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anibiotics > Inhibitors of Nucleic Acid And Others > Flashcards

Inhibitors of Nucleic Acid And Others Flashcards

1
Q

Other unclassified antibiotics.?

A

Nitrofurans
Rifamycin
Metronidazole
Polymixins

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2
Q

What drugs are known as DNA synthesis inhibitors

A

Sulphonamides
Diaminopyramidines
Quinolones

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3
Q

In the past what methods and countries had activities resembling antibiotics.

A

Chaulmoogra oil (from seeds) – treatment of leprosy in India since ancient times

Mercury – treatment for syphilis since 16th century

Other topical antiseptics – too toxic for systemic use

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4
Q

What did Paul Ehrlich do?

A

Since parasites could be differentiated from tissues of the infected host by laboratory dyes, such substances might display preferential affinity for the parasites in the body as well”
(Protosil red)

First to propose need for selective toxicity….

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5
Q

Discovery of the first antibacterial agent,

A

Protosil red, a sulponamide bound to a red dye, able to stain bacteria.
Cured mice of haemolytic strep.
But no in vitro activity, in vivo (body) sulphonamide released an active agent

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6
Q

Sulphanomides, what do they do and how is this antibiotic?

A

Sulphonamides prevent folic acid (needed for purines) production and therefore DNA synth. (Bacteriostatic).bacteria cannot uptake formed folic acid, must produce!

NB: mammals revive this nutrient from diet, can’t produce!

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7
Q

What are the requirements of folic acid for DNA synth.

A

folate is converted in tetrohydrofolate (THF)

THF co-factor to nucleotides biosynthesis

can transfer CH- or CHO- groups of nucleotides precursors during synthesis

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8
Q

Sulphanomides pro’s and action/how

A

Broad spectrum bacteriostatics
Block folate synthesis
Sulph. Competes for binding
Folate depletion - fail to prod. Purine nucleotides and thymidine

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9
Q

Sulphonamides con’s and action/how?

A

Slow to work - folate deplete generation

Sometimes combined with trimethoprim , etc

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10
Q

Side effects of sulphanomides

A

Steven Johnson syndrome
Inflam. Of skin and mucous membranes
Severe morbidity, can be fatal ..

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11
Q

Diaminopyrimadines : tripmethoprim

functions and interactions?

A

inhibit di-hydrofolate - late stage folate syth.

higher affinity for bacterial enzyme, than mammalian

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12
Q

trimethoprim - usage and side effects?

A

broad spectrum bacteriostatic
side effects rare
mostly used >uti, sometimes + sulphonamides
(e.g. co-trimaxazole) act on two loci in same pathway
… pobably as effective and less toxic alone!!

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13
Q

co- trimoxazole
(trimethoprim + sulphonamide)

interactions/usage and side effects?

A

both drugs synergist of one another
neither active against pseudomonas sp.
pneumonacytis - pneumonia AIDS
S.E: bone marrow toxicity same as chloramphenicol.
used rarely: only when sp. is resistant to Blactams & ciprofloxacin..

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14
Q

Quinalones: Fammily of natural synthetic broad spectrum drugs how do they work?

A

they interact and prevent bacterial DNA from unwinding and replicating

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15
Q

quinolones all share an essential structure but…

A

all have variable R groups

NB, if flouroine is this molecule: flouroquinolone

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16
Q

Quinolones: Nalidixin acid

usage and implications?

A

activity against G-ive except pseudomonas aureginosa.
well absorbed orally - exreted in urine.
used to treat UTI.
2 alterationss improved activity.

17
Q

flouroquinolones usage and implicaions?

A

active vs. G+ive & G-ive (+pseudomonas aureginosa)
oral administration
well distributed through tissues.
Concenrated in mammalian cells (intra infections) chlamydia, legionella and some mycobacteria

18
Q

flouroquinolones resistance and side effects?

A

R: recommend minimal use, held in reserve 4 resistants.

S.E: rashes, GI upset, non-specific neurological problems
• Not recommended for children or pregnant women
– Alter deposition of cartilage: damage musculoskeletal system
• Some have had to be withdrawn due to unexpected toxicity

19
Q

flouroquinalones - target?

