Hormone replacement therapy (HRT) skin patches containing low doses of oestrogen carry less risk of stroke than oral therapy and may represent a safer alternative to tablets, suggests a study published on bmj.com today.
However, the risk increases significantly with high dose patches.
HRT is regularly prescribed to women suffering from the effects of the menopause. However, most studies have shown an increased risk of stroke associated with taking HRT. There is also evidence that different routes of administering HRT may be associated with a different risk of cerebrovascular events.
So researchers in Canada and Germany assessed the risk of stroke associated with oral and transdermal (through the skin) HRT in post-menopausal women in the UK.
Their findings are based on data from the General Practice Research Database (GPRD), which holds the anonymised medical records of millions of patients registered with family doctors across the UK.
From a population of over 870,000 women aged 50-79 between January 1987 and October 2006, they identified 15,710 cases with a first recorded diagnosis of stroke occurring in the study period. Each case was matched to 59,958 controls.
Exposure to HRT was categorised into oestrogens only, oestrogens plus progestogen, progestogen only, and tibolone. Oestrogens were further subdivided according to the route of administration (oral or transdermal) and to the dose (high or low).
The risk of stroke was not increased with use of low oestrogen dose patches compared with no use, whereas the risk was increased by up to 88% with high dose patches.
Use of oral HRT increased the rate of stroke by around 25-30% compared with no use, regardless of the oestrogen dose or when combined with progestogen.
There was no risk increase with short-term use (less than one year) of the oral formulations, but longer-term users (more than one year) of the oral agents had a 35% increased risk.
The authors conclude: "Our study suggests that the use of transdermal oestrogen replacement therapy containing low doses of oestrogen could be associated with a lower risk of stroke than the oral route of administration."
They add: "Although these results alone do not represent definitive evidence to promote the use of the transdermal route over oral administration of oestrogen replacement therapy, this study should encourage further research on the importance of the route of administration to define the role of transdermal oestrogens in the therapeutic arsenal for the treatment of menopausal symptoms."
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