Dicyclomine (Bentyl)
Key Board Facts Grid
Target Receptors
Peripheral & central M1, M3 muscarinic antagonist + direct smooth muscle spasmolytic
BBB Penetration
Tertiary amine; crosses the BBB
Primary Indication
Irritable Bowel Syndrome (IBS), intestinal hypermotility, crampy visceral abdominal pain
First-Line Antidote
Supportive care; Physostigmine for severe anticholinergic delirium/toxicity
Mechanism of Action
- Competitive antagonism of muscarinic M1 and M3 receptors on gastrointestinal smooth muscle.
- Direct non-specific spasmolytic action on visceral smooth muscle independent of cholinergic innervation.
- Decreases intestinal motility, tone, and painful spasm frequency in functional bowel disorders.
Adverse Effects & Toxicities
- Anticholinergic toxidrome: dry mouth (xerostomia), blurred vision, cycloplegia, urinary retention, constipation, tachycardia, anhidrosis/hyperthermia.
- HIGH-YIELD BOARD CONTRAINDICATION: Strictly contraindicated in infants < 6 months of age (causes respiratory collapse, apnea, seizures, syncope, and death) and nursing mothers.
- Contraindicated in narrow-angle glaucoma, myasthenia gravis, obstructive uropathy (BPH), paralytic ileus, and severe toxic megacolon.
- Beers Criteria high-risk medication in elderly (causes acute delirium, cognitive impairment, and fall risk).
- NEVER administer IV (leads to local thrombosis, thrombophlebitis, and lethal systemic toxicity); oral or IM only.
DO / OMM Board Pearl
Viscerosomatic gastrointestinal tract modulation (T9–L2 sympathetic splanchnics vs vagal/pelvic splanchnic parasympathetics). In patients with IBS presenting with thoracolumbar tissue texture abnormalities and abdominal pain, dicyclomine blunts hyperactive parasympathetic visceral firing. Pair with mesenteric release and rib raising.