Fluoroquinolones part 2
As we studied in the previous notes, that newly synthesized
fluoroquinolones are effective against gram-positive bacteria. Their action in gram-positive bacteria is
to inhibit the enzyme called Topoisomerases
(type 4).
The main function of Topoisomerase type 4 is unlinking the
bacterial DNA after the replication process. After bacterial DNA replication,
the DNA coils each other and forms like a meshwork of DNA strands. This is
removed by topoisomerase type 4. It also
performs the same function of topoisomerase type 2.
So, our hero, Fluoroquinolones can also inhibit the ligase
portion of topoisomerase type 4 and exhibit the bactericidal effect.
Classification
of quinolones: (generations to generations)
1st
generation quinolones:
Nalidixic acid. It is effective against some gram-negative bacilli.
So, we can
prescribe these first-generation quinolones like nalidixic acid for
uncomplicated UTI. Because these drugs are primarily excreted by the renal
system.
2nd
generation quinolones:
These are
called fluoroquinolones.
Examples
include ciprofloxacin, norfloxacin, ofloxacin.
Among these norfloxacin have very little
bioavailability. They are not readily absorbed. They are not used
anymore.
These drugs
are effective against most of the types of gram-negative bacilli, and some
gram-positive cocci though they are not effective against streptococcus pneumonia or pneumococcus.
These drugs are effective against some intracellular atypical organisms like Chlamydia, mycoplasma, etc.
3rd
generation quinolones:
An example
of this class is Levofloxacin.
Levofloxacin is the L-isomer of ciprofloxacin. They are effective against more
gram-negative bacilli, more gram-positive cocci, and some intracellular
atypical organisms.
THEY ARE EFFECTIVE AGAINST THE STREPTOCOCCUS
PNEUMONIA AND PNEUMOCOCCUS.
They belong
to the group called respiratory
quinolones.
4th
generation quinolones:
An example
of this class is moxifloxacin.
They are
most effective against many types of gram-negative bacilli, gram-positive
cocci, gram-positive bacilli. They are also effective against anaerobic
organisms.
So, the Levofloxacin and moxifloxacin
are called Respiratory
Quinolones.
Uses of ciprofloxacin:
Very effective against the Enterobacteriaceae,
traveler’s diarrhea by E.coli.
This
ciprofloxacin fails on
MRSA, pneumococcus, enterococcus, streptococcus.
This drug
may be useful in patients who may develop pseudomonas aeruginosa infection
after being affected with cystic fibrosis in the lungs. This drug does not come
under respiratory quinolones as they are only effective against very few
microbes causing a lung infection.
General contraindication: should not be used on people under
the age of 18. When tested in animals, it showed breaking of joint cartilages
causing arthropathy. However, it is used in patients under 18, who are suffering
from cystic fibrosis to prevent the pseudomonas aeruginosa infection as this
pseudomonas infection may cause death to those patients.
0 Comments