text: Objective—To characterize the bioavailability and pharmacokinetics of oral and injectable formulations of methadone after IV, oral, and intragastric administration in horses.
  Animals—6 healthy adult horses.
  Procedures—Horses received single doses (each 0.15 mg/kg) of an oral formulation of methadone hydrochloride orally or intragastrically or an injectable formulation of the drug orally, intragastrically, or IV (5 experimental treatments/horse; 2-week washout period between each experimental treatment). A blood sample was collected from each horse before and at predetermined time points over a 360-minute period after each administration of the drug to determine serum drug concentration by use of gas chromatography–mass spectrometry analysis and to estimate pharmacokinetic parameters by use of a noncompartmental model. Horses were monitored for adverse effects.
  Results—In treated horses, serum methadone concentrations were equivalent to or higher than the effective concentration range reported for humans, without induction of adverse effects. Oral pharmacokinetics in horses included a short half-life (approx 1 hour), high total body clearance corrected for bioavailability (5 to 8 mL/min/kg), and small apparent volume of distribution corrected for bioavailability (0.6 to 0.9 L/kg). The bioavailability of methadone administered orally was approximately 3 times that associated with intragastric administration.
  Conclusions and Clinical Relevance—Absorption of methadone in the small intestine in horses appeared to be limited owing to the low bioavailability after intragastric administration. Better understanding of drug disposition, including absorption, could lead to a more appropriate choice of administration route that would enhance analgesia and minimize adverse effects in horses.
  Intracranial pressure and cardiovascular variables after iv administration of medetomidine (0.03 mg/kg of body weight) were evaluated in 6 healthy, mixed-breed dogs anesthetized with 1.3% end-tidal isoflurane concentration and mechanically ventilated to normocapnia (PaCO2, 35 to 45 mm of Hg). Baseline values were determined for intracranial pressure, heart rate, arterial blood pressure, cardiac output, mean pulmonary artery pressure, pulmonary capillary wedge pressure, central venous pressure, end-tidal CO2 tension and isoflurane concentration, arterial pH and CO2 and O2 tensions, and core body temperature. Cerebral perfusion pressure, cardiac index, systemic and pulmonary vascular resistances, plasma HCO3- concentration, and base excess were calculated. Intracranial pressure was measured, using a calibrated, fiberoptic transducer placed within the brain parenchyma and secured to the calvarium by means of a subarachnoid bolt. Cardiac output was determined by thermodilution. End-tidal CO2 tension and isoflurane concentration were determined, using an infrared gas analyzer. Administration of medetomidine did not change intracranial pressure, but was associated with significant (P < 0.05) decreases in values for heart rate, cardiac index, end-tidal CO2, and HCO3- and with significant increases in systolic, mean, and diastolic pressure; pulmonary artery pressure; systemic vascular resistance; central venous pressure; and pulmonary capillary wedge pressure.
  Case Description—A 7-year-old Quarter Horse gelding was hospitalized in Ocala, Fla, because of lethargy, fever, anorexia, and swelling of distal aspects of the limbs. A tentative diagnosis of equine piroplasmosis (EP) was made on the basis of examination of a blood smear. The case was reported to the Florida State Veterinarian, and infection with Babesia equi was confirmed. The subsequent investigation included quarantine and testing of potentially exposed horses for B equi and Babesia caballi infections, tick surveillance, and owner-agent interviews.
  Clinical Findings—210 horses on 25 premises were tested for infection with EP pathogens. Twenty B equi–infected horses on 7 premises were identified; no horses tested positive for B caballi. Seven horses, including the index case, had clinical findings consistent with EP Dermacentor variabilis was considered the only potential tick vector for B equi collected, and all D variabilis specimens tested negative for Babesia organisms via PCR assay. Results of the epidemiological investigation suggested that B equi was spread by use of shared needles and possibly blood transfusions. All horses that tested positive were involved in nonsanctioned Quarter Horse racing, and management practices were thought to pose substantial risk of transmission of blood-borne pathogens.
  Treatment and Outcome—Final outcome of B equi–infected horses was euthanasia, death from undetermined causes, or shipment to a US federal research facility.
  Clinical Relevance—This investigation highlights the importance of collaboration between private veterinary practitioners, state veterinary diagnostic laboratories, and regulatory officials in the recognition, containment, and eradication of foreign animal disease.