Safety profile of tadalafil: results from a prescription-event monitoring study
BackgroundTadalafil is a medicine used to treat men with impotence or erectile dysfunction (difficulty getting or keeping an erection).
The aim of the Drug Safety Research Unit (DSRU) is to study the safety of new medicines when they are first put on the market. The medicines studied are those which are widely prescribed by National Health Service (NHS) General Practitioners (GPs) in England. The DSRU conducted a study in 2003-4 to measure the frequency of known side effects of tadalafil and to identify any previously unknown side effects.
The study also investigated the possibility that tadalafil could have adverse effects affecting the heart/circulation and the eye.
Methods
The research method used is known as Prescription Event Monitoring (PEM). Patients prescribed tadalafil between February 2003 until November 2004 were identified from data on dispensed prescriptions supplied, in confidence, by the Prescription Pricing Division (PPD). This is a processing centre to which pharmacists send dispensed prescriptions for payment purposes.
After at least 12 months, GPs were asked to provide information on any medical events that patients experienced since tadalafil was first prescribed. A medical event is defined as anything that was important enough to have been recorded in the medical notes regardless of whether or not it was thought to be related to treatment.
The information received was then analysed and used to measure the frequency of known side effects and identify previously unknown effects of tadalafil.
All prescription information received from the PPA and anonymised medical information received from GPs is treated in strict confidence by the DSRU, which is allowed under the Data Protection Act of 1998 to hold such information for research purposes.
Results
Information was received relating to 16,129 patients (average age 60 years) who had been prescribed tadalafil. At least a third of patients had diabetes (high blood sugar levels) and nearly 30% had high blood pressure.
Comparison of the death rate due to heart disease in patients using tadalafil with that in the English male population of the same age showed fewer deaths than would have been expected.
One case of damage to the main nerve running between the eye and brain cause by an inadequate blood supply was reported. Several factors, including use of tadalafil, could have contributed to the cause of this condition.
Conclusion
This study suggests that tadalafil is generally well-tolerated when used in general practice. As expected from earlier studies, the most common side effects of tadalafil were headache, indigestion and back pain. Although the number of deaths due to heart disease was found to be lower than expected compared to the general male population in England, it is possible that this was due to the health status of users rather than a benefit of the drug. One case of a serious eye disorder was seen suggesting that this may be a rarely occurring side-effect of tadalafil.