Chlordiazepoxide and Clidinium
Chlordiazepoxide is a long-acting **benzodiazepine** primarily used for its anxiolytic and mild sedative properties. Clidinium bromide is a synthetic quaternary ammonium **antimuscarinic (anticholinergic)** agent that reduces gastrointestinal motility and spasms. In veterinary medicine, these drugs are occasionally used alone or in combination: * **Chlordiazepoxide alone**: Used as an adjunct for behavioral disorders, such as noise phobias in dogs, or intercat aggression and urine spraying in cats. * **Chlordiazepoxide + Clidinium (Librax®)**: This combination is uniquely positioned to treat stress-induced gastrointestinal disorders, such as **Irritable Bowel Syndrome (IBS)** in dogs. It addresses both the central anxiety component (via chlordiazepoxide) and the peripheral GI spasms (via clidinium). > **Clinical Pearl**: Because clidinium is a quaternary amine, it does not readily cross the blood-brain barrier, thereby avoiding the central anticholinergic side effects commonly seen with atropine.
Mechanism: The combination product exerts its effects through two distinct mechanisms targeting the central nervous system and the peripheral gastrointestinal tract: * **Chlordiazepoxide (Anxiolytic/Sedative)**: Binds to the benzodiazepine allosteric site on the **GABA-A receptor** complex in the CNS → enhances the affinity of the receptor for the inhibitory neurotransmitter **gamma-aminobutyric acid (GABA)** → increases the frequency of chloride channel openings → neuronal hyperpolarization. This dampens activity in the limbic system, thalamus, and hypothalamus, producing anxiolytic, muscle relaxant, and anticonvulsant effects. * **Clidinium (Antispasmodic)**: Acts as a competitive antagonist at **muscarinic acetylcholine receptors** (primarily M3 receptors in the gut) → inhibits parasympathetic nerve impulses → significantly reduces gastrointestinal smooth muscle spasms, motility, and gastric acid secretion.
Dosing by species
- As an anxiolytic · 0.5-1 mg/kg · PO · q12-24h · Chlordiazepoxide alone
- Behavior indications (thunderstorm/noise phobias) · 2.2-6.6 mg/kg · PO · as needed · Chlordiazepoxide alone; start low
- Symptomatic treatment of irritable bowel syndrome · 0.1-0.25 mg/kg of clidinium or 1-2 capsules · PO · two times to three times a day · Discontinued in a few days · Using the combination product (e.g., Librax). Give when abdominal pain or diarrhea first noticed or if stressful conditions are encountered.
- Symptomatic treatment of irritable bowel syndrome · 0.44-1.1 mg/kg of clidinium · PO · two to three times a day · 1 day to 2 weeks (some require long-term treatment at 1-2 doses per day) · Using the combination product (e.g., Librax). Use at first signs of cramping or abdominal pain.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Known hypersensitivity to benzodiazepines or antimuscarinics
- Coma, shock, or significant respiratory depression
- Aggressive patients (may disinhibit bite inhibition and worsen aggression)
- Tachycardia secondary to thyrotoxicosis or cardiac insufficiency
- Myocardial ischemia
- Gastrointestinal obstructive disease or paralytic ileus
- Severe ulcerative colitis
- Obstructive uropathy
- Myasthenia gravis
- Known or suspected GI infections (may prolong retention of toxins/pathogens)
Adverse effects
- Paradoxical CNS excitement or agitation (especially in dogs)
- Variable sedation and lethargy
- Behavioral changes (irritability, aberrant demeanor in cats)
- Potential hepatotoxicity (idiosyncratic hepatic failure reported with oral diazepam in cats; unknown if chlordiazepoxide shares this risk)
- Dry mouth (xerostomia)
- Constipation or dysphagia
- Urinary retention or hesitancy
- Tachycardia (at higher doses) or initial bradycardia
Drug interactions
- Digoxin · Pharmacologic effects of digoxin may be increased; clidinium may also increase serum levels of slow-dissolving digoxin.
- CNS Depressants (barbiturates, opiates, anesthetics) · Additive CNS depression and sedative effects.
- Probenecid · May interfere with benzodiazepine metabolism in the liver, causing increased or prolonged effects.
- Rifampin · May induce hepatic microsomal enzymes and decrease the pharmacologic effects of benzodiazepines.
- Cimetidine · May decrease the metabolism of chlordiazepoxide, leading to excessive sedation.
- Erythromycin · May decrease the metabolism of chlordiazepoxide, leading to excessive sedation.
- Fluoxetine · May decrease the metabolism of chlordiazepoxide, leading to excessive sedation.
- Isoniazid · May decrease the metabolism of chlordiazepoxide, leading to excessive sedation.
- Ketoconazole · May decrease chlordiazepoxide metabolism. Additionally, increased gastric pH from clidinium may decrease GI absorption of ketoconazole (administer clidinium 2 hours after ketoconazole).
- Metoprolol · May decrease the metabolism of chlordiazepoxide, leading to excessive sedation.
- Propranolol · May decrease the metabolism of chlordiazepoxide, leading to excessive sedation.
Monitoring
- Clinical efficacy (reduction in anxiety, resolution of GI spasms/diarrhea)
- Adverse effects (excessive sedation, paradoxical excitement, anticholinergic signs)
- Baseline and periodic liver function tests in cats (due to idiosyncratic hepatotoxicity risks associated with oral benzodiazepines)
Overdose
Overdoses of chlordiazepoxide alone are generally limited to significant **CNS depression** (confusion, coma, decreased reflexes). Hypotension, respiratory depression, and cardiac arrest are possible but rare. **Treatment**: * Standard protocols for acute oral toxicity (gastric decontamination, binding agents like activated charcoal). * Supportive systemic measures (fluids, cardiovascular support). * **Flumazenil** may be considered as a specific reversal agent for severe benzodiazepine-induced CNS depression. * Analeptic agents (CNS stimulants like caffeine) are generally not recommended.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.