Rifamycin

In prelicensure controlled trials in patients with traveler’s diarrhea, rates of serum ALT elevations were similar in subjects treated with rifamycin compared to placebo or comparator agent (ciprofloxacin) and no participants developed clinically apparent liver injury. Since its approval, there have been no published reports of hepatotoxicity attributed to rifamycin. Because of its minimal absorption rifamycin is considered unlikely to cause liver injury.

J04AB03

A - Alimentary tract and metabolism

S - Sensory organs

S - Sensory organs

J - Antiinfectives for systemic use

D - Dermatologicals

Rifamycin is known to be effective against Gram-positive and Gram-negative pathogens and mycobacteria. It is very effective against _E. coli_ reporting a MIC90 of 64-128 mcg/ml without showing cross-resistance with other antimicrobial agents. The specific indication of rifamycin is extremely important as ther were previous reports that indicated a high risk factor in the generation of resistant _E. coli_ strains in patients with inflammatory bowel disease. In clinical trials, rifamycin was tested in a randomized clinical trial of travellers' coming from Mexico and Guatemala. In this trial, rifamycin was proven to significantly reduce the symptoms of travellers' diarrhea.

Rifamycins, as well as all the other members of this group, present an antibacterial mechanism of action related to the inhibition of RNA synthesis. This mechanism of action is done by the strong binding to the DNA-dependent RNA polymerase of prokaryotes. The inhibition of the RNA synthesis is thought to be related with the initiation phase of the process and to involve stacking interactions between the naphthalene ring and the aromatic moiety in the polymerase. As well, it has been suggested that the presence of zinc atoms in the polymerase allows for the binding of phenolic -OH groups of the naphthalene ring. In eukaryotic cells, the binding is significantly reduced making them at least 100 to 10,000 times less sensitive to the action of rifamycins. The members of the rifamycin family present the same mechanism of action and the structural modifications are usually related to pharmacokinetic properties as well as to the interaction with eukaryotic cells.

DU69T8ZZPA

RIFAMYCIN

Established Pharmacologic Class [EPC] - Rifamycin Antibacterial

Chemical Structure [CS] - Rifamycins

Rifamycin is a Rifamycin Antibacterial.

Drugs that are used to treat RHEUMATOID ARTHRITIS.

Substances that inhibit the growth or reproduction of BACTERIA.

Rifamycin has a very poor absorption and thus, the generation of an oral modified-release formulation using the technology of the multi-matrix structure was required for the generation of the FDA approved product. This preparation allows the delivery of the active ingredient in the distal small bowel and colon without interfering with the flora in the upper gastrointestinal tract. The multi-matrix is made by a lipophiic matrix surrounded in a hydrophilic matrix which allows for the protection of the active ingredient from dissolution in the intestinal aqueous fluids before it arrives in the cecum. All this matrix is surrounded by a gastro-resistant polymer that only desintegrate in a pH lower than 7. All this administration-customed formulation allows for a bioavailability of <0.1% and the plasma concentrations are reported to be of <2 ng/ml in patients receiving a dose of 400 mg. This confirms that the site of action of rifamycin stays in the small intestine and colon which prevents the need for dose adjustments in special populations as well as systemic drug interactions. The reported Cmax, tmax, AUC and mean residence time after a dosage of 250 mg of rifamycin is 36 mg/L, 5 min, 11.84 mg.h/L and 0.49 h respectively.

From the administered dose, 18%, 50% and 21% is recovered in feces during the first 24, 48 and 72h after administration. This will represent about 90% of the administered dose eliminated by the feces while the urinary secretion is negligible.

The reported volume of distribution after measured after a dosage of 250 mg of rifamycin is 101.8 L.

The reported clearance when a dose of 250 mg of rifamycin was administered is 23.3 L/h.