The distribution of antibacterial agents between plasma and lymph in the dog.

1. Plasma, peripheral and thoracic lymph concentrations of penicillin V, phenethicillin, carbenicillin, ampicillin, cloxacillin, penicillin G, chloramphenicol and sulphadiazine were determined at various time intervals up to 6 h following intramuscular administration of 50 mg/kg to dogs.2. Peak plasma concentrations of the penicillins occurred within half an hour after administration with the peak lymphatic concentrations occurring 1.5 to 3 h afterwards. For the remaining period of the test the concentration in the lymph exceeded the corresponding concentration in the plasma. Sulphadiazine gave concentrations in thoracic lymph equal to the plasma concentration, but the peripheral lymph concentrations were lower while the concentrations of chloramphenicol in both peripheral and thoracic lymph were always lower than the plasma concentrations.3. After the peak concentrations were reached, the concentration curves for penicillins in lymph followed the same pattern as found in plasma, the penicillin concentrations declining exponentially. Sulphadiazine produced more persistent levels both in lymph and in plasma while the concentrations of chloramphenicol were still rising 6 h after administration.4. The free concentrations of penicillin in lymph were equal to the free concentrations in plasma, whereas the concentrations of free sulphadiazine and chloramphenicol in lymph were less than those in the plasma.

G1549, a new cyclic hydroxamic acid antibiotic, isolated from culture broth of Pseudomonas alcaligenes.

Antibiotic G1549, isolated from culture broth of Pseudomonas alcaligenes, is a new cyclic hydroxamic acid with a 1-hydroxy-2(1H)-pyridinone structure that complexes with metals. The structure of G1549 is suggested to be 1-hydroxy-5-methoxy-6-methyl-2(1H)-pyridinone. In vitro, G1549 and its copper and ferric complexes show moderate activity against Gram-positive bacteria, fungi and Trichomonas vaginalis. Topical application of G1549 and its copper and ferric complexes protect guinea pigs against cutaneous infection with Microsporum canis. The compounds, however, have some systemic toxicity in mice.

Therapeutic and kinetic properties of ceftazidime in animals.

The pharmacokinetic properties of ceftazidime were evaluated in laboratory animals. Peak serum concentrations following subcutaneous or intramuscular dosing of 25 mg/kg occurred 15-30 min after injection and ranged from 26 mg/l in mice to 63 mg/l in rabbits. Serum half-life values were 21 min in mice, 23 min in rats, 48 min in rabbits, 60 min in beagle dogs and 58 min in cynomolgus monkeys. Ceftazidime was not absorbed following oral dosing. Large amounts of unchanged ceftazidime were excreted in urine. Low biliary excretion, i.e. 1.2%, of subcutaneously administered ceftazidime was found in rats. This contrasted to high biliary excretion of cefmenoxime (20%), cefotiam (37.5%), moxalactam (40%) and cefoperazone (52%). The high intrinsic antibacterial activity of ceftazidime combined with good pharmacokinetics was reflected in excellent therapeutic effects in experimental infections. Ceftazidime was the most active of the newer beta-lactam antibiotics tested and only the aminoglycoside antibiotic gentamicin achieved the same level of activity. Ceftazidime, which is currently being assessed clinically, is a promising potential alternative to aminoglycoside antibiotics.

A morphological comparison of treatment with different beta-lactam antibiotics on experimental staphylococcal endocarditis and aortitis.

The effect of treatment of staphylococcal endocarditis and aortitis with five different beta-lactam antibiotics (ceftazidime, cephaloridine, cefotaxime, methicillin and flucloxacillin) was evaluated by light and electron microscopy. It was found that therapy with all five antibiotics produced similar morphological changes. At 3 and 8 h, the bacterial colonies showed zonal changes with the bacteria furthest from the lumen exhibiting less severe damage while the outer region consisted largely of lysed cells. However, in the outer zone a few apparently viable, thick-walled persistent bacteria were observed. At 24 and 48 h, many colonies consisted of large masses of lysed bacteria with only a few thick-walled persistent bacteria. In all cases, therapy was associated with an increased host inflammatory cell response resulting in invasion of leucocytes through the aortic wall or vegetation towards and engulfing the colonies. However, even at 48 h the inflammatory cells had not reached all the deep-seated colonies. It would appear that all the antibiotics reached bactericidal concentrations within the lesions. However, the eradication of the few 'persistent' bacteria was delayed by the inability of the inflammatory cells to reach all the colonies.

Differential response to benzylpenicillin in vivo of tolerant and non-tolerant variants of Streptococcus sanguis II.

