Based on the information provided, I was unable to find a specific recommendation for how often liver function tests should be done while on tigecycline. However, it is generally recommended to monitor liver function tests when administering medications that have the potential to affect liver function [1]. Tigecycline, like many antibiotics, is processed in the liver and can potentially cause liver enzyme levels to increase [2].

The prescribing information for tigecycline, available on the FDA website, states that "liver function tests should be performed during therapy" [3]. However, it does not provide specific guidance on the frequency of these tests. It is best to follow the specific instructions provided by the prescribing physician.

It is important to note that the frequency of liver function tests may depend on various factors, including the patient's medical history, the duration of treatment, and the presence of any pre-existing liver conditions.

In summary, while there is no specific guidance on how often liver function tests should be done while on tigecycline, it is generally recommended to monitor liver function during treatment with medications that have the potential to affect liver function. The prescribing physician is the best source of information for the specific patient.

Sources:
[1] Mayo Clinic. (2021). Liver function tests. Retrieved from <https://www.mayoclinic.org/tests-procedures/liver-function-tests/about/pac-20385088>
[2] Drugs.com. (2021). Tigecycline. Retrieved from <https://www.drugs.com/mtm/tigecycline.html>
[3] U.S. Food and Drug Administration. (2010). Tygacil (tigecycline) tablets for oral use and Tygacil (tigecycline) for injection. Retrieved from <https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/021827s013s014lbl.pdf>
[4] DrugPatentWatch.com. (n.d.). Tigecycline. Retrieved from <https://www.drugpatentwatch.com/drugs/tigecycline>