Lipid A constitutes the outer monolayer of the outer membrane of Gram-negative bacteria and is essential for bacterial growth. Synthetic antibacterials were identified that inhibit the second enzyme (a unique deacetylase) of lipid A biosynthesis. The inhibitors are chiral hydroxamic acids bearing certain hydrophobic aromatic moieties. They may bind to a metal in the active site of the deacetylase. The most potent analog (with an inhibition constant of about 50 nM) displayed a minimal inhibitory concentration of about 1 microgram per milliliter against Escherichia coli, caused three logs of bacterial killing in 4 hours, and cured mice infected with a lethal intraperitoneal dose of E. coli.

MK-0991 (L-743,872) is a potent antifungal agent featuring long half-life pharmacokinetics. The pharmacokinetics of MK-0991 administered intravenously to mice, rats, rhesus monkeys, and chimpanzees is presented. Unique to MK-0991 is its consistent cross-species performance. The range of values for the pharmacokinetic parameters were as follows: clearance, 0.26 to 0.51 ml/min/kg; half-life, 5.2 to 7.6 h; and distributive volume, 0.11 to 0.27 liters/kg. The level of protein binding of MK-0991 was determined to be 96% in mouse and human serum. The compound exhibited high affinities for human serum albumin and at least two lipid components. The rationale for the selection of MK-0991 as a drug development candidate was based on its two- to threefold superior pharmacokinetic performance in chimpanzees over the performance of an otherwise equivalent analog, L-733,560. Once-daily dosing for MK-0991 is indicated by a graphical comparison of levels in the circulations of chimpanzees and mice. In a study of the pharmacokinetics of MK-0991 in mouse tissue, the organs were assayed following intraperitoneal administration. The area under the concentration-versus-time curves (AUC) segregated the tissues into three exposure categories relative to plasma. The tissues with greater exposure than that for plasma were liver (16 times), kidney (3 times), and large intestine (2 times). The exposure for small intestine, lung, and spleen were equivalent to that for plasma. Organs with lower levels of exposure were the heart (0.3 times that for plasma), thigh (0.2 times), and brain (0.06 times). Kinetically, drug was cleared more slowly from all tissues than from plasma, indicating that terminal-phase equilibrium had not been achieved by 24 h. Thus, some measure of accumulation is predicted for all tissues. Single daily doses of MK-0991 should provide adequate systemic levels of fungicidal activity as a result of its long half-life pharmacokinetics, wide distribution, and slowly accumulating concentrations in tissue.

Difficidin and oxydifficidin, two novel macrocyclic polyene lactone phosphate esters were discovered in fermentation broths of each of two strains of Bacillus subtilis: ATCC 39320 and ATCC39374. Difficidin and oxydifficidin each showed a broad spectrum of activity against aerobic and anaerobic bacteria. Manyof the susceptible aerobes and anaerobes were humanpathogens resistant to one or more antibiotics. Difficidin and oxydifficidin when administered intraperitoneally protected mice against an otherwise lethal bacteremia caused by Klebsiella pneumoniae (ED50 in mg/kg of 1.31 and 15.6 respectively).Neither difficidin nor oxydifficidin were effective when administered via the subcutaneous route.In the course of screening for new antibiotics, difficidin and oxydifficidin, two novel macrocyclic polyene lactone phosphate esters0, (Fig. 1)

The isolation of difficidin (1) and oxydifficidin (2) from fermentation broth of Bacillus subtilis ATCC39320 and the physico-chemical characterization of these labile antibiotics are described. Thestructures of the compounds represent a newclass of antibiotics, characterized as highly unsaturated 22-membered macrolide phosphates. Difficidin and oxydifficidin undergo reversible thermal isomerization to 3 and 4 respectively. Biological evaluation of the isomers is presented.The preceding paper1} describes the discovery of two novel antibiotics, diffiddin (1) and oxydifficidin (2), as products of the fermentation of Bacillus subtilis strains ATCC39320 and ATCC39374.The compounds exhibit good antibacterial activity against both aerobic and anaerobic organisms.The mode of action of difficidin is addressed in the following the paper2). During isolation work on difficidin and oxydifficidin, minor antibacterial components 3 and 4 were also isolated from fermentation broth. This paper presents the isolation and physico-chemical properties of compounds 1~4. Experimental data show that 3 and 4 arise from thermal isomerization of difficidin and oxydifficidin respectively. The in vitro and in vivo antibacterial potencies of 3 and 4 are compared to those of difficidin and oxydifficidin.Scheme 1.

As a new prodrug approach to norfloxacin (NFLX) we prepared the acetoxyalkyl carbamates of the type NFLX-CO-OCHR-OAc by the reaction of sodium or mercuric acetate on NFLX alpha-chloroalkyl carbamates. These produrgs did not have the bitter taste of NFLX. In vitro, the acetoxyethyl carbamate exhibited activity only against Staphylococcus spp. and was inactive against Gram-negative organisms. However, in the presence of serum and intestinal homogenate, esterase-catalyzed hydrolysis of the ester bond in these modified carbamates led to a cascade reaction resulting in the rapid regeneration of NFLX. At high oral doses of the prodrug, the acetaldehyde produced as a side product in the breakdown of the promoiety caused a slight decrease in alcohol metabolism in a mouse model. The bioavailability of NFLX from the acetoxyethyl carbamate was lower compared to an equivalent dose of NFLX when given as an oral suspension in rhesus monkeys, presumably because of the lower aqueous solubility of the prodrug.

