This study is part of a research programme that aims to reduce postpartum haemorrhage (PPH). The use of oral oxytocics, with their positive effects on blood loss and maternal morbidity and mortality, was regarded as a possible means of reducing PPH in tropical countries. It is known that injectable oxytocin is more stable than injectable ergometrine and methylergometrine, but the stability of oral oxytocics under tropical conditions is unknown, and is the subject of this study. Four oral oxytocics were included: ergometrine tablets (E), methylergometrine coated tablets (ME), buccal oxytocin (OT) and buccal desamino-oxytocin (DOT).
The stability of oral oxytocics in tropical climates was examined by exposing the tablets to seven artificially regulated conditions. Temperatures ranged between 6-40°C and relative humidity (RH) between 20-85% in the dark, with ambient temperatures used under exposure to daylight. At nine different times during a period of one year, samples were taken and analysed on the content of active ingredients using High Performance Liquid Chromatography (HPLC).
Ergometrine and methylergometrine
After refrigerated storage of 14 and 21 weeks respectively, E and ME had less than 90% of the stated amount of active ingredient. In the dark at 40°C/75% RH the level fell below 90% within 3 and 21 weeks respectively. Stability of uncoated E-tablets was slightly less than that of the coated ME but for both instability increased with humidity and temperature. From week 31 onwards the coating no longer seemed to protect the stability of ME.
Oxytocin and desamino-oxytocin
Under refrigerated storage OT and DOT were slightly more stable then E and ME. Under humid conditions, the level of active ingredient in both drugs fell below 90% after 20 weeks, independent of temperature. DOT was more sensitive to light than OT (after one year’s exposure to light, 60% and 75% of active ingredient respectively remained). For 21 weeks the level of active ingredient in OT remained above 90% at 75% RH at 30 and 40°C. At 40°C/25% RH no difference in stability was noted between the tablets packed in a sealed aluminium package by the manufacturer, and unpacked tablets directly exposed to the defined test condition.
None of the oral oxytocics included in this study were stable under simulated tropical conditions. Oral ergometrine was the least stable under all simulated conditions. It is unlikely that oral oxytocics can be effective in the prevention of PPH in tropical climates.