Preliminary study on the pharmacokinetics of phenobarbital in the neonatal foal.
Abstract: Pharmacokinetic characteristics of the anticonvulsant phenobarbital were studied in seven pony and two Thoroughbred foals aged between four and 10 days. A single, 20 mg/kg bodyweight (bwt) dose of phenobarbital was given intravenously over 25 mins and the serum concentrations of the drug were measured using an EMIT AED assay (coefficient of variation 1.37 per cent at 30 micrograms/ml, n = 7). Phenobarbital elimination was found to follow first order kinetics. The mean (+/- sd) peak phenobarbital serum concentration was 18.6 +/- 2.1 micrograms/ml at 1 h after initiation of infusion with a mean (+/- se) half-life of 12.8 +/- 2.1 h. The mean (+/- se) volume of distribution was 0.86 +/- 0.026 litres/kg bwt and mean (+/- se) total body clearance was 0.0564 +/- 0.0065 litres/kg bwt/h. Sedation was noticed 15 to 20 mins after the beginning of infusion and lasted for up to 8 h. All foals could be aroused and could walk although they were ataxic for the first 1 to 2 h. A degree of delayed hyperexcitability occurred 3 to 8 h after infusion. In equine neonatal seizure disorders it is recommended to use a loading dose of 20 mg/kg bwt of phenobarbital, followed by maintenance doses of 9 mg/kg bwt at 8 h. With this regimen, average steady state serum phenobarbital concentrations should range between approximately 11.6 and 53 micrograms/ml. Phenobarbital serum concentrations should be monitored following the loading dose and 24 h after initiating the maintenance doses to check that levels remain within the suggested (human) therapeutic range of 15 to 40 micrograms/ml.
Publication Date: 1984-07-01 PubMed ID: 6479136DOI: 10.1111/j.2042-3306.1984.tb01946.xGoogle Scholar: Lookup
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The study broadly examines the pharmacokinetics of the anticonvulsant drug, phenobarbital, in young foals. With intricate tests and observations, the researchers propose an optimal dosage and frequency regime for treating neonatal seizure disorders in foals.
Research Methodology
- The study was conducted on a small sample of nine foals, aged between four and 10 days. This included seven pony and two Thoroughbred foals.
- A single, 20 mg/kg bodyweight (bwt) dose of phenobarbital was administered intravenously over 25 minutes.
- The serum concentrations of the drug were measured using an EMIT Automated Enzyme Immunoassay (AED assay) with a coefficient of variation of 1.37 per cent at 30 micrograms/ml.
- The effects of the drug on the foals were observed and documented.
Result of the Study
- The results revealed that phenobarbital elimination follows first-order kinetics in young foals.
- The average peak serum concentration of phenobarbital was found to be 18.6 +/- 2.1 micrograms/ml one hour after the beginning of the infusion. A mean half-life of 12.8 +/- 2.1 hours was noted.
- The mean volume of distribution was 0.86 +/- 0.026 litres/kg bwt and the mean total body clearance was 0.0564 +/- 0.0065 litres/kg bwt per hour.
- Sedation was noticed in the foals 15 to 20 minutes after the start of the infusion and lasted up to 8 hours. All foals could be aroused and could walk, although they showed signs of ataxia for the first 1 to 2 hours.
- A degree of delayed hyperexcitability was observed in the foals 3 to 8 hours after infusion.
Recommendations of the Study
- The researchers recommend the use of a loading dose of 20 mg/kg bwt of phenobarbital, followed by maintenance doses of 9 mg/kg bwt every 8 hours for treating neonatal seizure disorders in foals.
- With this regimen, mean serum phenobarbital concentration should range between approximately 11.6 and 53 micrograms/ml.
- The researchers also advise monitoring of phenobarbital serum concentrations following the loading dose and 24 hours after starting the maintenance doses to ensure the levels remain within the recommended therapeutic range of 15 to 40 micrograms/ml for humans which they have assumed for horses in this scenario.
Cite This Article
APA
Spehar AM, Hill MR, Mayhew IG, Hendeles L.
(1984).
Preliminary study on the pharmacokinetics of phenobarbital in the neonatal foal.
Equine Vet J, 16(4), 368-371.
https://doi.org/10.1111/j.2042-3306.1984.tb01946.x Publication
Researcher Affiliations
MeSH Terms
- Animals
- Animals, Newborn / blood
- Animals, Newborn / metabolism
- Female
- Half-Life
- Horses / blood
- Horses / metabolism
- Kinetics
- Male
- Phenobarbital / administration & dosage
- Phenobarbital / blood
- Phenobarbital / metabolism
Citations
This article has been cited 3 times.- Arndt S, Kilcoyne I, Heney CM, Wong TS, Magdesian KG. Bacterial meningitis after dental extraction in a 17-year-old horse. Can Vet J 2021 Apr;62(4):403-407.
- Cochrane SM, Black WD, Parent JM, Allen DG, Lumsden JH. Pharmacokinetics of phenobarbital in the cat following intravenous and oral administration. Can J Vet Res 1990 Jan;54(1):132-8.
- Cochrane SM, Parent JM, Black WD, Allen DG, Lumsden JH. Pharmacokinetics of phenobarbital in the cat following multiple oral administration. Can J Vet Res 1990 Jun;54(3):309-12.
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