Broad-spectrum antibiotic | Wikipedia audio article


The term broad-spectrum antibiotic can refer
to an antibiotic that acts on the two major bacterial groups, gram-positive and gram-negative,
or any antibiotic that acts against a wide range of disease-causing bacteria. These medications are used when a bacterial
infection is suspected but the group of bacteria is unknown (also called empiric therapy) or
when infection with multiple groups of bacteria is suspected. This is in contrast to a narrow-spectrum antibiotic,
which is effective against only a specific group of bacteria. Although powerful, broad-spectrum antibiotics
pose specific risks, particularly the disruption of native, normal bacteria and the development
of antimicrobial resistance. An example of a commonly used broad-spectrum
antibiotic is ampicillin.==Uses==
Broad-spectrum antibiotics are properly used in the following situations:
Empirically, when the causative organism is unknown, but delays in treatment would lead
to worsening infection or spread of bacteria to other parts of the body. This occurs, for example, in meningitis, where
the patient can become fatally ill within hours if broad-spectrum antibiotics are not
initiated. For drug-resistant bacteria that do not respond
to narrow-spectrum antibiotics. In the case of superinfections, where there
are multiple types of bacteria causing illness, thus warranting either a broad-spectrum antibiotic
or combination antibiotic therapy. For prophylaxis in order to prevent bacterial
infections occurring. For example, this can occur before surgery,
to prevent infection during the operation, or for patients with immunosuppression who
are at high-risk for dangerous bacterial infections.==Bacterial targets==
Antibiotics are often grouped by their ability to act on different bacterial groups. Although bacteria are biologically classified
using taxonomy, disease-causing bacteria have historically been classified by their microscopic
appearance and chemical function. The morphology of the organism may be classified
as cocci, diplococci, bacilli (also known as “rods”), spiral-shaped or pleomorphic. Additional classification occurs through the
organism’s ability to take up the Gram stain and counter-stain; bacteria that take up the
crystal violet dye stain are referred to as “gram-positive,” those that take up the counterstain
only are “gram-negative,” and those that remain unstained are referred to as “atypical.” Further classification includes their requirement
for oxygen (ie, aerobic or anaerobic), patterns of hemolysis, or other chemical properties. The most commonly encountered groupings of
bacteria include gram-positive cocci, gram-negative bacilli, atypical bacteria, and anaerobic
bacteria. Antibiotics are often grouped by their ability
to act on different bacterial groups. For example, 1st-generation cephalosporins
are primarily effective against gram-positive bacteria, while 4th-generation cephalosporins
are generally effective against gram-negative bacteria.==Empiric antibiotic therapy==Empiric antibiotic therapy refers to the use
of antibiotics to treat a suspected bacterial infection despite lack of a specific bacterial
diagnosis. Definitive diagnosis of the species of bacteria
often occurs through culture of blood, sputum, or urine, and can be delayed by 24 to 72 hours. Antibiotics are generally given after the
culture specimen has been taken from the patient in order to preserve the bacteria in the specimen
and ensure accurate diagnosis. Alternatively, some species may be identified
through a urine or stool test.===Selection of appropriate treatment===
Clinicians often use a step-wise approach to determining appropriate empiric therapy. First, the potential diagnoses are established
(for example, lobar pneumonia) and any predisposing risk factors are determined (for example,
alcoholism puts patients at risk for Klebsiella pneumonia). Then, the most likely bacterial species for
this type of infection are identified (for lobar pneumonia in healthy adults: S. pneumonia,
H. influenzae, etc). Lastly, an antibiotic or group of antibiotics
are chosen that are reliably effective against the potential species of bacteria (for example
in lobar pneumonia, levofloxacin covers the majority of relevant bacteria). Clinicians often aim to choose empiric antibiotic
combinations that cover all appropriate bacteria but minimize coverage of inappropriate bacteria,
as to reduce the incidence of antimicrobial resistance (see below). A community-wide antibiogram that lists the
susceptibility of community-acquired and hospital-acquired bacteria is helpful in guiding empiric therapy. Many professional organizations (for example,
the Infectious Disease Society of America) publish guidelines for empiric antibiotic
therapy, as do hospitals, with their choices tailored for their specific resistance patterns. Many of these guidelines also offer guidance
on antibiotic dose and duration of therapy. Once a specific species has been identified
and its susceptibilities determined, antibiotics can be “narrowed” to a medication which targets
a more specific range of bacteria. If no specific species are identified, patients
may continue on the empiric regimen.==Risks=====Disruption of normal microbiome===
There are an estimated 10-100 trillion multiple organisms that colonize the human body. As a side-effect of therapy, antibiotics can
change the body’s normal microbial content by attacking indiscriminately both the pathological
and naturally occurring, beneficial or harmless bacteria found in the intestines, lungs and
bladder. The destruction of the body’s normal bacterial
flora is thought to disrupt immunity, nutrition, and lead to a relative overgrowth in some
bacteria or fungi. An overgrowth of drug-resistant microorganisms
can lead to a secondary infection such as Clostridium difficile (“C. diff”) or candidiasis
(“thrush”). This side-effect is more likely with the use
of broad-spectrum antibiotics, given their greater potential to disrupt a larger variety
of normal human flora.===Antimicrobial resistance===After continued exposure to an antibiotic,
bacteria may develop changes in their structure or function that make them resistant to the
antibiotic. These resistant organisms will live, while
the susceptible organisms will die, leaving the population of bacteria entirely resistant
to a given antibiotics. For example, after the discovery of penicillin
and its subsequent use to treat bacterial infections, bacteria were found to have begun
producing an enzyme, penicillinase, which rendered the penicillin molecule inactive. In response to this newly-acquired resistance,
newer penicillins were produced that could not be de-activated by penicillinases. This cycle of bacteria evolving resistance
to antibiotics and necessitating the development of new antibiotics has been referred to as
a “bacterial arms race.”Some bacteria have developed resistance to multiple antibiotics,
so-called “superbugs.” Methicillin-resistant staphylococcus aureus
(MRSA) is one example, and can be life-threatening without the appropriate therapy. Other examples of emerging resistant organisms
include vancomycin-resistant enterococcus (VRE), Klebsiella pneumoniae carbapenemase
(KPC), and extended-spectrum beta-lactamase producing E coli (ESBL). In order to combat the rise of antimicrobial
resistance, antimicrobial stewardship programs have begun that focus on educating clinicians
to improve their use of antibiotics by focusing on evidence-based approaches to minimize resistance.==Examples of broad-spectrum antibiotics
==In humans: Aminoglycosides (except for streptomycin)
Ampicillin Amoxicillin
Amoxicillin/clavulanic acid (Augmentin) Carbapenems (e.g. imipenem)
Piperacillin/tazobactam Quinolones (e.g. ciprofloxacin)
Tetracyclines Chloramphenicol
Ticarcillin Trimethoprim/sulfamethoxazole (Bactrim)In
veterinary medicine, co-amoxiclav, (in small animals); penicillin & streptomycin and oxytetracycline
(in farm animals); penicillin and potentiated sulfonamides (in horses

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