Xifaxan (rifaximin) is an oral antibiotic in the 'rifamycin' family of antibiotics, structurally related to rifampin.
Xifaxan is used for numerous indications, including (1):
- Traveler's diarrhea caused by noninvasive strains of Escherichia coli (E. coli)
- Irritable bowel syndrome with diarrhea
- Reduce the risk of hepatic encephalopathy recurrence
Xifaxan has a fairly broad spectrum of activity and is effective against many gram-positive and gram-negative aerobes and anaerobes (2).
An interesting characteristic of Xifaxan is that it has relatively zero systemic bioavailability after oral administration, meaning it is not absorbed to a significant extent but rather concentrates in the gastrointestinal tract, exerting effects on the gastrointestinal flora. For hepatic encephalopathy specifically, Xifaxan is thought to reduce ammonia-producing enteric bacteria (3).
Below are the answers to each of your questions regarding the drug.
When Does Xifaxan Go Generic?
Xifaxan received FDA approval initially for the treatment of traveler's diarrhea caused by noninvasive strains of Escherichia coli on May 26, 2004.
Xifaxan is currently not available generically and there unfortunately is no set date in which a generic version will be available. The earliest it could be available in late 2019, but that is far from a definite date. Generic manufactures have applied to be allowed to produce a generic version but all have been denied thus far (4).
Valeant, in response to a 'New Drug Application' submitted by the generic manufacturer Actavis, released the following statement:
"Valeant confirms that its wholly owned subsidiary, Salix Pharmaceuticals, has received a notice letter dated February 11, 2016 from Actavis Laboratories FL, Inc. (Actavis) stating that the U.S. Food and Drug Administration (FDA) has received Actavis' Abbreviated New Drug Application (ANDA) containing a "Paragraph IV" patent certification seeking approval to market a generic version of Salix's Xifaxan® (rifaximin) 550 mg Tablets.
Valeant has 22 Orange Book-listed patents covering Xifaxan® 550 mg Tablets that are scheduled to expire between August 2019 and October 2029. Valeant is highly confident in its intellectual property rights relating to Xifaxan® 550 mg Tablets and intends to vigorously enforce such rights in all applicable venues."
Based on the patents on file for Xifaxan, it will not be available generically until at least the end of 2019, and potentially through 2029.
Can You Build A Tolerance To Xifaxan?
It hasn't been reported or documented that you can build a 'tolerance' to Xifaxan (meaning higher/escalating doses are needed to produce similar clinical effects). However, like all antibiotics, there is certainly a risk of bacterial resistance, which could decrease the efficacy of the drug over time.
Xifaxan Alternatives For Hepatic Encephalopathy
Xifaxan is extremely expensive, and its use for the treatment of hepatic encephalopathy averages about $1200 per month (5).
While expensive, many studies have shown that the combination of Xifaxan and lactulose (the combination you are taking) is more effective in maintaining remission of hepatic encephalopathy than lactulose alone (6).
As Xifaxan is expensive, in general, it is commonly recommended to hold off on use of the drug unless you are not responding well to lactulose therapy.
Several other antibiotics (e.g. neomycin, vancomycin and metronidazole), which may be more cost effective, have been used to treat hepatic encephalopathy but can cause significantly more side effects. If you are at a point where you are unable to afford or take Xifaxan for whatever reason, you should speak with your doctor regarding your available treatment options.