Ch. Twenty: Antimicrobial Drugs

Question 1

Penicillin

Answer 1

• destroy cell wall- prevent cross-linkin of peptidoglycans
• narrow spectrum: primarily gram postive
• 50 groups of species
• all have common core structure containing a B-lactam ring called the nucleus
• side chains are different

Question 2

Natural Penicillin

Answer 2

1. Pen G
   - requires injection
   - used against staphlycocci, streptococci and spirochetes
   - stomach acids destroy if taken orally
2. Pen V
   - taken orally
   adverse effect:
   - narrow spectrum
   - susceptibility to penicillinases: enzymes produces by many bacteria that cleave the B-lactam ring

Question 3

Semisynthetic Penicillins

Answer 3

developed in either two ways:
1. interrupt synthesis of the molecule by Penicillium and obtain only the common penicillin nucleus for use
2. can remove the side chains from the completed natural molecules and then chemically add other side chains that make them more resistant to penicillinase
- extended spectrum
ex. Methicilin (MRSA0): strains developed resistance
Oxacillin
Amplicillin: broader-spectrum; effective against gram negative bacteria

Question 4

Cephalosporin

Answer 4

• inhibit cell wall synthesis
• more widely used than any other B-lactam antibiotics
• differ slightly from penicillian but bacteria have developed B-lactamases that inactivate them
• more expensive
  adverse effect:
• cause minor gastrointestinal disturbances
• semisynathetic generations (1st, 2nd,…5th)

Question 5

Chloramphenicol

Answer 5

• inhibits formation of peptide bonds by reacting with 50S portion of prokaryotic ribosome
• less expensive, simple, and readible
• broad spectrum, small size helps penetration
• can penetrate BBB
  drug of choice: meningitis, and Thyphoid fever
  adverse effects:
• suppression of bone marrow activity- affects formation of RBCs
• Aplastic anemia

Question 6

Erythromycin

Answer 6

• acts on 50S subunit; movement of ribosome stopped along mRNA
• least toxic
• syrup or flavored
  drug of choice: for those allergic to penicillin
  adverse effect: G.I. tract problems

Question 7

Streptomycin

Answer 7

• aminoglycosides
• made up of sugars
• interfere with initial steps of protein synthesiss by changing the shape of the 30S portion which interferes with the genetic code of the mRNA to be read incorrectly
• give in low doses and with other drugs
  drug of choice: was TB (now resistant)
  adverse effects:
• hearing loss (destroy vestochochlear nerve)
• kidney failure

Question 8

Tetracycline

Answer 8

• broadest spectrum, natural, and semisynthetic
• interfere with the attachment of the tRNA carrying the amino acids to the ribosome at the 30S portion perventing the addition of a.a. to peptide chain
  drug of choice: gram positive and negative, STD (penetrate body tissues well), farmers
  adverse effects:
• diarrhea: destroy normal flora and lead to superinfections
• in children: brownish discolorations of the teeth
• in pregnant women: cause liver damage
• fetus: abnormal skull; binds to calcium ions (drawn to bones)

Question 9

Rifampin

Answer 9

• inhibit synthesis of mRNA and replication; RNA polyermase
• able to penetrate tissues
• low doses; combine
  drug of choice: mycobacterium TB and leprosy
  adverse effects: liver damage; orange-red urine, feces, saliva, sweat, and tears
• do not give to pregnant women

Question 10

Fluoroquinolones or Quinolones

Answer 10

• inhibit enzyme DNA gyrase needed for DNA replication
  adverse effects: pregnancy, teens, and elders
  drug of choice: Legionellosis, UTIs
  ex. Cipro

Question 11

Polymyxin B

Answer 11

• bactericidal antibiotic effective against gram-negative bacteria
• cellular contents leak out
  drug of choice: Pseudomonas sp.
  adverse effect:
• kidney dysfunction

Question 12

Amphotericin B

Answer 12

• fungal diseases
  drug of choice: nail infections and athlete’s foot
  adverse effect:
• GI tract, fever (chills)

Question 13

Sulpha Drugs

Answer 13

• shut down folic acid synthesis
• attack PABA
• low doses and combine
  drug of choice: UTIs and burn patients
  adverse effect:
• preganancy (3rd): harmful, causes mental defects
• jaundice and anemia

Question 14

Trimethoprim

Answer 14

• shut down folic acid synthesis
• competitive inhibitor
• can give at lower level (only 10% needed) when combined
• larger spectrum and reduce likely hood of resistant strains
  adverse effects:
• jaundice and anemia

Question 15

Antiviral Agents

Answer 15

• are nucleoside (base + sugar) no phosphate group
• add P in vivo and makes a false nucleotide
• stops DNA synthesis and decreases new virions
  ex. Zidovudine: thymine (HIV and HepB)
  Lamivudine: cytosine (HIV, HepB, and HepC)
  Gancicovir: gyanine (Herpes)
  Acyclovir: guanine (Herpes two)