Antibiotics Flashcards
What are antibiotics?
Substances produced by
microbes, fungi, animal-based and plant-based organisms that have a powerful antibacterial, antimycotic, partially also antiviral and anti-tumour activity.
Chemotheraphy
A systematic administration of substances with an antimicrobial effect.
MIC
Minimum inhibitory concentration,
the lowest concentration of
antibiotics that inhibits the growth of microorganisms. Measured in micrograms per ml.
Superinfection
The action of antibiotics, a portion of the normal microflora will also die.
Microbes that are otherwise in
balance/inhibited, will start to grow (such as Candida albicans).
Hospital-acquired infection
An infection caused by the microbes existing in the hospital environment.
Mechanisms of actions
- Inhibit cell wall synthesis (bactericidal)
- Inhibit cell membrane functions (bactericidal)
- Inhibit microbial protein synthesis (bacteriostatic)
- Impact microbial nucleic acid metabolism (bacteriostatic)
Resistance
Microbes adapt to the substances that ae harmful to them, result of selection or adaption.
Capable of passing from one generation of bacteria to the next and from one type to another.
Reasons for failures in ab treatment
Infection caused by resistant strain.
Transfer of resistant gene from one bacteria to another.
Treatment without bacterial diagnosis.
Natural resistance
Natural barriers to certain ABs
Aquired resistance
Mutations in bacterial chromosome
Cross-resistance
Microbes resistant to one ab can be resistant to other AB with same action mechanism.
Acquisition of Antimicrobial resistance
Mutation of genes involved in normal physiological processes and cellular structures.
Transmission of resistant genes
Transformation, transduction, conjugation.
Plasmids: Extrachromosomal self-replicating elements which carry resistant genes.
Transposons: Fragments of DNA, cannot replicate themselves.
Integrons: Carried in plasmids
Tetracyclines
Bacteriostatic, prevents protein synthesis.
Resistance occurs relatively quickly.
Cross-resistance with penicillins.
Pharmacokinetics:
Well absorbed in all administration routes. Penetrate the barriers of the organism well.
Accumulate into bones, forming a stable complex with calcium -> not recommended to young animals.
Eliminated through kidneys and in bile.
Toxicity:
Irritates - oral & injection
Vomiting, pain at injection site. Animal may collapse if administrate into vein.
Horses: diarrhea and enterocolitis.
Chloramphenicol, thiamphenicol and florfenicol
Broad-spectrum, bacteriostatic, suppress the metabolism of microbes.
Chemically similar while toxicity and pharmacokinetics are different.
Chloramphenicol:
Most toxic existing ab drug, do not administer with other abs.
Do not use with barbiturates, phenylbutazone, xylazine and ketamine -> death.
Use locally due to extremely high toxicity -> eye & ear infections.
Toxicity: damages to bone marrow, suppress immune system.
Well absorbed in all adm. routes.
Thiamphenicol:
Chloramphenicol derivative, but lower toxicity and activity.
Absorbed and distributed well.
Florfenicol:
Derivate of thiamphenicol. Prolonged use may lead to bm damage.
Fluoroquinolones
Broad spectrum
Bactericidal, inhibit DNA synthesis of microbes, resistence occurs relatively quickly.
Pharmacokinetics:
Well absorbed and distributed in all adm. routes. Metabolized in liver. May lead to joint cartilage erosions -> not rec. to youngs.
Nitrofurans and nitroimidazoles
Bactericidal, toxic. Nitrofurans also carcinogenic and mutagenic. Dont use either one in farm animals.
Rational use of antibiotics
- Make sure it’s bacterial infection, ideally take a sample.
- Select one narrow spectrum ab that acts against this specific agent
- Broad spectrum abs are reserve preparations (if others are ineffective), used in case of mixed infections
- Course of treatment should have optimal duration
5.Correct doses and administration intervals - Correct combination
Complex approach in the farm
- Avoid unnecessary use of AB
- Decrease necessity to treat
- Avoid infections
- When treatment necessary, do the best
- Monitore the use of AB and antimicrobial resistance.
Penicillin
Easily hydrolysable -> main reason for inactivation. It can happen either in syringe or in stomach.
Classification:
Natural and synthetic broad spectrum penicillins
Spectrum activity:
Streptococci, staphylococci, some G+ and G- bacteria
Absorption quick when adm. into muscle or subcutaneous.
Elimination and excretion mainly with urine.
Pharmacodynamics:
Bactericidal, inhibit microbial cell wall synthesis, outcome is lysis of the cell. Primarily act against gram+.
Toxicity lowest among abs. Most common side effect is allergy, hives, hypersalivation, vomiting, cramps.
Macrolides and lincosamides
Macrolides:
Used if microbe is resistant to beta-lactam ABs. Bacteriostatic, bactericidal in large concentrations.
Pharmacokinetics, metabolism:
Absorbed well via all routes, distributed evenly. MB in liver.
Toxicity:
If adm. orally -> vomiting, diarrhea, hypersalivation, horses have most serious side effects
Lincosamides:
Chem similar to macrolides, bacteriostatic, acts against many G+ microbes.
Pharmacokinetics:
Abs. and distr. well if adm. orally or in muscle. MB in liver.
Toxicity:
Diarrhea in horses and rabbits
Cattle; lack of appetite, diarrhea, ketosis, decreased milk production
Aminoglycosides
Bactericidal, against G- and some mycobacteria and mycoplasma.
Absorptionpoor in GI, good from muscle, short half life. Excreted through kidneys, accumulates there.
Interactions:
Synergistic activity with beta-lactam abs
Toxicity:
Some of the most toxic abs. Ototoxicity (hearing and balance problems) and nephrotoxicity (kidney weakening). Treatment must be a short as possible.
Aminocyclitols: spectinomycin
Act against G-.
Less toxic compared to aminoglycosides.
Increased potency of neuromuscular blockade.
Beta-lactams
Penicillin, cephalosporins, carbapenems, monobactams
Cephalosporins
Semisynthetic ABs, bactericidal, adm. orally or parenterally
5 generations, 5th not used in vetmed.
1st gen: for streptococci, staphylococci, e. coli; narrow spectrum
2-4 broad spectrum
Low toxicity, allergy at injection site may occur.
