antimicrobial drugs Flashcards
Dr Indran Balakrishnan
what are antibiotics
- substances produced by microorganisms that inhibit the growth of other organism/ microbe
what are examples of microbes that produce antibiotics
- fungi (penicillin, cephalosporium)
- gram positive bacteria rods (polymyxin)
- actinomycetes
what are the five mechanisms of antibiotics that affect pathogen
- inhibit cell wall synthesis
- inhibit protein synthesis
- inhibit nucleic acid synthesis
- affect/disrupt membrane permability
- inhibit metabolite synthesis
what are the antibiotics that inhibit cell wall synthesis
- beta lactams examples include penicilin (amoxcillin), cephalosporins, carbapenems
- beta lactams inhibit enzyme involved in peptidoglycan synthesis- bacteria cells undergoes osmotic lysis.
- beta lactams all have beta lactam ring- attachment site can vary
- glycopeptides which inhibit assembly of subunits to form peptidoglycan cell wall examples vancomycin
what bacteria organisms does beta lactam and glycopeptides not work on
- mycoplasma
- legionella
-chlamydia - do not have a cell wall
what 3 antibiotics inhibit protein synthesis
- aminoglycosides (gentamicin)
- macrolide (erythromycin)
- tetracyclines
how do macrolide antibiotics work
- prevent peptide bond being formed between adjacent amino acids in ribosome
- example erythromycin
what antibiotics cause injury to plasma membranes and how do they work
- cause changes to membrane permabillity- causes cell lysis and loss of metabolites
- polymyxin B (antibacterial) or fluconazole (antifungal)
what antibiotics inhibit synthesis of nucleic acids and how
- quinolones (ciprofloxacin)
- interfere with dna replication and transcription
how do quinolones work
- inhibit enzyme dna gyrase- DNA supercoiled in bacteria
what antibiotics inhibit metabolite synthesis
- antifolates such as trimethoprim ( inhibit synthesis of folates)
- act as competitive inhibitor
what is an example of an antibiotic which inhibits folate synthesis
trimethoprim
what is an example of an quinolones
ciprofloxacin
what are 3 factors that influence antibiotic efficacy
- distribution
- metabolism
-excretion
how do we give antibiotics
- external (topical) or systemic (blood stream)
- systemic drugs can be administered intravenously, intramuscularly or orally
what are 5 safety concerns with regards to antibiotics
- toxicity (aminoglycosids can cause reversible renal failure or irreversible deathness). liver failure, pseudomembranous colitis
- interact with other medications e.g. neutralise effects of contraceptive pill
- foetal damage/risk to pregnancy- tetracycline causes discolouration of teeth in children and may cause liver damage in pregnant women
- hypersensititvity reactions- anaphylactic reactions to penicillin
- amr
what is the action of beta lactamases
- break down beta lactam antibiotic
why are susceptible bacteria more advantagerous to resistant
- susceptible bacteria grow/divide faster than resistant bacteria- allows them to outnumber the resistant bacteria- resistant bacteria biological disadvantage
when can resistant bacteria be a biological advantage compared to susceptible
- antibiotics= selective pressure
- antibiotics kill susceptible bacteria, resistant survive
- resistant divide and multiply growing their population
- this disadvantage leads to an advantage when there is a selective pressure
how can we reduce resistant?
- reducing antibiotic spectrum- so keeping it narrow
- narrower the spectrum the less selective pressure exerted
what are examples of narrow spectrum antibiotics
trimethoprim (inhibits synthesis of folic acid)- uti
what is an example of a wide spectrum antibiotic
- cefotaxim
-ceftriaxone
-meropenem
( all beta lactams)
before a patient starts on antibiotics you need to..
-send of all lab tests
- review in 48 hours
- ask question does patient need antibiotic
when should you stop antibiotic course
-if lab test is sent and the result shows that there is no bacterial infection
- no need to complete course as theres no bacteria which would mutate
how long does most infections resolve in
5 days
what are some antibiotic resistant mechanisms
- bypass pathway- e.g. using a different pathway to synthesis a metabolite such as folate so different enzymes used
- enzyme modification (production of beta lactamases)
- altered target site
- mutations in porings which allow antibiotic to get in, mutation does not less antibiotic in cell
what is the evolution of resistance
- deletion of nucleotides
-alteration of dna (mutation) - acquisition of dna (plasmids, naked dna, transposons)
what are the major groups of antibiotics
- beta lactams
- gylcopeptides
-aminoglycosids
-macrolide - tetracycline
- quinolones