A variant that was highly tolerant to benzylpenicillin was obtained from a non-tolerant clinical isolate of Streptococcus sanguis II by repeated exposure to penicillin. The rabbit model of endocarditis was used to investigate the efficacy of a high dose regimen of benzylpenicillin (250 mg/kg; peak serum concentration c. 25 mg/l) in the prophylaxis and treatment of endocarditis during challenge or infection with the non-tolerant parent strain or its tolerant variant. The two strains exhibited a similar capacity to initiate infection. A single dose of penicillin administered 0.5 h before bacterial challenge protected six of nine rabbits infected with the non-tolerant parent strain, but none of nine infected with the tolerant variant. Treatment of established infection with penicillin administered twice daily for four days cured eight of 13 (61%) rabbits infected with the non-tolerant parent strain, but only one of 14 (7%) rabbits infected with the tolerant variant. These results support the view that tolerance to penicillin has therapeutic implications.

Comparison of ceftazidime, cefuroxime and methicillin in the treatment of Staphylococcus aureus endocarditis in rabbits.

Ceftazidime, cefuroxime and methicillin proved equally effective in the therapy of experimental Staphylococcus aureus endocarditis in rabbits with a dosing regimen of 40 mg/kg intramuscularly at 8-hourly intervals for three days. Treated animals all demonstrated a thousand to 10,000-fold reduction in the levels of bacteria in the vegetations compared with untreated controls. In-vitro sensitivities of the organism to the test antibiotics were not predictive of therapeutic efficacy in vivo.

A morphological study of the effect of treatment with the antibiotic ceftazidime on experimental staphylococcal endocarditis and aortitis.

The morphological effects of antibiotic therapy with either single or repeated (8 hourly) injections of ceftazidime were examined in rabbits with experimentally induced staphylococcal endocarditis and aortitis. At 3 h after initiating treatment, many of the bacteria, irrespective of the location of the colony, showed evidence of abnormal ultrastructural changes of the cytoplasm and/or cell wall. By 8 h many degenerate lysed bacteria were present. By 24 h, in rabbits which received a single injection, bacterial colonies contained many normal and dividing bacteria. In comparison, bacterial colonies at 24 h in rabbits receiving repeated injections consisted of large masses of lysed bacteria with only a few viable appearing thick-walled 'persistent' cells. At 48 and 72 h, no viable appearing bacteria were observed although they could be isolated by culture methods. Treatment was associated with an increased inflammatory cell response at the surface of the vegetation and within the vasculature. In the later stages there was evidence of healing with endothelialization of the lesions. It would appear, therefore, that ceftazidime penetrates efficiently into the vegetations with only a short transitory phase at sub-bactericidal concentrations. The few 'persistent' bacteria appear to be protected from the host defences by the surrounding thrombus which prevents their eradication.

Evaluation of ceftazidime in experimental Klebsiella pneumoniae pneumonia: comparison with other antibiotics and measurement of its penetration into respiratory tissues and secretions.

The activity of ceftazidime was examined in a murine model of Klebsiella pneumoniae pneumonia in which the antibiotic was administered subcutaneously 6 h after intranasal infection and then twice daily for the next three days (i.e. seven doses). In a series of experiments using this test, the dose of ceftazidime giving 50% survival relative to controls (SD50) ranged from 1.0-9.0 mg/kg/dose while the dose required to reduce the log10 cfu/lung by 50% (CD50) ranged from 24-64 mg/kg/dose. Ceftazidime was considerably more effective than cefotiam, amoxycillin-clavulanic acid or kanamycin in the test. Pharmacokinetic studies with ceftazidime showed that no differences in respiratory tract penetration existed between uninfected mice and mice infected for 48 h with K. pneumoniae. The percentage penetration of ceftazidime from serum was 73% for pleural fluid, 44% for tracheal fluid, 27% for tracheal wall tissue and 17% for whole lung tissue after a subcutaneous injection of 100 mg/kg. At this dose, ceftazidime remained at supra-MIC concentrations for 2-3 h in all compartments examined.

Experimental staphylococcal endocarditis and aortitis. Morphology of the initial colonization.

The initial colonization, by Staphylococcus aureus, of the catheter damaged aortic valve and aorta of the rabbit, was examined by light and electron microscopy at 15 min, 3 h and 24 h post inoculation (PI). At 15 min PI, the majority of bacteria (80%) were located on the lateral surfaces of the thrombic vegetations while 20% were attached directly to the connective tissue of the aortic valve and aorta in areas where the endothelial lining was disrupted. By 3 h the bacteria on the thrombic vegetations were covered by fibrin. At this time, the bacteria both within the vegetations and on the surface of the vasculature were undergoing multiplication to form small groups. The precipitation of thrombus around the bacteria attached to the surface of the aorta to form microscopic infected vegetations had occurred by 24 h PI. The colonizing bacteria did not elicit any phagocytic response. The colonization of the cardiovasculature by Staph. aureus did not necessarily require pre-existing vegetations.