MK-826 (formerly L-749,345), is a potent 1-β-methyl carbapenem with a long half-life and broad spectrum of activity. This compound is presently in phase-II clinical trials. Its activity against a number of gram-positive and gram-negative organisms was compared to those of imipenem (IPM) and eight other β-lactam agents in two in vivo murine infection models. The distribution in tissue and pharmacokinetic properties of MK-826 and ceftriaxone (CTRX) were also evaluated in CD-1 mice following a single intraperitoneal dose (10 mg/kg of body weight). In addition, concentrations in plasma as well as biliary and urinary recovery of MK-826 were compared to that of CTRX in a cannulated rat model. In a localized murine thigh infection model, MK-826 and IPM were superior to a variety of β-lactam antibiotics in reduction ofStaphylococcus aureus CFU compared with results from nontreated controls (eliminating ≥4 log10 CFU). Similar activities of IPM and MK-826 were observed in a gram-positive bacterial murine systemic infection model. While IPM demonstrated greater efficacy than MK-826 against Enterobacter cloacae (50% effective doses [ED50s] of 0.062 and 0.227 mg/kg, respectively) and Pseudomonas aeruginosa (ED50s of 0.142 and 3.0 mg/kg, respectively) systemic infections, MK-826 was 8- to 350-fold more efficacious than IPM against all other gram-negative organisms in this infection model. In mice, MK-826 demonstrated a higher peak concentration in serum (62.8 versus 42.6 μg/ml) and a larger area under the curve (AUC) (150.8 versus 90.0 μg · hr/ml) than CTRX. The concentrations of MK-826 and CTRX in serum declined slowly, with levels of 3.6 and 2.0 μg/ml remaining, respectively, at 6 h posttreatment. The rat pharmacokinetic model showed the average AUC of MK-826 to be greater than that of CTRX (284 versus 142 μg · hr/ml) following a single 10-mg/kg dose. Also, a half-life of MK-826 longer than that of CTRX (3.2 versus 2.3 h) was observed in this species. The total amount of drug excreted in the bile in 8 h was greater for CTRX (55 to 64% of the dose) than for MK-826 (6 to 12.5% of the dose). Urinary recovery was similar for both antibiotics, with 16 to 18% of the dose recovered over an 8-h period. This excellent broad-spectrum in vivo efficacy of MK-826, together with advantageous pharmacokinetics, supports the argument for its further clinical development.

Pharmacokinetic studies were conducted with norfloxacin administered by the oral and subcutaneous routes to mice and rats, and by the oral route to rhesus monkeys. The compound was moderately well absorbed following oral dosing in these animal species. Serum levels in monkeys ranged from 1.0 to 2.35 μg/ml after an oral drug dose of 25 mg/kg of animal body weight and were similar to those in mice. Serum half-life of norfloxacin in rodents and monkeys was similar to that in humans. Concentrations of norfloxacin in tissues of mice, rats and monkeys were greater than those in serum suggesting a large volume of distribution for the drug.

Cefoxitin, 3-carbamoyloxymethyl-7-a-methoxy-7-[2-(2-thienyl)acetamido]-3-cephem-4-carboxylic acid, a semisynthetic cephamycin antibiotic shown to have broad-spectrum activity in vitro, is active also in vivo against a wide variety of bacteria including penicillin-resistant staphylococci. It is, however, particularly effective against gram-negative organisms including strains of indole-positive Proteus against which cephalothin and cephaloridine are ineffective. When cefoxitin is given subcutaneously, concentrations in mouse blood, urine, and other tissues are higher than those seen for cephalothin. Higher concentrations in the blood and greater therapeutic efficacy are achieved with cefoxitin when it is given with probenecid. For this reason it is believed that cefoxitin is excreted mainly by way of the renal tubules. The data indicate that cefoxitin has potential as a therapeutically useful antibiotic.Two naturally occurring 7-methoxylated cephalosporins were described by Nagarajan et al. (10). One of these was among the three described independently by Stapley et al. (13) who designated this class of compounds cephamycins. To produce agents of greater activity and a broader spectrum, these naturally occurring antibiotics have been modified chemically (1, 5). In one analogue of cephamycin C, the aminoadipoyl sidechain at C-7 is replaced with a thienylacetyl group. This antibiotic, cefoxitin, 3 -carbamoyloxymethyl -7 -a -methoxy -7 -[2 -(2-thienyl)acetamido] -3 -cephem -carboxylic acid was shown to have broad antibacterial activity in vitro (14). The present paper describes some of the pharmacological properties of cefoxitin and its therapeutic efficacy in mice against a number of systemic infections. MATERIALS AND METHODSCrystalline cefoxitin sodium salt and a laboratory sample of cephamycin C sodium, of approximately 70% purity, were used as water solutions in these tests. Commercial samples of cephalothin, (Keflin, Lilly), cephaloridine (Loridine, Lilly), ampicillin (Penbritin-S, Ayerst), and methicillin (Staphcillin, Bristol) were solubilized aseptically with sterile water.Efficacy studies. As a standard procedure, Charles River CD1 female mice, weighing 18 to 20 grams, were infected intraperitoneally with 3 to 100 times the number of organisms that should kill 50% of the infected, nontreated animals (LD,0). Five mice were used at each of the fourfold drug concentrations tested. Therapy was given by the indicated route at the time of infection and again 6 h later. The test was terminated 7 days after infection, and the survival records of that day were used to calculate the number of organisms in the challenge LD,0 and also the ED50, i.e., the amount of antibiotic that should protect 50% of the infected, treated animals (7).For most of the test organisms the challenge preparation consisted of appropriate dilutions in brain heart infusion of broth cultures of the test strain. Some organisms, however, were used as suspensions in 5% hog gastric mucin. These were strains of Enterobacter, Proteus vulgaris, and P...