ANTRENYL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ANTRENYL (ANTRENYL).
Antrenyl (oxyphenonium bromide) is a quaternary ammonium anticholinergic agent that competitively blocks acetylcholine at muscarinic receptors in smooth muscle, exocrine glands, and the CNS, leading to reduced gastrointestinal motility and secretion.
| Metabolism | Primarily hepatic; undergoes ester hydrolysis; excreted via bile and urine as metabolites. |
| Excretion | Renal (80% as unchanged drug and metabolites), biliary/fecal (20%) |
| Half-life | 2-4 hours (terminal), requiring q6-8h dosing for sustained anticholinergic effect |
| Protein binding | Approximately 50%, primarily to albumin |
| Volume of Distribution | 1.5-2.5 L/kg, indicating extensive tissue distribution |
| Bioavailability | Oral: 10-20% (due to extensive first-pass metabolism); IM: near 100% |
| Onset of Action | Oral: 1-2 hours; Parenteral (IM/IV): 15-30 minutes |
| Duration of Action | Oral: 4-6 hours; Parenteral: 3-4 hours. Note: Longer duration in elderly due to reduced clearance. |
| Action Class | Anticholinergics |
50 mg orally 3 times daily initially, then adjust to 50-100 mg 3 times daily; 20 mg intramuscularly or intravenously every 4-6 hours as needed.
| Dosage form | TABLET |
| Renal impairment | GFR <10 mL/min: avoid use; GFR 10-50 mL/min: reduce dose by 50% and extend interval; GFR >50 mL/min: no adjustment. |
| Liver impairment | Child-Pugh class B or C: reduce dose by 50%; class A: no adjustment. |
| Pediatric use | Not recommended for use in children; safety and efficacy not established. |
| Geriatric use | Initiate at low end of dosing range (50 mg twice daily) and titrate slowly due to increased sensitivity to anticholinergic effects and risk of cognitive impairment. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ANTRENYL (ANTRENYL).
| Breastfeeding | Excreted in breast milk; M/P ratio unknown. Avoid use in nursing mothers due to potential anticholinergic effects (e.g., irritability, feeding difficulties) in the infant. |
| Teratogenic Risk | Pregnancy Category C. First trimester: limited data; anticholinergic effects may cause fetal tachycardia. Second/third trimester: potential for neonatal meconium ileus, hyperthermia, and respiratory depression. Avoid near term due to possible anticholinergic toxicity. |
| Fetal Monitoring |
■ FDA Black Box Warning
None.
| Serious Effects |
["Glaucoma","Obstructive uropathy (e.g., bladder neck obstruction due to prostatic hypertrophy)","Obstructive gastrointestinal disease (e.g., pyloroduodenal stenosis)","Myasthenia gravis","Severe ulcerative colitis","Toxic megacolon"]
| Precautions | ["Risk of heat prostration in hot environments due to decreased sweating","May cause blurred vision, drowsiness, or dizziness; avoid driving or hazardous activities","Use with caution in patients with glaucoma, prostatic hypertrophy, or hepatic/renal impairment"] |
| Food/Dietary | Avoid high-fat meals as they may reduce absorption. Antrenyl should be taken on an empty stomach, at least 1 hour before or 2 hours after food. No specific food interactions reported. |
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| Monitor maternal heart rate and bowel sounds; fetal heart rate monitoring for tachycardia. Assess for signs of anticholinergic toxicity in neonate (e.g., constipation, urinary retention). |
| Fertility Effects | No known impairment of human fertility; animal studies show no adverse effects on reproduction. |
| Clinical Pearls | Antrenyl (oxyphenonium bromide) is a quaternary ammonium anticholinergic with poor CNS penetration, reducing central side effects. Given IM/IV for acute GI spasm or as adjunct in peptic ulcer. Avoid in glaucoma, myasthenia gravis, obstructive uropathy, and GI obstruction. Monitor for anticholinergic toxicity: tachycardia, dry skin, ileus, urinary retention. |
| Patient Advice | Take on an empty stomach 1 hour before meals for best absorption. · Do not crush or chew tablets; swallow whole with water. · May cause dry mouth, blurred vision, and constipation; report difficulty urinating or eye pain. · Avoid driving or operating machinery until you know how this medication affects you. · Do not use antacids within 1 hour of taking this medication; they reduce absorption. |