A morphological study of experimental rabbit staphylococcal endocarditis and aortitis. I. Formation and effect of infected and uninfected vegetations on the aorta.

In this study the development of sterile thrombic vegetations on the aorta resulting from catheterization and the effect of subsequent infection with Staphylococcus aureus were examined by light and electron microscopy. Thrombi of various sizes, comprising fibrin, platelets and a few leucocytes and erythrocytes, develop on the damaged surface of the aorta with minimal changes in the underlying aortic wall. After intravenous inoculation of Staph. aureus most vegetations become infected, as shown by the presence of bacterial colonies, and the underlying aortic wall is markedly inflamed. The inflammatory cells invade the wall from the base of the aorta and cause swelling plus disruption of the elastic laminae with ulceration of the luminal surface in some cases. This structural damage appears to be a direct result of the bacterial infection of the lesions on the luminal surface.

A morphological study of experimental staphylococcal endocarditis and aortitis. II. Inter-relationship of bacteria, vegetation and cardiovasculature in established infections.

The inter-relationship of the bacteria, vegetations and cardiovasculature was studied by light and electron microscopy in experimental staphylococcal endocarditis and aortitis in acute and fatal infections. A specific spatial relationship was observed with the majority of bacterial colonies located along the junction between the cardiovasculature and the overlying thrombic vegetation. The bacterial colonies within the vegetations on the ventricular and aortic walls were smaller and embedded in a thick layer of thrombus with certain colonies showing evidence of bacterial cell death. By comparison, the lesions on the aortic valve consisted of large masses of bacteria with little or no thrombic coating. The structural damage to the aortic valve appeared to be the direct result of bacterial invasion into the connective tissue of the cusp. The acute nature of the disease may be related to bacterial destruction of the aortic valve whereas the colonies within the aortic wall vegetations are probably the source of 'resistance' to antibiotic treatment.

The in-vivo antibacterial activity of ceftazidime (Gr 20263)--a comparison with other new beta-lactam antibiotics and gentamicin.

Ceftazidime was compared with cefotaxime, ceftizoxime, cefmenoxime, cefotiam, cefoperazone, moxalactam, piperacillin, carbenicillin, mezlocillin, cefsulodin and the aminoglycoside antibiotic gentamicin in a series of mouse protection tests. Ceftazidime, together with the other cephalosporin antibiotics and moxalactam were equally effective against infections caused by Staphylococcus aureus with ED50 values ranging from 3.5 to 25 mg/kg. Gentamicin was the most active antibiotic with ED50 values of 0.4 and 1.6 mg/kg. Ceftazidime showed excellent activity against Enterobacteriaceae with ED50 values ranging from 0.2-0.9 mg/kg for Escherichia coli strains, 1.1-13.8 mg/kg for indole positive and negative Proteus spp, and 0.1-25 for Enterobacter cloacae, Klebsiella pneumoniae and Serratia spp. Similar activity against many of the test strains of Enterobacteriaceae was found for gentamicin, cefotaxime, ceftizoxime, cefmenoxime and moxalactam, although cefotiam and cefoperazone were significantly less active than ceftazidime. Ceftazidime was significantly more active than the other beta-lactam antibiotics tested against Pseudomonas aeruginosa infections with ED50 values ranging from 02-108 mg/kg. Only the aminoglycoside antibiotic gentamicin, with ED(50,S) 0.6-6.3 mg/kg, was as effective as ceftazidime. Very poor activity was found for moxalactam, cefoperazone, piperacillin, carbenicillin and mezlocillin against the majority of the test strains of Pseudomonas. The results of these in-vivo indicate that ceftazidime is a promising potential alternative to aminoglycoside antibiotics.

GR 20263, a new broad-spectrum cephalosporin with anti-pseudomonal activity.

GR 20263 is a new broad-spectrum injectable cephalosporin which is stable to most beta-lactamases. Its in vitro activities were of the same order as those of cefotaxime against most gram-negative bacteria, were clearly inferior to cefotaxime against Staphylococcus aureus, but were significantly more active against Pseudomonas aeruginosa. Against the 25 strains used, GR 20263 was significantly more active than any of the other agents tested: piperacillin, azlocillin, gentamicin, amikacin, and carbenicillin. GR 20263 protected mice against experimental infections with P. aeruginosa more effectively than other beta-lactam antibiotics; its general effectiveness in this test was comparable with gentamicin. Studies on human volunteers showed that it produces high, long-lasting blood levels, with much of the antibiotic being recovered in the urine. Intramuscular and intravenous injections were well tolerated by the volunteers, and there were no untoward side effects.