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The LD50 dose for mice of Salmonella typhimurium, strain RIA, is 4.1 X 105 for animals individually housed without bedding and maintained at 25 C. It is 3.8 X 103 for animals similarly housed but kept at 5 C. An intravenous injection of 0.1 ml of Proferrin 2 hr

Cephradine, a new semisynthetic cephalosporin derivative, is 7[D(-)-2-amino-2-(1 ,4-cyclohexadien-1-yl)acetamido]-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid hydrate. The compound has a broad spectrum of antimicrobial activity in vitro. When given subcutaneously to mice, cephradine was appreciably more effective than cephalothin against infections induced by penicillinase-producing Staphylococcus, Escherichia coli, Klebsiella pneumoniae, or Enterobacter cloacae strains. Cephradine and cephaloridine possessed equivalent activity in treating infections caused by these same three gram-negative bacteria. The mean total bioactivity of cephradine in the serum of mice peaked within 30 min (59 ug/ml) after parenteral administration and was approximately threefold that of cephalothin (20 pg/ml), but less than that of cephaloridine (83 ug/ml). Nearly all of the administered cephradine (84%) and cephaloridine (70%) were excreted in the urine as the parent compounds. In contrast, only 47% (total bioactivity) of administered cephalothin was recovered, an amount that represented only 15 to 20% of the parent substance.

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Prasinomycin, a new antibiotic from the green spore streptomycete, Streptomyces prasinus , primarily inhibits the growth of gram-positive microorganisms. Like penicillin, it is effective only against growing cells. Though primarily bacteriostatic at levels about the minimal inhibitory concentration, it is bactericidal at higher levels. Neither synergism nor antagonism could be demonstrated for prasinomycin with a variety of other antibiotics. It is highly active upon subcutaneous administration to mice infected with Staphylococcus aureus, Streptococcus pyogenes C203, or Diplococcus pneumoniae . Prasinomycin has a unique prophylactic action whereby one dose protects mice against experimental infections for as long as 2 months. It is more effective against S. aureus infections in mice when administered subcutaneously 20 hr prior to infection than when given in divided doses 1 hr before and 4 hr after infection.