16 - Anti- infective drugs Flashcards
why/how are bacterial cells different to human cells
- unique cell wall
- diff cell membrane
- differences in DNA and protein synthesis
differences form the basis for selective toxicity of anti bacterial drugs
which drugs affect cell wall synthesis
- penicllins
- cephalosporins
which drugs affect bacterial cell membrane
- polymyxin B
- propamidine
which drugs affect bacterial protein synthesis
- aminoglycosides
- tetracyclines
- chloramphenicol
- fusidic acid
which drugs affect bacterial DNA synthesis
- fluoroquinolones
which drugs affect bacterial metabolism
- sulphonamides
what are some general considerations of antibiotics
- spectrum of cover
- narrrow vs broad
- single vs combo - penetrations into the appropriate tissue
- superficial - route of administration
- side effects
- tolerability
- pregnancy/lactation
why do we do antibiotic sensitivty testing
- if bacterial infection isnt responding to antibiotic
how is a kirby-bauer A.S test conducted
when the bacteria is isolated
steps of KB antibiotic testing
- take sample of bacteria (biopsy or swab)
- put on agar plate emulsified in saline
- spread on plate
- paper disc impregnanted with antibiotics placed on top of culture
- incubated 37C for 18 hrs
bacteria starting to grow across agar plate
- zone of antibiotic around each plate
anti infectives availible to optoms
- chloramphenicol
- fusidic acid
- propamidine
Chloramphenicol POM
P for acute bacterial conjunctivitis
- bacteriostaic
- broad spectrum (not effective against pseudomanas - can cause severe BK)
-resistence low - good safety profile
formulations available of chloramphenicol
- CPL 0.5% eye drops
- CPL 1% ointment
- CPL minims 0.5%
dose drops - 1 drop every 2 hours for 48 days then every 4 hours or 5 days
what is the mode of action of chloramphenicol
inhibition of bacterial protein synthesis
- CPL binds to peptidyl transferase on the 50s ribosomal subunit
- this prevents the incorporation of new amino acids ot the growing peptide chin
what isolates are associated withh bacterial conjunctivitis
- stapha
- stephe
- haemop
- pseudo
- strep
most common isolates associated with bacterial conjunctivitis ?
staph
least common: strep
Fusidic acid POM - what is it effective against
- gram +ve organisms
particularly staph A
what is fusidic acid lisenced for the treatment of
bacterial conjunctivitis
is fusidic acid an appropriate agent for acute bacterial conjunctivits in children>
why or why not
- ineffective against gram - H influenza
-most common causative pathogen in kids
formulations of fusidic acid
only 1
Fusidic acid 1% modified release eye drops POM
- twice daily
Concentration of fusidic acid in tears
Overtime, the concentration of fusidic acid in tears decline. the decline is relatively low after instillation
It is an antibiotic that doesnt really penentrate ocular tissues very readily
Comparison between chloramphenicol and fusidic acid
fusidic acid not really recommended these days BUT advantage is safe for pregancy
expensive
Polymyxin B (POM) - what does it do
- PB attatches to and interferes with the functioning of the cell membrane of aerobic gram -ve bacteria
- bacitracin inhibits synthesis of cell wal in gram +ve bacteria
OTC propamidine
not an antibiotic! disinfectant
- active against gram +ve,
- less active against gram -ve
antifungal properties
- may be used topically for minor eye conditions such as conj and bleph
Fluoroquinolones - what for
treatment for BK
Fluoroquinolones - how do they work
- inhibit DNA gyrase so prevent DNA synthesis
which bacteria are Fluoroquinolones effective against
gram negative e.g pseudomonas
broad spectrum of Fluoroquinolones
- ofloxacin
- ciproflaxacin
aminoglycosides - effective against?
- both gram + and -
how do aminoglycosides work
- inhibit protein synthesis
- bactericidal
side effects of aminoglycosides
epithelial toxicity
Tetracylines - effective against?
both gram + and -
how do Tetracylines work
- inhibit bacterial synthesis by blocking the attatchment of the transfer RNA-amino acid to the ribosome
how are Tetracylines usually delivered
- systemically - tablets
treatment of meibomiam disease
when are Tetracylines used - treatment of __
- lid margin disease
reducing the bacterial load reduces inflammation
Azithromycin - lisenced for?
trachomatous conjunctivits caused by chlamydial conjunctivitis
- acute bacterial conj.
explainn viral life cycle
- infectious agents only replicate inside living cells
- once virus binds to target cell, it releases viral DNA that is used to replicate further viruses - which exit from the cell to infect other cells
what type of virus is herpes viruses
- DNA viruses
VIRAL KERATITIS - hsv
HERPES SIMPLEX VIRUS
primary/recurrent/congenital
- mostly HVS1
- thin dentritic ulcer
- contain live virus
VIRAL KERATITIS - vzv
VARICELLA ZOSTER VIRUS
- ophthalmic shingles
- should be obvious
affects dermatome of branch of trigeminal nerve
herpes virus Cytomegalovirus - cmv
- infections with CMV can occur in immunosuppressed inidivualds e.g AIDS, post-transplant
what does cmv most commonly present in eye
- viral necrotizing retinitis
antiviral drug: acyclovir (discontinued in 2018)
action of drug
- aiclovir enters sell
- convered to aciclover monophosphate by hsv enzyme Thymidine Kinase (TK)
- enzymes add 2 more phosphates to form the active drug aciclovir trophosphate
- aclicover tiphosphate competes with 2- dGTP as a substrate for viral DNA polymerase
Antiviral drugs: Ganciclover - replacement for acyclovir
available for treatment of HSK
ganclicover eye gel
acanthamoeba
- free living amoeba
- specialised
treatment for acanthamoeba keratitis
-propamide 0.1%
and (PHMB) 0.02%
or chlorhexidine 0.02%
have acitivity against cyst form
