Exemestane vs Letrozole: An Overview
Exemestane
Exemestane is a steroidal aromatase inactivator primarily used in the treatment of hormone-sensitive breast cancer in postmenopausal women [1]. It works by suppressing in vivo aromatase activity by 97.9%, leading to a reduction of over 85% in circulating estrogen levels [1]. This drug is orally active and is typically administered at a dosage of 25 mg once daily [1].
Exemestane is unique in its class as it irreversibly inactivates the aromatase enzyme, differing from other approved aromatase inhibitors [2]. It is highly potent, selective, and well-tolerated [1].
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Letrozole
Letrozole, also known by its brand name Femara, is a medication primarily used in the treatment of breast cancer in postmenopausal women. It belongs to a class of drugs known as nonsteroidal aromatase inhibitors, which reduce the amount of estrogen produced by the body [3].
Letrozole is primarily used in the treatment of breast cancer in postmenopausal women. It is particularly effective in cases where the cancer is hormone-sensitive, as it decreases the amount of estrogen produced by the body, thereby slowing or stopping the growth of cancer cells that need estrogen to grow [3, 4].
In addition to its use in treating breast cancer, letrozole has also been found to be effective in inducing ovulation in infertile pre-menopausal women. It enhances the production of follicle-stimulating hormone (FSH), which is crucial for ovulation induction [5].
Letrozole has also been used in the treatment of anovulation, preventing ovarian hyperstimulation syndrome (OHSS), and retrieving oocytes in breast cancer patients [6].
Furthermore, there is some evidence to suggest that letrozole may affect gastric cancer, although further studies are needed to confirm this [7].
Finally, letrozole has been used in the management of advanced ovarian cancer, both in the primary and recurrent setting. It has been shown to provide a prolonged recurrence-free interval, mainly as a maintenance treatment [8].
Exemestane vs Letrozole: Side effects
Side effects of Exemestane
Some of the most common include:
- hot flashes,
- sweating,
- muscle or joint pain,
- and tiredness.
Other frequently reported symptoms are:
- headache,
- dizziness,
- feeling worried or anxious,
- depression, and
- difficulty falling asleep or staying asleep [9].
Nausea, vomiting, increased appetite, and diarrhoea are also common. Some patients may experience hair loss, red, itchy skin, changes in vision, and swelling of the arms, hands, feet, ankles, or lower legs. In some cases, Exemestane can cause thirst, giddiness, and weight gain [10, 11].
More severe side effects include shortness of breath and chest pain. If you experience these symptoms, seeking medical attention immediately is essential [9].
Exemestane can also cause a decrease in bone mineral density, which may increase the risk of developing osteoporosis, a condition in which the bones become fragile and break easily [9].
In rare cases, Exemestane has been associated with cholestatic liver injury, characterized by pruritus, diarrhoea, and hyperbilirubinemia [12].
Side effects of letrozole
Letrozole, a medication often used in the treatment of breast cancer, can cause a variety of side effects. These can range from mild to severe, and not everyone who takes the medication will experience them.
Common side effects of letrozole include hot flashes, bone pain, weakness, and joint pain. Some people may also experience headaches during their treatment [13].
Mild side effects that have been reported with letrozole include:
- fatigue,
- swelling in your arms,
- hands, legs, or feet,
- increased sweating or night sweats,
- nausea,
- vaginal bleeding spotting, dryness or irritation,
- constipation,
- weight gain,
- hair loss,
- and mild allergic reactions [13].
Serious side effects, although rare, can occur. These include high cholesterol levels, osteoporosis (weakened bones), bone fractures, high blood pressure, cardiovascular side effects such as heart attack and stroke, depression, and severe allergic reactions [13].
It's important to note that side effects can depend on your age, other health conditions, and other medications you may be taking. If you experience any side effects that are ongoing or bother you, it's essential to talk with your doctor or pharmacist [14].
Choosing between Exemestane and Letrozole
When choosing between Exemestane and letrozole for the treatment of estrogen receptor-positive breast cancer in postmenopausal women, several factors need to be considered.
Firstly, the biochemical effect of these drugs on the aromatase enzyme differs. Letrozole is a competitive aromatase inhibitor, while Exemestane binds irreversibly to the aromatase enzyme [15]. This difference is clinically significant as it has been shown that Exemestane may cause a disease regression following resistance to nonsteroidal aromatase inhibitors like letrozole [15].
Secondly, the plasma half-lives of these drugs differ. At clinically administered doses, the plasma half-life of letrozole (2.5 mg once daily) is 2-4 days, while that of Exemestane (25 mg once daily) is 27 hours [16]. This means that letrozole stays in the body longer than Exemestane, potentially influencing the dosing schedule and the onset of therapeutic effects.
Thirdly, the impact of these drugs on plasma lipid levels varies. Letrozole has been reported to have an unfavourable effect on plasma lipid levels, while the impact of Exemestane on plasma lipid levels is not clearly stated [16]. This could be a consideration for patients with pre-existing lipid disorders.
Lastly, the sequence of administration of these drugs can also be a factor. Some studies have shown that patients can receive Exemestane as their first anti-aromatase agent and still benefit from letrozole or anastrozole after progression [17].
In conclusion, the choice between Exemestane and letrozole should be individualized, considering the patient's specific clinical situation, the potential side effects, and the biochemical properties of the drugs.