Aminophylline / Theophylline
1,3-dimethyl-7H-purine-2,6-dione (Theophylline); Theophylline ethylenediamine (Aminophylline)
Also known as: Theochron · Theo-Cap · Theo-24 · Uniphyl · Bronkodyl · Elixophyllin · Theo-Dur · Slo-Bid · aminofilina · aminophyllinum · euphyllinum · metaphyllin · theophylline and ethylenediamine · theophylline ethylenediamine compound · theophyllinum ethylenediaminum · anhydrous theophylline · teofillina
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Bronchodilation (Extended-Release) | 10 mg/kg PO every 12 hours initially, if no adverse effects are observed and the desired clinical effect is not achieved, give 15 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Tracheal collapse (mild clinical signs, <50% collapse) | 11 mg/kg PO, IM or IV three times daily. | PO/IM/IV | q8h | — | 🌎 NA |
| Severe, acute pulmonary edema and bronchoconstriction | Aminophylline 4-8 mg/kg IV or IM, or 6-10 mg/kg PO every 8 hours. | IV/IM/PO | q8h | — | 🌎 NA |
| Cough | Aminophylline: 10 mg/kg PO, IV three times daily | PO/IV | q8h | — | 🌎 NA |
| Collapsing trachea (bronchodilator) | 11 mg/kg PO or IV q6-12h | PO/IV | q6-12h | — | 🌎 NA |
- Bronchodilation (Extended-Release): Using Theochron Extended-Release Tablets or Theo-Cap Extended-Release Capsules
- Tracheal collapse (mild clinical signs, <50% collapse): Aminophylline
- Severe, acute pulmonary edema and bronchoconstriction: Long-term use is not recommended.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Bronchodilation (Extended-Release) | 20 mg/kg PO once daily in the PM; using Slo-Bid: 25 mg/kg PO once daily in the PM | PO | q24h | — | 🌎 NA |
| Bronchodilation | 6.6. mg/kg PO twice daily; using sustained release tablets (Theo-Dur): 25-50 mg (total dose) per cat PO in the evening | PO | q12h or q24h | — | 🌎 NA |
| Tracheal collapse (mild clinical signs, <50% collapse) | aminophylline: 5 mg/kg PO, two times daily. | PO | q12h | — | 🌎 NA |
| Bronchoconstriction associated with fulminant CHF | Aminophylline 4-8 mg/kg SC, IM, IV q8-12h. | SC/IM/IV | q8-12h | — | 🌎 NA |
| Cough | Aminophylline: 5 mg/kg PO twice daily | PO | q12h | — | 🌎 NA |
- Bronchodilation (Extended-Release): Products Theo-Dur and Slo-Bid are no longer available in the USA. Cautious use of dog dose/products is a reasonable alternative.
- Bronchodilation: Using aminophylline tablets or sustained release tablets
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Bronchodilation | 4.25 mg/kg PO 2-3 times a day | PO | q8-12h | — | 🌎 NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Pulmonary edema | Aminophylline 2-7 mg/kg IV q6-12h; Theophylline 5-15 mg/kg PO q12h | IV/PO | q6-12h | — | 🌎 NA |
| Pulmonary edema | 11 mg/kg PO or IV q8-12h. | PO/IV | q8-12h | — | 🌎 NA |
| Heaves (RAO) | Aminophylline: 5-10 mg/kg PO or IV twice daily. | PO/IV | q12h | — | 🌎 NA |
| Heaves (RAO) | Aminophylline: 4-6 mg/kg PO three times a day. | PO | q8h | — | 🌎 NA |
- Pulmonary edema: IV aminophylline should be diluted in at least 100 mL of D5W or normal saline and administered slowly (not >25 mg/min).
- Pulmonary edema: To 'load' may either double the initial dose or give both oral and IV dose at the same time. IV infusion in ~1L fluids over 20-60 mins.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Aminophylline and theophylline are methylxanthine derivatives primarily utilized in veterinary medicine for their potent bronchodilatory effects. They are frequently employed in the management of lower airway diseases (such as feline asthma, equine recurrent airway obstruction, and canine bronchitis), collapsing trachea, and as adjunctive therapy for cardiogenic pulmonary edema.
Clinical Pearl: Aminophylline is essentially a water-soluble salt of theophylline, created by adding ethylenediamine. 100 mg of hydrous aminophylline contains approximately 79 mg of anhydrous theophylline. Dosage conversions must be carefully calculated when switching between the two forms.
While highly effective, these drugs possess a narrow therapeutic index. Toxicity is dose-dependent, though dogs and cats generally tolerate higher serum concentrations than humans. Due to significant interpatient variability in metabolism, therapeutic drug monitoring is strongly recommended, especially in patients with concurrent hepatic or cardiac disease.
Mechanism of action
The primary mechanism of action involves the competitive inhibition of phosphodiesterase (PDE) enzymes.
- PDE Inhibition → Decreased breakdown of cyclic AMP (cAMP) → Elevated intracellular cAMP levels.
- Increased cAMP → Enhanced release of endogenous epinephrine → Relaxation of bronchial and pulmonary vascular smooth muscle.
- Elevated cAMP also inhibits the release of inflammatory mediators like histamine and slow-reacting substance of anaphylaxis (SRS-A) from mast cells.
- Intracellular Calcium Translocation: Methylxanthines alter intracellular ionized calcium dynamics, contributing to increased diaphragmatic contractility (reducing respiratory fatigue) and weak positive inotropic/chronotropic effects on the heart.
