Posanat 100mg is used to prevent certain fungal infections in patients who have severely weakened immune systems. It belongs to a class of drugs known as azole antifungals. It works by stopping the growth of fungi. It can be taken with food. Side Effects Unusual tiredness Weakness Muscle cramps Mental/mood changes Swelling of the ankles/feet Signs of infection (such as chills, fever) Vaginal bleeding Shortness of breath Increased thirst/urination.