Losartan, often prescribed under the brand name Cozaar, is an Angiotensin II Receptor Blocker (ARB). Its primary function is managing high blood pressure, but it is also used for conditions like heart failure and kidney disease in patients with type 2 diabetes. Losartan works by blocking the action of the hormone angiotensin II, which relaxes blood vessels and decreases blood pressure. While this mechanism offers health benefits, it can also cause adverse effects, ranging from minor discomforts to severe, life-threatening reactions. Understanding the most serious risks associated with this medication is important for overall health management.
Common and Expected Adverse Effects
Most individuals tolerate Losartan well, but many experience mild side effects, especially when first starting the medication. These effects often fade as the body adjusts to the drug. Dizziness is frequently reported, which can occur due to the blood pressure-lowering effect, particularly when standing up quickly.
Patients may also notice symptoms similar to a common cold, such as a stuffy nose or an upper respiratory tract infection. Minor aches, including joint pain, back pain, or general fatigue, are sometimes reported. Digestive issues like nausea, vomiting, or diarrhea can also occur, though taking the medication with food may help mitigate these effects. These mild effects should be reported to a healthcare provider but usually do not require stopping the medication.
Acute Emergency Reactions
A small number of patients can experience an immediate and potentially life-threatening reaction to Losartan, requiring emergency medical attention. The most severe reaction is angioedema, which involves rapid swelling of the deeper layers of the skin and mucous membranes. Angioedema commonly affects the face, lips, tongue, and throat, and swelling in the throat can quickly obstruct the airway, making breathing difficult.
This reaction occurs because Losartan can indirectly affect the metabolism of bradykinin, causing it to accumulate. While angioedema is more commonly associated with older blood pressure medications, ARBs carry a risk, and any sign of facial or throat swelling must be treated as a medical emergency. Other acute reactions include severe allergic symptoms like widespread hives, a severe rash, or difficulty breathing, which may signal anaphylaxis. If any of these symptoms appear, the medication should be stopped, and emergency services contacted immediately.
Serious Systemic Risks
Losartan can lead to severe internal complications related to organ function and electrolyte balance. A major concern is hyperkalemia, a dangerously high concentration of potassium in the bloodstream. Losartan interferes with the renin-angiotensin system, causing the kidneys to retain too much potassium.
High potassium levels can cause serious symptoms, including muscle weakness, tingling sensations, and an irregular heartbeat that can be fatal. The risk of hyperkalemia is higher in patients with impaired kidney function, diabetes, heart failure, or those taking other potassium-sparing medications or supplements. Losartan can also induce acute kidney injury, especially in patients with pre-existing conditions or those who are severely dehydrated. Regular blood tests to monitor potassium and markers of kidney function, such as creatinine and blood urea nitrogen, are necessary while on this drug.
Risks During Pregnancy
Losartan carries a contraindication for women who are pregnant or planning to become pregnant due to its potential for severe fetal harm. The medication must be discontinued as soon as pregnancy is detected because exposure, particularly during the second and third trimesters, can cause injury and death to the developing fetus.
Losartan directly interferes with the renin-angiotensin system, which is crucial for normal fetal kidney development and function. This interference can lead to oligohydramnios, a reduction in amniotic fluid that restricts fetal lung development. Other documented risks include underdeveloped skull bone formation, skeletal deformations, and impaired renal function in the newborn. Female patients of childbearing age must use reliable contraception and discuss alternative blood pressure treatments with their doctor before conception.