; Deborah Kallick, PhD, Medicinal Chemistry