Tracleer (Bosentan)

Tracleer was the first oral medication to gain a licence specifically for the treatment of PH in 2001. Tracleer is part of a class of medications called endothelin receptor antagonists or ERA's. It has been used and studied in children and appears to be safe.

How does it work in PH?

Endothelin is a chemical messenger normally found within the body. Endothelin is made by the body in the endothelium (a layer of cells which line the heart and blood vessels). Endothelin constricts blood vessels and increases blood pressure. Endothelin is a very powerful vasoconstrictor that plays an important role in blood flow. In PH, the body produces excess endothelin, contributing to the constriction of blood vessels and affecting the blood pressure in the lungs. It is one of the chemicals involved in the overall control of blood vessel activity. Although endothelin is present in healthy people, high concentrations of the substance have been found in the plasma and lungs of patients with PH suggesting that it plays a part in keeping the pressure in the lungs high.

The blood vessels in the lung need to be able to adapt to the changing needs of the body in order to maintain balance/health. For the body to achieve this it needs to produce some chemicals that cause the vessels to open up and some that cause them to become narrow. In other words endothelin is not a bad chemical that harms the body, but too much of it is not a good thing! Using a traffic jam analogy, PH is the equivalent of rush hour on the M25. Despite clear road signs and speed cameras, the system cannot cope with such increased demands. Treatment with ERA drugs is like adding another lane to the M25. Whether or not this will solve the root cause of the problem or whether it will simply act as a short-term pressure release is yet to be seen.

Endothelin causes blood vessels to narrow and can also aggravate scarring and overgrowth of the muscle in the walls of blood vessels in the lungs. By blocking the action of endothelin, Tracleer can lead to a reduction in the blood pressure in the lungs and to improvement in activity levels and well-being. While improved exercise capacity and increased sense of well-being have been seen in short-term studies of Tracleer, there is less information regarding long-term effects.

Tracleer - are there any side effects?

Reported side effects include nasal congestion, headache, increased blood flow to the skin on the face (facial flushing) and swelling in the legs. It is also thought to have some interaction with warfarin requiring an increase in the dose necessary to maintain the effectiveness of warfarin.

The major potential side effect is liver problems. The development of abnormal liver function tests (which are measured by a simple blood test) is seen in about 7-10% of adults. This side effect is less common in children. It is important to know that it has now been given to thousands of patients without any reports of permanent liver damage. It is important that patients have regular (normally monthly) blood tests to measure its effects on the liver.

It is also believed that Tracleer can decrease the effectiveness of hormonal contraceptives (e.g. the contraceptive pill) and such hormonal contraceptives should not be used alone for the prevention of pregnancy during treatment with Tracleer. In animal studies, Tracleer has been shown to be harmful to the growing foetus, therefore it is very important that women being treated with this drug avoid becoming pregnant.

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