It can also cause serious hypersensitivity reactions including anaphylactic shock, urticaria, serious skin rashes, including Stevens–Johnson syndrome and toxic epidermal necrolysis, angioedema, facial edema, bronchospasm, granulomatous hepatitis, and itchiness.The most common adverse effects involve a group of symptoms called cinchonism, which can include headache, vasodilation and sweating, nausea, tinnitus, hearing impairment, vertigo or dizziness, blurred vision, and disturbance in color perception. More severe cinchonism includes vomiting, diarrhea, abdominal pain, deafness, blindness, and disturbances in heart rhythms. Cinchonism is much less common when quinine is given by mouth, but oral quinine is not well tolerated (quinine is exceedingly bitter and many people will vomit after ingesting quinine tablets). Other drugs, such as Fansidar (sulfadoxine with pyrimethamine) or Malarone (proguanil with atovaquone), are often used when oral therapy is required. Quinine ethyl carbonate is tasteless and odourless, but is available commercially only in Japan. Blood glucose, electrolyte and cardiac monitoring are not necessary when quinine is given by mouth. Quinine has diverse unwanted interactions with numerous prescription drugs, such as potentiating the anticoagulant effects of warfarin. Mechanism of action
Quinine is used for its toxicity to the malarial pathogen, Plasmodium falciparum, by interfering with its ability to dissolve and metabolize hemoglobin. As with other quinoline antimalarial drugs, the precise mechanism of action of quinine has not been fully resolved, although in vitro studies indicate it inhibits nucleic acid and protein synthesis, and inhibits glycolysis in P. falciparum. The most widely accepted hypothesis of its action is based on the well-studied and closely related quinoline drug, chloroquine.
Hypereosinophilic syndrome  is a disease characterized by a persistently elevated eosinophil count (≥ 1500 eosinophils/mm³) in the blood for at least six months without any recognizable cause, with involvement of either the heart, nervous system, or bone marrow.HES is a diagnosis of exclusion, after clonal eosinophilia (such as FIP1L1-PDGFRA-fusion induced hypereosinophelia and leukemia) and reactive eosinophilia (in response to infection, autoimmune disease, atopy, hypoadrenalism, tropical eosinophilia, or cancer) have been ruled out.There are some associations with chronic eosinophilic leukemia as it shows similar characteristics and genetic defects. If left untreated, HES is progressive and fatal. It is treated with glucocorticoids such as prednisone. The addition of the monoclonal antibody mepolizumab may reduce the dose of glucocorticoids. Signs and symptoms
As HES affects many organs at the same time, symptoms may be numerous. Some possible symptoms a patient may present with include:

Cardiomyopathy
Skin lesions
Thromboembolic disease
Pulmonary disease
Neuropathy
Hepatosplenomegaly
Reduced ventricular size
Atopic eczema

Diagnosis
Numerous techniques are used to diagnose hypereosinophilic syndrome, of which the most important is blood testing. In HES, the eosinophil count is greater than 1.5 × 109/L. On some smears the eosinophils may appear normal in appearance, but morphologic abnormalities, such as a lowering of granule numbers and size, can be observed. Roughly 50% of patients with HES also have anaemia.Secondly, various imaging and diagnostic technological methods are utilised to detect defects to the heart and other organs, such as valvular dysfunction and arrhythmias by usage of echocardiography.