What is Methylhyoscine (Hyoscyamine) Bromide Phosphate?

What is Methylhyoscine (Hyoscyamine)?

Hyoscyamine sulfate is an anticholinergic/antispasmodic medication derived from belladonna alkaloids, used primarily to treat gastrointestinal and genitourinary spasms, peptic ulcer disease, irritable bowel syndrome, and excessive secretions. 1

Chemical Structure and Formulation

• Hyoscyamine sulfate has the empirical formula (C17H23NO3)2 • H2SO4 • 2H2O with a molecular weight of 712.85 1
• It is chemically classified as benzeneacetic acid, (α-(hydroxymethyl)-, 8-methyl-8-azabicyclo [3.2.1.] oct-3-yl ester, [3(S)-endo]-, sulfate (2:1), dihydrate 1
• Available formulations include oral drops (0.125 mg/mL with 5% alcohol), elixir (0.125 mg per 5 mL with 20% alcohol), tablets, and injectable forms 1

Primary Clinical Indications

Gastrointestinal disorders:

• Adjunctive therapy for peptic ulcer disease to control gastric secretion 1
• Treatment of irritable bowel syndrome, spastic colitis, and functional gastrointestinal disorders 1
• Management of visceral spasm and hypermotility in conditions including diverticulitis and acute enterocolitis 1
• Symptomatic relief of biliary and renal colic when combined with morphine or other narcotics 1

Genitourinary conditions:

• Treatment of spastic bladder, cystitis, neurogenic bladder, and neurogenic bowel disturbances 1

Other applications:

• Infant colic management (elixir and drops formulations) 1
• "Drying agent" for acute rhinitis symptoms 1
• Parkinson's disease therapy to reduce rigidity, tremors, sialorrhea, and hyperhidrosis 1
• Treatment of anticholinesterase poisoning 1

Dosing Guidelines

• Standard adult dosing: 0.125 mg PO/ODT/SL every 4 hours as needed, with a maximum daily dose of 1.5 mg 2, 3
• For excessive secretions in palliative care: 0.125 mg every 4 hours as needed (maximum 1.5 mg/day) as a second-line option after glycopyrrolate 2, 3
• Injectable form: 0.5 mg IV has been studied for colonoscopy premedication 4

Clinical Efficacy Evidence

Procedural applications:

• In colonoscopy, IV hyoscyamine (0.5 mg) significantly reduced cecal intubation time (median 9.2 vs. 12.9 minutes, p=0.01) and total procedure time (median 20.5 vs. 25.0 minutes, p=0.01) compared to placebo 4
• Improved patient sedation (p=0.02), easier colonic insertion (p=0.001), and less spasm on insertion (p=0.01) were observed 4
• Patients reported greater comfort (p<0.001) and willingness to repeat the procedure (p=0.0001) 4

Combination therapy:

• A 2004 guideline suggested potential benefit when combining hyoscyamine with DDAVP for enuresis treatment, though more evidence was needed before considering it standard therapy 5

Important Safety Considerations

Cardiovascular effects:

• Sinus tachycardia occurred in 27% of patients receiving IV hyoscyamine for colonoscopy, with two cases being extremely rapid 4
• This high frequency of tachycardia necessitates further study before routine procedural use can be recommended 4

Central nervous system effects:

• Unlike glycopyrrolate, hyoscyamine can cross the blood-brain barrier and may cause more CNS effects in elderly or post-stroke patients 3
• This makes glycopyrrolate preferable for managing secretions in vulnerable populations 2

Common anticholinergic side effects to monitor:

• Dry mouth, urinary retention, constipation, and blurred vision 3

Special populations:

• Can be used for chronic abdominal pain in hypermobile Ehlers-Danlos syndrome 3
• Alternative administration routes (rectal, transdermal, subcutaneous, or IV) are available when oral route is not feasible in palliative care 3

Clinical Positioning

• Hyoscyamine is considered a second-line option for managing excessive secretions, with glycopyrrolate preferred first-line due to fewer CNS effects 2
• In malignant bowel obstruction, it serves as an anticholinergic option alongside scopolamine and glycopyrrolate when other measures fail 3
• For irinotecan-induced diarrhea in cancer patients, atropine (a related anticholinergic) is specifically recommended 6

Critical Safety Warning

• Anticholinergics may increase risk of severe outcomes, including death, from C. difficile and Clostridium perfringens diarrhea, according to the Infectious Diseases Society of America 6
• Exercise extreme caution in older adults who are more susceptible to cognitive decline, QT prolongation, and cardiac effects 6