Ergometrine and methylergometrine tablets are not stable under simulated tropical conditions

This study is part of a programme on reduction of postpartum haemorrhage (PPH). Ergometrine and methylergometrine have a favourable effect on both blood loss and maternal morbidity and mortality and oral preparations were regarded as a possible treatment for use in tropical countries. The stability of oral preparations of the two ergometrine compounds under tropical conditions was unknown and was therefore examined in this study.

The 'experimental shelf lives' of ergometrine and methylergometrine tablets were examined by exposing the tablets to seven artificially controlled conditions. Samples were analysed by high performance liquid chromatography at nine different sampling times over a period of 1 year to determine the content of ergometrine and methylergometrine.

Under refrigeration (test I), less than 90% of the stated amount of active ingredient was found in the tablets after 14 weeks in the case of ergometrine and 21 weeks in the case of methylergometrine. When stored in the dark at 40 degrees C and 75% relative humidity (test VI), the tablets fall outside accepted specification (= 90-110% of state amount of active ingredient) within 3 weeks in the case of ergometrine and 21 weeks in the case of coated methylergometrine tablets. The stability of uncoated ergometrine tablets was far less than that of coated methylergometrine tablets. Instability worsened under extreme humid conditions (test IV and VI), and hot conditions (test V), for both ergometrine and methylergometrine. From week 31 onwards the coating did not seem to protect the compound anymore, irrespective of the condition of exposure.

Tropical conditions make the tablets unstable with humidity as the main adverse factor. The sugar-coated methylergometrine tablets are more stable under humid/hot conditions than the non-coated ergometrine tablets. Under all simulated conditions both oral ergometrine and methylergometrine tablets are unstable.