Pharmacology of Antibiotics Part 1 Flashcards
(45 cards)
Describe the general antimicrobial spectra.
Aerobic gram positive (enterococci, staph and strep)
Aerobic gram negative (enterobacter, salmonella)
Anaerobic (Bacteroides, Clostridium)
Atypical bacteria (Chlamydia, Mycoplasma)
Which antibiotics have the best activity against atypical bacteria and why?
Tetracyclines, quinolones and macrolides have the best activity against atypical bacteria because they penetrate into host cells. These bacteria are intracellular.
Define bacteriostatic. When are bacteriostatic antibiotics most effective?
Bacteriostatic drugs stop the growth of bacteria. They are more efficacious if given early when infectious burden is lower.
Describe bactericidal drugs.
Kill bacteria. May be concentration dependent (a single, very large dose may eliminate infection) or be time-dependent (killing rate does not depend on concentration. Time within the therapeutic range is important).
Give 3 examples of concentration dependent bactericidal antibiotics.
Aminoglycosides, quinolones and bacitracin.
Give 5 examples of time-dependent bactericidal antibiotics.
Beta lactams, vancomycin, isoniazid, rifampicin and metronidazole.
Give 5 examples of bacteriostatic antibiotics.
Chloramphenicol, clindamycin, macrolides, sulfonamides, tetracyclines and trimethoprim.
What are the three types of antibiotics that target the cell envelope?
Betalactams, glycopeptides and daptomycin.
What are the adverse effects of beta lactams?
Most common are hypersensitivity (urticarial drug rash and fever) and anaphylaxis.
Less common effects include C difficile colitis and seizures (occur at high doses of IV penicillin, imipenem and meropenem).
What is clavulanic acid? What is it’s mechanism of action?
Clavulanic acid is a beta lactamase inhibitor that is often administered with amoxycillin. It has a beta lactam ring which is preferentially degraded by beta lactamases, thus increasing the plasma concentration of amoxycillin.
What are the indications for use of penicillins?
Drug of choice for many infections, Eg bacterial meningitis, infections of bone, joints, skin, soft tissue, throat, bronchi and urinary tract.
Gonnorhea and syphilis.
What are the adverse effects associated with penicillins?
Generally have very low toxicity, but may cause hypersensitivity or anaphylaxis.
Describe the activity of narrow-spectrum penicillins.
Narrow spectrum penicillins are mainly active against gram positive organisms, but inactivated by beta lactamases.
Active against some gram negative, some anaerobes and some spirochetes.
What is benzylpenicillin and benzathine penicillin.?
Penicillin G. Administered parenterally and is treatment of choice for susceptible infections if parenteral treatment is warranted. benzathine penicillin is the salt form of penicillin G, and Slowly releases penicillin G to provide low but long-lasting levels after a single dose. effective against bacteria with low MICs but requiring long exposure (e.g. syphylis).
What is procaine penicillin?
IM preparation designed to extend the half life of benzyl penicillin. Provides blood levels for up to 24 hours, but this is only adequate for highly susceptible organisms.
What is phenoxymethylpenicillin?
Penicillin V. Can be given orally due to acid stability, although food impairs absorption. Intrinsically less active than benzylpenicillin. Used for treating skin infections caused by strep pyrogenes.
Which narrow-spectrum penicillins have anti staphylococcal activity? Why do they have this activity?
flucloxacillin and dicloxacillin. They have anti staphylococcal activity because they are penicillase (beta lactamase) resistant.
Describe Flucloxacillin and its rare side effect. Compare with dicloxacillin.
Flucloxacillin is rarely associated with cholestatic jaundice, particularly in older patients on prolonged therapy. May occur after oral or IV administration and up to 6 weeks after treatment. it may last for months, can be irreversible and sometimes fatal.
Dicloxacillin appears to cause less irreversible hepatotoxicity but results in more infusion phlebitis, and may be preferable for oral therapy.
How should oral dicloxacillin or flucloxacillin be taken?
Half to one hour before food. Food reduces the absorption.
Describe aminopenicillins, including spectrum, combination therapy and its side effects.
Moderate to broad spectrum: amino group increases hydrophilicity and allows entry into bacterial cells through porins of some enteric gram negative rods (E coli, S enteric) and are drugs of choice for enterococcal infections (anaerobic).
Vulnerable to betalactamases. Spectrum dramatically broadened by combining amoxycillin with clavulanic acid.
Amoxycillin and clavulanate can cause diarrhoea and hepatotoxicity, which occur more frequently than with amoxicillin alone.
Compare oral and parenteral ampicillin with amoxicillin.
Amoxicillin is better absorbed orally than ampicillin, and is not significantly affected by food, and also requires fewer oral doses per day.
When administered parenterally, they are equivalent.
Which penicillins have broad spectrum and antipseudomonal activity? How can their spectra be extended?
Piperacillin and ticarcillin are the only penicillins with activity against P aeruginosa. This is because their polar side chain increases their ability to pass through porins. High doses are required because passage through porins is slow.
They are also active against most aerobic G+ and G-, and nearly all anaerobes (not C difficile).
Spectra can be extended by combining ticarcillin with clavulanate, and piperacillin with tazobactam.
Which has the broadest activity: piperacillin or ticarcillin?
Piperacillin.
What is tazobactam and how does it work?
Tazobactam is combined with piperacillin to extend its spectrum of action. this combination is one of the most powerful antibiotics available. Tazobactam is a beta-lactamase inhibitor.
