Organisms are said to be susceptible to<unk>  if their minimum inhibitory concentration is 32 μg/ml or less. The peak blood concentration of<unk>  following an oral dose of<unk>  100 mg is less than 1 μg/ml and may be undetectable. Its bioavailability is about 90% and the urinary excretion is 40% tissue penetration is negligible; the drug is well concentrated in the urine: 75% of the dose is rapidly metabolised by the liver, but 25% of the dose is excreted in the urine unchanged, reliably achieving levels of 200 μg/ml or more. In studies of dogs, the majority of urinary excretion is through glomerular filtration with some tubular secretion. There is also tubular absorption which is increased with urine acidification. However the activity of<unk>  is also pH dependent and mean inhibitory concentration rises sharply with increased pH above 6.<unk>  cannot be used to treat infections other than simple cystitis. At the concentrations achieved in urine (>100 μg/ml),<unk>  is a bactericide. It is bacteriostatic against most susceptible organisms at concentrations less than 32 μg/ml.<unk>  and the quinolone antibiotics are mutually antagonistic in vitro. It is not known whether this is of clinical significance, but the combination should be avoided. Resistance to<unk>  may be chromosomal or plasmid-mediated and involves inhibition of nitrofuran reductase. Acquired resistance in E. coli continues to be rare.<unk>  and its metabolites are excreted mainly by the kidneys. In renal impairment, the concentration achieved in urine may be subtherapeutic.<unk>  should not be used in patients with a creatinine clearance of 60 ml/min or less. However, a retrospective chart review may suggest<unk>  is not contraindicated in this population. Formulations There are two formulations of<unk> . *Macrocrystals - (Macrodantin, Furadantin) - 25, 50, or 100 mg capsules - taken once every 6 hours *Monohydrate/macrocrystals - (Macrobid) - 100 mg capsules - taken once every 12 hours or 2 times a day (written on prescriptions as BID, which is the last part of the trade name MacroBID). It is 75% monohydrate and 25% macrocrystals.
Nitrofurantoin
Cethromycin
Phenoxymethylpenicillin
Tetracycline
Ciprofloxacin
Oxytetracycline
Chloramphenicol
Carbenicillin