Time of dissolving of the lozenges and the dose of zinc in the lozenges
| Trial (ref.) | N (Zn)/N (placebo) | RR (95% CI) for the rate of recovery from colds* | Weight of the lozenge (g) | Zn in the lozenge (mg) | Time of dissolving in the mouth (min) | Number of Zn lozenges per day† | Total Zn per day (mg) | Total time of dissolving per day (hours) |
| Eby1 20 | 37/28 | 3.5 (1.8 to 6.7) | 1.0 | 23 | 15‡ | 9 | 207 | 2.3 |
| Al-Nakib2 3 | 29/28 | § | 1.0 | 23 | 20 | 9 | 207 | 3.0 |
| Godfrey4 20 | 35/38 | 1.55 (1.13 to 2.1) | 4.5 | 23.7 | – | 8.1 | 192 | – |
| Mossad5 20 | 49/50 | 2.8 (1.8 to 4.5) | 4.4 | 13.3 | – | 6.0 | 80 | – |
| Petrus6 20 | 52/49 | 1.77 (1.16 to 2.67) | 2.7 | 9 | 15 | 9.9 | 89 | 2.5 |
| Prasad7 20 | 25/23 | 7.5 (3.5 to 16) | 4.0 | 12.8 | 30 | 6.2 | 80 | 3.1 |
| Prasad8 20 | 25/25 | 22 (7.7 to 64) | 3.8 | 13.3 | 30¶ | 6.9 | 92 | 3.4 |
| Turner and Cetnarowski**9 | 69/67 | 1.45 (1.03 to 2.1) | – | 13.3 | – | 6 | 80 | – |
| The current trial | 45/42 | 0.68 (0.40 to 1.14) | 0.9 | 13 | 8 | 5.05 | 65 | 0.7 |
Comparison of the current zinc lozenge with the zinc lozenges of trials in which zinc lozenges were significantly beneficial in common cold treatment. Five previous trials used zinc gluconate1–5 9 and three used zinc acetate.6–8 All studies investigated natural common cold, except Al-Nakib (1987) and Turner (2000), which investigated experimental rhinovirus colds. This table shows the results and dissolving time in eight trials in which zinc lozenges were effective. The potential problems with lozenges in the 12 trials with negative results are described in table S1 in online supplementary file 2.
*The RR calculations are described in Ref. 20, except for Turner (2000) for which the RR was based on the measurements of the recovery rates from their figure 1A,9 see table S2 in online supplementary file 2. RR>1 indicates that recovery is faster in the zinc lozenge group.
†The number of zinc lozenges per day is either planned1 2 9 or counted.
‡15 min is the average for ‘dissolved in the mouth as lozenges (about 10–20 min each)’.1
§The Al-Nakib (1987) study2 3 did not report data suitable for the calculation of the RR. The study reported a significant reduction in cold symptoms and in the number of tissues used by the patients,2 and a significant effect on the common cold-induced reduction in response time in a psychological test.3
¶The dissolving time is based on reporting that the lozenges in Prasad (2008)8 were similar to those in Prasad (2000).7
**The Turner and Cetnarowski study9 reported that in the experimental rhinovirus colds trial, the median duration of colds was 2.5 days in the zinc group and 3.5 days in the placebo group (p=0.035). The same report9 published four trials with zinc acetate lozenges that had problems in their composition, which can explain the lack of effect (see Ref. 17; online supplementary table S1). A sixth trial in the same report9 administered zinc gluconate lozenges (80 mg/day) to patients with natural colds and found no benefit (online supplementary table S1). The size of the lozenge and its dissolving time were not reported. The number of lozenges per day shown in the table is planned frequency, but actual frequency was not reported.
RR, rate ratio.