Antimicrobial Chemotherapy Flashcards
Define MIC.
Minimal Inhibitory Concentration (minimum concentration of antimicrobial needed to inhibit visible growth of micro-organisms)
Define MBC.
Minimal Bacteriocidal Concentration (minimum concentration of antimicrobial needed to kill a given organism).
Define sensitive.
If organism is inhibited or killed by levels of the antimicrobial that are available at the site of infection.
Define resistant.
If organism is not killed or inhibited by levels of the antimicrobial that are available at the site of infection.
Define synergy.
Two cidal drugs combined or two static drugs combined (enhanced effect together)
Define antagonism.
Combination of one static and one tidal drug (less effect together).
Describe the main mechanisms of action of antibiotics.
- Inhibit cell wall synthesis
- Inhibit protein synthesis
- Inhibit nucleic acid synthesis
Give examples of antibiotics that inhibit cell wall synthesis.
Penicillins, Cephalosporins and glycopeptides
Give examples of antibiotics that inhibit protein synthesis.
Amioglycosides, macrocodes, tetracyclines, oxazolidinone, cyclic lipopeptides.
Give an example of antibiotics that inhibit nucleic acid synthesis by direct DNA synthesis inhibition.
Fluoroquinolones
Give examples of antibiotics that inhibit different steps in purine synthesis.
Nitrofurantoin, Trimethoprim and sulphamethoxazole (co-trimoxazole), Fusidic acid, Metronidazole, Clindamycin
What antibiotics are used for patients with a penicillin allergy.
Macrolides (Clarithromycin and erythromycin)
Give an example of an aminoglycoside.
Gentamicin
What type of bacteria is gentamicin effective against?
Gram negative, pseudomonas and staphylococci.
What antibiotic is used to to treat chlamydia?
Tetracyclines e.g doxycycline.
What is Trimethoprim used to treat?
UTI’s and respiratory tract infections.
What is nitrofurantoin used for?
Gram negative bacteria e.g in urinary tract infections.
Why is Ciprofloxacin contraindicated in children?
Interfere with cartilage growth.
Describe the mechanism of action of beta-lactams.
Prevent cross-linking of peptidoglycan chains by inhibiting PBP on cell wall.
What is the mechanism of action of clavulonic acid?
Inhibits beta-lactamases.
What type of bacteria do beta-lactams target?
Gram positive.
What is the first line therapy for staphylococcus aureus?
Flucloxacillin (beta lactam)
What type of antimicrobial targets gram positives only and is used for MRSA and C.difficile?
Vancomycin
Name a class of broad spectrum antibiotic which also targets anaerobes.
Carbapenems.
Name an indication for use of Nalidixic acid.
Urinary antiseptic.
Name indications for the use of metronidazole.
Intra-abdominal abscess and C.difficile.
Describe the mechanism of action of Polyenes.
Bind to ergosterol in cell wall which increases permeability.
What are polyenes used to treat?
Systemic fungal and yeast infections.
Give two examples of polyenes.
Amphotericin B and Nystatin.
Describe the mechanism of action of azoles.
Inhibit ergosterol synthesis in the fungal cell wall.
Give an example of an azole.
Fluconazole.
What are azoles used to treat?
Yeasts, filamentous fungi and aspergillus.
Describe the mechanism of action of Echinocandins.
Inhibit glucan polysaccharide synthesis.
Describe the mechanism of action of allylamines.
Suppress ergosterol synthesis at different stages in the pathway.
What are allylamines used to treat?
Dermatophytes.
What are Echincoandins used to treat?
Candida and aspergillus.
What drug is used to treat HSV and VZV?
Acliclovir
What is the mechanism of action of anti-herpes drugs?
Nucleoside analogue, converted to active form by thymidine kinase.
What combination of drugs are used in for the treatment of HIV?
- Two nucleoside analogue reverse transcriptase inhibitors.
- One non-nucleoside reverse transcriptase inhibitor (nivirapine, efavirenz) OR a protease inhibitor (saquinavir, darinavir)
What drug is sometimes used to treat RSV?
Ribavarin (nucleoside analogue)
What is used to treat chronic hep B and C?
Interferon - alpha (Pegylated to PEG)
What protein synthesis inhibitor is used to treat MRSA?
Linezolid.
What causes the toxicity associated with polyenes?
Binds to other sterols (e.g cholesterol) in cell membranes.
Describe the resistance mechanisms of Beta-lactam antibiotics.
- Beta-lactamase production
2. Alteration of penicillin binding protein target site.
Describe glycopeptide resistance.
Vancomycin resistance enterococci - peptidoglycan precursor in which vancomycin binds has altered structure.
List factors to be considered in choosing suitable anti-microbial agents.
Age, renal function, liver function, pregnancy, risk of resistance, mono therapy vs combination therapy, monitoring, dose, duration.
List common side-effects.
Allergy, GI side effects, thrush, liver toxicity, renal toxicity, neurological toxicity, haematological toxicity.
Explain the role of the lab in influencing usage in clinical practice.
- Advice on choice of antibiotic.
- Monitoring and efficacy of toxicity.
- Susceptibility testing - automated methods to calculate MIC of antibiotic.
What antibiotics inhibit purine synthesis?
Trimethoprim.
Name one drug used in HIV therapy?
Saquinavir
What is Nitrofurantoin used for?
UTIs
MRSA is treated intravenously with?
Vancomycin
Serious gram negative organisms such as E. coli should be treated intravenously with?
Gentamicin
Serious systemic fungal infections are treated with?
Amphotericin B
