Antibiotics

Question 1

what are some of the common antibiotics in small animals

Answer 1

• Amoxycillin (a semi-synthetic penicillin)- Clavulanic Acid (“Noroclav”, “Amoxyclav”, “Clavulox”)
• Enrofloxacin (“Baytril”)

Question 2

what are some of the common antibiotics in equines

Answer 2

• Procaine Penicllin (“Norocillin”, “Depocillin”) • Gentamicin (“Gentam”)

Question 3

what are some of the common antibiotics in production animals

Answer 3

• Oxytetracycline (“Alamycin”, “Engemycin”, “Oxytet”)

* [Procaine Penicillin (“Norocillin”, “Depocillin”, “Duplocillin”)]

Question 4

why are culture and sensitivity tests sometimes not performed prior to treatment

Answer 4

results take a while to come in (up to a week) and an animal may die int he meantime.

Question 5

explain Empirical therapy

and when it is considered

Answer 5

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

Question 6

explain some ways of selecting empirical therapy options

Answer 6

1. books and papers
2. four quadrant therapy
3. experience
   - be careful of updated science, but can sometimes prove more useful then books
   four quadrant therapy
4. other factors: licenced: on-label, off-label; WHP?; cost of Tx vs cost of animal/herd; practicalities of dosing

Question 7

list four quadrant therapy for equines, dogs, cats and ruminants

Answer 7

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

Question 8

True or false

when giving antibiotic dosages it is ok to trust the label dosage.

Answer 8

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.

Question 9

explain implications of the withholding period

Answer 9

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

Question 10

true or false

never give a lactating cow a dry cow therapy

Answer 10

TRUE
due to the milk withholding period
• lactating cow intramammaries ~1.5-3d • dry cow intramammaries ~49d

Question 11

what are some of the reasons for treatment failure?

Answer 11

• 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

Question 12

explain MIC and S/R

Answer 12

• 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.

Question 13

What are some limitations of in vitro antibiotic sensitivity testing and C & S…?

Answer 13

• 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.

Question 14

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

Answer 14

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

Question 15

Why can’t Enroflaxacin be used?

Answer 15

• there is no MRL set by the APVMA and MRLs are used to set WHP.

Question 16

If it was accidentally used

Answer 16

if it is picked up when animal is tested at slaughter farmer can receive a serious punishment
should get rid of flock

Question 17

How much efficiency dose an antibiotic typically loose per day

Answer 17

10%

Question 18

very few antibiotics go toxic after the expiry date. name one that does

Answer 18

oxytetracycline

Question 19

For penicillin, describe the mechanism and spectrum of activity, species application, route and frequency of administration, indications/contraindications for use and potential side-effects

Answer 19

• 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)

Question 20

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

Answer 20

• 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)

Question 21

For oxytetracycline, describe the mechanism and spectrum of activity, species application, route and frequency of administration, indications/contraindications for use and potential side-effects

Answer 21

• 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

Question 22

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

Answer 22

• 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)

Question 23

Define cross-resistance…eg?

Answer 23

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

Question 24

Discuss the applications & limitations of long acting ABs…

Answer 24

One off dose of LA penicillin (benzathine pen) effective only for the most sensitive bacteria

Question 25

What is the registered dose for procaine pen G for cattle?

Answer 25

12mg/kg

Question 26

What are the MICs for procain penicillin?

Answer 26

< 0.1ug/mL strep, listeria, clostridia | < 2ug/mL actinobacillus, lepto, proteus

Question 27

Eg of long acting penicillin (LAP) & [ ]...?

Answer 27

benzathine penicillin at ~5mg/kg

Question 28

Re. AB storage...If it comes from a brown bottle? eg.

Answer 28

protect it from the light eg. enro (baytril)

Question 29

Re. AB storage...Other general rules...

Answer 29

- protect from excessive heat eg. procaine penicillin | - if individually wrapped, to protect from moisture eg. clav, baytril

Question 30

Storage info is found where?

Answer 30

MIMS or packet/bottle