An 86 year-old female participant with a history of diabetes, Alzheimer’s/dementia, hypertension, tremors, and pulmonary fibrosis, presented with symptoms of a urinary tract infection (UTI). Her current medication regimen included:
- Duloxetine (Cymbalta) 60mg delayed release PO QD
- Furosemide (Lasix) 20 mg PO QD
- Hydrochlorothiazide–lisinopril (Zestoretic) 12.5mg-/10mg PO QD
- Lorazepam (Ativan) 0.25mg PO BID
- Topiramate (Topomax) 25mg PO BID
The physician e-prescribed ciprofloxacin 500mg PO Q12h for a 7-day UTI treatment course duration.
Upon performing the targeted medication review during the verification process, the Medication Risk Mitigation (MRM) Matrix indicated to the clinical pharmacist that other alternative therapeutic options should be considered.
There is a potential major drug-drug interaction with concomitant ciprofloxacin and duloxetine. As ciprofloxacin is a strong inhibitor of CYP1A2 and duloxetine is a CYP1A2 substrate, the metabolism of duloxetine would be affected, resulting in potentially increased concentration of duloxetine and increasing the participant’s risk of adverse effects.
The clinical pharmacist alerted the physician of this potential major drug-drug interaction and discussed alternative therapeutic options for UTI treatment. It was decided that levofloxacin was the safer alternative because it is not metabolized by CYP1A2. As levofloxacin is renally eliminated, in consideration of the participant’s age and likely age-related renal impairment (unknown creatinine clearance), it was recommended that the physician prescribe a low dose levofloxacin, 250mg PO daily for 3 or 5 day course of therapy, depending on whether the diagnosis was found to be an uncomplicated or complicated UTI.