Antibiotics: basic principles of Antimicrobials Flashcards
define antibiotic, antimicrobial
antibiotic: a chemical that is produced by one microbe and has the potential to harm other microbes.
antimicrobial: any agent, natural or synthetic, that has the ability to kill or suppress microorganisms.
define bactericidal drugs vs. bacteriostatic drugs
bactericidal: drugs that are directly lethal to bacteria at clinically available concentrations.
bacteriostatic drugs: can slow bacterial growth but do not cause cell death
define selective toxicity and superinfection
selective toxicity is the ability of a drug to injure a target cell or target organism without injuring other cells or organisms that are in intimate contact with the target.
a superinfection is defined as an infection occurring after or on top of an earlier infection, especially following treatment with broad-spectrum antibiotics.
explain how antibiotics can be synthesized to achieve selective toxicity.
The selective toxicity of antibiotics is brought about by finding vulnerable targets for the drug in the microbe that do not exist in the animal (eucaryote) that is given the drug.
contrast narrow-spectrum vs. broad-spectrum antibiotics
narrow spectrum antibiotics are those that are active against only a few species of microorganisms.
broad spectrum antibiotics are those that are active against a wide variety of microbes.
**narrow spectrum drugs are generally preferred to broad spectrum drugs.
list mechanisms of drug resistance
reduction of drug concentration at it’s site of action
microbes can: cease active uptake of drugs (tetracycline and gentamicin)
microbes can: increase active export of certain drugs (tetracyclines, fluoroquinolones, and macrolides)
alteration of drug target molecules
microbes can alter the structure of drug target molecules, thus resulting in resistance
antagonist production (RARE) microbes can synthesize a compound that antagonizes drug actions.
drug inactivation
microbes can be resistant to penicillin, and the NDM-1 gene can deactivate all forms of beta-lactam antibiotics (which includes penicillins, cephalosporins, and carbapenems.
explain reasons why the use of antibiotics makes conditions favorable for the overgrowth of drug resistant microbes.
continuous use of antibiotics makes the microbes adapt and recognize the antibiotics more easily which then makes the microbes more resistant. Further, excessive use of antibiotics also promotes the overgrowth of normal flora, which possesses mechanisms for resistance. Normal flora can then transfer resistance to pathogens.
also if a drug resistant organism is present, antibiotics will create selection pressure favoring growth by killing of sensitive organisms. In doing so, they will eliminate the toxins they produce and thereby facilitate survival of the drug resistant microbe.
define selection pressure.
an agent of differential mortality or fertility that tends to make a population change genetically.
discuss use of antibiotics in agricultural products (Box 83-1)
antibiotics are used in some agricultural products, especially in poultry and livestock. this has created drug resistant bacteria, which can now infect humans. these infects pose two big threats: detriment to health, and passage of resistance genes to normal intestinal flora.
for these threats, the WHO recommended that all antibiotics used by humans be banned from use to promote growth in animals. Some countries complied and the resistance rates dropped dramatically.
Also, the FDA banned the use of enrofloxacin in chicken and turkeys in September of 2005.
explain factors to select the best antibiotic. Under what conditions would antibiotics be started before lab results are in?
factors to select the best antibiotic: effective for infection you are treating, minimal side effects, well tolerated.
if the patient has a severe infection, you may need to initiate treatment before test results are available.
be able to explain to a patient the importance of taking the whole course of antibiotics, even if he or she starts to feel better.
You must take your whole course of antibiotics so that they can do their job. Just because you feel better doesn’t mean that you should stop taking them. You don’t stop painting a picture or building a house or etc. before it’s done, right? Even if it looks good? Same principle here, they’ve got to be able to finish the job and kill all the microbes (eliminate the stronger ones) that have caused some damage in your body.
what factors in the patient (host) influence the effectiveness of antibiotics?
host defenses (goal is to suppress microbial growth so that balance is tipped in favor of the host)
infection site (an antibiotic must be present at the site of infection in a concentration greater than the MIC–can be tricky in meningitis)
age (stay away from certain meds depending on client’s age)
pregnancy (stay away from certain meds in pregnancy)
previous drug reactions– bad or allergic (avoid meds if bad or allergic reaction)
foreign materials (cardiac pacemakers, prosthetic joints/heart valves, synthetic vascular shunts)
genetic factors (know if your patient has risk factors due to genetics-- eg RBCs that are deficient in glucose-6-dehydrogenase and don't give them antibiotics that will exacerbate those risk factors--eg antibiotics that will induce red blood cell lysis) also genetics can affect the rates of metabolism.
list acceptable situations for prophylactic use of antibiotics.
Antimicrobial prophylaxis is commonly used by clinicians for the prevention of numerous infectious diseases, including herpes simplex infection, rheumatic fever, recurrent cellulitis, meningococcal disease, recurrent uncomplicated urinary tract infections in women, spontaneous bacterial peritonitis in patients with cirrhosis, influenza, infective endocarditis, pertussis, and acute necrotizing pancreatitis, as well as infections associated with open fractures, recent prosthetic joint placement, and bite wounds.
Perioperative antimicrobial prophylaxis is recommended for various surgical procedures to prevent surgical site infections.
Optimal antimicrobial agents for prophylaxis should be bactericidal, nontoxic, inexpensive, and active against the typical pathogens that can cause surgical site infection postoperatively.
