Miscellaneous Antibiotics Flashcards
What is the MOA of tetracyclines?
They reversibly bind the 30S ribosome and prevent elongation of the polypeptide by blocking the addition of amino acids.
How does resistance to tetracyclines occur?
- Efflux pumps
- Enzyme inactivation
- Ribosomal protection
What are the pharmokinetics of tetracyclines?
Bacteriostatic
***Bactericidal when present at high concentrations against very susceptible organisms
What are drugs in the tetracycline class?
Tetracycline
Doxycycline
Tigecycline
What is the Gram + spectrum of action of tetracyclines?
- Staphylococcus aureus (primarilyMSSA)
- Streptococcuspneumoniae–PSSP (doxycycline – 83% susceptible)
- Bacillus spp, Listeria spp,Nocardia spp
What is the Gram - spectrum of action of tetracyclines?
- N.gonorrhea and meningitidis
- Haemophilus influenzae (90% susceptible)
- Haemophilus ducreyi(chancroid)
- Campylobacter jejuni
- Helicobacter pylori
- Vibrio cholerae, Vibrio vulnificus
- Burkholderiapseudo mallei
What are the holes in coverage of tigecycline?
Proteus
Pseudomonas
What is the spectrum of activity of tigecycline?
Has a wide spectrum of action with notable ones bing MRSA, VRE, S. maltophilia
Gram-Negative Aerobes • Acinetobacter baumannii • Aeromonas hydrophila • Citrobacter spp. • Escherichia coli • Klebsiella spp. • Serratia marcescens • Stenotrophomonas maltophilia • NOT Proteus spp or Pseudomonas aeruginosa
Gram-Positive Aerobes
• Staphylococcus aureus • MSSA, MRSA
• Enterococcus spp • VRE, VSE
Anaerobes
• Clostridium perfringens
• Bacteroides spp
What should tigecycline NOT be used for?
NOT for bacteremias or UTIs
How are the tetracyclines best absorbed?
On an empty stomach
What is the administration method of tetracycline and demeclocycline?
Oral
What is the administration method of doxycycline?
IV and oral
What is the administration method of tigecycline?
IV only
Why aren’t tetracyclines a good choice for UTIs?
They don’t concentrate well in the bladder
What is the CSF penetration of the tetracyclines?
Minimal
What is the penetration of the prostate by tetracyclines?
Good
Is dosage adjustment in renal failure necessary for tetracycline/demeclocycline?
Yes
Is dosage adjustment in renal failure necessary for tigecycline/doxycycline?
No. But adjustment for liver failure must be made for tigecycline
Are tetracyclines and tigecycline removed in hemodialysis?
No. Only minimally.
What are the main uses of the tetracyclines?
Respiratory Infection STDs RMSF Q fever Lyme Disease Polymicrobial infections (tigecycline)
What are the SE of tetracyclines?
Nausea
Vomiting
Hypersensitivity
Photosensitivity
Why should tetracyclines not be used in pregnant women?
Discoloration of permanent teeth and decreased bone growth in children
What is the mechanism of sulfonamides?
Inhibits dihydropteroate synthetase – which inhibits incorporation of p-aminobenzoic acid (PABA) into tetrahydropteroic acid
What are the pharmokinetics of the sulfonamides?
Bacteriostatic
What is the most frequently used sulfonamide?
Sulfamethoxazole (SMX)
What is the MOA of trimethoprim?
Inhibits dihydrofolate reductase which interferes with conversion of dihydrofolate to tetrahydrofolate
What are the PKs of trimethoprim (TMP)?
Bacteriostatic
Why is Trimethoprim-Sulfamethoxazole used?
TMP-SMX has synergistic activity which makes it bactericidal and gives it a broader spectrum of activity.
What is the MOA of TMP-SMX?
Inhibition to two different steps that lead to purine synthesis
What are the MOR to TMP-SMX?
PABA overproduction
Structural change of dihydropteroate synthetase
Plasmid mediated production of drug resistant DHPS or decreased bacterial cell wall permeability to sulfonamides
What is TMP-SMX the choice treatment for?
S. maltophilia
How is TMP-SMX administered?
Oral and IV
Is dose adjustment of TMP-SMX required in renal failure patients?
Yes
What are the clinical uses of TMP-SMX?
- Acute, chronic, or recurrent infections of the urinary tract
- Acute or chronic bacterial prostatitis
- Skin infections due to CA-MRSA
- Bacterial Sinusitis
- Nocardia **
What are the main SE of TMP-SMX?
GI tract problems (nausea, etc)
Leukopenia, thrombocytopenia
Hypersensitivity (many have a sulfa allergy)
What is the interaction of TMP-SMX and methotrexate?
Decreases the clearance of methotrexate which leads to toxicity
What is the MOA of chloramphenicol?
Binds to the 50S ribosome to prevent peptide bond formation
What are the PKs of chloramphenicol?
Bacteriostatic
What bacteria does chloramphenicol have bactericidal activity towards?
Haemophilus influenza
Streptococcus pneumoniae
Neisseria meningitidis
How does chloramphenicol resistance occur?
- Reduced uptake
- Ribosome mutation
- Acetyltransferase inactivation
Is dose adjustment for chloramphenicol required in renal failure?
No
Is dose adjustment for chloramphenicol required in liver failure?
Yes
Is chloramphenicol active against Pseudomonas?
No
Is chloramphenicol active against S. aureus or Enterococcus?
No
What are the main SE of chloramphenicol?
- Gray baby syndrome
- Bone marrow suppression
What are some of the specific urinary tract agents?
Nitrofurantoin
Methenamine
Nitrofurantoin MOA
Binds to ribosomal proteins and inhibits translation as well as bacterial respiration and pyruvate metabolism
Methenamine MOA
Converted in acid pH to ammonia and formaldehyde which is a non-specific denaturant of proteins and nucleic acids
How is nitrofurantoin resisted?
Production of nitrofuran reductase
How is methenamine resisted?
No MOR as no formaldehyde resistance has been found
What enhances nitrofurantoin absorption?
Food
Nitrofurantoin Clinical Use
Acute, uncomplicated UTIs
Methenamine Clinical Use
Suppression or prophylaxis against recurrent UTIs
Nitrofurantoin Contraindications
Do not use for:
Pyelonephritis
Complicated UTI
Methenamine Contraindications
Do not use for:
Established infections
Prophylaxis against catheter-associated UTI
Elderly and those with impaired renal function
ElNitrofurantoin Spectrum of Activity
E. coli Citrobacter, sp. Group B Streptococcus Staphylococcus saprophyticus Enterococcus (including some strains of VRE)
Methenamine Spectrum of Activity
NO antimicrobial activity
Methenamine SE
Generally well tolerated
Can have GI symptoms and a rash though
Nitrofurantoin SE
- GI intolerance
- Rashes
- Acute pulmonary symptoms – reversible hypersensitivity phenomenon