Theophylline
Theophylline is a methylxanthine bronchodilator used in selected veterinary respiratory disorders. Applications include feline asthma, canine chronic bronchitis and some equine asthma cases with reversible bronchoconstriction. Oral formulation and species strongly influence exposure. Its respiratory role is adjunctive and may include effects on airway muscle and diaphragmatic function.
Group
Methylxanthine bronchodilator
Mechanism of Action
Theophylline inhibits phosphodiesterase activity and antagonizes adenosine receptors, altering cyclic-nucleotide and receptor-mediated signaling. Increased cyclic AMP contributes to airway smooth-muscle relaxation, while additional actions may support diaphragmatic contraction and modulate inflammatory responses. The relative contribution of these mechanisms at clinical concentrations remains incompletely defined. The overall effect can reduce reversible airway resistance.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Bronchoconstriction with immediate release | 9 mg/kg | PO | Every 8 h | |
| Bronchoconstriction with sustained release | 10 mg/kg | PO | Every 12 h | |
| Bronchoconstriction with sustained release | 15 mg/kg | PO | Every 12 h | Theochron/Theo-Cap studied alternative after 10 mg/kg twice daily is insufficient and tolerated. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Bronchoconstriction with immediate release | 4 mg/kg | PO | Every 8–12 h | |
| Bronchoconstriction with sustained-release tablet | 20 mg/kg | PO | Every 24 h | Reported guidance also gives 100 mg/cat; adjust by serum level. |
| Bronchoconstriction with extended-release capsule | 25 mg/kg | PO | Every 24 h | Reported guidance also gives 125 mg/cat. |
| Long-term modified-release therapy | Reference only | PO | Every 48 h | After long-term treatment, the interval may extend to every 48 hours. Continue the individually established tablet or capsule dose; no single amount applies to both formulations. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Equine asthma | 5 mg/kg | PO | Every 12 h | |
| Pulmonary edema bronchodilator adjunct | 5–15 mg/kg | PO | Every 12 h | Explicit theophylline oral amount. |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Bronchoconstriction | 20 mg/kg | PO | Every 12 h | |
| Bronchoconstriction with viral illness | 20 mg/kg | PO | Every 24 h |
Indications
- Adjunctive treatment of reversible bronchoconstriction in cats with asthma or chronic inflammatory airway disease.
- Bronchodilator support in selected dogs with chronic bronchitis or other disease with a reversible lower-airway component.
- Selected adjunctive treatment of canine airway-collapse syndromes when bronchodilator or diaphragmatic effects are clinically relevant, with limited evidence.
- Treatment of selected reversible airway obstruction in horses with equine asthma.
Contraindications
- Cardiovascular disease or seizure susceptibility requires caution.
Interactions
- Cimetidine, erythromycin, fluoroquinolones and propranolol can increase exposure; phenobarbital and rifampin decrease it.
- Other phosphodiesterase inhibitors may compound effects.
- Aminophylline and theophylline are related but not identical preparations; do not combine amounts or substitute formulations without an explicit conversion.
Adverse effects
- GI upset, tachycardia, excitation, tremor, seizures and hypokalemia.
Toxicity
Severe theophylline excess can cause tachyarrhythmias, seizures, hyperthermia and electrolyte disturbance. Monitor ECG, temperature and drug concentrations; protect airway and support fluids/electrolytes.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Theophylline immediate-release 100 mg | Tablet | 100 mg / tablet | PO |
| Theophylline immediate-release 125 mg | Tablet | 125 mg / tablet | PO |
| Theophylline immediate-release 200 mg | Tablet | 200 mg / tablet | PO |
| Theophylline immediate-release 250 mg | Tablet | 250 mg / tablet | PO |
| Theophylline immediate-release 300 mg | Tablet | 300 mg / tablet | PO |
Monitoring and Administration
Monitor serum concentrations during chronic therapy; reported target 10-20 mcg/mL. Preserve release characteristics: immediate and extended-release formulations are not interchangeable, and transdermal formulations were ineffective.
Do not disrupt modified-release coating.
The combined aminophylline/theophylline monograph contains many injectable aminophylline regimens. Aminophylline molecular composition and dose are different from theophylline; no numeric transfer is made. Use lean body weight in obese patients and monitor serum concentrations.