Co-administration of 5α-reductase inhibitors worsens the adverse metabolic effects of prescribed glucocorticoids.

CONTEXT Glucocorticoids (GC) are commonly prescribed, but their use is associated with adverse metabolic effects. 5a-reductase inhibitors (5aRI) are also frequently prescribed, mainly to inhibit testosterone conversion to dihydrotestosterone. However, they also prevent the inactivation of GCs. OBJECTIVE We hypothesised that 5aRIs may worsen the adverse effects of GCs. DESIGN Prospective, randomised study. PATIENTS 19 healthy male volunteers (age; 45±2 years, BMI; 27.1±0.7kg/m2). INTERVENTIONS Participants underwent metabolic assessments; 2-step hyperinsulinemic, euglycemic clamp incorporating stable-isotopes, adipose tissue microdialysis and biopsy. Participants were then randomised to either prednisolone (10mg daily) or prednisolone (10mg daily) plus a 5aRI (finasteride 5mg daily or dutasteride 0.5mg daily) for 7 days; metabolic assessments were then repeated. MAIN OUTCOME MEASURES Ra glucose, glucose utilization (M-value), glucose oxidation, non-esterified fatty acids (NEFA) levels. RESULTS Co-administration of prednisolone with a 5aRI increased circulating prednisolone levels (482±96 vs. 761±57nmol/L, p=0.029). Prednisolone alone did not alter Ra glucose (2.55±0.34 vs 2.62±0.19mg/kg/min, p=0.86), M-value (3.2±0.5 vs 2.7±0.7mg/kg/min, p=0.37), or glucose oxidation (0.042±0.007 vs 0.040±0.004mmol/hr/kg/min, p=0.79). However, co-administration with a 5aRI increased Ra glucose (2.67±0.16 vs. 3.05±0.18mg/kg/min, p<0.05) and decreased M-value (4.0±0.5 vs. 2.6±0.4mg/kg/min, p<0.05), and oxidation (0.043±0.003 vs. 0.036±0.002mmol/hr/kg, p<0.01). Similarly, prednisolone did not impair insulin-mediated suppression of circulating NEFA (43.1±28.9 vs. 36.8±14.3μmol/L, p=0.81), unless co-administered with a 5aRI (49.8±8.6 vs. 88.5±13.5μmol/L, p