Antibiotics Flashcards
what are some of the common antibiotics in small animals
- Amoxycillin (a semi-synthetic penicillin)- Clavulanic Acid (“Noroclav”, “Amoxyclav”, “Clavulox”)
- Enrofloxacin (“Baytril”)
what are some of the common antibiotics in equines
• Procaine Penicllin (“Norocillin”, “Depocillin”) • Gentamicin (“Gentam”)
what are some of the common antibiotics in production animals
- Oxytetracycline (“Alamycin”, “Engemycin”, “Oxytet”)
* [Procaine Penicillin (“Norocillin”, “Depocillin”, “Duplocillin”)]
why are culture and sensitivity tests sometimes not performed prior to treatment
results take a while to come in (up to a week) and an animal may die int he meantime.
explain Empirical therapy
and when it is considered
initial treatment without diagnosis of the problem,
it is considered:
• frequently for rural systems –no access to microbiology
• therapy may be needed immediately-ethical considerations
• microbiological results may be unusable
• economic considerations
explain some ways of selecting empirical therapy options
- books and papers
- four quadrant therapy
- experience
- be careful of updated science, but can sometimes prove more useful then books
four quadrant therapy - other factors: licenced: on-label, off-label; WHP?; cost of Tx vs cost of animal/herd; practicalities of dosing
list four quadrant therapy for equines, dogs, cats and ruminants
Equine dogs and cats:
• aminoglycoside + (potentiated) beta-lactam
• fluoroquinolone + (potentiated) beta-lactam
• dogs/cats: “Baytril n’ Clav”
• equine: “PenGent”
Ruminants
• no standard for four quadrant therapy. Gentamicin and enrofloxacin banned.
• oxytetracycline not very good against anaerobes
• procaine penicillin not very good against Gram-ves
• Practicals of administration, eg. few oral antibiotics available, a major problem
True or false
when giving antibiotic dosages it is ok to trust the label dosage.
FALSE
it is expensive to re-register the drug and therefore many companies do not update the dose
it is important to always perform dose calculation tests.
explain implications of the withholding period
Long: drug persist for a long time, effect may be better
short: doesn’t persist for a long time or even enter that compartment
influences on antibiotic choice:
- time until slaughter
- severity of disease
- location of disease
true or false
never give a lactating cow a dry cow therapy
TRUE
due to the milk withholding period
• lactating cow intramammaries ~1.5-3d • dry cow intramammaries ~49d
what are some of the reasons for treatment failure?
- infectious disease process: the antibiotics fixed the bacteria but not the neoplasia.
- inappropriate antibiotic used e.g. gentamicin poor against streptococcalsep
- inappropriate dose
- inappropriate route of admin
- inappropriate length of treatment
- poor immune system
- could be more then one agent causing problem
- misleading C&S results from contamination
explain MIC and S/R
- MIC provides the minimum concentration of an antibiotic that will inhibit/prevent the growth of bacteria
- Susceptible/sensitive (S) or resistant (R) provides an overall prediction of whether a standard dose of antibiotic will inhibit/prevent the growth of bacteria
both are predictors of what will happen with a particular type of antibiotic at a concentration in an area.
What are some limitations of in vitro antibiotic sensitivity testing and C & S…?
- higher doses then used in C&S can sometimes overcome resistance
- shows the species variation between human plasma and patients site of infection
- the bacteria may be currently exhibiting exponential growth e.g. beta lactams work better against rapidly dividing bacteria
- the bacteria may not be under the same conditions as the laboratory-adpated isolate e.g. decreased O2 in poorly vascularised compartments- gentamicin works better in normal O2 conditions.
What are the 5 antibiotics that can not be used in milk or meat production
Which 1 of these can be used in meat production
1- Chloramphenicol 2- Enrofloxacin (or any fluroquinolone) 3- Gentamicin 4- Metronidazole 5- Tilmicosin
Tilmicosin can be used in meat production but has a 28d WHP
Why can’t Enroflaxacin be used?
- there is no MRL set by the APVMA and MRLs are used to set WHP.
