Antibacterial Treatment of Ocular Disease Flashcards
Define Antibiotic and Antibacterial
Antibiotic - A naturally created compound produced by a microorganism that suppresses the growth/kills other microorganisms (Penicillin, tetraycycline)
Antibacterial - Any chemical, natural or synthetic that can suppress or kill other microorganisms
What is the difference between Antibiotic and Antibacterial?
Antibiotic is just the natural selection while Antibacterial is both natural and synthetic, or rather antibiotics are kind of antibacterial
Define Bacteriostatic and Bacteriocidal
Bacteriostatic - Inhibiting the organism’s growth and reproduction but not killing it; need something else to kill it
Bacteriocidal - Destroys the microorganism
Define Spectrum of Activity and give some examples of a narrow vs a broad spectrum
Based on ability of antibiotic to inhibit/kill bacteria.
Gram (+) Narrow - Penicillin, Bacitracin (typically eye meds)
Gram (-) Narrow - Aminoglycosides, Polymyxin B
Broad (+ and -) - Tetracyclines, fluroquinolones
Describe some of the general problems with antibacterials
No benefit for treating viral diseases
There are specific toxicities with each kind
Describe the general problem of resistance with antibacterials
Bacteria becoming less sensitive to an AB.
This problem of resistance is the most frequent problem with AB
Overuse of ABs has led to resistance and more rational use of ABs for treatment can slow the development
Describe the general problem of allergic sensitivity with antibacterials
A common problem with penicillin or neomycin as these are foreign to the body
May have to treat with a more toxic AB should one be allergic to another
Describe the general problem with altering the normal flora with antibacterial use
You’re destroying the good microorganisms with the bad ones, can lead to ‘super-infection’ because you’re destroying a good bacteria keeping a bad one in check
Could lead to diarrhea and other GI issues if you’re killing GI flora for example
Talk about the prophylactic use of ABs
Used as preventative treatment, but the most controversial form of AB treatment
May not be too effective and actually not reduce chance of infection
List and briefly describe the ways a microorganism can develop resistance.
Synthesizing enzyme to destroy the AB
Altering cell membrane to prevent AB entry
Altering metabolic pathway to avoid a blockade due to AB
Altering receptors to decrease AB binding
All mechanisms have common cause of resistance
Describe the difference between plasmid transfer and spontaneous mutation
Plasmid is a free floating piece of DNA that can be in the cell and incorporate or dissociate from genome, can also be transfered from bacteria to bacteria
Mutations cannot be transferred from one bacteria to another
What is the problem with sub-optimal dosing with AB?
Need a certain amount to be used or else there won’t be enough of an effect
List the factors that can encourage the development of resistance
Indiscriminate use of ABs or for the wrong indications
Delaying optimal treatment (bacteria growing exponentially)
Administration of sub-optimal dosing
Selection of the wrong AB
Inability of drug doesn’t get to site of action (topical drugs don’t make it into an intraocular infection)
Defective immune system.
Give examples of antibacterials that work via inhibiting the synthesis of bacterial cell walls.
Penicillin
Bacitracin
Cephalosporins
Bacteriocidal
Give examples of AB’s that work by causing the cell membrane to leak
Antibacterial -Polymyxin B (detergent like effect)
Antifungal - Natamycin and Amphotericin B
Give examples of AB’s that work with reversible inhibition of protein synthesis
Chloramphenicol
Tetracycline
Erythromycin
Macrolides
Bacteriostatic
Give examples of AB’s that work by inhibiting the 30S ribosome in bacterial protein synthesis
Aminoglycosides (These also alter membranes and transparent to allow for further AB to enter the cell more easily and are thus both bacteriostatic and bacteriocidal)
Give examples of AB’s that act as antimetabolites
Sulfonamides (Competitively block folic acid synthesis and inhibit cell growth/replication)
Give examples of ABs that block DNA gyrase and topoisomerases to ultimately disrupt DNA repair and synthesis
Fluroquinolones (Ciprofloxacin)
Describe characteristics of the ideal antibacterial agent
Selective, effective and has high therapeutic index (good effect with low toxicity)
Bactericidal over bacteriostatic
Wont’ develop resistance
Pharmacokinetics that can reach a high serum level and maintained for a long time
Compatible with other AB’s
Abundantly available and cost effective
How many AB’s meet the criteria of the ideal AB?
