Propantheline Bromide
**Propantheline bromide** is a synthetic quaternary ammonium antimuscarinic (anticholinergic) agent. It is primarily utilized in veterinary medicine for its antispasmodic and antisecretory properties. **Key Clinical Uses:** * **Small Animals:** Management of diarrhea, hyperreflexic detrusor (urge incontinence), and anticholinergic-responsive bradycardias. * **Horses:** Administered intravenously to reduce colonic peristalsis and relax the rectum, facilitating safer rectal examinations and surgical procedures. **Clinical Pearl:** Because propantheline is a quaternary ammonium compound, it is permanently ionized and highly water-soluble. This structural feature prevents it from readily crossing the blood-brain barrier (BBB) or penetrating the eye. Consequently, it provides peripheral anticholinergic effects (like GI relaxation and heart rate elevation) with significantly fewer central nervous system (CNS) or ocular adverse effects compared to tertiary amines like atropine.
Mecanismo: **Propantheline** acts as a competitive antagonist at **muscarinic acetylcholine receptors** (primarily M1, M2, and M3 subtypes) located on smooth muscle, cardiac muscle, and exocrine glands. * **Gastrointestinal Tract:** Blockade of M3 receptors → decreased smooth muscle tone and peristalsis (antispasmodic effect) + reduced gastric acid secretion. * **Urinary Tract:** Blockade of M3 receptors on the detrusor muscle → relaxation of the bladder wall → increased bladder capacity and reduced urge incontinence. * **Cardiovascular System:** Blockade of M2 receptors on the sinoatrial (SA) node → vagolytic effect → increased heart rate. * **Exocrine Glands:** Blockade of muscarinic receptors → decreased salivation and respiratory secretions.
Dosificación por especie
- Detrusor hyperreflexia, urge incontinence · 0.25-0.5 mg/kg PO q12-24h · PO · q12-24h · Empirical dosage. Further studies required to substantiate beneficial effect.
- Detrusor hyperreflexia, urge incontinence · 5-7.5 mg (total dose) PO once a day to once every 3 days · PO · q24h to q72h
- Detrusor hyperreflexia, urge incontinence · 5-7.5 mg (total dose) PO q8h; 7.5 mg PO q72h · PO · q8h or q72h
- Sinus bradycardia, incomplete AV block, etc. · 0.8-1.6 mg/kg three times daily · PO · TID · Although generally ineffective, a trial may be attempted.
- Sinus bradycardia, incomplete AV block, etc. · 7.5 mg PO q8-12h · PO · q8-12h · Usually well tolerated, but improvement is usually partial and often temporary.
- Chronic colitis · 0.5 mg/kg two to three times daily · PO · BID-TID
- As an antiemetic/antidiarrheal · 0.25 mg/kg PO q8h · PO · q8h
- To reduce rectal contractions during oocyte collection · 0.04 mg/kg IV · IV · Once · Must be freshly prepared and filtered through a 0.22 micron-filter from oral tablets.
- To inhibit peristalsis for 2 hours during rectal surgery · 30 mg IV · IV · Once · Must be freshly prepared and filtered through a 0.22 micron-filter from oral tablets.
Vías de administración
Contraindicaciones
- Hypersensitivity to anticholinergics
- Tachycardias secondary to thyrotoxicosis or cardiac insufficiency
- Myocardial ischemia
- Unstable cardiac status during acute hemorrhage
- Gastrointestinal obstructive disease
- Paralytic ileus
- Severe ulcerative colitis
- Obstructive uropathy
- Myasthenia gravis (unless used to reverse adverse muscarinic effects secondary to therapy)
Efectos adversos
- Dry mouth (xerostomia)
- Dry eyes (keratoconjunctivitis sicca)
- Urinary hesitancy or retention
- Tachycardia
- Constipation
- Vomiting (especially in cats)
- Hypersalivation (especially in cats)
- Ileus (at high doses, potentially leading to bacterial overgrowth)
Interacciones farmacológicas
- Antihistamines · May enhance the anticholinergic activity of propantheline.
- Benzodiazepines · May enhance the activity of propantheline.
- Cimetidine · Propantheline may decrease the absorption of cimetidine.
- Corticosteroids · Long-term concurrent use may increase intraocular pressure.
- Meperidine · May enhance the activity of propantheline.
- Nitrates · May potentiate the adverse effects of propantheline.
- Nitrofurantoin · Propantheline may enhance the actions of nitrofurantoin.
- Phenothiazines · May enhance the anticholinergic activity of propantheline.
- Sympathomimetics · Propantheline may enhance their actions.
- Ranitidine · Propantheline delays absorption but increases peak serum levels of ranitidine; relative bioavailability of ranitidine may increase by 23%.
- Thiazide Diuretics · Propantheline may enhance their actions.
Monitorización
- Clinical efficacy (resolution of diarrhea, incontinence, or bradycardia)
- Heart rate and rhythm (if indicated)
- Adverse effects (dry mouth, constipation, urinary retention)
Sobredosis
**Toxicity Profile:** Because of its quaternary structure, minimal CNS effects are expected following an overdose compared to tertiary amines like atropine. **Treatment:** * **Decontamination:** If recent oral ingestion, empty gut contents and administer activated charcoal and saline cathartics. * **Supportive Care:** Treat clinical signs symptomatically. Fluid therapy and standard treatments for shock may be instituted. **Do not use phenothiazines** as they may exacerbate anticholinergic effects. * **Antidote (Physostigmine):** Controversial. Reserve for extreme agitation/risk of injury, or severe/life-threatening supraventricular and sinus tachycardias. * *Human pediatric dose (reasonable for small animals):* 0.02 mg/kg slow IV; may repeat q10 minutes until reversal of toxic effects. * *Note:* Physostigmine adverse effects (bronchoconstriction, bradycardia, seizures) may be treated with small doses of IV atropine.
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