Assessment of Chronic Supraphysiological Glucocorticoid Dosing Needs of Patients With Adrenal Insufficiency

Abstract

Background: Patients who require higher than replacement glucocorticoid doses to avoid symptoms of adrenal insufficiency (AI) may have inadequate adherence or abnormal drug absorption or metabolism. The goal of this study was to identify why excessive glucocorticoid doses were needed in patients with ongoing AI symptoms. Methods: We performed pharmacokinetic (PK) analysis of glucocorticoid plasma concentrations (prednisone, prednisolone and dexamethasone measured by tandem mass spectrometry, Mayo Laboratories, and cortisol by immunoassay, Clinical Center) in 8 AI patients after weight-based oral hydrocortisone (HC) dose (1), IV HC 20 mg and /or prednisone 5 mg PO. The time (Tmax) to maximal plasma concentrations (Cmax), time to a 50% decrease in concentration (T1/2), elimination rate (ER) and area under the concentration curve (AUC) were determined using MATLAB and SimBiology, and compared to literature reference ranges (RR) (1,2). Results: Patients included one man; six had secondary AI due to previous supraphysiologic hydrocortisone or prednisone treatment and two had primary autoimmune AI. One of the latter was appropriately replaced with thyroid hormone. No patient was taking any medication known to be a strong inhibitor or inducer of CYP3A4 and none were taking oral estrogens. To study the potential contribution of intestinal absorption to abnormal pharmacokinetics, serum cortisol values were compared to expected values at 3.5 or 4 hours after a weight-based oral dose of HC in eight patients (1); 7 patients had values at the 50 - 80th centile of expected values. The eighth patient’s cortisol level at 4 hours after 5 mg HC was 30.3 nmol/L, below the 10th centile. She then underwent the same sampling with a 15 mg dose, with values also at the 10th centile. To uncover any discrepancy between PK oral and IV HC administration, four patients, including the patient with a low 4 hour value (LowHC4h) underwent sampling after 20 mg hydrocortisone, IV (2). Tmax and Cmax were within the RR in all four patients, while one patient had a faster T1/2 but an AUC similar to others. The LowHC4h patient had a dexamethasone level 8 hours after a 1 mg dose that was also within the RR and was maintained on dexamethasone. All others were eventually able to be weaned to a conventional glucocorticoid replacement dose. Conclusions: Evaluation of oral and IV HC PK may be useful in patients suspected of having abnormal absorption of oral glucocorticoids. Ref: 1. Mah PM et al. Clin Endo 61:367,20042. Thomson AH et al. Clin Endo 66:789,2007