Rifaximin

About Rifaximin

Rifaximin is a rifamycin antibiotic that is barely absorbed, so it acts on bacteria in the bowel rather than the whole body. The label approves it for three uses: travelers’ diarrhea caused by noninvasive strains of E. coli in adults and children 12 and older (200 mg three times a day for three days); reducing the risk of a return of overt hepatic encephalopathy, the confusion caused by advanced liver disease, in adults (550 mg twice a day, taken long term); and irritable bowel syndrome with diarrhea in adults (550 mg three times a day for 14 days, which can be repeated up to two times if symptoms come back). It is not for travelers’ diarrhea with fever or blood in the stool, or diarrhea caused by other germs. It can be taken with or without food.

There is no boxed warning. Rifaximin must not be taken by anyone allergic to it or to other rifamycins such as rifampin; reported allergic reactions include severe skin peeling, swelling and anaphylaxis. If travelers’ diarrhea gets worse or lasts more than 24 to 48 hours, the drug is stopped and another treatment considered, because the cause may not be E. coli. Like nearly every antibiotic it can lead to Clostridioides difficile diarrhea, which has been reported more than two months after a course of antibiotics, and using it without a proven or suspected bacterial cause breeds resistant bacteria. Headache is the usual side effect in travelers’ diarrhea; in hepatic encephalopathy, where it is taken for months, swelling of the legs, nausea, constipation, dizziness and tiredness were among the most common; in IBS, nausea and a rise in liver enzymes.

What is distinctive is the three different regimens: a three-day course, a two-week course that may be repeated, and an open-ended twice-daily prescription, each a different quantity and strength. Rifaximin is used with caution in severe liver impairment and with cyclosporine or other P-glycoprotein inhibitors, which raise how much reaches the bloodstream. Animal studies showed harm to the fetus at doses near or above the human dose, so the label advises telling pregnant patients of the potential risk. For hepatic encephalopathy, MedlinePlus warns not to stop without talking to the prescriber, since the confusion can return. Rifaximin is not a controlled substance.

Taking Rifaximin

How to take it

Take it by mouth with or without food, at about the same times each day, two or three times a day as prescribed. Finish the course for travelers’ diarrhea or IBS even if you feel better; for hepatic encephalopathy, do not stop without talking to the prescriber.

If you miss a dose

Take it as soon as you remember, unless it is almost time for the next dose; then skip the missed dose. Do not take a double dose.

Storage

In the original tightly closed container at room temperature, away from heat and moisture (not in the bathroom), out of reach of children.

Interactions to know about

Cyclosporine and other P-glycoprotein inhibitors can raise rifaximin levels in the blood, and the label reports changes in INR in people taking warfarin, so INR is monitored while the two are taken together. Tell the pharmacist about every prescription and nonprescription medicine, vitamin and supplement you take, and about any allergy to rifampin or other rifamycin antibiotics.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Rifaximin differs from pharmacy to pharmacy

Rifaximin is priced as a brand, so quotes differ mainly by the pharmacy’s markup and by whether it has the strength in stock; a pharmacy may keep one strength and order the other in. A ninety-day supply of the 550 mg tablet for hepatic encephalopathy is a large quantity, so ask whether the pharmacy can fill it at once.

The three regimens mean very different quantities: nine 200 mg tablets for travelers’ diarrhea, forty-two 550 mg tablets for an IBS course, and sixty a month for hepatic encephalopathy. A quote applies only to the strength and count written, so make sure the prescription matches the use.

Ways to pay less for Rifaximin without insurance

• Ask the maker whether its savings or patient assistance program applies to someone paying cash; many copay cards require commercial insurance, so ask rather than assume.
• Compare more than one pharmacy for the exact strength and count on your prescription, and ask whether the pharmacy stocks it or must order it.
• For hepatic encephalopathy, once you are settled on treatment, ask the prescriber whether a ninety-day supply suits you, so you pay fewer dispensing fees.
• Ask the pharmacy whether a generic 550 mg tablet has reached the market since the FDA approved one in 2026, and ask the prescriber to allow substitution if so.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Rifaximin

1. 1.Is my prescription for the 200 mg or the 550 mg tablet, and does the quantity match how long my doctor wants me to take it?
2. 2.Do any of my medicines, such as cyclosporine, change how my rifaximin works?
3. 3.What should I do if my diarrhea gets worse or I see blood or have a fever while taking it?
4. 4.If I am taking it for liver disease, what happens if I run out before my next fill?

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