Gen. Pharmac. Vol. 17, No. 1, pp. 93 96, 1986 0306-3623/86 $3.00 + 0.00 Printed in Great Britain. All rights reserved Copyright © 1986 Pergamon Press Ltd THE LYMPHATIC ROUTE--II. PHARMACOKINETICS OF HUMAN RECOMBINANT INTERFERON-~ 2 INJECTED WITH ALBUMIN AS A RETARDER IN RABBITS* VELIO BOCCI,t MICHELA MUSCETTOLA, ANTONELLA NALDINI, ENRICA BIANCHI 1 a n d GIORGIO SEGRE l Institute of General Physiology and qnstitute of Pharmacology. University of Siena, 53100 Siena, Italy (Received 18 March 1985) Abstraet--l. The aim of the present investigation was to define whether multisite subcutaneous (s.c.) administration in unanesthetized, unrestrained rabbits of human recombinant interferon-~2 (rec. IFN-~2) either in saline, human albumin (ALB) solution (4, 7 and 10% final concentrations), or in a solution containing 75 U of hyaluronidase, modified the pharmacokinetic parameters calculated from the IFN plasma levels. 2. Plasma disappearance rates of rec. IFN-c~ 2 were measured in rabbits after intravenous (i.v.) administration and the kinetic was adequately represented by a three-pools mammillary model. This model was the basis for evaluating the absorption and distribution of rec. IFN-c~ 2 after s.c. administration. 3. The increase of ALB concentration (from 4 to 10%) caused a significant reduction of the plasma IFN Cm, ~ while both the mean residence time and the release time of IFN increased linearly with the ALB concentration. 4. The data support the postulation that s.c. administration of albumin acts as an interstitial fluid expander and may favour absorption of IFN via lymphatics rather than blood capillaries. Improvement of therapeutic index of IFN by using this route remains to be shown in clinical trials. INTRODUCTION So far interferon (IFN) has been administered in cancer patients on an empirical basis, and neither an optimal route, nor a schedule is yet at hand (Strander, 1982). Bocci (1983, 1984) has postulated that if lymphatic (rather than hematic) absorption can be promoted after multisite s.c. administration of IFN with human albumin (ALB), the therapeutic index may improve. For this reason it was proposed to inject IFN via the "lymphatic route", a term coined to indicate that this particular form of IFN adminis- tration may yield a lymph/plasma gradient similar to the one observed in natural conditions (Bocci, 1981). The rationale stands in increasing the colloid osmotic pressure of interstitial fluid which is the main force driving lymphatic absorption (Guyton, 1983). A ma- jor shift of IFN in the lymphatic pool ought to result in: (a) marked interaction of IFN with effector cells in lymph and nodes (T and B lymphocytes, NK cells, monocytes); (b) delayed and fractionated arrival of IFN in the plasma pool due to different transit times along lymphatic pathways; (c) lower IFN plasma levels with reduced general toxicity and renal loss. In a parallel study (in preparation) we have as- sessed the lymph/plasma concentration ratios (L/P) of IFN injected via the s.c. route with saline, 4% ALB and hyaluronidase (HYAL). However, in this in- *Supported by contract 84.00461.44, Progetto Finalizzato Oncologia, CNR, Roma and by a grant from the M.P.I., Roma. tReprint requests to: Professor V. Bocci, Institute of General Physiology, via Laterina, 8, 53100 Siena, Italy. 93 vestigation, owing to collection of thoracic lymph we could not determine with accuracy the pharma- cokinetic parameters evaluable from the IFN plasma curves. Therefore the present study was designed to evaluate these parameters and to define the optimal concentration of ALB acting as an interstitial fluid expander. MATERIALS AND METHODS The New-Zealand male rabbits (2.6 kg) were used for evaluating the plasma disappearance rates of human re- combinant (rec.) IFN-ct2 (Schering Corporation, Bloomfield, N. J.) after intravenous (i.v.) as a bolus administration. The IFN used had a potency of 42.0 x l0 s IU/ml and it was at least 98% pure. Doses of 62 x 106IU were used for each animal. A volume of 2 ml containing 0.6 mg Evans Blue in saline added to the IFN sample was injected into the right auricularis vein and small samples of blood were withdrawn at various times thereafter from the left auricularis vein into tubes containing dry heparin (15 IU/ml of blood). Fifteen New-Zealand male rabbits (2.26-2.48 kg) were randomly assigned to one of the five groups necessary for investigating the s.c. route. Each animal received 6 s.c. symmetrical injections in the lower, median and upper part of the abdomen of 9.5 mega Units (MU) human rec. IFN-ct2. The volume injected was 170/~1 per s.c. site and contained rec. IFN-ct2 diluted either in saline (controls) or in human albumin (ALB) for therapeutical use (obtained from ISVT A. Sclavo, Siena, Italy) at a final concentration of 4, 7 and 10%. The fifth group (of which one animal was lost during the experiment) was injected with rec. IFN-ct2 diluted in saline containing 75 U of hyaluronidase (Jaluran, Bio- industria Farmaceutici Spa, Novi Ligure). HYAL was tested on the assumption that will favour IFN absorption from the injection site. During the experiment the animals