ABSTRACT The influence of dosing time on the pharmacological effects (fever and antiviral activity) and the pharmacokinetics of interferon-␣ (IFN-␣) was investigated in ICR male mice under lightdark (12:12) cycle. There was a significant circadian rhythm in rectal temperature, as an index of fever, at 0.5 hr after IFN-␣ (10.0 MIU/kg i.v.) injection. The rhythmic pattern resembled overall the rhythm that occurs in the nondrugged state. However, the percent change from basal level of rectal temperature varied according to the dosing time. The rhythmicity corresponded to the dosing time-dependent difference of PGE 2 levels in thalamus after IFN-␣ injection, but it did not correspond to that of plasma IFN-␣ concentrations. A significant dosing time-dependent difference was also demonstrated for 2Ј-5Јoligoadenylate synthetase activities, as an index of antiviral activity, in plasma and liver at 24 hr after IFN-␣ injection. It was related to the rhythmicity in plasma IFN-␣ concentrations that was caused by the rhythmicity in clearance of IFN-␣. The choice of the most appropriate time of day for drug administration may help to achieve rational chronotherapeutics of IFN-␣ in certain experimental and clinical situations. A large number of physiological rhythmic variables are demonstrated in the CNS, in hormone secretion and so on Interferons, which belong to a group of cytokines, have been widely used as antiviral and antitumor agents in the human. However, interferons cause unavoidable adverse effects such as fever, fatigue, headache, rigors and myalgias. In particular, fever is an indispensable side effect in nearly all patients during the early phase of interferon treatment. Administration of IFN-␣ in cancer patients is better tolerated in evening than in morning Rectal temperature and immune functions show significant circadian rhythms in mammals under both nondrugged and drugged conditions The purpose of this study was to examine the diurnal change of IFN-␣ induced fever and antiviral activity in mice. The mechanisms underlying these phenomena were also investigated from the perspective of IFN-␣ pharmacokinetics. Methods Animals and treatments. Male ICR mice (5 weeks old) were purchased from Charles River Japan Inc. (Kanagawa, Japan). Mice were housed 6 or 10 per cage in a light-controlled room (light on from 07:00 to 19:00) at a room temperature of 24°C Ϯ 1°C and a humidity of 60% Ϯ 10% with food and water ad libitum. All mice were adapted to their light-dark cycle for 2 weeks before the experiments. In order to study the fever induced by IFN-␣ (Sumiferon, Sumitomo Seiyaku Co., Osaka, Japan), groups of six mice injected i.v. with 1.0, 5.0 or 10.0 MIU/kg IFN-␣ or sterilized saline at the same circadian phase (09:00). IFN-␣ was diluted by sterilized saline to adjust the concentration to 0.2, 1.0 and 2.0 MIU/ml. The volume of injection was 0.05 ml/10.0 g b.wt. The drug solutions were used within 30 min after preparation in order not to decrease their biologic activity. Rectal temperature was continuously determined before, and at 0.5, 1.0, 2.0 and 4.0 hr after, IFN-␣ or saline injection. In the study of the circadian rhythms of IFN-␣-induced fever and plasma IFN-␣ concentrations, groups of 8 to 10 mice were injected i.v. with 10.0 MIU/kg IFN-␣ or saline at one of six times: 09:00, 13:00, 17:00, 21:00, 01:00 or 05:00. Rectal temperature was determined before, and at 0.5, 1.0, 1.5 and 2.0 hr after, IFN-␣ or saline injection. Percent change of rectal temperature (%) from basal level was calculated as follows: % ϭ ([rectal temperature after IFN-␣ injection Ϫ rectal IFN-␣ before Received for publication December 27, 1996. ABBREVIATIONS: IFN-␣, interferon-␣; 2Ј-5ЈOAS, 2Ј-5Јoligoadenylate synthetase; CL, clearance; V c , central volume of distribution; K 12 , distribution rate constant from central to peripheral compartment; K 21 , distribution rate constant from peripheral to central compartment
