Antimicrobial chemotherapy Flashcards
Define ‘bactericidal’
An antimicrobial that kills bacteria (eg the penicillins)
Define bacteriostatic
An antimicrobial that inhibits growth of bacteria (eg. erythromycin)
Define ‘sensitive’
An organism is considered sensitive if it inhibited or killed by levels of the antimicrobial that are available at the site of infection
Define ‘resistant’
An organism is considered resistant if it is not killed or inhibited by levels of the antimicrobial that are available at the site of infection
Define ‘MIC’
Minimal inhibitory concentration - The minimum conc. of an antimicrobial needed to inhibit visible growth of a given organism
Define ‘MBC’
Minimal bactericidal conc. - The minimum conc. of the antimicrobial needed to kill a given organism
What are the 3 routes of administration
Systemic - taken internally, either orally or parenterally
Topical - Applied to the surface, usually skin or to mucous membranes e.g. conjunctiva
Parenteral - Administered either intra-venously (iv) or intra-muscularly (im), occasionally subcutaneously
What are the 3 mechanisms of action of antimicrobial agents
Inhibition of cell wall synthesis
Inhibition of protein synthesis
Inhibition of nucleic acid synthesis
what two types of drugs are β-lactams
Penicillins and cephalosporins
β-lactam antibiotics disrupt peptidoglycan synthesis
by inhibiting the enzymes which are responsible for cross-linking the carbohydrate chains.
(Peptidoglycan is an important structural component of the bacterial cell wall and the enzymes
involved in its synthesis_
What are the two types of antimicrobials which inhibit cell wall synthesis
Glycopeptides and β-lactams
What are two common glycopeptides
Vancomycin and teicoplanin
Describe the mechanism of glycopeptides
These both act on cell wall synthesis at a stage prior to β-lactams, inhibiting assembly of
a peptidoglycan precursor. Due to their inability to penetrate the gram negative cell wall,
they act only on gram positive organisms
What route of administration must glycopeptides take (unless special circumstances)
Parenterally
What is one side effect of vancomycin
It is toxic
What are the 4 types of antimicrobial which inhibit protein syntehsis
- Aminoglycosides
- Macrolides and tetracyclines
- Oxazolidinones
- Cyclic lipopeptides
What type of bacteria are aninoglycosides useful for?
Serious gram negative Infection
What type of drug is getamicin and what is a common side effect of adminsitration
It is an Aminoglycoside and is toxic - requiring a careful dosing regime and motoring of levels
What are the uses of macrolides and tatracyclines
Useful in treatment of gram positive infections in patients who are penicillin allergic - however CANNOT BE USED WITHOUT LABORATORY TESTING
What class of drug is linezolid and what is it commonly used for?
It is an oxazolidonones (protein synthesis inhibitor). It has good activity against MRSA - Typically held in reserve for the treatment of serious infection
What class of drug is daptomycin and what it is commonly used for?
Cylic lipopeptide (protein synthesis inhibitor). Activity against gram positives in general and MRSA in particular
What are the 2 classes of drug which inhibit nucleic acid synthesis
- Trimethoprim and sulphamethoxazole
- Fluoroquinolone’s
What type of drug is ciprofloxacin? What it is commonly used for? What are some of the drawbacks of the
Ciprofloxacin is a fluoroquinolone (nucleic acid inhibitor). commonly used against gram negative organisms. Can be taken orally
Not to be used in children
Describe inherent or intrinsic resistance
In some cases all strains of a given species are naturally resistant to an antibiotic. This is usually due to inability of drug to penetrate the bacterial cell wall to exert its action
What are the 2 ways in which acquired resistance may be acquired?
- A spontaneous mutation during multiplication or bacterial DNA can result in a change in structure or function which no longer allows the antibiotic to act as its target may have changed
- The gene or genes that code for resistance can spread from organism to organism or indeed from species to species. This is by far the most common mode of the spread of resistance and genes can be carried on by plasmids (extra chromosomal packages for DNA) or on transposons (packets of DNA which insert themselves into the chromosome
What are the 2 mechanisms of resistance to β–lactam antibiotics?
β-lactamase production - β-lactamases are bacterial enzymes which cleave the β–lactam ring of the antibiotic and thus
render it inactive
Alteration of penicillin binding protein (PBP) target site - Mutations in PBP genes result in a
modified target site to which β–lactams will no longer bind