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Antibacterial Therapy in Dermatology
Terms in this set (120)
Do all bacteria have cell walls?
No, but 90% do.
What color do gram-positive bacteria stain?
What color do gram-negative bacteria stain?
What are the functions of a bacteria's cell wall?
Cell strength, maintains cell shape, protects from osmotic lysis, can keep out certain molecules and can contribute to pathogenicity or disease
What is in a gram-positive cell wall?
Mainly peptidoglycan with teichoic acid that is embedded within the layers
What does teichoic acid do?
Important for overall rigidity of the cell wall (specifically in rod-shaped organisms)
What is in a gram-negative cell wall?
Thin peptidoglycan layer with a thick outer lipid bilayer
What is the unusual bacteria that lacks peptidoglycan?
Chlamydiae, but in all other regards, their cell walls have gram-negative structure
What factors should you consider when choosing an antimicrobial-therapy?
1. Bacteriostatic vs. bactericidal
2. Spectrum of activity
3. Dosage and route of administration
4. Potential for adverse side effects
5. Potential interactions between drugs
Inhibits growth of pathogen, but does not kill. Growth restarts after elimination of the drug
Kills their target bacteria
What does the spectrum of activity relate to?
The diversity the antibacterial has on targeted bacteria
Describe narrow-spectrum antimicrobials
Targets a specific subset of bacterial pathogens
When is it best to use a narrow-spectrum antimicrobial?
If the pathogen has been identified, to minimize collateral damage to the normal microbiota
Describe broad-spectrum antimicrobials
Targets a wide variety of bacterial pathogens
When do clinicians use broad-spectrum antimicrobials?
Frequently used as empiric therapy to cover a wide range of potential pathogens
What is the risk when using broad-spectrum antimicrobials?
They target normal microbiota too, which increases the risk of a superinfection
What is a superinfection?
Develops when the antibacterial intended for the preexisting infection kills the protective microbiota allowing another pathogen resistant to the antibacterial to proliferate and cause a secondary infection
What is the goal for dosing antimicrobials?
To select the optimum dosage that will minimize the risk of adverse effects while still achieving a good therapeutic outcome
What factors influence appropriate dose and time interval between doses?
Half-life and Cmax
What is the advantage and disadvantage of a longer half-life?
Advantage: due to convenient dosing intervals
Disadvantage: serious side effects due to drug levels remaining toxic for a longer time
The maximum plasma concentration achieved from administration of a dose
What route of administration is generally preferred?
When should you not use oral as the route of administration?
Some drugs are not absorbed easily from the GI tract into the bloodstream.
Also not the best choice if a patient is vomiting or intubated
What route of administration is used most in dermatology?
What is topical antibiotic use usually limited to?
Infections that do not involve deep skin layers
What classes of antimicrobials inhibit cell wall biosynthesis?
ß-lactams, Glycopeptides and Bacitracin
What drugs are included in the ß-lactam class?
Penicillins, Cephalosporins, Monobactams, and Carbapenems
What are some examples of penicillins?
Penicillin G and V, Aminopenicillins and Methicillins
What are penicillin G and V mainly active against?
How are aminopenicillins created?
Adding an amino group to penicillin G
T/F Aminopenicillins have increased spectrum of activity against gram-negative bacteria
True (they do have increased spectrum against gram-negative)
What are two examples of aminopenicillins?
Ampicillin and amoxicillin
Is methicillin still used today?
Bacteria that genetically alter PBPs are referred to as what? Why is it called this?
It identifies dangerous infections that are difficult to treat and pose a threat to public health
What are the 1st generation cephalosporins spectrum of activity?
Narrow spectrum with increased gram-negative spectrum
What are the 3rd/4th generation cephalosporins spectrum of activity?
Broad-spectrum against gram negative and gram positive bacteria
What is an example drug in the glycopeptide class?
What is vancomycin's spectrum of activity?
Narrow spectrum against gram-positive bacteria only, including multidrug-resistant strains
What is bacitracin's spectrum of activity?
Which drug that inhibits cell wall biosynthesis is nephrotoxic and more commonly combined with neomycin and polymyxin in topical ointments?
What drug classes are inhibitors of protein biosynthesis?
Aminoglycosides, tetracyclines, macrolides, lincosamides, and chloramphenicol (drug not a drug class)
Are aminoglycosides bacteriostatic or bactericidal? Broad-spectrum or narrow-spectrum?
Bactericidal and broad-spectrum
Are tetracyclines and macrolides bacteriostatic or bactericidal? Broad-spectrum or narrow-spectrum?
Bacteriostatic and broad-spectrum
Are lincosamides bacteriostatic or bactericidal? Broad-spectrum or narrow-spectrum? If narrow, what are they specifically against?
Narrow-spectrum; specifically against streptococcal and staphylococcal infections
Is Chloramphenicol broad-spectrum or narrow-spectrum? If narrow, what are they specifically against?