Well, none really. But the topical ocular drugs are very close
Good selectivity, good AB efficacy, minimal resistance developing but large concentration can be applied, limited distribution and low total dose used to limit systemic toxicity
What is the MIC? (Minimum Inhibitory Concentration)
The minimum drug concentration that can cause a bacteriostatic effect
What is the MBC? (Minimum Bacteriocidal Concentration)
Minimum drug concentration required to cause a bacteriocidal effect
What is the problem with the use of penicillin?
Developing allergies to penicillin and its many derivatives
What is the problem with chloramphenicol?
Developing aplastic anemia
What is the problem with streptomycin (and other aminoglycosides)?
Ototoxicity (hearing loss)
What is the problem with the use of tetracycline?
Permanent tooth discoloration and bone abnormalities in children and nursing mothers
What is the problem seen with the use of some antifungals
Nephrotoxicity
What selection factors should be considered for selecting an AB?
Cost of the drug Sensitivity of the patient to AB Sensitivity of bacteria to AB Seriousness of infection General health of the patient Establish a diagnosis!
List the reasons for AB failure
Inaccurate diagnosis Resistant microorganism Inadequate drug dose Patient noncompliance Inadequate supplemental physical procedure Inadequate patient immune system
How does a gram stain look for a + bacteria versus a - bacteria?
Gram (+) - Purple
Gram (-) - Pink
In general what kinds of cocci (ball) bacteria infect the eye?
Gram (+) cocci bacteria (Streptococcus, staphylcoccus)
Niceria is an exception as a cocci (-) bacteria more commonly seen if the patient has gonorrheal disease
In general what kinds of bacilli (rod) bacteria infect the eye?
Pseudonomas and enteric bacteria
What is the very best way to determine the cause of an ocular infection?
Taking a culture swab; but timely and can cause treatment delay
Cost not always justified for a minor infection/self-limiting infection like blepharitis and conjunctivities
In what cases will you ALWAYS send for a culture due to the chronicity/severity?
Any Red Eye Neonatal ophthalmia Chronic conjunctivitis Corneal ulcers (treat this one aggressively) Orbital cellulitis Endophthalmatis
Without a culture result on hand how would you go about treatment?
Base treatment on gram stain and morphology
Avoid systemics at first unless required
Select appropriate drug
If your patient had a gram (+) cocci infecting them, what would you treat with?
Penicillins
Cephalosporins
Fluroquinolones
Bacitracin
These are the more heavy duty drugs and are bacteriocidal
Assuming you selected the proper drug for a gram (+) cocci infection but wanted an additional adjunct drug on top of it (bacteriostatic) what would you select?
Erythromycin
Chloramphenicol
Tetracyclines
If your patient had a gram (-) bacilli infecting them, what would you treat with?
Aminoglycosides
Fluroquinolones
Extended spectrum penicillins (Ticarcillin and carbenicillin)
Assuming you selected the proper drug for a gram (-) bacilli infection but wanted an additional adjunct drug on top of it (bacteriostatic) what would you select?
Chloramphenicol
Tetracyclines
What ocular related conditions are best treated with topical ocular administration?
Common ocular infections Blepharitis Conjunctivitis Corneal ulcer External hordeolum
What ocular related conditions are best treated with oral administration?
Internal hordeolum
Preseptal cellulitis
Severe conjunctivitis may require supplemental oral treatment
What topical ABs have good ocular penetration?
Chloramphenicol - Use it if only indicated
Ampicillin and other cephalosporins penetrate into the eye after systemic administration
What are some non-drug related treatments (physical procedures) that can be done for ocular disease?
Irrigate the site, especially with the site of an infection
Apply some heat to increase circulation and healing
What are the guidelines for effective antimicrobial treatment?
Establish accurate clinical and laboratory diagnosis
Select appropriate AB for the infective cause
Select the least toxic AB
Establish adequate drug levels at site of infection
Select best route of administration
Use appropriate drug regimen and for the appropriate length of time
Augment the drug therapy with the physical procedures
Describe the antibiotic activity in the healthy eye
Resident/transient bacteria present in the healthy eye
Tear film flushing out bacteria and debris also with blinking
Lysozymes in the tear layer
Some immunoglobins in tears that may inactivate organisms
WBCs that may migrate into the tears to phagocytise bacteria
The intact cornea serving as a physical barrier
