Most storage guidelines mention that ergometrine and methylergometrine should be protected from light (Table 1), However, it is widespread practice in African countries and probably also in other developing countries to take the ampoules from their boxes and keep them in trays in the dispensary or in open kidney dishes in the labour ward (Figure 5). Apart from elevated temperatures, the drugs may then be exposed to the influence of light for weeks or possibly months.
The effects of light on ergometrine are summarized in Annex 5/1 and visualized in Figure 6. When stored at 21-25°C in the dark the mean loss of potency is about 21% after one year. At the same temperature but subjected to indirect light, on average 27% potency is lost in one month and over 90% within a year. Results for methylergometrine are very similar, with 21% loss after one month exposure to light and 90% after one year (see Annex 5/2).
Although there are gradual differences, all products show a similar effect. One brand of ergometrine is considerably worse then the other three. This was the only product that was delivered in transparent rather than brown ampoules and the result shows that the brown glass prevents some, but by far not all harmful effects of light. Methylergometrine shows the same picture, with the same brand in transparent ampoules showing the strongest effect.
Figure 6 Stability of ergometrine at 21-25°C with and without exposure to light
For oxytocin no effect of light could be found (Annex 3). This is in line with the information supplied by manufacturers and storage guidelines from the textbooks. However, it contradicts the information supplied by Sandoz and their warning to protect the product from light (Table 1).
The conclusion is that for ergometrine and methylergometrine exposure to indirect light results in a rapid loss of active ingredient. In the worst case, in transparent ampoules, ergometrine lost 57% potency in one month and methylergometrine 61%, On average the loss in one month was 21% and 27% respectively. No such effect was found with oxytocin.