Determination of the disappearance rate of iodine-125 labelled oils from the injection site after intramuscular and subcutaneous administration to pigs.

The rate of disappearance of clinically used vegetable oils, Viscoleo, sesame oil, castor oil and isopropyl myristate, from the injection site after intramuscular (i.m.) or subcutaneous (s.c.) administration to pigs were determined by using a non-invasive gamma-scintigraphy method. All the oil vehicles were spiked with 2.5% (v/v) (125)I-triolein and six injections of 1.9 ml were given to each of 12 pigs. No significant difference (ANOVA) in disappearance rate of each individual oil vehicle from the different injection sites was observed after administration of the oils: i.m. in the lower back, s.c. in the neck and s.c. in the mid-back. Likewise, no inter-individual difference between the pigs was observed. The half-life of 14 days for Viscoleo was significantly smaller than those of the other oil vehicles (P<0.0001), i.e. 23,20,20 days for sesame oil, castor oil and isopropyl myristate, respectively. Due to the spreading effect of the oils and reflux of the oils through the injection canal, the half-lives were calculated omitting the data for the first sampling day.