J Vet Intern Med 2008;22:227–230
Exposure to Phenobarbital in a Foal after Nursing a M are T reated with Phenobarbital
D.M. Wong, M.G. Papich, and J.L. Davis
7-year-old, 672-kg, pregnant Thoroughbred mare presented with a 3-week history of premature lactation and lameness. The mare was a maiden, 336 days in gestation, and had been treated with 2 doses of ﬂunixin meglumine (1mg/kg, PO) the day before examination. Historically, the mare had experienced intermittent seizures while in race training. A complete diagnostic investigation to determine the cause of the seizures had been performed, but the origin of seizures remained undetermined. A weak positive Western blot analysis on cerebrospinal ﬂuid for Sarcocystis neurona was reported at that time, and the mare wastreated with ponazurila (5 mg/kg PO q24h) for 30 days.1 At examination, pertinent physical examination ﬁndings included mild tachycardia (56 beats/min), sensitivity to hoof testers involving all 4 feet, and the presence of thick, purulent exudate from the left mammary gland. Rectal palpation revealed anterior presentation of a live fetus, and transrectal and transabdominal ultrasonography demonstratedareas of uteroplacental thickening (14 mm; reference interval 7.14–11.98).2 While restrained in stocks, the mare demonstrated a mild partial seizure characterized by anxiousness, muscle fasciculations of the head and neck, and ataxia. Hematologic and serum biochemical abnormalities were limited to an increased plasma ﬁbrinogen concentration (600 mg/dL; reference interval 100–400). Lateralradiography of the feet revealed mild soft tissue swelling at the coronary band in the right front foot, suggestive of laminitis with sinking of the 3rd phalanx within the hoof. Because of laminitis and suspicion of placentitis and mastitis, the mare was administered sulfamethoxazole-trimethoprimb (30 mg/ kg PO q12h for 10 days) and phenylbutazonec (3 mg/kg PO q12h for 3 days, then 1.5 mg/kg PO q12h for3 days), the left mammary gland was milked out q8h, and supportive pads were applied to all 4 feet. Two generalized seizures were observed 14 and 16 hours after initial examination, characterized by anxiousness, generalized muscle fasciculations most prominent around the head and neck,
From the Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa StateUniversity, Ames, IA, (Wong); the Departments of Molecular Biomedical Sciences (Papich); and the Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, (Davis). Corresponding author: Dr Wong, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011; e-mail: firstname.lastname@example.org
Submitted April 24, 2007;Revised August 1, 2007; Accepted August 28, 2007.
Copyright r 2008 by the American College of Veterinary Internal Medicine 10.1111/j.1939-1676.2007.0036.x
hyperesthesia, collapse, and recumbency. At this point, treatment with phenobarbitald (5.5 mg/kg PO q12h) was initiated. Seizure activity was not subsequently noted. Uncomplicated parturition of a 42.7 kg ﬁlly occurred 3 days after admission. Theﬁlly was lethargic and hypothermic (96.41F; reference interval 99.5–101.3), had weak peripheral pulses, and maintained a low heart rate (52– 56 bpm) for 45 minutes after birth. Heart rate and temperature progressively improved over the following 90 minutes. Blood and milk samples were collected from the mare and blood was collected from the foal immediately after parturition to measurephenobarbital concentrations. Phenobarbital concentration in the mare’s serum was considered therapeutic (16.3 mg/mL; reference interval 15–40).3 The concentrations of phenobarbital in the mare’s milk and foal’s serum were 7.5 and 12.2 mg/mL, respectively. Initial treatment for the foal included intranasal oxygen (8 L/min for 1 hour) and intravenous administration of 2 L of hyperimmunized equine plasmae...