Ergometrine and methylergometrine
When stored at D6/83, ergometrine and methylergometrine were not stable and contained less than 90% of the active ingredient within 7 and 21 weeks, respectively. D6/83 is the least harmful condition, although the high humidity factor must be taken into consideration. Packed in a closed tin and stored in a refrigerator, the humidity will be lower and stability probably better. Still, the results are alarming, indicating that storage is such a critical factor that these tablets are in no way suitable for use under (primitive) tropical conditions.
Improvement in stability might be obtained by protecting the tablets from humidity by coating or special packaging, as humidity seems a more harmful factor in the process than temperature. The influence of light is not so striking as for the ampoules (13).
A remarkable difference between the results of E and ME occurs. Under extreme conditions the active ingredient of E quickly reduces to levels below 50% of the stated amount and finally falls to below 1% (at D40/75), whereas the active ingredient of ME, even at D40/75, does not fall below 45%. Probably ME is converted into a metabolite, which is not separately measured by HPLC. It is known that in an alkaline (methanol) environment E and ME can be converted into their inactive enantiomer: (methyl) ergometrinin. In E and ME ampoules that vulnerability to an alkaline environment has been avoided by dissolving the compound in an acid solution (pH = 1-2). The fact that injectable E and ME are not sensitive to environmental pH-changes (while tablets are prone to these changes) might be one of the factors that unexpectedly makes the stability of E and ME tablets even worse than that of the ampoules.
Buccal oxytocin and desamino-oxytocin
As the stability results show, OT and DOT are more stable than E and ME. However, within ± 23 weeks, both products show levels of the active ingredient below 90%. This is too quickly for use in tropical countries, considering that transportation and intermediate storage alone may take several weeks. The negative influence of humidity seems stronger than that of high temperature.
Because of their observed instability under tropical conditions, buccal OT and DOT tablets cannot be considered as an alternative for PPH prevention either. Moreover, their route of administration may pose several problems. Data on their pharmaco-kinetics when used for preventing PPH are still far from adequate.