Theophylline

Methylxanthine bronchodilator Xanthine derivatives

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 10-15 mg/kg q12h Duration: Variable; often long-term for chronic conditions
Notes: Sustained-release formulations may be given q12h; immediate-release may require q8h. Monitor serum levels if possible.
Cat PO 4-5 mg/kg q12h Duration: Variable; often long-term for asthma
Notes: Cats have slower metabolism; use lower doses. Sustained-release formulations preferred.
Horse PO 8-10 mg/kg q12h Duration: Variable; often for chronic heaves
Notes: May also be given IV (aminophylline) at 5-10 mg/kg q12h. Monitor for excitement.
Cattle PO 10-15 mg/kg q12h Duration: 3-5 days
Notes: Not FDA-approved; use with caution. May be used as adjunct to antibiotics.
Small Ruminants PO 10-15 mg/kg q12h Duration: Variable
Notes: Limited data; use cautiously.
Rabbit PO 10-20 mg/kg q12h Duration: Variable
Notes: Limited data; monitor for GI upset.
Birds PO 4-10 mg/kg q8-12h Duration: Variable
Notes: Limited data; use with caution.

Clinical Indications & Species Uses

General Indications
  • Bronchodilation in reversible airway obstruction
  • Enhancement of mucociliary clearance
Dog (Canine)
  • Bronchodilation in chronic bronchitis
  • Tracheal collapse
  • Heartworm-associated respiratory disease
  • Adjunct therapy for asthma
Cat (Feline)
  • Feline bronchial asthma
  • Chronic bronchitis
Horse (Equine)
  • Recurrent airway obstruction (heaves)
  • Chronic obstructive pulmonary disease (COPD)
  • Exercise-induced pulmonary hemorrhage (adjunct)
Cattle (Bovine)
  • Bovine respiratory disease complex (adjunct)
  • Enzootic pneumonia (adjunct)
Rabbit & Small Mammals
  • Respiratory disease (e.g., pasteurellosis) as adjunct therapy

Pharmacology & Mechanism of Action

Drug Class: Methylxanthine bronchodilator | Pharmacological Group: Xanthine derivatives

Mechanism of Action: Theophylline is a nonselective phosphodiesterase inhibitor that increases intracellular cyclic AMP (cAMP) and cyclic GMP (cGMP) concentrations by inhibiting their breakdown. Elevated cAMP leads to bronchodilation via relaxation of bronchial smooth muscle. Additionally, theophylline antagonizes adenosine receptors (A1 and A2), which may contribute to bronchodilation and central nervous system stimulation. It also enhances mucociliary clearance, improves diaphragmatic contractility, and has mild anti-inflammatory effects.

Pharmacodynamics: Theophylline produces bronchodilation, particularly in patients with reversible airway obstruction. It also stimulates the respiratory center, increases cardiac output, and has diuretic effects. In veterinary medicine, it is used primarily for its bronchodilator effects in chronic obstructive pulmonary disease (COPD) in horses and feline asthma. Theophylline can also reduce pulmonary hypertension and improve exercise tolerance in some species.

⚑ Pharmacokinetics Summary

Absorption: Theophylline is well absorbed after oral administration in most species. Absorption may be slower in horses and ruminants due to gastrointestinal physiology. Food can affect absorption, with peak concentrations delayed when administered with a meal.
Distribution: Theophylline is widely distributed throughout the body, including into the central nervous system and across the placenta. It crosses into milk. Volume of distribution is approximately 0.5 L/kg in dogs and cats.
Metabolism: Theophylline is extensively metabolized in the liver, primarily by cytochrome P450 enzymes (CYP1A2 in humans, but species-specific). In dogs, metabolism is via demethylation and oxidation. In cats, metabolism is slower, leading to a longer half-life.
Excretion: Theophylline and its metabolites are excreted primarily in the urine. In dogs, approximately 10-20% is excreted unchanged; in cats, a higher percentage may be excreted unchanged due to slower metabolism.
Half-Life: Dog: 5.7-9.8 hours; Cat: 7.9-12.9 hours; Horse: 14-15 hours; Cattle: 10-15 hours (variable); Rabbit: 4-6 hours; Birds: variable, often shorter.
Bioavailability: Oral bioavailability is nearly complete (90-100%) in dogs and cats. In horses, oral bioavailability is approximately 50-70% due to incomplete absorption.
Protein Binding: Theophylline is approximately 40-60% protein-bound in plasma, with binding varying by species.

