Men on testosterone therapy are exposed to a greater risk of venous thromboembolism (VTE) during the first few months of treatment, warn experts who say that until now, a failure to investigate the timing and duration of use on VTE risk has masked the association.
The risk increases rapidly over the first three months of use and peaks at six months, claim the international and Australian experts involved in the population-based cohort study.
The findings are based on data from 19,215 patients with confirmed VTE and 909,530 age-matched controls from over 2.2 million men registered with the UK Clinical Practice Research Database between January 2001 and May 2013.
Three mutually exclusive testosterone exposure groups were identified: current treatment, recent treatment, and no treatment in the previous two years. Current treatment was subdivided into duration of more or less than six months.
According to the investigators, in the first six months of testosterone treatment, they found a 63% increased risk of VTE among current testosterone users, corresponding to 10 additional VTEs above the base rate of 15.8 per 10,000 person years.
The risk declined substantially after more than six months’ treatment and after treatment stopped.
Men who had a VTE were more often obese and had more comorbidities, notably polycythaemia, chronic pulmonary disease, congestive heart failure, myocardial infarction, and peripheral vascular disease, compared to the controls.
Additionally, corticosteroids, non-steroidal anti-inflammatory drugs, and antiplatelets were used more frequently among cases than controls.
While the authors pointed out that the increased risks are temporary, and still relatively low in absolute terms they said that failure to investigate the timing of VTE in relation to the duration of testosterone use “could result in masking of an existing transient association.”
They also stressed that new research should investigate the risk in first time users and confirm that those risks really are absent with long-term use.
In Australia a clampdown on GP prescribing of testosterone initiated by the government last year slashed in half the number of scripts for the hormone.
The measures were introduced in April last year following a PBS review which raised concerns that GPs were overprescribing testosterone.
Under the new PBS criteria GPs can prescribe testosterone after a consultation with a specialist and only for men with a serum testosterone level of 6nmol/L, down from a level of less than 8nmol/L.