The British Medical Journal has published the results of a systematic review and meta-analysis that aimed to assess the risk of venous thromboembolism (VTE) in women using hormone replacement therapy.
The study included eight observational studies and nine randomised controlled trials. All of the randomised studies involved oral treatments only while four of the observational studies involved both oral and transdermal products.
The study found an overall increased risk of VTE in patients using HRT as follows:
- Oestrogen only - increased risk (Odd Ratio = 2.2; 95%CI 1.6 - 3.0)
- Oestrogen and Progestogen - increased risk (OR = 2.6; 95% CI 2.0 - 3.2)
- Use for less than 1 year - increased risk (OR = 4.0; 95% CI 2.9 - 5.7)
- Use for more than 1 year - increased risk (OR = 2.1; 95% CI 1.3 - 3.8)
- Past Use - no significant difference (OR = 1.2; 95% CI 0.9 - 1.7)
The study also noted that transdermal products appear to have a lower risk (OR = 1.2; 95% CI 0.9 - 1.7) however this finding was based on four of the observational studies and it is unclear from this analysis how many patients were involved in these studies or how many were treated with transdermal HRT. As such the authors sates that, "the results should be interpreted with caution therefore and further investigation of transdermal oestrogen is needed".
Action: Clinicians should continue to prescribe the lowest effective dose of oestrogen for the shortest time possible. Transdermal products may pose a lower risk of VTE however more research is required to establish confidence in this finding, a cautious approach is still warranted.