wk5 Flashcards
Classifications
of Antibioitics
Spectrum of activity
Type of microorganism it fights
Bacteria, viruses, fungi, protozoa
Goals of Antimicrobial Therapy
Kill or disable pathogens without killing the host
Considerations for Antimicrobial Therapy
Pathogen must be SUSCEPTIBLE to the drug
Drug must REACH SITE OF INFECTION in high enough [ ] to kill or inhibit the pathogen
Animal must TOLERATE high [ ] of the drug
Other factors
Client compliance
Cost
MIC
Minimum inhibitory concentration
Lowest [ ] of drug which will inhibit growth
Antimicrobial must reach infection site in high enough [ ] to exceed the MIC
SENSITIVE
MIC is low enough to not produce significant side effects in the patient
RESISTANT
MIC is so high that there are significant side effects
Antibiotic Resistance
Genetic changes Mutations of chromosomes R plasmids Additional piece of DNA responsible for antibiotic resistance “R” = “resistance” Transferred to other bacteria
Plasmid
A circle of double-stranded DNA that is separate from the chromosomes, and which is found in bacteria and protozoa. A plasmid contains genes normally not essential for cell growth or survival.
How can resistance be prevented?
Administer the appropriate dose at correct intervals, for the appropriate time, & in the appropriate manner
Educate clients importance of following the instructions, including giving for the entire prescribed time
How does Resistance happen?
Inappropriate use of antimicrobials
Residue
Presence of a drug or chemical in animal tissues or food products
Adm of drug or chemical to animal
Contamination of food
Most antimicrobial residues are not degraded by cooking or pasteurization
Exposure can cause 2 effects in humans
Hypersensitivity
Killing off of susceptible (beneficial) GIT bacteria leaving resistant (pathogenic) bacteria to proliferate
What are withdrawal times?
Use of drugs in animals intended for food must be withdrawn a specific number of days
Allows enough time for drug to be excreted
sites that antimicrobials may effect to kill or inhibit bacteria or fungi
Cell wall
Cell membrane
Inhibit protein synthesis
Interfere with critical enzymes or bind with intermediate compounds the bacteria need
Impair production of bacterial nucleic acids (RNA and DNA)
How drugs work on Cell wall
drugs work while cell wall is forming during bacterial division; bacteria are lysed as they draw in water thru osmosis
Penicillin, cephalosporins
Cell membrane
makes organism leaky
Antimicrobials can enter or cytoplasmic components can leave
Drugs work on dividing or static bacteria
Antifungals
Inhibit protein synthesis
some drugs enter the bacterium, combine with the ribosomes and disrupt normal protein production
Cell stops dividing or dies
Lincosamides, macrolides, tetracyclines, aminoglycosides
Interfere with critical enzymes or bind with intermediate compounds the bacteria need
bacterium is unable to function
Sulfonamide antibiotics
Impair production of bacterial nucleic acids (RNA and DNA):
bacterium or fungus is unable to divide; may be unable to produce critical proteins
May also attack mammalian DNA!*
Inability to reproduce, fetal abnormalities, or death
Some antifungals can cause fetal abnormalities
Quinolones work at sites on the pathogen’s nucleic acid that are not found in mammalian cells
Penicillins
Only effective against actively dividing bacteria*
Mostly gram pos and some neg
Don’t use with bacteriostatic drug!**
Penicillin is effective against
Most gram (+) and some gram (-) bacteria Bactericidal
Bactericidal
Block enzymes essential for cell wall assembly
Different enzymes are involved 🡪 different penicillins affect different enzymes
Penicillin Pharmacokinetics
Well-absorbed from GIT and injection sites (except pen-G = inj only) Hydrophilic .: does not reach therapeutic levels in the eye, brain or prostate Excreted unchanged by kidneys – also actively transported into urine .: can attain much higher [ ] in urine than blood Many gram (-) bacteria are resistant to penicillins EXCEPT at the high [ ] in the urinary tract
Penicillin Cross-resistance
If bacteria become resistant to one type of penicillin, it is also resistant to most other penicillins
β-lactamase
Some bacteria, esp Staphylococci, acquire resistance by producing an enzyme, β-lactamase**** that attacks a part of the penicillin molecule: the β-lactam ring
A penicillin can sometimes be combined with another compound to produce a modified penicillin that is resistant to the β-lactamase enzyme
Clavulanic acid plus amoxicillin = Clavamox® (veterinary) or Augmentin® (human)
Packaged individually in foil 🡪 clavulanate absorbs moisture from air
Penicillin Precautions
Hypersensitivity reactions are most common adverse reaction*
If allergic to one, is likely to be allergic to others
Cross-reactivity**
May destroy beneficial GIT bacteria allowing pathogenic bacteria to proliferate
Superinfection**
Can result in severe diarrhea and death in some species: guinea pigs, ferrets, hamsters, rabbits, snakes, birds, turtles and chinchillas
Observe withdrawal times in food animals
Penicillins are readily available to food animal producers
Cephalosporins
β-lactam antibiotic
Disrupts cell wall synthesis
Classified by generations according to when they were first developed
Cephalosporin 1st Generation
= gram (+) bacteria (Strep and Staph) Cefadroxil (Cefa-Tabs® and Cefa-Drops®) Cephalothin (Keflin®) Cephalexin (Keflex®) Cefazolin
Cephalosporin 2nd Generation
gram (-) bacteria
