Patients taking an ARB to control their blood pressure should be warned the drug may no longer work at very high altitudes, according to researchers who found the drug telmisartan became ineffective in people trekking at 5,400 metres above sea level.
The researchers said their findings could also have implications for patients who experience hypoxia at normal altitudes, such as those suffering from sleep apnoea.
The randomised trial included 47 healthy, normotensive people who took telmisartan 80 mg or a placebo daily for eight weeks and then went on a trekking expedition in Nepal.
People taking telmisartan initially experienced a much smaller increase in their blood pressure levels than those on placebo as they gained altitude, with their average systolic blood pressure around 4 mmHg lower than the placebo group’s both at sea level and once they reached 3,400m.
But after hiking to Everest base camp, at 5,400 m above sea level, the difference in blood pressure between the two groups almost disappeared.
The Italian team said that at a practical level, the finding implies that ‘for people already being treated with angiotensin II blockers, such as telmisartan, the treatment will remain effective at altitudes reached by trekkers, climbers, skiiers and workers, but will not work at very high altitudes where their blood pressure will probably become uncontrolled more easily’.
The researchers claim that their findings will enable doctors to ‘take appropriate action to warn cardiovascular patients of the need for caution whenever they are going to be exposed to high altitudes’.