Plasma theophylline concentration and lung function in ponies with recurrent obstructive lung disease

Area of Science:

• Veterinary Medicine
• Pharmacology
• Pulmonology

Background:

• Equine recurrent obstructive lung disease ('heaves') significantly impacts pony respiratory health.
• Aminophylline is a potential therapeutic agent, but its effective dosage range in ponies requires definition.

Purpose of the Study:

• To determine the therapeutic range of intravenous aminophylline for ponies with recurrent obstructive lung disease.
• To evaluate the effects of aminophylline on pulmonary function and excitability in affected ponies.

Main Methods:

• Six ponies with recurrent obstructive lung disease received infusions of aminophylline or sterile water.
• Measurements included dynamic lung compliance, pulmonary resistance, respiratory rate, tidal volume, blood gases, and heart rate.
• Plasma theophylline concentrations were monitored, and pony excitability was subjectively assessed.

Main Results:

• Aminophylline significantly decreased pulmonary resistance and increased lung compliance in ponies.
• Bronchodilator activity was observed at plasma theophylline concentrations between 59 and 84 mumol/litre.
• Higher concentrations led to excitement and tachycardia, limiting therapeutic utility.

Conclusions:

• The therapeutic range for intravenous theophylline in ponies with obstructive lung disease is 59–84 mumol/litre.
• Aminophylline demonstrates bronchodilator effects within this range, but side effects occur at higher concentrations.
• This study provides crucial pharmacokinetic and pharmacodynamic data for aminophylline use in equine respiratory disease.