Prophylaxis and treatment of rhinovirus colds with zinc gluconate lozenges

Following a tolerance study, double-blind placebo controlled trials were conducted to determine the prophylactic effect of zinc gluconate lozenges on rhinovirus challenge and, in a third study, their therapeutic efficacy when given at the start of colds caused by virus inoculation was tested.

In the prophylaxis study a total of 57 volunteers received lozenges of either zinc gluconate (23 mg) (29 volunteers) or matched placebo (28 volunteers) every 2 h while awake during a period of four and a half days. They were challenged with 10² tissue culture infecting dose (TCID₅₀) of human rhinovirus 2 (HRV-2) on the second day of medication, and were monitored daily for symptoms and signs of colds and laboratory evidence of infection. Zinc reduced the total mean clinical score from 8.2 in the placebo group to 5.7 and the reduction of the mean clinical score was statistically significant on the second day after virus challenge.

In the therapeutic study 69 volunteers were inoculated with 10² TCID₅₀ of HRV-2 and those who developed cold symptoms were randomly allocated to receive either zinc gluconate lozenges (six volunteers) or matched placebo lozenges (six volunteers) every two hours they were awake for six days. Treatment of colds with zinc reduced the mean daily clinical score and this was statistically significant on the fourth and fifth day of medication. Similarly, medication also reduced the mean daily nasal secretion weight and total tissue count and these reductions were statistically significant on days two and six for nasal secretion weights and days four to six of medication for tissue counts when compared with placebo. There were also statistically significant reductions in the mean total nasal secretion weights and total tissue counts. Zinc, however, had no significant effect on the rate or amount of virus excreted by volunteers.

We conclude that zinc gluconate lozenges are reasonably well tolerated and that they have a significant effect on the signs and symptoms of colds caused by rhinoviruses, although the mechanism of action remains obscure.