A

gram-ive : target DNA topoisomerase type II (DNA gyrase), with topoisomerase type IV as 2nd target!
Gram +ive (opposite) - Type IV primary target, type II, 2nd.
Enzyme activity:
DNA gyrase: without it DNA supercoils.
Topoisomerase II/IV - unlinks DNA during replication.

20
Q

flouroquinolones - mode of action

A

binds (enzyme - DNA) complex.
inhibits function.
release of broken DNA strand..

21
Q

Fluoroquinolones - resistance ..?

A

• Usually due to chromosomal mutation
• Modified structure of DNA gyrase and topoisomerase IV
• Decrease membrane permeability – downregulation of outer membrane porin
proteins
• Overactive efflux pumps actively removing drug

22
Q

how do drugs manage to Inhibit DNA synthesis?

A

Interfere with DNA and RNA functions
• May be due to different pathways
• Different structure of bacterial genome
• Enzymes not possessed by mammalian cells
• Important due to universal nature of the target
• Not PDG or “different ribosomes”

23
Q

Nitrofurans - usages

A

• Nitrofurantoin – UTIs only
• Oral dosage followed by rapid excretion in the urine, also inactivated in tissues
• Active against Gram negative and positive urinary pathogens – except Proteus sp. and Pseudomonas sp.
• More active in acidic conditions

24
Q

Nitrofurans - resistance ?

A

Resistance uncommon
• Side effect – nausea
• Mode of action uncertain
• Possible the nitro compound is reduced by the organism – affects DNA

25
Q

Rifampicin - coverage and mode of action

A

Well absorbed orally - bactericidal
• One of the most effective drugs against M. tuberculosis, M. leprae, staphylococci, legionella
• Binds to β-subunit of DNA-dependant RNA polymerase – inhibits mRNA synthesis

26
Q

Rifampicin - resistance ?

A

Resistance can be rapid due to subunit mutations, encoded on the chromosome (Thus normally combine with other drugs)
• Used in the treatment of TB, leprosy, Legionnaires and staphylococcal infections (never alone see WHO recommendations)
• Prophylaxis against meningococcal and H. influenzae type b disease

27
Q

Rifampicin - side affects?

A

Side effects – hepatotoxicity can occur
• Interfere with other drugs handled by the liver – oral contraceptives
• Pigmentation can lead to red bodily secretions

28
Q

metronidazole - used for? coverage?

A

Very active against strict anaerobes
• Often used for treatment of plaque-induced gingivitis
• Mode of action uncertain – possible reduction product formed at low redox potential induce DNA strand breakage
• Resistance uncommon

29
Q

metronidazole - side effects

A

Side effects with alcohol: nausea/vomiting, vasodilatation
flushing, headaches, palpitations & tachycardia
Other side effects:
Damages DNA, Genotoxic and tumourogenic,
(while no evidence, avoid use in pregnancy!)

30
Q

Membrane active agents, what, where and how

A

Polymixins
• Polymixin B and Colisitin (E)
• Polypeptides with long hydrophobic tail
• Bind to cell membrane causing leakage of cytoplasm
• Considerable toxicity
• Systemic use limited, intra-muscular injection
• Used topically
• Active against Gram negatives except Proteus sp.
• Cystic fibrosis – installation in the lungs: Pseudomonas infection

31
Q

Diaminopyrimadines : tripmethoprim

functions and interactions?

A

inhibit di-hydrofolate - late stage folate syth.

higher affinity for bacterial enzyme, than mammalian

32
Q

trimethoprim - usage and side effects?

A

broad spectrum bacteriostatic
side effects rare
mostly used >uti, sometimes + sulphonamides
(e.g. co-trimaxazole) act on two loci in same pathway
… pobably as effective and less toxic alone!!

33
Q

co- trimoxazole
(trimethoprim + sulphonamide)

interactions/usage and side effects?

A

both drugs synergist of one another
neither active against pseudomonas sp.
pneumonacytis - pneumonia AIDS
S.E: bone marrow toxicity same as chloramphenicol.
used rarely: only when sp. is resistant to Blactams & ciprofloxacin..

34
Q

Quinalones: Fammily of natural synthetic broad spectrum drugs how do they work?

A

they interact and prevent bacterial DNA from unwinding and replicating

35
Q

quinolones all share an essential structure but…

A

all have variable R groups

anibiotics (4 decks)

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