Case report: boldo (Peumus boldus) and tacrolimus interaction in a renal transplant patient

Introduction: Boldo is an extract of a Chilean tree leave (Peumus boldus mol) that have been traditionally employed in folk medicine. We have presented a case of subtherapeutic tacrolimus levels in a renal transplant patient while taking boldo. In the literature search, no interaction has been reported between boldo and tacrolimus.

Case report: A 78-year-old Hispanic man with history of diabetes mellitus, hypertension, and deceased donor renal transplant in 2005 presented to the renal clinic for regular follow-up on September 1, 2010. No complaints were reported and physical examination was unremarkable. Laboratory tests taken on July 26, 2010, were significant for tacrolimus level of <3 ng/mL (measured by liquid chromatography/tandem mass spectrometry) and serum creatinine of 1.2 mg/dL (106 μmol/L). Medications included tacrolimus 2 mg bid and mycophenolate 500 mg bid. On further inquiry, the patient admitted taking herbal medication, boldo 300 mg bid, for the last few weeks. There was no change in his regular medications. He was adherent to his medication. He had been taking tacrolimus from the same company and pharmacy since August 2009. The last dose of boldo was on September 1, 2010. One week after he stopped taking boldo, tacrolimus level was 6.1 ng/mL (9/8/2010) on the same tacrolimus dose of 2 mg bid. Tacrolimus dose was increased to 3 mg bid (9/9/2010), awaiting tacrolimus levels. Subsequent levels (ng/mL) were 8.6 and 9.5, which made us resume the prior tacrolimus dose (2 mg bid).

Conclusions: We have reported a case of an allograft renal transplant recipient who presented to the clinic with subtherapeutic levels of tacrolimus while taking the herbal remedy boldo. Tacrolimus levels rose to the intended target after discontinuation of boldo. Although it is a single case report, our observation suggests a possible herb-drug interaction.