Thrombolytic activity of a novel plasminogen activator, LY210825, compared with recombinant tissue-type plasminogen activator in a canine model of coronary artery thrombosis.

LY210825, a recombinant tissue-type plasminogen activator (rt-PA), which contains the kringle-2 and serine protease functional domains of native tissue-type plasminogen activator, was previously produced by site-directed mutagenesis in a Syrian hamster cell line. We studied the thrombolytic potential of this molecule in a canine thrombosis model. Male hounds (16-22 kg) were anesthetized; a 2.0-cm segment of the left circumflex coronary artery (LCX) was isolated proximal to the first main branch, and the dogs were instrumented with an electromagnetic flow probe to measure coronary blood flow. An occlusive thrombus was formed after injury of the intimal surface of the LCX with an electrical current applied by a needle-tipped anode placed distal to the electromagnetic flow probe. After 1 hour of occlusion, either LY210825 or rt-PA was administered intravenously according to the following protocols: 1) a 1-hour infusion of either 0.25 mg/kg LY210825 or 0.4 mg/kg rt-PA, 2) single injections of 0.15-0.6 mg/kg LY210825, and 3) a single injection of 0.45 mg/kg LY210825 and a 3-hour infusion of 1.0 or 1.7 mg/kg rt-PA. Plasma half-lives of LY210825 and rt-PA were 58 +/- 7 and 3.3 +/- 0.3 minutes, respectively. LY210825 produced more rapid reperfusion of the LCX than did rt-PA. In the third study, 90% of the rt-PA-treated vessels reoccluded within 1 hour after cessation of drug, whereas only 25% of the LY210825-treated vessels reoccluded during a 4-hour washout period. There were significant, but relatively small, reductions produced by both plasminogen activators on plasma fibrinogen and plasminogen (25-35% decreases). Because of its longer plasma half-life, LY210825 could be administered intravenously as a single injection. In a canine model of coronary artery thrombosis, LY210825 was a more effective thrombolytic agent than was rt-PA.

Oral absorption of cephalosporin antibiotics. 1. Synthesis, biological properties, and oral bioavailability of 7-(arylacetamido)-3-chloro cephalosporins in animals.

A number of 7-(arylacetamido)-3-substituted cephalosporins were prepared and tested in animals for oral absorbability. Bioavailability in mice, rats, dogs, and monkeys was determined after oral or parenteral administration. Oral bioavailability of five compounds selected for more intensive study was generally higher than that of penicillin V in all species tested. The results of ED50 testing against experimental infections in mice generally supported the bioavailability studies. Antibiotic activities were evaluated against Gram-positive and Gram-negative organisms with some derivatives expressing in vitro activity similar to cefaclor. The plasma half-life in rats was relatively short and the plasma curves were strongly influenced by probenecid, indicating rapid renal secretion. Some 7-(arylacetamido)-3-chloro cephalosporins are orally absorbed in animals to a greater extent than penicillin V, and antibacterial agent of proven clinical utility.

Liquid chromatographic analysis of enviradene, a new antiviral agent, in plasma and its application in bioavailability studies in the dog.

A rapid and specific high-performance liquid chromatographic (HPLC) assay has been developed for the determination of enviradene, 1, at concentrations of 2-5 ng/mL in plasma. The drug was extracted from the samples using benzene. The benzene extract was evaporated and the residue dissolved in the mobile phase. The HPLC system consisted of a reversed-phase column and a 75% methanol:25% 0.2 M sodium acetate mobile phase. Either a UV detector set at 268 nm or an electrochemical (EC) detector set at a potential of +0.9 V (versus Ag/AgCl/3 M NaCl) was used to monitor the drug. A column-switching system was used to remove late-eluting plasma constituents that interfered in subsequent chromatograms. The limit of sensitivity was 2 ng/mL for the HPLC-EC procedure and 5 ng/mL for the HPLC-UV procedure. Recovery from plasma was approximately 97%; the procedure had a relative error of approximately 3% and a relative standard deviation of 4.5% over the range of 20-200 ng of 1/mL of plasma. Following intravenous administration of 1 or 2 mg/kg of 1 to dogs, the parent drug was quantitated in plasma for 24 h using this procedure. The terminal phase half-life in plasma was calculated to be 10 h. Oral administration to dogs of single 8 mg/kg doses of 1, formulated with povidone-30 or polysorbate 80 and microcrystalline cellulose, produced high and persistent plasma concentrations of drug. At doses below 2 mg/kg, plasma concentrations were found to be nonlinearly related to the amount of the dose administered. The bioavailability of the drug in dogs was found to be increased by the concomitant administration of food.