- Additional Effects: Induces mild diuresis, stimulates the central nervous system (CNS) and respiratory centers, and increases gastric acid secretion.
Safety & warnings
Contraindications
- Hypersensitivity to any xanthines (including theobromine or caffeine)
- Hypersensitivity to ethylenediamine (specific to aminophylline)
Adverse effects
- Nausea and vomiting
- Diarrhea
- Insomnia / Restlessness
- Polyphagia (increased appetite)
- Polydipsia and polyuria (increased thirst and urination)
- Tachycardia (rapid heart rate)
- Nervousness, excitability, and tremors (especially in horses)
- Diaphoresis (sweating in horses)
- Ataxia
- Seizures (in severe toxicity)
- Cardiac dysrhythmias (in severe toxicity)
Precautions
Use with extreme caution in patients with severe cardiac disease, seizure disorders, gastric ulcers, hyperthyroidism, renal or hepatic disease, severe hypoxia, or severe hypertension.
- Arrhythmias: May cause or worsen preexisting cardiac arrhythmias; enhanced monitoring is required.
- Clearance Issues: Neonatal, geriatric, and congestive heart failure (CHF) patients may have decreased clearance and prolonged half-lives, making them more susceptible to toxicity.
- Dosing Weight: Because of low lipid solubility and low volume of distribution, obese patients should be dosed based on lean body weight.
- IM Injection: Aminophylline causes intense local pain when administered IM and is rarely recommended via this route.
Drug interactions
May decrease theophylline levels via hepatic enzyme induction.
Can significantly increase theophylline levels. Consider reducing theophylline dose by 30% and monitor for toxicity.
Can increase theophylline levels.
Can increase theophylline levels by inhibiting hepatic metabolism.
Concurrent use can cause an increased incidence of seizures.
Concurrent use may cause an increased incidence of cardiac dysrhythmias.
Toxic synergism; can lead to severe cardiac arrhythmias.
Can increase theophylline levels and antagonize bronchodilatory effects.
Can increase theophylline levels.
Monitoring
- Therapeutic efficacy (improvement in breathing/cough)
- Clinical signs of toxicity (GI upset, CNS stimulation, tachycardia)
- Serum trough levels at steady state (Target: >8-10 mcg/mL in small animals; do not exceed 15 mcg/mL in horses. Human therapeutic range is 10-20 mcg/mL)
Pharmacokinetics
Half-life
Absorption
Nearly 100% bioavailable after oral administration of non-sustained release products. Sustained-release products have variable bioavailability ranging from 30-76%.
Distribution
Distributes throughout extracellular fluids and body tissues. Crosses the placenta and distributes into milk (70% of serum levels). Low plasma protein binding (7-14% in dogs). Volume of distribution: dogs 0.82 L/kg, cats 0.46 L/kg, horses 0.85-1.02 L/kg.
Metabolism
Metabolized primarily in the liver to 3-methylxanthine, which possesses weak bronchodilatory activity.
Elimination
Renal clearance contributes only about 10% to overall plasma clearance.
Overdose
Clinical signs of toxicity are usually associated with serum levels greater than 20 mcg/mL in humans, though dogs appear to tolerate higher levels.
Life-threatening signs:
- Tachycardia and severe cardiac arrhythmias
- CNS effects including seizures and hyperthermia
Treatment is supportive:
- Decontamination: Empty the gut, administer activated charcoal and a cathartic if oral ingestion was recent.
- Seizures: Maintain an adequate airway and treat with IV diazepam.
- Monitoring: Continuous ECG monitoring for arrhythmias. Monitor and correct fluid/electrolyte imbalances.
- Symptomatic Care: Hyperthermia may be treated with phenothiazines; severe tachycardia may be treated with propranolol if life-threatening.
Available products
Formulations
- Tablets (immediate and extended-release)
- Capsules (extended-release)
- Injection (solution)
- Oral elixir/solution
- Compounded oral suspension
Human-labeled
- Aminophylline Tablets: 100 mg & 200 mg
- Aminophylline Injection: 250 mg/10 mL (25 mg/mL)
- Theophylline Extended-Release Capsules and Tablets: 100 mg, 125 mg, 200 mg, 300 mg, 400 mg, 450 mg, & 600 mg
- Theophylline Tablets and Capsules: 100 mg, 200 mg, & 300 mg
- Theophylline Elixir: 80 mg/15 mL
- Theophylline & Dextrose Injection: Various concentrations (0.4 mg/mL to 4 mg/mL)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store oral products in tight, light-resistant containers at room temperature. Aminophylline injection should be stored below 30°C, protected from freezing and light. Do not inject solutions that contain a precipitate or visible crystals. Compounded oral suspensions should be protected from light and kept at room temperature (refrigeration causes precipitation).
Client information
This medication is used to help open your pet's airways and make breathing easier.
- Administration: Give exactly as prescribed by your veterinarian. Do not skip doses. If using extended-release tablets or capsules, do not crush or allow your pet to chew them unless specifically instructed by your vet.
- Side Effects: Mild stomach upset, increased drinking/urination, or slight restlessness can occur when starting the medication but often resolve.
- When to Call the Vet: Contact your veterinarian immediately if you notice severe vomiting, extreme restlessness, muscle tremors, rapid breathing, or seizures, as these can be signs of an overdose.
- Diet: Avoid giving your pet chocolate or caffeine, as these contain similar compounds and can increase the risk of toxicity.
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.