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Abstract

Objectives

To describe changes in renal function of horses after oral and IV administration of sodium bicarbonate (NaHCO3) and to determine whether changes are dose dependent.

Animals

6 Standardbred mares.

Procedure

Blood and urine samples for determination of renal function were collected immediately before and at hourly intervals for 12 hours after administration of each of 3 oral doses (1,500, 1,000, and 250 mg/kg of body weight, in 3 L of water) and 1 IV dose (250 mg/kg, 5% solution) of NaHCO3, or water (3 L orally).

Results

NaHCO3 induced increases in urine flow; electrolyte-free water reabsorption; urine concentrations of sodium and bicarbonate; fractional excretion of sodium, potassium, chloride, and bicarbonate; urinary excretion and clearance of sodium and bicarbonate; urine pH and anion gap; and mean plasma concentration of antidiuretic hormone. NaHCO3 induced attenuation in reduction with time of urine excretion and clearance of potassium, chloride, and osmoles, and induced reduction in urine osmolality. Plasma aldosterone and atrial natriuretic peptide concentrations and glomerular filtration rate were not modified.

Conclusions

Renal responses to NaHCO3 load emphasize conservation of plasma volume and re-establishment of acid-base balance over control of hyperosmolality by means of diuresis, natriuresis, and increased bicarbonaturia. These responses imply a large fluid shift from the extravascular space to the vascular compartment, which was eliminated via diuresis, thus preventing hypervolemia. (Am J Vet Res 1997;58:664–671)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To describe changes in blood constituents of horses after oral and IV administration of sodium bicarbonate (NaHCO3), and to determine whether the changes are dose dependent.

Animals

6 adult Standardbred mares.

Procedure

3 oral doses (1,500, 1,000, and 250 mg/kg of body weight) or 1 intravenous dose (250 mg/kg, 5% solution) of NaHCO3 in 3 L of water, or water (3 L orally), were given to the mares; then changes in blood constituents were measured. Access to food and water was denied during the experiment. Blood samples were collected immediately before treatment and at hourly intervals for 12 hours after treatment, and were analyzed for blood gas tensions; serum osmolality; serum sodium, potassium, chloride, and creatinine concentrations; PCV; and total solids concentration in plasma.

Results

All NaHCO3 treatments induced significant (P < 0.05) metabolic alkalosis, hypernatremia, hypokalemia, and hyperosmolality for at least 8 hours. In mares given the 1,500- and 1,000-mg doses of NaHCO3 orally, hypercapnia persisted for at least 12 hours, whereas hypercapnia lasted 2 hours in mares given the 250-mg dose orally or IV (P < 0.05). A tendency for reduction in PCV, proteins in plasma concentration, and serum concentration of chloride was observed 1 hour after IV administered doses of NaHCO3.

Conclusions

Oral or IV administration of NaHCO3 (≥ 250 mg/kg) to resting horses without ad libitum access to water induces significant and persistent acidbase and electrolyte changes. (Am J Vet Res 1997;58:658–663)

Free access
in American Journal of Veterinary Research

SUMMARY

Pharmacokinetics and bioavailability of rifampin in adult sheep were investigated by use of high-performance liquid chromatography for determination of serum concentrations. Eight adult ewes were given rifampin po at the rate of 50 mg of rifampin/kg of body weight. Three weeks after the first experiment, the sheep were given rifampin po and iv at the rate of 20 mg/kg in a cross-over design, with 1 week between treatments. Serum obtained over a 36-hour period was analyzed for rifampin and a potential metabolite, 25-desacetyl-rifampin, using reverse-phase chromatography with uv detection at 254 nm. Data were analyzed by compartmental and noncompartmental models. Analysis by the noncompartmental model of rifampin serum concentrations after iv administration yielded a mean ± sd total body clearance of 1.16 ± 0.21 ml/min/kg, apparent volume of distribution at steady state of 0.45 ± 0.06 L/kg, and terminal elimination rate constant of 0.15 ± 0.04 hour−1. The harmonic mean of the elimination half-life was 4.56 hours. Because of incomplete and continuing absorption, bioavailability was extremely variable after oral administration. Desacetylrifampin was not detected. On the basis of pharmacokinetic values, serum concentrations measured in this study, and published minimal inhibitory concentrations, the dosage of 20 mg of rifampin/kg, po, every 24 hours should provide adequate serum concentrations for treatment of rifampin-susceptible bacterial infections in sheep.

Free access
in American Journal of Veterinary Research

Summary

In August 1986, an extensive serosurvey for prevalence of IgG and IgM antibodies against Ehrlichia risticii, the causative agent of equine monocytic ehrlichiosis (eme), was performed at 2 Ohio racetracks, River Downs (rd) and Beulah Park (bp). Of 840 horses at rd and 574 at bp, 13 and 20%, respectively, were IgG antibody-positive (by indirect fluorescent antibody test results), with antibody titer ranging from 1:20 to 1:10,240. The titer observed at highest frequency at both racetracks was 1:80. A higher proportion of horses was ill at rd (operating during the summer months) than at bp (winter track). Of ill horses, 41% (24/58) at rd and 58% (11/19) at bp were seropositive. At rd, 70% (589/840) of all horses and 95% (102/107) of IgG seropositive horses had been stabled only at rd during the month prior to testing.

Analysis of these sera by use of an elisa to detect IgM antibody against E risticii antigen indicated that at rd, 42% (57/137) of the seropositive horses were IgM seropositive. At bp, 17% (20/120) of seropositive horses were IgM seropositive. The larger number of IgM seropositive horses at rd indicates that more horses were recently infected at rd than at bp (P = 0.0001). Therefore, at least half the seropositive horses at rd seemed to have acquired the infection at rd. These serosurvey data also indicate that at bp and rd, 78% (85/109) and 91% (111/122) of IgG seropositive horses, respectively, had subclinical infection. At ≤ 1:40 titer, there was no difference in seropositive rates between healthy and ill horses. However, the higher the titer, the greater the difference in seropositive rates between healthy and ill horses. Thus, the higher the titer, the more reliable the serodiagnosis of eme seems to be. In contrast, sera submitted from 285 horses in Ohio for serologic testing for E risticii had a higher (63%) positivity rate than sera from horses of the racetrack serosurvey. Of 120 horses with clinical signs compatible with eme, 69% were seropositive. Typical clinical signs of eme in seropositive horses were those of enteric disease (72%; 60/83), with laminitis being a secondary sign (12%; 10/83). Results indicate that seroprevalence is much greater than prevalence of clinical disease. Combination of IgG and IgM testing with horse movement history should help to identify the location of actual infection.

Free access
in Journal of the American Veterinary Medical Association