Antibiotics Flashcards
1
Q
Beta-lactam antibiotics
A
- Agents: Penicillins, Cephalosporins, Monobactams, Carbapenems
- MOA: Irreversibly inhibit enzymes that crosslink peptidoglycan polymers in cell wall > cell bursts - inhibit Penicillin Binding Proteins (PBPs)
- Effective against: gram +organisms
- Do not penetrate normal BBB
- Toxicity: Hypersensitivity reactions, Anorexia, nausea, vomiting, diarrhea (aminopenicillins), Procaine penicillin- CNS excitation
- Emergent resistent organisms HUGE problem
- Very commonly used in small and large animals
2
Q
What does the beta-lactam ring confer?
A
- Antibacterial activity
- Hydrolytic instability
- Microbial resistance (most)
3
Q
What are the 5 subgroups of penicillins?
A
- Natural
- Beta-lactamase resistant
- Aminopenicillins
- Extended-Spectrum
- Augmented
4
Q
Describe properties of beta-lactamase-resistant penicillins
A
Agents: dicloxacillin, methicillin, cloxacillin
- narrower spectrum than pen G
- must confirm sensitivity
5
Q
Describe cephalosporins
A
- 4 generations
- newer agents: greater gram - coverage, greater resistance to b-lactamase, and are more expensive (limits use in LA- cephapirin only)
- Toxicity: relatively non-toxic, cross-hypersensitivity w/ penicillin, GI disturbances, chronic use = overgrowth
- Cats: cephaloridine + furosemide (nephrotoxic): Discontinued
6
Q
2nd generation cephalosporins: Cefoxitin
A
Spectrum: Good Q1/Q2, better Q3 than 1st gen.
Uses: limit to cases supported by C&S
7
Q
1st Generation Cephalosporin: Cephalexin
A
- 1st gen
- approved ONLY for dogs
- Uses: 1st line in S.A.; treatment for bacterial pyoderma
- Spectrum: Good Q1/Q2 + some Q3
- good oral bioavailability (chewable)
8
Q
3rd Generation Cephalosporin: Ceftiofur
A
- 3rd gen
- Formulations approved in: cattle, horses, swine, chickens, turkeys, goats, dogs
- given parenteral, IM or SC, once daily protocols for most species
- good tissue distribution
- Spectrum: improved gram - over 2nd gen
- Uses: Most have limited use
9
Q
Imipenem
A
- beta lactam
- belongs to carbapenem class
- expensive (IV)
- Effective against Q1/2/4
-
limit use to highly-resistant causes
- Gram - beta-lactamase + organisms that are pen-resistant
10
Q
Cell Wall Inhibitors/Beta Lactams
A
- two major groups (penicillin, cephalosporins)
- most orally absorbed and distribute in body
- do not cross BBB
- ineffective against intracellular organisms
- Elimination: primarily renal acid secretion pump/filtration
- Penicillins are commonly used for UTIs
- Safe: little organ toxicity
- widely used in small/large animals
11
Q
Aminoglycosides: Gentamycin, Amikacin
A
-
Agents:
- Gentamycin: dogs & cats
- Amikacin: dogs, horses, neonatal foals
- bactericidal agents (concentration-dependent)
- MOA: Cause irreversible inhibition of protein synthesis by binding to ribosomal subunit (30S)
- Organ Toxicities: Nephrotoxicity, ototoxicity, neuromuscular weakness, anaphylactic reactions
- Resistance: enhanced enzymatic degradation (not amikacin), decr membrane transport, altered ribosomal binding site
- Effective against: Gram - (esp. aerobic bacilli), a few Gram +
- Drug interactions: synergystic w/ beta-lactams, loop diuretics- concurrent use may incr toxicity, Cisplatin, amphotericin B, polymixin B = incr nephrotoxin
12
Q
Tetracyclines
A
-
Agents:
- Oxytetracycline: large animals ONLY
- Doxycycline: dogs/cats, crosses BBB, hepatic, not renal elimination, DO NOT DRY PILL, erlichiosis
- bacteriostatic - (time-dependent w/ persistent effects)
- MOA: reversible inhibition of protein synthesis by binding 30S ribosomal subunit
- amphoteric compounds
- Effective against: gram +, gram - anaerobes, and Mycoplasmas
- Toxicity: GI disturbances, superinfections (cats, horses), ruminal dysfunction, pain & swelling (IM), arrhythmias (IV) shock - horses (oxytetracycline)
-
Drug interactions:
- Sucralfate- decr absorption
- Antacids/Al- bind> decrabsorption
- Warfarin: dose reduction due to decrease in prothrombin
13
Q
Macrolides
A
-
Agents:
- Azithromycin: less GI effects, long T1/2 with good Fpo, effective against Toxoplasma & resistant-type R. Equi in foals
- Clindamycin
- Tylosin
- all contain a lactone ring (basic)
- MOA: Reversible inhibition of ribosomal protein synthesis (50S)
- bacteriostatic (can be -cidal at high doses); time-dependent w/ pesistent effects
- Uses: resp infections
- Effective against: gram +, few gram -, and intracellular organisms (Rickettsia and Mycoplasma spp)
- Does not cross BBB
-
Toxicity: major effects within GI system
- EXTREME CAUTION in adult horses - colitis/diarrhea
- guinea pigs and rabbits - Clostridial colitis
- Tylosin causes rectal swelling in sheep
- Drug interactions: Bind directly to many drugs, prolongs effect of warfarin, elevated digoxin levels (dogs), major cross-resistance within group
14
Q
Phenicols
A
-
Agents:
- Chloramphenicol: NOT APPROVED IN FOOD ANIMALS
- Florfenicol: derivative of chloramphenicol that is approved for use in FOOD ANIMALS
- MOA: reversible inhibitor of ribosomal protein synthesis (50S)
- Bacteriostatic
- All are organic bases
- Crosses BBB
- Toxicity: - GI disturbances esp. cats, reduced liver metabolism, decr clearance, b.m. suppression
- Drug Interactions: Aspirin - decr hepatic metabolism, may prolong ketamine/midazolam effects, may delay hepatic metabolism of lidocaine
15
Q
Potentiated Sulfonamides
A
- Agents: Sulfamethoxazole/Trimethopri, trimethoprim/sulfadiazine
- Bacteriocidal combo of two drugs > dual block of folic acid synthetic pathway
- MOA: interfere w/ folic acid synthesis necessary for pyramidine synthesis (DNA precursors)
- Effective against: gram + and gram - (not Pseudomonas or B. Fragilis)
- Toxicity: local tissue irritation, irreversible KCS, renal crystallization, idiosyncratic immune reactions, hypersensitivity, IMHA (rare)
- Drug Interactions: -Disrupt protein binding/renal tubular secretion of acidic drugs (e.g. Penicillins, barbiturates, phenylbutazone), antagonized by procaine (PABA), oral antacids reduce absorption
