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[[Image: Nalidixic Acid.png|thumb|right|250px|Nalidixic Acid - The Parent Drug of the Fluoroquinolones]]
[[Image: Nalidixic Acid.png|thumb|right|250px|Nalidixic Acid - The Parent Drug of the Fluoroquinolones]]
The parent drug of the quinolone family was '''Nalidixic acid''', this was found to be very narrow spectrum. It worked well only against gram negative enterobacteriaceae and resistance quickly developed. This limited it's use now for just urinary tract infections and for treatment of ''Aeromonas salmonicida'' in fish. Due to the restricted spectrum of the quinolones fluoroquinolones were developed to increase the range. The most commonly used in practice are '''Enrofloxacin, Marbofloxacin, Danofloxacin, Difloxacin, Ibafloxacin and Orbifloxacin.'''
The parent drug of the quinolone family was '''Nalidixic acid''', this was found to be very narrow spectrum. It worked well only against gram negative enterobacteriaceae and resistance quickly developed. This limited it's use now for just urinary tract infections and for treatment of ''Aeromonas salmonicida'' in fish. Due to the restricted spectrum of the quinolones fluoroquinolones were developed to increase the range. The most commonly used in practice are '''Enrofloxacin, Marbofloxacin, Danofloxacin, Difloxacin, Ibafloxacin and Orbifloxacin.'''
These drugs also have the ability to cross animal's cell membranes through porins. This means that this group of drugs is capable of acting upon intracellular pathogens.
These drugs also have the ability to cross animal's cell membranes through porins. This means that this group of drugs is capable of acting upon intracellular pathogens.
==Spectrum of Activity==
==Spectrum of Activity==
It should be noted that they are active at very low concentrations, they don't kill protective enterococci and anaerobes, and they will inhibit aminoglycoside and beta-lactam resistant bacteria.
It should be noted that they are active at very low concentrations, they don't kill protective enterococci and anaerobes, and they will inhibit aminoglycoside and beta-lactam resistant bacteria.
==Pharmacokinetic Considerations==
==Pharmacokinetic Considerations==
* They are excreted in both the bile and urine, 70% in the bile. Urine concentrations do reach high levels and remain high up to a day after a single dose.
* They are excreted in both the bile and urine, 70% in the bile. Urine concentrations do reach high levels and remain high up to a day after a single dose.
* Some metabolites are active (such as ciprofloxacin of enrofloxacin). The formation of these active metabolites are highly species dependent as it depends upon the liver enzymes present in each species. For example the horse doesn't metabolise enrofloxacin very well.
* Some metabolites are active (such as ciprofloxacin of enrofloxacin). The formation of these active metabolites are highly species dependent as it depends upon the liver enzymes present in each species. For example the horse doesn't metabolise enrofloxacin very well.
==Side Effects and Contraindications==
==Side Effects and Contraindications==