Influence of Age on the Pharmacokinetics and Pharmacodynamics of Oral Transmucosal Fentanyl Citrate

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Abstract
Background: Cancer pain is primarily a problem of older persons. Oral transmucosal fentanyl citrate (OTF) was developed to provide rapid analgesia and is the first drug specifically approved for treating breakthrough cancer pain. Fentanyl in OTF is absorbed across the oral mucosa but a considerable portion is swallowed and absorbed enterally. The effects of age on OTF pharmacokinetics and pharmacodynamics are unknown. This investigation evaluated OTF disposition and clinical effects in older (60-75 yr) compared with younger (18-40 yr) volunteers. Methods: Healthy young (26 +/- 6 yr) and older (67 +/- 6 yr) volunteers (n = 12 each) were studied in an Institutional Review Board approved protocol. They received OTF (10 microg/kg). Plasma fentanyl and norfentanyl concentrations were determined by mass spectrometry. Fentanyl effects were measured by dark-adapted pupil diameter and by subjective self-assessments using visual analog scales. Results: Plasma fentanyl and norfentanyl concentrations and pharmacokinetic parameters did not differ between younger and older subjects. Maximum pupil diameter change from baseline was significantly less in older (3.1 +/- 0.7 mm) compared with younger (4.5 +/- 1.1 mm) subjects (P < 0.05). OTF-dependent subjective assessments of alertness/sedation, energy level, confusion, clumsiness, anxiety, and nausea did not differ in the older subjects. Discussion: The pharmacokinetics of OTF were not altered in older volunteers. In contrast, there was a somewhat diminished response to the miotic effects of fentanyl in older subjects. No change in OTF dosing in the elderly would appear necessary because of altered pharmacokinetics. If the response to OTF in older patients is similar to that in older volunteers and miosis is representative of analgesia and respiratory depression, then changes in OTF dosing with age alone do not appear indicated.