Tolerance of one‐month intranasal interferon

Under double‐blind conditions, groups of volunteers (68 in total) were allocated at random to take intranasal solutions of placebo or one of three doses of highly purified leucocyte interferon by intranasal spray twice a day for 28 days. The highest dose would have been expected to protect against experimental colds. Treatment was discontinued because of upper respiratory symptoms as often in each of the interferon groups as in the placebo group. However, it was possible to distinguish clinically between “colds” on placebo and low‐dose interferon and “reactions to treatment” on high‐dose interferon. The features of the reactions to treatment were a protracted build‐up of local symptoms and minor epistaxis. None of the volunteers on the high‐dose interferon were thought to have a definite cold, but viruses were isolated from four out of six volunteers on low‐dose interferon who had definite colds. Previous experiments had also shown this dose to be insufficient to protect against experimental rhinovirus challenge.