Benzylpenicillin of penicillin allergy. Use during pregnancy is generally safe. It is in the penicillin and β-lactam class of medications. Benzylpenicillin was discovered in 1929 by Alexander Fleming and came into commercial use in 1942. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost in the developing world is about US$0.24–2.72 per day. In the United States a course of treatment costs $100–200. As an antibiotic, benzylpenicillin is noted to possess effectiveness mainly against Gram-positive organisms. Some Gram-negative organisms such as "Neisseria gonorrhoeae" and "Leptospira
History of penicillin to concentrate the active substance involved, which he named penicillin, in 1928. Penicillin was the first modern antibiotic. During the next twelve years Fleming grew, distributed, and studied the original mold, which was determined to be a rare variant of "Penicillium notatum" (now "Penicillium chrysogenum"). Many later scientists were involved in the stabilization and mass production of penicillin and in the search for more productive strains of "Penicillium". Important contributors include Ernst Chain, Howard Florey, Norman Heatley, and Edward Abraham. Shortly after the discovery of penicillin, scientists found that some disease-causing pathogens display antibiotic resistance to penicillin. Research that aims