Available Formulations & Strengths

Oral Tablet (immediate-release) 100 mg, 200 mg, 300 mg (PO)
Oral Tablet (sustained-release) 100 mg, 200 mg, 300 mg, 400 mg, 450 mg, 500 mg, 600 mg (PO)
Oral Capsule (sustained-release) 100 mg, 200 mg, 300 mg (PO)
Oral Elixir 80 mg/15 mL (PO)
Injectable Solution (as aminophylline) 25 mg/mL (aminophylline) (IV)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to theophylline or other xanthines
  • Concurrent use with other xanthines (e.g., caffeine, theobromine)
  • Severe cardiac arrhythmias
  • Hyperthyroidism (may exacerbate)
  • Seizure disorders (may lower seizure threshold)
Warnings & Clinical Precautions:
  • Use with caution in patients with hepatic impairment, renal impairment, or severe respiratory failure.
  • Monitor serum theophylline concentrations in patients on long-term therapy or with concurrent diseases.
  • In cats, use lower doses due to slower metabolism.
  • In horses, may cause CNS stimulation and excitement.
  • Use with caution in animals with gastric ulcers or gastrointestinal irritation.
  • Avoid in animals with a history of cardiac disease, especially tachyarrhythmias.
  • Pregnancy and lactation: Use only if clearly needed; theophylline crosses the placenta and is excreted in milk.

Adverse Effects & Reactions

Common:

  • Gastrointestinal upset (vomiting, diarrhea, anorexia)
  • Restlessness
  • Tachycardia
  • Polyuria
  • Polydipsia

Serious / Severe:

  • Cardiac arrhythmias (ventricular tachycardia, atrial fibrillation)
  • Seizures
  • Hypotension
  • Hyperthermia
  • Respiratory arrest

Rare:

  • Allergic reactions (rash, urticaria)
  • Hepatotoxicity
  • Hyperglycemia
  • Hypokalemia

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Fluoroquinolones (e.g., enrofloxacin, ciprofloxacin) Decreased clearance of theophylline, leading to increased serum levels and toxicity. High
Cimetidine Inhibits hepatic metabolism of theophylline, increasing serum levels. High
Erythromycin Decreases theophylline clearance, increasing risk of toxicity. Moderate
Phenobarbital Induces hepatic enzymes, increasing theophylline metabolism and reducing efficacy. Moderate
Beta-agonists (e.g., albuterol) Additive bronchodilation but increased risk of cardiovascular effects. Moderate
Ketamine May increase risk of seizures. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Tachycardia
  • Hyperactivity
  • Tremors
  • Seizures
  • Cardiac arrhythmias
  • Hyperthermia
  • Hypotension

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Induce emesis if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids to maintain hydration and promote excretion. Control seizures with diazepam or barbiturates. Treat cardiac arrhythmias with appropriate antiarrhythmic agents (e.g., lidocaine for ventricular arrhythmias). Monitor vital signs and serum electrolytes. In severe cases, consider hemoperfusion or hemodialysis.

Food Animal Withdrawal Times

πŸ₯© Meat: 7 daysπŸ₯› Milk: 3 days

Withdrawal times are not established for theophylline in food animals; these are estimates based on pharmacokinetic data. Consult regulatory authorities for specific guidance.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25Β°C), protect from moisture.

Handling & Special Conditions: Keep container tightly closed. Do not freeze oral liquid formulations.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use.

Extra-Label (Off-Label) Use: In the US, theophylline is not FDA-approved for veterinary species; use in animals is extra-label. Under AMDUCA, extra-label use is permitted by or on the order of a veterinarian within a valid VCPR, provided that appropriate withdrawal times are observed for food animals.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Theophylline is a valuable bronchodilator in veterinary medicine, particularly for chronic respiratory conditions in dogs, cats, and horses. Due to its narrow therapeutic index, monitoring serum concentrations is recommended to avoid toxicity. Sustained-release formulations are preferred for maintenance therapy to provide consistent blood levels. In cats, dosing must be adjusted due to slower metabolism. In horses, theophylline may be used as an adjunct to corticosteroids for heaves. Always consider potential drug interactions, especially with fluoroquinolones and cimetidine. For food animals, observe appropriate withdrawal times.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)