Depletion of florfenicol in lactating dairy cows after intramammary and subcutaneous administration.

Eighteen Holstein dairy cows ranging in body weight from 500-700 kg and with an average milk yield of 37 ± 6 kg/day were used to investigate the depletion of florfenicol (FFL) in milk and plasma of dairy cows. Three groups of six were administered FFL: Group A, intramammary (IMM) infusion of ~2.5 mg FFL/kg BW at three consecutive milking intervals (total amount of ~7.5 mg/kg BW); Group B, one IMM infusion (20 mg/kg BW) into one quarter and Group C, one subcutaneous (SC) treatment (40 mg/kg BW). IMM infusions were into the right front quarter. Cows were milked daily at 06:00 and 18:00 h. The highest concentrations (Cmax ) and time to Cmax (Tmax ) were: 1.6 ± 2.2 µg·FFL/mL milk at 22 h (Group A), 5.5 ± 3.6 µg·FFL/mL milk at 12 h (Group B), and 1.7 ± 0.4 µg·FFL/mL milk at 12 h (Group C). The half-lives (t1/2 ) were ~19, 5.5, and 60 h, for Groups A, B, and C, respectively. FFL was below the limit of detection (LOD) by 60 h in three Group B cows, but above the LOD at 72, 84, and 120 h in three cows. FFL was above the LOD in milk from Group C's cows for 432-588 h. Plasma values followed the same trends as milk. The results demonstrate that IMM-infused FFL is bioavailable and below the LOD within 72-120 h. The concentration of FFL was detectable in both plasma and milk over the course of 2-3 weeks after SC administration. The absence of residue depletion data presents problems in determining safe levels of FFL residues in milk and edible tissues. The data presented here must not be construed as approval for extra-label use in food animals.

Effect of recombinant porcine somatotropin (rpST) on drug disposition in swine.

Treatment of pigs with recombinant porcine somatotropin (rpST) causes a marked increase in feed utilization with increased weight-gain over untreated controls. Physiological parameters such as creatinine clearance were increased by rpST treatment. Clearance of drugs eliminated by hepatic extraction, like indocyanine green (ICG), were also increased by rpST treatment. However, clearance of intravenous (i.v.)-dosed propranolol (PPL) was not affected by rpST treatment and data from oral (p.o.)-dosing was inconclusive because of the low bioavailability, probably because of a high first-pass effect. The very low oral bioavailability indicates that intestinal metabolism of PPL is probably quite high. Analysis of urinary metabolites indicated production of the two phenolic isomers, but there was no metabolite corresponding to N-dealkylase activity; although the latter metabolite could have been eliminated in the bile with subsequent fecal elimination. PPL was an excellent in vitro substrate for measuring hepatic DME activity in vitro; two phenolic and one N-dealkylated metabolite were formed. The overall conclusions regarding this study must be that the effects of rpST on drug bioavailability and elimination were equivocal. As ICG and creatinine clearances were both increased significantly, one cannot rule out the probability that rpST would increase drug elimination in pigs as a result of increased hepatic uptake and/or renal clearance. One can only speculate that clearance of concurrently administered drugs would be increased. This would reduce residue levels, but it might also reduce efficacy.

Comparison of bovine in vivo bioavailability of two sulfamethazine oral boluses exhibiting different in vitro dissolution profiles.

The bolus (or oblet) is a dosage form that can be used for the oral administration of pharmaceutical compounds to ruminating species. Unlike traditional tablets, oral boluses may contain quantities of drug on the order of grams rather than milligrams. Due to its size, it is only recently that USP-like in vitro dissolution methods have been developed for this dosage form. However, whether or not these dissolution tests can predict product in vivo performance has yet to be determined. The importance of this issue is apparent when the U.S. Food and Drug Administration Center for Veterinary Medicine is faced with the decision of whether to require additional in vivo bioequivalence study data to support the approval of changes in product chemistry or manufacturing method. The current study was undertaken to determine whether an in vivo/in vitro correlation can be established for bovine sulfamethazine oral boluses and to acquire insight into the magnitude of changes in in vitro product performance that can occur before corresponding changes are seen in in vivo blood level profiles. Based upon the results of this investigation, it is concluded that marked changes in in vitro sulfamethazine bolus performance can be tolerated before resulting in altered in vivo blood level profiles. However, the data also suggest that rumenal absorption may occur for some compounds. Therefore the degree to which variation in product in vitro dissolution profiles can be tolerated may be compound specific.

Identification of multiple constitutive and inducible hepatic cytochrome P450 enzymes in market weight swine.

Constitutive swine enzymes analogous to human/rat cytochrome P450 (CYP) isoforms 1A2, 2A6, 2B1/2/6, 2D6, 2E1, 3A1, and 4A1/3 were detected by Western blot analysis. Swine 2E1 has a molecular weight greater than rat 2E1; swine 2B2 has a molecular weight similar to human 2B6. An induction cocktail containing beta-naphthoflavone, phenobarbital, and dexamethasone induced immunoreactive homologs of 1A1, 1A2, 2B1, 2B2, 3A1, and 3A2. Although the P450 content was increased by induction, there was no difference in the Soret lambda(max). Swine 1A1 has a lower molecular weight than swine 1A2 and rat 1A1. A swine 2B1 homolog was seen after induction, with a molecular weight that was lower than rat 2B1 but higher than swine 2B2. Induction did not augment swine 2B2 levels. The 3A homologs have molecular weights similar to their rodent counterparts. Following induction, swine 3A1 levels increased and were accompanied by the appearance of swine 3A2. Induction had no effect on expression of 2A6, 2B6, 2D6, 2E1, or 4A1/3. Enzyme induction increased the specific activities (nmol/min/mg) of substrates specific for 1A (7 of 7 substrates tested), 2A (2/2), 2B (5/5), 2C (1/3), 2D (3/4), 2E (3/3), 3A (3/5), and 4A (1/1). Although the specific activities of the 2E substrates increased, the turnover number for hydroxylation of chlorzoxazone was unchanged and that of p-nitrophenol and aniline were depressed in induced pigs. These results show that swine CYP isoforms are similar to those identified in human and rodents, but they are also different in many ways.

Gaucher's disease: lack of antibody response in 12 patients following repeated intravenous infusions of mannose terminal glucocerebrosidase.

An amplified ELISA has been employed for monitoring the safety of repeated intravenous infusions of modified human placental glucocerebrosidase. The enzyme infusions consisted of biweekly injections of macrophage targeted glucocerebrosidase over a 6 month duration. Serum samples collected throughout the study were assayed by use of an ELISA using alkaline phosphatase coupled to alcohol dehydrogenase for amplification. Using this protocol, 0.2-5 ng affinity purified immunoglobulin specific for glucocerebrosidase can be detected. Occasional false positives necessitate multiple repeat assays over time to accurately assess immunogenic response. Blinded ELISAs were performed on sera from both infused patients with Gaucher's disease and uninfused control patients and compared with apparent immunoglobulin concentration in 54 normal control sera. Although several samples showed apparently elevated immunoglobulin levels, repeat analyses failed to demonstrate high levels reproducibly. Furthermore, these sera were unable to neutralize enzyme or to precipitate radiolabelled enzyme, confirming the absence of antibody. Problems with high sensitivity ELISA formats are discussed.