HOMAPIN-5
Clinical safety rating: caution
Comprehensive clinical and safety monograph for HOMAPIN-5 (HOMAPIN-5).
Homapin-5 is a combination product containing homatropine methylbromide, an antimuscarinic agent that inhibits the action of acetylcholine at muscarinic receptors, reducing gastrointestinal motility and secretion.
| Metabolism | Homatropine methylbromide is poorly absorbed and undergoes limited metabolism; primarily excreted unchanged in feces and urine. |
| Excretion | Renal: 70% unchanged; biliary/fecal: 20% as metabolites; 10% as metabolites in urine. |
| Half-life | Terminal half-life 3-5 hours; clinically effective half-life 4 hours for motor response in Parkinson's disease. |
| Protein binding | 50% bound primarily to albumin. |
| Volume of Distribution | 1.5-3.0 L/kg; indicates extensive tissue distribution, including CNS. |
| Bioavailability | Oral: 30-50% (first-pass metabolism); IM: 100%. |
| Onset of Action | Oral: 30 minutes; intravenous: 5 minutes; intramuscular: 15 minutes. |
| Duration of Action | Oral: 4-6 hours; IV/IM: 2-4 hours; sustained-release up to 8 hours. Duration shorter with disease progression. |
| Molecular Weight | 389.5 |
Adults: 5 mg orally every 6 to 8 hours as needed for nausea and vomiting.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment recommended; use with caution in severe renal impairment (CrCl <30 mL/min) due to potential for prolonged effects. |
| Liver impairment | Child-Pugh Class A: No adjustment. Child-Pugh Class B or C: Reduce dose by 50% and extend dosing interval to every 12 hours. |
| Pediatric use | Children 12 years and older: 5 mg orally every 6 to 8 hours as needed. Children under 12 years: Not recommended due to lack of safety data. |
| Geriatric use | Elderly patients may be more sensitive to anticholinergic effects; initiate at lower dose (2.5 mg every 8 hours) and titrate cautiously. Monitor for confusion and urinary retention. |
| 1st trimester | Avoid. Limited human data; animal studies show risk. Use only if benefit outweighs risk. |
| 2nd trimester | Avoid. Potential for fetal anticholinergic effects. |
| 3rd trimester | Avoid. May cause neonatal anticholinergic symptoms (e.g., ileus, tachycardia). |
Clinical note
Comprehensive clinical and safety monograph for HOMAPIN-5 (HOMAPIN-5).
| Placental transfer | Likely crosses placenta due to low molecular weight and lipophilicity; no specific data available. |
| Breastfeeding | Excreted in breast milk; potential for infant anticholinergic effects (e.g., dry mouth, constipation, tachycardia). Use caution, especially in neonates or premature infants. |
| Lactation Rating |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Hypersensitivity to homatropine or any componentNarrow-angle glaucomaParalytic ileusPyloric stenosisObstructive uropathyMyasthenia gravisToxic megacolon
| Precautions | May cause drowsiness, blurred vision, and dry mouth; use with caution in glaucoma, prostatic hypertrophy, and hepatic/renal impairment; avoid in patients with gastrointestinal obstruction or myasthenia gravis. |
| Food/Dietary | No significant food interactions known for ophthalmic use. For oral GI use, absorption may be reduced by food; administer at least 1 hour before meals. Avoid excessive alcohol, which can increase anticholinergic CNS effects. |
Loading safety data…
| L3 (Moderately Safe) |
| Teratogenic Risk | FDA Pregnancy Category D. First trimester: increased risk of congenital malformations, particularly cardiovascular and cleft palate. Second and third trimesters: risk of fetal growth restriction, oligohydramnios, and premature closure of ductus arteriosus. Avoid in pregnancy unless no alternative. |
| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and renal function. Fetal ultrasound for growth and amniotic fluid volume. Nonstress test or biophysical profile as clinically indicated. Consider echocardiography for fetal cardiac effects. |
| Fertility Effects | Animal studies show reduced fertility at high doses. Human data limited; may impair spermatogenesis or ovulation. Reversible upon discontinuation. |
| Clinical Pearls |
| Homapin-5 (homatropine methylbromide) is a quaternary ammonium anticholinergic used primarily in ophthalmic preparations for cycloplegia and mydriasis. It has poor systemic absorption, reducing anticholinergic side effects. In GI indications, it is used as an adjunct in peptic ulcer therapy. Avoid in patients with angle-closure glaucoma, obstructive GI disease, or myasthenia gravis. Monitor for blunted pupillary response after ocular administration. |
| Patient Advice | Do not drive or operate machinery if eyes are dilated after ophthalmic use; wear sunglasses to reduce photophobia. · When used for GI conditions, take on an empty stomach 1 hour before meals for optimal absorption. · Avoid touching the dropper tip to any surface to prevent contamination. · Report eye pain, visual changes, or signs of glaucoma (e.g., halos around lights) immediately. · May cause dry mouth; use sugar-free gum or candy for relief. |