Diphenoxylate/Atropine

Overview

Diphenoxylate/atropine is an opioid-based gastrointestinal motility modifier used primarily in dogs for the management of diarrhea and, less commonly, as an antitussive agent. It is a controlled drug and is administered orally in clinical practice.

Diphenoxylate acts on the gastrointestinal tract to reduce motility and prolong transit time, while atropine is included in subtherapeutic amounts to discourage misuse and is not expected to produce significant clinical effects at therapeutic doses.

Mechanism of Action (MOA): Diphenoxylate, an opioid agonist, decreases intestinal motility and secretions while enhancing absorption within the gastrointestinal tract. This results in reduced frequency and volume of diarrhea. Atropine has minimal clinical effect at standard doses but contributes mild anticholinergic properties.

Indications

Diphenoxylate/atropine is used in dogs primarily for its antidiarrheal effects and, in selected cases, for its antitussive properties. Its use in cats is limited and generally not recommended.

• Diarrhea (dogs): Used to reduce intestinal motility and manage non-infectious diarrhea.
• Antitussive effect (dogs): May be used to suppress coughing in certain conditions due to its opioid activity.
• Tracheal collapse (dogs): May be used as part of medical management to reduce cough associated with airway collapse.
• Use in cats: Generally not recommended due to risk of excitatory behavioral responses.

Dosage (Reference)

Dog

In dogs, dosing is based on the diphenoxylate component and is administered orally. Multiple dosing regimens are described depending on indication and clinician preference.

Cat

In cats, diphenoxylate/atropine is generally not recommended; however, dosing has been described for antidiarrheal use when deemed necessary.

Warnings & Precautions

Diphenoxylate/atropine should be used cautiously in dogs and cats due to its opioid effects on gastrointestinal motility and central nervous system function. Appropriate case selection is essential to avoid masking serious underlying disease.

• Contraindications: Do not use in patients with hypersensitivity to opioids, intestinal obstruction, biliary obstruction, or diarrhea caused by infectious agents or toxic ingestion.
• Infectious diarrhea: Use may delay elimination of pathogens or toxins by reducing gastrointestinal motility, potentially worsening disease or prolonging recovery.
• Respiratory and CNS disease: Use with caution in patients with respiratory compromise or conditions associated with CNS depression, as effects may be exacerbated.
• Systemic disease: Use cautiously in patients with renal insufficiency, uncontrolled hypothyroidism, Addisonian crisis, or in debilitated animals.
• Acute abdominal conditions: May obscure diagnosis or worsen clinical course in conditions such as hemoabdomen or splenic torsion.
• Small dogs: Accurate dosing may be difficult in dogs <10 kg due to tablet strength; liquid formulations may improve dosing precision.
• Use in cats: Use is controversial due to risk of excitatory behavior; avoid when possible.

Drug Interactions

Clinically relevant interactions with diphenoxylate/atropine are primarily related to additive central nervous system depression, anticholinergic effects, and altered gastrointestinal motility. Careful monitoring is required when used with the following medications.

• Anticholinergic agents (e.g., glycopyrrolate, oxybutynin): Additive anticholinergic effects such as dry mucous membranes, tachycardia, constipation, and urinary retention.
• First-generation antihistamines (e.g., diphenhydramine, chlorpheniramine): Increased risk of CNS depression and additive anticholinergic effects.
• CNS depressants (e.g., anesthetics, barbiturates): Enhanced CNS and respiratory depression when used concurrently.
• Digoxin: May increase serum digoxin concentrations.
• Laxatives (e.g., magnesium salts, polyethylene glycol): May reduce the efficacy of diphenoxylate.
• Monoamine oxidase inhibitors (e.g., selegiline, amitraz): Concurrent use should be avoided due to risk of severe adverse effects, including hypertensive reactions.
• Opioids (e.g., morphine, tramadol): Increased risk of CNS and respiratory depression and additive anticholinergic effects.
• Phenothiazines (e.g., acepromazine): Increased risk of CNS depression and additive anticholinergic effects.
• Oral potassium salts: Reduced GI motility may increase risk of gastrointestinal irritation and ulceration.
• Prokinetic agents (e.g., metoclopramide, cisapride, erythromycin): Decreased efficacy of both drugs when used together.
• Tricyclic antidepressants (e.g., amitriptyline, clomipramine): Increased risk of CNS depression and additive anticholinergic effects.

Side Effects & Overdose

Side Effects

Adverse effects of diphenoxylate/atropine are primarily related to reduced gastrointestinal motility and central nervous system depression. Most effects are dose-dependent.

• Constipation and bloating: Most common effects due to decreased intestinal motility.
• Sedation: CNS depression may occur, especially at higher doses.
• Gastrointestinal complications: Paralytic ileus, toxic megacolon, vomiting, and pancreatitis may develop in some cases.
• Delayed GI transit: May prolong nutrient absorption and contribute to bacterial overgrowth in infectious diarrhea.
• Behavioral effects (cats): May cause excitatory behavior rather than sedation.

Overdose

Acute overdose can result in significant opioid and anticholinergic toxicity affecting multiple organ systems.

• CNS depression: Ranging from sedation to coma.
• Respiratory depression: Potentially life-threatening in severe cases.
• Gastrointestinal effects: Severe ileus or constipation.
• Cardiovascular effects: May include tachycardia or other autonomic disturbances.
• Atropine toxicity: May occur with large overdoses of combination products.
• Management: Supportive care is required; naloxone may be used to reverse opioid effects.

Key Notes

Practical clinical considerations for the use of diphenoxylate/atropine in dogs and cats:

• Primarily used in dogs: Clinical use is mainly focused on dogs, with limited and cautious use in cats.
• Onset and duration: Effects typically begin within 45–60 minutes and last approximately 3–4 hours.
• Active metabolite: Converted to diphenoxylic acid, which contributes to its clinical effect.
• Combination product rationale: Atropine is included to discourage misuse rather than for therapeutic benefit.
• Controlled drug status: Classified as a Schedule V controlled substance, requiring appropriate handling and prescribing regulations.