Side effects and uses
Every drug will have few side effects and many of the times they may be related wth their pharmacological actions. Here we will discuss important side effects of cholinergic agonists.
- Excessive secretions
- Diaphoresis – excessive secretion of sweat
- All these due to stimulation of exocrine glands
- Due to pupilary constriction
- Due to increase in GI motility
- Due to bronchoconstriction
- Due to cardiac inhibition
- Due to bladder constriction
Ok, fine. We have seen pharmacological actions of cholinergic agonists and many of them again listed as side effects. So practically these drugs have very few indications.
Glaucoma is a condition with enhanced intraocular pressure due to accumulation of aqueous humour within the anterior chamber of eye. Since cholinergic agonists decrease intraocular tension, they can be indicated in treatment of glaucoma. Two drugs used for this condition include Pilocarpine and carbachol.
Pilocarpine is more preferred due to its more selectivity than carbachol.
Pilocarpine alsow some advantages.
Pilocarpine is used in emergency treatment of glaucoma
Xerostomia is a condition of dry mouth due to reduced saliva secretion. So many factors are responsible for this condition including radiation therapy of head and neck, autoimmune destruction of salivary glands and uses of several medication such as atropine, phenothiazine, TCAs and antihistamines etc.
Pilocarpine, as it increases salivary secretion, can be used to stimulate secretions particulary after radiation therapy of head and neck.
Cevimeline is a newer agonist with activity at M3 muscarinic receptors. These receptors are found on lacrimal and salivary gland epithelia. Cevimeline has a long-lasting sialogogic action and may have fewer side effects than pilocarpine .
Atonic bladder may result in bladder hypotonia either after a surgery or delivery and can be associated with urinary retention. As bethanechol increases contraction of bladder it can be used in atonic bladder associated with urinary retention.
Note: Atonic bladder is disorder of bladder tone which is poorly controlled leading to either hypotonia or hypertonia. Bladder hypotonia results in urinary retention and hypertonia may cause urinary incontinence. bethanechol is only used in condition associated with urinary retention.
Megacolon is a condition in which large is enlarged and dilated with decreased motility. So in this condition bethanechol can increase GI motility.
Points to remember
Pilocarpine can be used in both open angular and closed angular glaucoma
It can also be used in emergency treatment of glaucoma
It is a natural alkaloid