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5305160 
Technical Report 
Pharmacokinetic comparison of etilefrine to its prodrug, the stearic acid ester of stilifrine 
Rominger, KL; Hitzenberger, G 
1980 
18 
Apr 1980 
English 
IPA COPYRIGHT: ASHP Etilefrine (Effortil; I), 20 mg, and its stearic acid ester, stilifrine (II), 44.4 mg, were compared in 6 subjects to determine the relative bioavailability by means of plasma levels and renal excretion. The stearic acid ester of I was intended to reduce metabolic inactivation during absorption. Both drugs were tritiated, then diluted with a non-radioactive substance to give a specific activity of 14.8 muCi/mg for I and 4.7 muCi/mg of II. Capsules of the drugs were administered 0.5 hr after a standard light breakfast. Plasma specimens were obtained at 0, 1, 2, 3, 4, 6, 8, 12 and 24 hr. Urine was also collected at 0-4, 4-8, and 8-24 hr. Maximum plasma levels of the active substance after administration of I were reached after 0.5 hr. After II, mean peak level is delayed to one hr after administration and is only 33% of I level. The area under the curve after I is 3.18 ng/ml/hr and after administration of II 15.95 ng/ml/hr, which is highly significant. The relative bioavailability of I when administered in the form of prodrug is 51.4% as compared to I by itself. After the administration of etilefrine 84.4% is excreted in the urine and 72.6% when administered as prodrug.