Pharmacology Flashcards
What is guided antibiotic therapy?
Antibiotic usage dependent on identifying the cause of infection and selecting the best antibiotic based on sensitivity testing.
What is antibiotic empirical therapy?
Best (educated) guess therapy based on clinical/epidemiological acumen. Used when therapy cannot wait for culture eg. meningitis or sepsis.
What is prophylactic therapy?
Used to prevent infection before it begins. For example healthy people exposed to surgery/injury/infectious agent or in immunocompromised individuals eg. transplantation/HIV.
What is nitrofurantoin?
A narrow spectrum antibiotic used to treat uncomplicated UTI.
Penicillin
A beta-lactam antibiotic that works on cell walls. Rapid bacterial killing and low toxicity.
Describe type I hypersensitivity reactions
Urticaria (hives), wheeze and anaphylaxis.
Describe type II hypersensitivity reactions
Haemolytic anaemia
Describe type III hypersensitivity reactions
Vasculitis
Describe type IV hypersensitivity reactions
Delayed hypersensitivity
Vancomycin
A glycopeptide that directly inhibits cell wall formation. Main use is in treatment of MRSA. Difficult to deliver, needs n IV infusion. Can cause renal toxicity, bone marrow toxicity, ototoxicity and red man syndrome. Cannot cross cell membranes so not useful against gram negative bacteria.
What are macrolides?
Antibiotics that are protein synthesis inhibitors, they inhibit the bacterial ribosome to prevent peptide chain extension. Usually bacteriostatic. Good activity against gram positive pathogens and respiratory gram negative pathogens. Highly concentrated intracellularly so useful against intracellular pathogens. Macrolides bind to and inhibit CYP-3A4. Has complex drug interactions with statins and warfarin.
What are aminoglycosides?
Gentamicin is an example. Gentamicin reversibly binds to 30S ribosome (bacteriostatic) but also has a poorly understood effect on the cell membrane (bactericidal) which is prominent at high concentrations and causes rapid killing.
What are quinolones?
DNA gyrase inhibitors that cause extensive DNA fragmentation and cell death. They are useful against a wide range of microorganisms but unfortunately resistance is becoming increasingly common.
Trimethoprim
A bacteriostatic agent that inhibits folate metabolism and terminates DNA synthesis. Principally used in UTIs. Causes (usually) mild renal toxicity- high K+.
What are the 3 principal mechanisms of resistance to antibiotics?
1) Mutation of target site. 2) Inactivating enzymes. 3)Limit access- reduced permeability or increased efflux. Genes mediating resistance can often be easily transferred.
How does beta lactam resistance occur?
1)Mutation of penicillin binding proteins. 2)Production of beta lactamases (irreversibly inactivate beta lactams enzymatically). 3) Altered outer membrane porins-reduced access of certain beta lactam to targets.
What are beta lactamases?
Enzymes that lyse and inactivate beta-lactam drugs. Commonly secreted by gram -ve bacteria and staphylococcus aureus. They confer a high level of antibiotic resistance.
What are beta lactamase inhibitors?
Drugs that effectively inhibit some beta-lactamases. They are often co-administered with penicillin antibiotics (ie. co-amoxiclav=clavulanic acid and amoxicillin) and so greatly broaden the spectrum of penicillin against gram -ve and S. aureus.
What is co-amoxiclav?
Clavulanic acid, a beta lactmase inhibitor, co-administered with amoxicillin, a penicillin antibiotic.
What is zero-order kinetics?
In drugs with zero-order kinetics the rate of elimination is constant and independent of plasma concentration- examples include ethanol and phenytoin (anti-epileptic).
Advantages and disadvantages of intravenous drug routes
Advantages: rapid immediate onset, by-passes liver, permits titration. Disadvantages: increased risk of adverse effects, requires IV access, infection, pain.
Advantages and disadvantages of intramuscular drug route
Advantages: rapid onset and shorter duration, by-passes liver. Disadvantages: absorption depends on blood flow, neurovascular damage, bleeding, pain, infection, delayed absorption in shock.
Advantages and disadvantages of subcutaneous drug route
Advantages: prolonged effect, by-passes liver, constant and slow absorption. Disadvantages: absorption depends on blood flow, pain, infection and delayed absorption in shock.
Advantages and disadvantages of enteral (oral or rectal) drug route
Advantages: convenient, safe, cheap, slower onset, prolonged but less potent. Disadvantages: Drug passes through liver, absorption rate can be highly variable, absorption is influenced by stomach contents, gastric acid interferes with absorption, uncooperative patients may not take them.
