INTRAVENOUS CONTRAST-ENHANCED COMPUTED TOMOGRAPHY IN ADULT KOI (CYPRINUS CARPIO).

IV iodinated contrast is undocumented in koi (Cyprinus carpio). IV contrast-enhanced computed tomography (CT) provides detailed imaging of the vascular structures and parenchymal organs. The goals of this study were to (1) document feasibility of IV contrast into the caudal vein, (2) determine distribution of contrast media and conspicuity of organs, (3) evaluate for differences in contrast uptake with two different doses of IV contrast, and (4) evaluate for contraindications of IV iodinated contrast in a small cohort of fish. Thirty adult koi were split into three groups (n = 10) in a prospective interrupted time series design with nonequivalent groups, receiving 480 mg iodine per kg (mg I/kg), 800 mg I/kg, and saline. Contrast doses were selected based on the range of doses used in other species. Half of the fish given IV contrast (n = 10) were imaged with CT. Physical exams, blood smears, and biochemistries were performed on all fish. Half of the fish in each group were euthanized 24 h after injection and the other half two weeks later. Necropsies and histopathology were performed to evaluate pathology associated with contrast. For the CT examinations, precontrast, immediate postcontrast, and 5-m delayed postcontrast CT scans were obtained. Contrast in coelomic organs and circulatory system was measured using Hounsfield units. The caudal kidney was the most contrast-enhancing organ. Both doses produced good vascular enhancement and similar distribution. The delayed postcontrast scans showed repeatable parenchymal enhancement of organs. No mortality was encountered. No abnormalities were detected on blood smears, necropsies, or histopathology. Results suggest IV contrast administration is feasible, both contrast doses provided valuable anatomical information in the study with CT of coelomic organs, and no contraindications of contrast administration were detected.

INTRAVENOUS IOPAMIDOL PHARMACOKINETICS IN COMMON CARP (CYPRINUS CARPIO).

Koi carp (Cyprinus carpio), a variety of common carp, has gained popularity as an ornamental fish worldwide. Their high monetary and sentimental value has necessitated the development of antemortem diagnostic options. Contrast-enhanced computed tomography (CT) scanning with intravenous iopamidol has been shown to be safe and diagnostically effective at a minimum dose of 480 mg iodine (I)/kg in koi. The purpose of this study was to evaluate the pharmacokinetic parameters of this dose of iopamidol, as well as excretory mechanisms specific to fish, using common carp as a model. Blood, posterior kidney, gill, and bile were collected, necessitating sacrificial sampling. Thirty-five adult fish were randomly divided into six sampling groups. Five sampling groups (n = 6/group) received 480 mg I/kg; the control group (n = 5) received an equivalent volume of saline. The iopamidol groups were sampled at the following time points postinjection: 5 min, 1 hr, 6 hr, 24 hr, and 48 hr. The control group was sampled at 48 hr. Concentrations of iopamidol were determined using liquid chromatography tandem mass spectrometry; noncompartmental analysis was used to calculate pharmacokinetic parameters. Total clearance (3.04 ml/hr per kilogram) was slower, the volume of distribution smaller (79.92 ml/ kg), and the elimination half-life (20.39 hr) prolonged compared to similar studies in mammals. The time-concentration profiles of kidney and gill were similar; these organs appear to be responsible for the majority of iopamidol excretion. However, that of bile was much different, showing slower, low-level accumulation with time, suggesting that in fish, multiple organ systems play a role in elimination beyond just the kidney. In particular, they may rely more heavily upon biliary excretion, which thus far has been noted only in mammals with renal impairment. Further research is warranted to investigate if the slower elimination allows diagnostic CT images to be acquired at different time points postinjection.