Nonaqueous cephalosporin suspension for parenteral administration: cefazolin sodium.

The flocculation-deflocculation behavior of cefazolin sodium (I) in nonaqueous media and the effect of surfactants as measured by zeta potential, sedimentation, and porosity were studied. A significant difference in zeta potential was observed when the particles were suspended in different nonaqueous media. The addition of surfactant produced a deflocculated state. The surfactant deflocculated the particles by a process of supersaturation and crystallization involving a surfactant-cefazolin complex. The shielding effect of the surfactant on the surface of the particles also apparently affected their electrophoretic properties. Kinetic studies on the stability of the drug as a function of temperature were conducted; it appears that the chemical stability in ethyl oleate at room temperature is adequate for a reasonable shelf life. The efficiency of absorption of the drug from the ethyl oleate suspension was evaluated after intramuscular administration in dogs. The area under the plasma concentration versus time curve and urinary recovery indicated that cefazolin was 100% bioavailable from this nonaqueous preparation.

Metabolic fate of [14C]cefamandole, a parenteral cephalosporin antibiotic, in rats and dogs.

The biotransformation of the parenterally effective cephalosporin antibiotic cefamandole nafate (I) has been studied in rats and dogs. After rapid in vivo hydrolysis of the nafate pharmaceutical form to cefamandole (II), the antibiotic was found to be very resistant to metabolic degradation in both species. In dogs, cefamandole escaped metabolism and was eliminated as unaltered antibiotic almost exclusively by renal excretion. In rats, cefamandole was somewhat labile to metabolism; however, a major portion of the administered antibiotic was eliminated unchanged principally by renal excretion.

Metabolism of (14C) cefaclor, a cephalosporin antibiotic, in three species of laboratory animals.

The metabolic fate of the orally effective cephalosporin antibiotic cefaclor (Lilly 99638) has been studied in rats, mice, and dogs. Cefaclor is efficiently absorbed from the gastrointestinal tract as the intact antibiotic. In rats and mice, cefaclor, for the most part, escapes metabolism in the body and is eliminated unchanged as unaltered antibiotic, primarily by renal excretion. In dogs, however, cefaclor is more labile to metabolism and only a portion of the administered antibiotic is eliminated unchanged via the kidney.

Intestinal secretion of erythromycin base.

Erythromycin fluxes into rabbit midjejunal segments were studied. When erythromycin was infused into the jugular vein of anesthetized rabbits, the antibiotic was secreted into the segments at a rate of 0.0136 +/- 0.0023 mg/min. Preloading of the segments with five and 20 times the plasma concentration did not diminish this secretion. Protein binding of the antibiotic within the lumen could not explain this secretion, since both ultrafiltration and chromatography of luminal solutions indicated that the biological activity was free erythromycin. Moreover, the transmural potential across the intestinal mucosa is likely to be theprincipal driving force, since greater than 80 mv would be required to sustain the observed secretion against an imposed 20-fold concentration difference between blood and lumen. The best explanation for the intestinal secretion of erythromycin appears to be an active transport pathway capable of concentrating erythromycin in the lumen. It is not clear what endogenous substances are transported by this pathway.