Multiple-use preparations must contain a preservative to prevent spoilage or contamination. Preservatives are effective at a certain concentration and often only active at a certain pH range. Preparations containing sufficiently high concentrations of glycerol (30% m/m), propylene glycol (>15% m/m), ethanol (>15% m/m) or sucrose (>62% m/m) are self-preserving. Furthermore, the addition of aqua conservans can replace distilled water to promote preservation.
Table 1. Preservatives
|
Preservative |
Concentration (% m/v) |
prerequisite pH |
|
benzalkoniumchloride |
0.004% - 0.010% |
3-9 |
|
benzoëzuur |
0.10% - 0.26% |
2-5 |
|
benzethoniumchloride |
0.01% - 0.02% |
|
|
benzylalcohol |
0.90% - 1.50% |
<5 |
|
cetrimide |
0.10% |
7-9 |
|
cetylpyridinechloride |
0.01% - 0.02% |
|
|
chlorobutanol |
0.50% |
<5 |
|
chlorocresol |
0.075% - 0.200% |
<6 |
|
chloorhexidine digluconaat |
0.01% |
|
|
fenol |
0.25% - 1.50 % |
<9 |
|
fenoxyethanol |
0.50% - 1.00% |
<7 |
|
fenylmercuri-acetaat |
0.002% - 0.004% |
>7 |
|
fenylmercuriboraat |
0.002% - 0.004% |
>7 |
|
nipagine (methylparahydroxybenzoaat) |
0.10% - 0.20% |
4-8 |
|
nipasol (propylparahydroxybenzoaat) |
0.03% |
4-8 |
|
sorbinezuur |
0.10% - 0.25% |
<4 |
|
β-fenylethylalcohol |
0.30% - 0.50% |
<5 |