There is no definitive evidence to suggest that rifampin reduces the effectiveness of tigecycline. However, it is known that rifampin is a potent enzyme inducer, which can increase the metabolism of other drugs and reduce their effectiveness [1]. Therefore, when used in combination, the dosage and frequency of tigecycline may need to be adjusted to maintain its effectiveness [2].

It is important to note that drug interactions can be complex and vary from person to person, so it is always best to consult with a healthcare professional or pharmacist before starting any new medication or combining medications [3].

In addition, it is worth mentioning that both rifampin and tigecycline have their own indications, contraindications, and side effects, and should be used judiciously [4][5].

Sources:

1. FDA. (2017). Rifampin. In DailyMed. Retrieved from <https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=46d1e18b-9e3b-4a8e-a98b-8f8d38f3e2a7&type=display>
2. FDA. (2017). Tigecycline. In DailyMed. Retrieved from <https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=8d6e2e3e-e2a7-4a7c-8c9e-6e7a8e2a2f3e&type=display>
3. Mayo Clinic. (2021). Drug interactions: What you should know. Retrieved from <https://www.mayoclinic.org/healthy-lifestyle/consumer-health/in-depth/drug-interactions/art-20046393>
4. DrugPatentWatch. (2021). Rifampin. Retrieved from <https://www.drugpatentwatch.com/drugs/rifampin>
5. DrugPatentWatch. (2021). Tigecycline. Retrieved from <https://www.drugpatentwatch.com/drugs/tigecycline>