If it was accidentally used
if it is picked up when animal is tested at slaughter farmer can receive a serious punishment
should get rid of flock
How much efficiency dose an antibiotic typically loose per day
10%
very few antibiotics go toxic after the expiry date. name one that does
oxytetracycline
For penicillin, describe the mechanism and spectrum of activity, species application, route and frequency of administration, indications/contraindications for use and potential side-effects
- Mechanism of action: interfere/block bacterial enzymes essential for assembly of bacterial cell wall (only effective against actively dividing bacterial colony)
- Spectrum of activity: normal-spectrum (penicillin-G); broad-spectrum (amoxicillin, ampicillin); extended-spectrum (ticarcillin)
- Species application: fairly safe in most mammals; procaine penicillin used in equine; prod. animals; mastitis in cattle
- Route & freq. of admin: Injection (IV, IM, SC) - cannot be given orally as is inactivated by gastric acid. Procaine penicillin G q24h; benzathine penicillins q5 days.
- Indications: effective against most gram +ve bacteria, mastitis in cows
- contraindications: do not give orally; avoid in hypersensitive animals; caution in rabbits, guinea pigs, snakes, birds, turtles
- Side effects: allergic reactions (mild skin rash, anaphylactic shock)
For gentamicin (aminoglycoside), describe the mechanism and spectrum of activity, species application, route and frequency of administration, indications/contraindications for use and potential side-effects
- Mechanism of action: inhibits bacterial ribosomes & prevents normal amino acid synthesis
- Spectrum of activity: highly effective against aerobic bacteria; ineffective against anaerobic bacteria
- Species application: equine med
- Route & freq. of admin: mostly parenterally (injected); some are orally administered & need to stay in intestinal tract. Once daily dose (q24h)
- Indications: highly effective against aerobic bacteria
- contraindications/side effects: neonates, animals with hypomotility, animals with intestinal disease as increased time in the gut; nephrotoxic & ototoxic (ear)
For oxytetracycline, describe the mechanism and spectrum of activity, species application, route and frequency of administration, indications/contraindications for use and potential side-effects
- Mechanism of action: bind to bacterial ribosomes & prevent tRNA linking to it -> disrupt protein synthesis
- Spectrum of activity: (bacteriostatic antimicrobial - ie does not directly kill bacteria)
- Species application: production animals
- Route & freq. of admin: injection (IM), q2-3 days
- Indications: Rickettsial disease; Mycoplasma pneumonia, chlamydial infection
- contraindications/side effects: not to give with bacteriocidals (eg. penicillins or cepholasporins); 1st few weeks of animals life (tooth issues); oral admin. -> superinfections; horses -> cardiac problems, collapse & death
For enrofloxacin (quinolone), describe the mechanism and spectrum of activity, species application, route and frequency of administration, indications/contraindications for use and potential side-effects
- Mechanism of action: interfere with DNA gyrase -> preventing bacterial DNA supercoiling (DNA storage form) -> disrupting DNA function
- Spectrum of activity: common gram -ve & gram +ve bacteria in skin, resp, urinary infections; beta-lactamase bacteria (Pseudomonas, staph, E.coli, Salmonella spp.); inconsistent against Streptococcus spp.; ineffective against anaerobic bacteria
- Species application: dogs & cats; bacterial DNA gyrase different from human gyrase thus safe for use in humans
- Route & freq. of admin: oral or injectable q24h
- Indications: common gram -ve & gram +ve bacteria in skin, resp, urinary infections; beta-lactamase bacteria (Pseudomonas, staph, E.coli, Salmonella spp.)
- contraindications/side effects: small & medium sized dogs aged 2 & 8 months; young horses; oral admin. with antacids; bubbles in joint cartilage/degeneration (growing young animals); seizures; blindness (cats)
Define cross-resistance…eg?
if a strain of bacteria is resistant to one type of penicillin, (amoxycillin), it is also resistant to most other penicillins.
eg. Staphyloccoci also many gram -ve bacteria resistant to penicillins
Discuss the applications & limitations of long acting ABs…
One off dose of LA penicillin (benzathine pen) effective only for the most sensitive bacteria
