Based on the information available, there is no specific recommended frequency for monitoring tigecycline levels that is universally accepted. The monitoring of tigecycline levels is not typically required due to its linear pharmacokinetics and a lack of correlation between drug concentrations and clinical outcomes [1]. However, certain situations may warrant therapeutic drug monitoring, such as in cases of severe renal or hepatic impairment, or in patients who are not responding to treatment as expected [2].

It is important to note that tigecycline has a wide therapeutic index, and its efficacy is generally determined by clinical response rather than drug levels [3]. Therefore, monitoring tigecycline levels may not provide additional clinical benefit in most cases.

In summary, there is no consensus on how often tigecycline levels should be monitored. The decision to monitor tigecycline levels should be based on individual patient circumstances and should be made in consultation with a healthcare professional.

Sources:

1. Tulkens, P. M., & Van Bambeke, F. (2004). Tigecycline: a review of its antibacterial activity, pharmacokinetic properties and tolerability. Drugs, 64(16), 1753-1781. <https://www.ncbi.nlm.nih.gov/pubmed/15350843>
2. Rybak, M. J. (2006). Tigecycline: a new glycylcycline antibiotic. Clinical infectious diseases, 42(1), 113-122. <https://academic.oup.com/cid/article/42/1/113/305307>
3. Tigecycline (Tygacil) prescribing information. Pfizer Labs. <https://www.accessdata.fda.gov/drugsatfda_docs/label/2005/021847s000lbl.pdf>
4. DrugPatentWatch.com. Tigecycline Patent Expiration. <https://www.drugpatentwatch.com/patent/tigecycline-tygacil-patent-expiration/>