What drugs are included in the class of aminoglycosides?
What drugs are included in the class of macrolides?
Erythromycin (first macrolide made)
Azithromycin (semisynthetic macrolide)
What drugs are included in the class of lincosamides?
Lincomycin (naturally produced)
What drugs are included in the class of tetracycline?
How does chloramphenicol cause anemia?
1. Reversible, dose-dependent suppression of blood cell production (once drug is stopped, blood cell production returns to normal)
2. Idiosyncratic (specific to humans)
What class of drugs are inhibitors of membrane function?
Are polymyxins broad-spectrum or narrow-spectrum? If narrow, what are they specifically against?
Narrow-spectrum; specifically against gram-negative bacteria
Are fluoroquinolones broad-spectrum or narrow-spectrum? If narrow, what are they specifically against?
What class of drugs are inhibitors of nucleic acid synthesis?
What drugs are included in the class of fluoroquinolones?
What class of drugs are inhibitors of metabolic pathways?
Sulfonamides and trimethoprim (drug, not drug class)
Are sulfonamides bacteriostatic or bactericidal? Broad-spectrum or narrow-spectrum?
Bacteriostatic and broad-spectrum
Is trimethoprim broad-spectrum or narrow-spectrum?
What is an example of a sulfonamide?
Sulfamethoxazole used in combination with trimethoprim is used to treat what?
UTI's, ear infections and bronchitis
What are the adverse reactions and side effects of Amoxicillin?
Usually well tolerated, allergic reactions are possible.
Side effects: diarrhea and vomiting are common with oral doses
What is the mechanism of action for amoxicillin?
inhibition of bacterial cell wall synthesis
Is Amoxicillin broad-spectrum or narrow-spectrum? If narrow, what are they specifically against?
Narrow-spectrum; includes non-beta-lactamse-producing staphylococci and other gram-positive cocci and bacilli
What strains are resistant to Amoxicillin and why?
Staphylococcus strains because of beta-lactamase production
What is the mechanism of action for amoxicillin and clavulanate potassium?
Amoxicillin behaves normally and clavulanate has no antibacterial effects alone, but does cause inhibition of ß-lactamase.
Adding these two together, the spectrum is extended to include ß-lactamase-producing strains of Staphylococcus and some gram-negative strains of bacilli.
What are the adverse reactions and side effects of amoxicillin and clavulanate potassium?
Usually well tolerated, but allergic reactions are possible.
Side effects: diarrhea and vomiting are common with oral doses As the dose of clavulanate increases because of high proportion of clavulanate in some formulations, vomiting is more likely.
What precaution should clinicians use when giving oral amoxicillin and clavulanate potassium to horses and ruminants?
Know that it may produce diarrhea
What generation of cephalosporin is cephalexin?
1st generation and the most common oral cephalosporin used in vet med.
How is Cephalexin used in a dermatology?
Treating skin infections in dogs caused by S. pseudintermedius
What are the adverse reactions and side effects of cephalexin?
Generally safe, but sensitivity can occur in individuals with allergies
Side effects: gastrointestinal upset, including vomiting (most common side effect), diarrhea is also possible.
What class of drug does cefovecin (Convenia) fall into?
What generation of cephalosporin does cefovecin belong to?
3rd generation (cefovecin)
What is cefovecin active against?
Streptococci, staphylococcus spp., and some gram-negative bacilli.
More active against S. pseudintermedius than S. aureus
T/F cefovecin is active against methicillin-resistant staphylococcus
False, MRS is considered resistant to cefovecin
What are the adverse reactions and side effects of cefovecin?
Side effects: vomiting and diarrhea have been noted in dogs and cats. Injection-site irritation and transient edema have occurred with repeat injections.
Does Cefovecin have a long or short half-life and how does this effect the drug?
Has a long half-life, but this can persist in animals for at least 60 days after injection, but has not been shown to produce adverse reactions to tissues.
What are the instructions for use for Cefovecin?
That approved label in the US indicates that therapeutic concentrations are maintained for an interval of 7 days in dogs.
What class of drug does cefpodoxime proxetil fall into?
What generation of cephalosporin does cefpodoxime proxetil belong to?
3rd generation (cefpodoxime proxetil)
Cefpodoxime proxetil has better activity against what compared to other oral third-generation cephalosporins?
What is Cefpodoxime proxetil not active against?
Enterococcus spp., MRS or P. aeruginosa
When is cefpodoxime used?
For treatment of skin and other soft tissue infections in dogs
What are the adverse reactions and side effects of cefpodoxime?
Some vomiting and diarrhea can occur, but since it is administered as an inactive pro-drug, the GI reactions may be less than other oral cephalosporins.
When is chloramphenicol indicated?
