*Purpose: Mycophenolic acid (MPA) is an essential drug in maintenance immunosuppressive regimens. In spite of increased kidney transplants in the elderly, limited pharmacokinetic investigations comparing age differences in MPA exposure are available. This sub-study investigated the influence of adult age on 12-hour mycophenolic acid exposure in stable renal transplant recipients receiving maintenance regimen of mycophenolate sodium and tacrolimus.

*Methods: A 12-hour pharmacokinetic study was conducted in 67 stable patients at least 1-year post renal transplant without prior MPA therapeutic drug monitoring. Tacrolimus doses were adjusted to troughs (4 to 10 ng/ml) based upon time post transplant. Patients were categorized as: young: >21 & ≤ 40 years; middle age: >40 &≤ 60 years and elderly>60 years. Non-compartmental pharmacokinetic analysis determined area under the concentration-time curve 0-12hours (AUC0-12), AUC 4 to 12 hours(AUC4-12); AUC4-12/AUC0-12 (to define enterohepatic recirculation of MPA) and 0 hour troughs. Univariate ANOVA was conducted using SAS V 9.4.

*Results: Elderly participants received the lowest MPA doses. In the combined groups, irrespective of age, 34.3% of recipients achieved the target AUC0-12 of 30 to 60 mg.hr/ml and 56.7% of patients exceeded the upper therapeutic range of 60 mg.hr/ml (non-significant). Elderly recipients achieved the lowest troughs and exhibited reduced enterohepatic recirculation of MPA (AUC4-12/AUC0-12) with pair-wise comparisons noted between young and older patients; P<0.040.(Results are summarized in table below.)

*Conclusions: Mycophenolic acid dosing regimens require age-adjusted individualization to achieve therapeutic AUC0-12 range. Further investigation of factors that may influence achieving an age-related target AUC of mycophenolic acid and clinical outcomes is needed.

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