The effect is due to the blockade of the AT1 receptor. The hormone angiotensin II normally binds to this receptor, increasing blood pressure. Olmesartan competitively inhibits the receptor, reducing the frequency with which angiotensin II binds to AT1, resulting in a decrease in blood pressure. In addition, olmesartan also shows beneficial effects on renal function and also possesses antisclerotic properties, which has additional beneficial effects on blood pressure and the cardiovascular system.
Olmesartan is administered in the form of its prodrug olmesartan medoxomil, which in its pure form is not absorbed by the body. It is converted to the active form during the first liver passage. Thus, the bioavailability is about 26%. The maximum plasma concentration is reached after 1-3 hours and plasma protein binding is about 99%. The degradation of olmesartan is not catalyzed by the enzymes of the CYP450 system, which significantly reduces the likelihood of interactions with other drugs. A large proportion of the given dose is excreted unchanged in the faeces. The plasma half-life is 10-15 hours.
Drug interactions occur mainly in association with other antihypertensive drugs. As a result, the antihypertensive effect may be too strong, which may have life-threatening consequences. Acetylsalicylic acid may damage the kidneys when used together. Antacids can lower the serum concentration of olmesartan and thus weaken its effect. In rare cases, olmesartan may increase the concentration of lithium to toxic levels.