Pharmacokinetics and bioavailability of theophylline in horses

Abstract

The pharmacokinetics and bioavailability of theophylline in horses were investigated following both intravenous and intragastric administration of aminophylline solutions at doses corresponding to 15 and 10 mg/kg theophylline base. A rapid distributive phase with a half-life of approximately 15-30 min was followed by a slower elimination half-life averaging 15-17 h. The apparent volume of distribution averaged 850-900 ml/kg. Theophylline, administered as aminophylline solution, was both rapidly and completely absorbed from the equine digestive tract. Based on the bioavailability and disposition kinetics of theophylline, an intragastric dosage regimen for aminophylline consisting of the administration of 5 mg/kg at 12 h intervals would be expected to maintain plasma theophylline concentrations within the therapeutic range.

The pharmacokinetics of a slow-release theophylline preparation in horses after intravenous and oral administration

“…This value agrees with some previous reports (Errecalde et al, 1984;Ingvast Larson et al, 1985), although a faster elimination rate was reported by Short et al (1986).…”

“…Such variation has been reported in previous studies (Ingvast Larson et al, 1985). The first distribution phase (a) was rapid, being faster than that in some previous reports (Errecalde et aL, 1984;Ingvast Larson et al, 1985) but agreeing with that reported by Ayres et al (1985). This difference may have been caused by the different models used in the analysis.…”

“…However, the majority of authors use bicompartmental models (Errecalde et aL, 1984;Ingvast Larson et al, 1985).…”

“…There are previous reports concerning the pharmacokinetic behaviour of theophylline after intravenous and/or oral administration (Errecalde et al, 1984;Kowalczyk et al, 1984;Ayres et al, 1985;Ingvast Larson et aL, 1985;Short et al, 1986). However, there are no reports of the pharmacokinetics of the sustained release form of this drug in horses.…”

“…A long biological half-life of theophylline in horses after oral administration has been reported (Errecalde et aL, 1984;Ingvast Larson et al, 1985). The aims of this study were to determine the pharmacokinetic characteristics of a slow-release formulation of theophylline (TheoDur, Pfizer, Argentina) in horses and to ascertain whether it offers pharmacological advantages in the horse as it does in humans.…”