Release and elimination of 14C-fluphenazine enanthate and decanoate esters administered in sesame oil to dogs.

The rates of release of 14C-fluphenazine enanthate and 14C-fluphenazine decanoate were compared in two groups of five male dogs. Each dog was given a single dose (2 mg/kg im) of either the enanthate or decanoate ester in sesame oil. The times required to attain maximum concentrations of radioactivity in plasma were 3.8 +/- 0.5 days (+/-SE) for the enanthate ester and 10.6 +/- 1.1 days for the decanoate ester (p less than 0.001); maximum concentrations of radioactivity in the plasma at these times were 16.7 +/- 1.1 and 11.1 +/- 1.2 ng/ml, respectively (p less than 0.01). However, 35 days after dosing, the concentrations of radioactivity in plasma were greater for the decanoate ester than for the enanthate ester. The times required for 50% of the dose to be excreted in the urine and feces were 7.8 +/- 0.5 days for the enanthate ester and 22.6 +/- 4.4 days for the decanoate ester (p less than 0.05). The total amounts excreted in 35 days were 85.4 +/- 1.8 and 68.8 +/- 6.6% of the dose for the enanthate and decanoate esters, respectively; the average half-times for the rates of release of radioactivity from depot and body, as calculated from the data for total excretion, were 5.55 days for the enanthate ester and 15.4 days for the decanoate ester. Thirty-five days after dosing, the amount of the dose present in the injection site was 4.6 +/- 1.6% for the enanthate ester and 18.6 +/- 5.7% for the decanoate ester. Two groups of six dogs each were protected against the emetic effects of apomorphine more than twice as long by the decanoate ester than by the enanthate ester after the subcutaneous administration of single 8-mg/kg doses of either drug in sesame oil (p less than 0.05). Based on measurements of total radioactivity, it was concluded that the decanoate ester was released from the depot at less than one-half the rate of the enanthate ester.