Tags: Cefazolin

Toxin-Mediated Infections

Tetanus is a disease of global incidence produced by the toxin of Clostridium tetani. The risk of acquiring it increases in people > 60 years of age and in neonates, especially in Third World countries where poor sanitary conditions predispose to umbilical stump contamination. Immunization campaigns have played a crucial role in bringing about the observed decreasing incidence in the United States. The pathogenesis of tetanus involves the absorption of preformed toxin, or, less commonly, invasion of toxin-producing organisms from contaminated wounds; it may complicate surgical wounds colonized with C tetani.

Streptococcus Dysgalactiae Subspp. Equisilimis & Streptococcus Zooepidemicus: Clinical Syndromes

The symptoms of pharyngitis caused by these organisms mimic those of S pyogenes pharyngitis (Box 50-1; see also site). Poststreptococcal glomerulonephritis has been described following S dysgalactiae subspp. equisimilis and S zooepidemicus pharyngitis.

Other Gram-Positive Cocci

Viridans streptococci are part of the normal microbial flora of humans and animals and are indigenous to the upper respiratory tract, the female genital tract, all regions of the gastrointestinal tract, and, most significantly, the oral cavity. Clinically significant species that are currently recognized as belonging to the viridans group of streptococci include Streptococcus anginosus S constellatus, S cristatus, S gordonii, S intermedius, S oralis, S mitis, S mutans, S cricettus, S rattis, S parasanguis, S salivarius, S thermophilus, S sanguinis, S sobrinus, and S vestibularis. Detailed studies of the ecology of strains in the oral cavity and oropharynx have been performed.

Viridans Group Streptococci: Clinical Syndromes

Viridans streptococci have a strong association with bacterial endocarditis (see site) (Box 1). A defectiva and A adjacens were once an important cause of culture-negative endocarditis. However, current laboratory media and techniques enable these “nutritionally variant streptococci” to be identified more readily.

Streptococcus Pneumoniae

S pneumoniae may exist in humans as either a nasopharyngeal colonist or as a pathogen in one of many clinical syndromes (Box 1). Although S pneumoniae has been found in other mammals, humans are thought to be the principal reservoir. As a colonist, S pneumoniae is found in up to 40% of children and 10% of adults.

Staphylococci

Staphylococcus aureus colonizes the human skin, vagina, nasopharynx, and gastrointestinal tract. Colonization occurs shortly after birth and may be either transient or persistent. Published studies differ widely in estimates of the prevalence of S aureus carriage.

Cardiovascular Infections

Acute endocarditis is life-threatening and often requires surgical intervention. Subacute endocarditis is an indolent disease that can continue for months. Infective endocarditis remains a serious but relatively uncommon problem.

Intravascular Catheter-Related Infections

Can be life-threatening. Often prolong hospital stay, and can be complicated by metastatic lesions and bacterial endocarditis. A 53-year-old white woman was admitted to the hospital with complaints of severe shaking during infusion of her hyperalimentation solution. She had been receiving intravenous hyperalimentation for 16years for a severe dumping syndrome that prevented eating by mouth.

Anti-Infective Agent Dosing

The characteristics that need to be considered when administering antibiotics include absorption (when dealing with oral antibiotics), volume of distribution, metabolism, and excretion. These factors determine the dose of each drug and the time interval of administration. To effectively clear a bacterial infection, serum levels of the antibiotic need to be maintained above the minimum inhibitory concentration for a significant period. For each pathogen, the minimum inhibitory concentration is determined by serially diluting the antibiotic into liquid medium containing 104 bacteria per millihter.

Specific Anti-Infective Agents

Clinicians should be familiar with the general classes of antibiotics, their mechanisms of action, and their major toxicities. The differences between the specific antibiotics in each class can be subtle, often requiring the expertise of an infectious disease specialist to design the optimal anti-infective regimen. The general internist or physician-in-training should not attempt to memorize all the facts outlined here, but rather should read the pages that follow as an overview of anti-infectives. The chemistry, mechanisms of action, major toxicities, spectrum of activity, treatment indications, pharmacokinetics, dosing regimens, and cost are reviewed.