What are the potential interactions with rifaximin (antibiotic) in a patient with Small Intestine Bacterial Overgrowth (SIBO), post-norovirus infection, and currently on Proton Pump Inhibitors (PPIs)?

Drug Interactions with Rifaximin

Rifaximin has minimal clinically significant drug interactions due to its negligible systemic absorption (<0.4%), making it one of the safest antibiotics for concurrent use with other medications, including proton pump inhibitors. 1, 2

Key Interaction Profile

No Significant Interactions with PPIs

• Rifaximin can be safely used with proton pump inhibitors without dose adjustment or contraindication. 3, 1
• Unlike rifampin and rifabutin (systemic rifamycins), rifaximin does not induce hepatic CYP450 enzymes because it remains in the gastrointestinal lumen and is not systemically absorbed 1, 2
• PPIs may actually increase SIBO risk, making rifaximin treatment appropriate in patients on chronic PPI therapy 1, 4

Contrast with Systemic Rifamycins

The evidence provided focuses heavily on rifampin and rifabutin interactions, which are not applicable to rifaximin due to fundamental pharmacokinetic differences:

• Rifampin and rifabutin cause extensive drug interactions through CYP450 induction, affecting antiretrovirals, anticoagulants, oral contraceptives, immunosuppressants, cardiovascular agents, and anticonvulsants 3
• Rifaximin does not share these interactions because it lacks systemic absorption and does not induce hepatic enzymes 1, 2, 5

Specific Clinical Scenarios

Your Patient Context (SIBO Post-Norovirus on PPIs)

• Continue PPIs during rifaximin treatment if medically necessary, though consider discontinuing PPIs after SIBO treatment since acid suppression is a well-established SIBO risk factor 1
• Standard rifaximin dosing: 550 mg twice daily for 1-2 weeks 1, 2
• No dose adjustments needed for concurrent PPI use 1

Antibiotic Considerations

• Avoid concurrent use of other antibiotics during rifaximin treatment, as this may counteract therapeutic effects or promote resistance 1, 6
• Discontinue probiotics during rifaximin treatment as they may interfere with bacterial eradication 6

Medications That Can Be Safely Combined

• Antiplatelet agents (though bleeding risk increases with any antibiotic) 3
• Anticoagulants (no dose adjustment needed, unlike rifampin which requires 2-3 fold warfarin increase) 3
• Oral contraceptives (remain effective, unlike with rifampin) 3
• Immunosuppressants (no monitoring needed, unlike rifampin/rifabutin) 3
• Antiretroviral medications (no interactions, unlike rifampin/rifabutin) 3

Important Clinical Pitfalls

Do Not Confuse Rifaximin with Other Rifamycins

• The extensive interaction tables in tuberculosis guidelines 3 apply to rifampin and rifabutin only
• These systemic rifamycins require complex dose adjustments with protease inhibitors, NNRTIs, and numerous other medications 3
• Rifaximin's non-systemic nature eliminates these concerns 1, 2, 5

Post-Treatment Considerations

• Consider discontinuing PPIs after successful SIBO eradication to prevent recurrence, as gastric acid suppression is a primary SIBO risk factor 1
• If acid suppression remains necessary, H2-blockers may be preferable alternatives to PPIs 1
• The norovirus infection from 3 months ago is unlikely to still cause dysmotility; PPI use is the more likely SIBO culprit 1

Safety Profile

• Rifaximin demonstrates no clinically relevant bacterial resistance patterns 5
• Adverse events are minimal and less frequent than with metronidazole or systemic antibiotics 5, 7
• No routine monitoring required during treatment 1, 2