Testosterone implantation experiments

Drug administration route Published experience with testosterone pellets of an older type has noted relatively high rates of pellet extrusion (8.5-12%) and infection (1.4-6.8%). A study in 80 men with long-acting testosterone implants (Testopel ), which are smaller and have a smooth surface, has shown that with this formulation extrusion occurred in only 0.3% of cases and infection also in only 0.3% [105 ]. 

Fifteen ewes were subcutaneously implanted with 0 to 10 cm of silicone implants containing testosterone propionate. The implants were made as described in Experiment 1. Implants were subcutaneously implanted in the axilla. Blood plasma was collected before and 13 days after implantation and assayed for plasma testosterone concentrations by a validated testosterone enzyme immunoassay (described later). 

Twenty-four beef heifers were assigned to one of two groups. Twelve heifers were subcutaneously implanted with a commercially manufactured testosterone propionate ear implant on day 0 and re-implanted with another implant on day 84. The other twelve heifers were implanted with two 15 cm silicone implants filled with testosterone propionate. These implants were implanted subcutaneously behind the shoulder or over the rib cage and were left in situ for 156 days. Blood samples were collected via jugular venipuncture immediately before implantation (day 0) and 28, 56, 84, 112, 140 and 156 days into the experiment. All samples were... 

Increasing the length of implants (surface area) increased plasma testosterone concentrations linearly (r = 0.93 P < 0.01) as in beef females in Experiment 1 Table 2). 

Results in this experiment were similar to Experiment 1 for testosterone propionate in that the secretion rate was directly related to surface area implanted and increased surface area elevated plasma testosterone concentrations (Table 3). 

Mean testosterone concentrations in plasma (1.10 ng/mL) were very similar to predicted concentrations (1.09 ng/mL based on results in Experiment 1 and corrected for time in situ). Concentrations of testosterone in the plasma for the silicone implanted heifers were not only higher than for the heifers implanted with compressed pellets but concentrations were also less variable as illustrated in Figure 5. The coefficient of variation was four times greater for testosterone concentrations in the heifers implanted with compressed pellets than for the silicone implanted heifers. 

Results in the four experiments also demonstrate that total surface area, regardless of whether by increasing diameter or by increasing implant length, increased secretion rate and elevated testosterone concentrations proportionally. 

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