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Chapter 18

PHAR 100 Chapter Notes - Chapter 18: Pneumocystis Jirovecii, Selman Waksman, Beta-Lactamase


Department
Pharmacology and Toxicology
Course Code
PHAR 100
Professor
Bill Racz
Chapter
18

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Lesson D.1 Antibacterial, Antifungal, Antiviral and Antimalarial agents
Objectives:
- Describe the history of introduction of antibiotics
- Define and classify antibiotics
- Describe the mechanism of action of penicillin
- Describe the properties of selected penicillin’s and cephalosporin
- Describe the properties of ciprofloxacin, erythromycin, tetracyclines, chloramphenicol
and aminoglycosides
- Describe the current method for treating tuberculosis
- Describe the rationale for the combination of trimethoprim with sulfamethoxazole
- Describe the properties of antifungal agents
- Describe the properties of antiviral agents, paying special attention to the life cycle of
HIV and the rational design of drugs to combat it
- Describe the advantages and disadvantages of the use of antibiotic combinations
- General principles of the use of antimicrobial agents
- Describe the life cycle of the malaria parasite and the drugs available to combat the
parasite
History
- Paul Ehrlich (Germany, 1854) introduced the concept of chemotherapy; designed
organoarsenical drugs which lead to the creation of the cyphilis cure
- Gerhard Domagk (Germany, 1930s) synthesized sulfonamide drugs, used efficacious
against a variety of bacterial diseases
- Alexander Fleming (St. Mary’s Hospital, London, England, 1929) discovered
penicillium mold (inhibits growth of Staphylococcus aureus); penicillin was later isolated
from the mold by Florey and Chain at Oxford University and is currently used to treat
infections of gram-positive bacteria
- Selman Waksman (Rutgers University, 1943) introduced streptomycin; efficacious
treatment of tuberculosis, gram-negative microorganism target
Antibiotics
- Antibiotics a chemical substance produced by microorganisms that suppress the
growth of other microorganisms and may eventually destroy them
- Antimicrobial compounds a synthetic chemical (ie. sulfonamides)
- Gram-positive bacteria refers to microorganisms which take up the colour of stain
- Gram-negative bacteria refers to microorganisms which do not take up the colour of stain
- Resistant strains are currently emerging, this being said individuals are trying to exploit
differences between bacterial and human cells that are not distinctly obvious; this would
lead to highly selectively toxic compounds
- Classification
o Narrow spectrum gram-positive bacteria (ie. penicillin G)
o Broad spectrum gram-negative bacteria (ie. tetracyclines, chloramphenicol)
AND/OR
o Bactericidal antibiotics that destroy microorganisms (ie. penicillin G)
o Bacteriostatic - antibiotics that prevent multiplication of microorganisms as
they facilitate the immune system to destroy the invading bacteria (ie.
tetracycline)
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Penicillin (antibiotic)
- Interior of a bacterium is under high internal pressure surrounded by a rigid cell wall;
penicillin is closely related to the chemical D-alanyl-D-alanine, which is required for the
formation of a new cell wall
- By interrupting the formation of the bacterial cell wall, penicillin facilitates the formation
of a protoplast (bacterial cell without a cell wall)
- Protoplasts are fragile and can readily burst
- Selectively toxic
- Penicillin G purified from Penicillium mold; narrow spectrum (destroys mainly gram-
positive bacteria such as Pneumococccus and Streptococcus
o Treats pneumonia, middle ear infection, skin infection, meningitis, syphilis
- Penicillin V semisynthetic group of penicillins; more acid stable than penicillin G,
preferable for oral administration, higher blood levels are achieved
- Bacterial resistance to penicillin can be produced by the formation of an enzyme
penicillinase breaks down the penicillin molecule inactivating it
- Cloxacillin synthetic, resistant to the attack by penicillinase; used against penicillinase-
producing Staphylococcus aureus
- Ampicillin and Amoxacillin broader spectrum of antibacterial activity, active against
several gram-negative bacteria (ie. Escherichia coli), used to treat urinary tract infections
- Carbenicillin even broader spectrum of antibacterial activity, effective in sever
infections caused by gram-negative bacterium (ie. Pseudomonas aeruginosa)
- Augmentin a combination of amoxacillin and clavulinic acid; effective against
penicillinase-producing strains of bacteria (ie. Staphylococcus aureus and Haemphilus
influenza)
- Clavulinic acid is an inhibitor of penicillinase, it does not have antibacterial activity of
its own
- Adverse Effects: allergic reactions are common characterized by rash, diarrhea, face
and tongue swelling, eruption of itching wheels (urticarial), severe difficulty breathing,
fall in pressure, death
Cephalosporins (antibiotic)
- Similar to penicillins
- More resistant to penicillinase
- Selective inhibitors of bacterial cell wall synthesis
- Divided into four generations depending on their spectrum of antimicrobial activity:
- First Generation:
o Good against gram-positive microorganisms
o Moderate activity against gram-negative microorganisms
o Ie. Cephalothin
- Second Generation:
o Increased activity against gram-negative microorganisms
o Ie. Cefamandole
- Third Generation:
o Less active then the first generation against gram-positive microorganisms
o More active against gram-negative microorganisms
o Active against Pseudomonas aeruginosa
o Ie. Ceftriaxone (treatment of gonorrhea)
o Cefotaxime and Ceftriaxone (treatment of meningitis)
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