Subcutaneous absorption kinetics and local tissue distribution of interferon and other solutes

The subcutaneous absorption and consequent tissue distribution of interferon g was studied in an anaesthetized rat model. Interferon g showed a biphasic disappearance profile from a solution in a subcutaneous absorption cell. Both the initial rapid distribution phase and slower removal phase followed first order kinetics. The steady-state clearance of interferon g from the cell was 1.41 +/- 0.38 x 10(-3) mL min-1, and the absorption half-life (t1/2) was 3.8 +/- 1.1 h (n = 4). Noradrenaline did not significantly alter either the clearance or absorption of interferon g (1.18 +/- 0.44 x 10(-3) mL min-1, P > 0.05, absorption t1/2 4.96 +/- 1.9 h, P > 0.05). Given that the clearance of smaller solutes, such as tritiated water, is significantly reduced when noradrenaline is coadministered, it is suggested that interferon g is removed via the lymphatic system rather than by the local blood supply. The amount of interferon g recovered in the plasma, urine and muscle is minimal relative to other solutes where the recovery is almost complete.