To treat infections caused by a broad spectrum of organisms, including gram-positive cocci, gram-negative bacilli, anaerobic bacteria and Rickettsia.
Has been used to treat infections caused by bacteria that are resistant to other common drugs (MRS in drugs)
What are the adverse reactions and side effects of chloramphenicol?
Has a narrow margin of safety, high doses can produce toxicity in dogs and cats.
What are some precautions when using chloramphenicol?
Avoid use in pregnant or neonate animals. Avoid long-term use in cats. Veterinarians should caution pet owners about handling the medications to prevent severe consequences in humans.
What is some regulatory information for chloramphenicol?
It is illegal to administer to food animals
What class of drug does Ciprofloxacin hydrochloride fall into?
Is Ciprofloxacin bactericidal or bacteriostatic?
Are MRS strains of Staphylococcus and other multi-drug resistant bacteria likely to be resistant to Ciprofloxacin?
Yes, they are likely.
What is the oral absorption of ciprofloxacin in dogs? What about in cats?
Dogs: it may approach 74%-97%, but has been as low as 42%
Cats: it is low (22%-33%) and not effective for gram-positive bacteria
What are the adverse reactions and side effects of ciprofloxacin?
May cause occasional vomiting. High doses may cause some nausea, vomiting and diarrhea.
In horses can cause colic, enteritis and diarrhea (therefore it is not recommended)
What are adverse reactions for any fluoroquinolones?
High concentrations may cause CNS toxicity, especially in animals with renal failure. In young animals can cause arthropathy (mainly large rapidly growing dogs)
What is some regulatory information for ciprofloxacin?
Extra-label administration to food animals in the US is a violation of FDA regulations.
What class of drug does Enrofloxacin and Marbofloxacin fall into?
Fluoroquinolone (enrofloxacin and marbofloxacin)
T/F Enrofloxacin and Marbofloxacin can kill Staphylococcus spp.
True (can kill staph)
What are the side effects when using enrofloxacin in cats?
Blindness can occur due to retinal degeneration; this could be dose-related.
When should you not use enrofloxacin?
In young dogs, young foals, animals prone to seizures, and older cats
When should you not use extra-label fluoroquinolones?
In food animals; it is in violation of FDA regulations
Are the side effects from using enrofloxacin in cats seen when using marbofloxacin?
No; there have been no reports of blindness, but it has been shown that it can cause articular cartilage injury in young cats
Can you use marbofloxacin in food animals?
No it is prohibited in the US
What class of drug is clindamycin hydrochloride found in?
When is clindamycin used?
Bacterial skin infections that are gram-positive or anaerobic
What are potential side effects for clindamycin in cats?
Esophageal lesions. High doses have caused vomiting and diarrhea and may alter bacterial population in intestines.
What species should you use oral clindamycin in?
Dogs and cats; fermenting animals should not take this because of the possibility to alter bacterial population in intestines
What are potential side effects when using tetracyclines?
Renal tubular necrosis and can affect bone and teeth formation in young animals.
What are some side effects when using oral doxycycline in cats?
Can cause esophageal irritation, tissue injury and esophageal stricture. Cats should be given water or food after administration to prevent this.
What are some side effects when using doxycycline in horses?
If given IV, can be fatal. Oral is safe, but diarrhea is possible.
T/F Minocycline is not licensed for use in animals, so it should never be used
False; extra-label administration is used in dogs, cats, horses and other animals
Is there resistance when using minocycline?
Some Staphylococcus spp. and gram-negative bacilli, but some MRS species may be susceptible to minocycline that are not susceptible to doxycycline
When is use of minocycline indicated?
When tetracyclines are needed for treating bacterial infections; should be supported by C & S testing first.
What are some side effects seen when using minocycline?
Vomiting and nausea
What are some side effects seen when using Trimethoprim and Sulfamethoxazole combo in horses?
Oral administration may be associated with diarrhea; have also seen neurologic reactions such as behavior changes, gait abnormalities and hyperesthesia (effects stopped after discontinuing medication).
What are some side effects seen when using sulfas in dogs?
Type II and III hypersensitivity reactions, arthropathy, anemia, thrombocytopenia, hepatopathy, KCS, and skin reactions.
Why are dogs more sensitive to sulfas?
Because they lack the ability to acetylate sulfonamides to metabolites
What breed of dog is most sensitive to sulfas?
T/F extra-label use of sulfas is okay to use in lactating dairy cattle
False, it is prohibited
Is drug combination Ormetoprim and Sulfadimethoxine bacteriostatic or bactericidal? Narrow-spectrum or broad?
It can be both bactericidal and bacteriostatic depending on the organism. It is broad-spectrum against common gram-positive and gram-negative bacteria
What are potential side effects seen with ormethoprim in dogs?
Some CNS effects such as behavioral changes, anxiety, muscle tremors, and seizures
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