Unfortunately, as the need has grown in recent years, development of novel antibiotics has slowed. Several of the largest pharmaceutical companies have abandoned research and development in this area because of diminished success and profits; the resulting reduction in new drug introductions is shown in the figure below, which shows new systemic antibacterial agents approved by the FDA per 5-year period through 2012. Several new antimicrobial agents have been approved between 2013 and 2015; however, most are slight modifications of existing drugs. Some novel targets are under investigation. For example, tarocin was found to successfully inhibit teichoic acid, a structure essential for bacterial cell wall synthesis. When combined with a β-lactam antibiotic in a mouse model, tarocin effectively killed methicillin-resistant strains of Staphylococcus aureus that were resistant to either agent alone.
Decline in the number of new systemic antibacterial drugs approved by the FDA over a 30-year period. (Reproduced, with permission, from Boucher HW et al: 10 × '20 progress-development of new drugs active against Gram-negative bacilli: An update from the Infectious Diseases Society of America. Clin Infect Dis 2013;56:1685. By permission of Oxford University Press on behalf of the Infectious Diseases Society of America. Modified, with permission, from Spellberg B et al: Trends in antimicrobial drug development: Implications for the future. Clin Infect Dis 2004;38:1279. By permission of Oxford University Press.)
Camille E. Beauduy, PharmD, & Lisa G. Winston, MD*
A 45-year-old man is brought to the local hospital emer-gency department by ambulance. His wife reports that he had been in his normal state of health until 3 days ago when he developed a fever and a productive cough. Dur-ing the last 24 hours he has complained of a headache and is increasingly confused. His wife reports that his medical history is significant only for hypertension, for which he takes hydrochlorothiazide and lisinopril, and that he is allergic to amoxicillin. She says that he developed a rash many years ago when prescribed amoxicillin for bron-chitis. In the emergency department, the man is febrile (38.7°C [101.7°F]), hypotensive (90/54 mmHg), tachypneic (36/min), and tachycardic (110/min). He has no signs of meningismus but is oriented only to person. A stat chest x-ray shows a left lower lung consolidation consistent with pneumonia. A CT scan is not concerning for lesions or elevated intracranial pressure. The plan is to start empiric antibiotics and perform a lumbar puncture to rule out bacterial meningitis. What antibiotic regimen should be prescribed to treat both pneumonia and meningitis? Does the history of amoxicillin rash affect the antibiotic choice? Why or why not?
The penicillins share features of chemistry, mechanism of action, pharmacology, and immunologic characteristics with cephalosporins, monobactams, carbapenems, and β-lactamase inhibitors. All are β-lactam compounds, so named because of their four-membered lactam ring.
All penicillins have the basic structure shown in Figure 43–1. A thiazolidine ring (A) is attached to a β-lactam ring (B) that carries a secondary amino group (RNH–). Substituents (R; examples shown in Figure 43–2) can be attached to the amino group.
Structural integrity of the 6-aminopenicillanic acid nucleus (rings A plus B) is essential for the biologic activity of these compounds. Hydrolysis of the β-lactam ring by bacterial β-lactamases yields penicilloic acid, which lacks antibacterial activity.
A. Classification