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The antimalarial drugs commonly used in dermatology ─ chloroquine and hydroxychloroquine ─ are 4-aminoquinoline compounds and derivatives of quinine.
Quinine is a naturally occurring white crystalline alkaloid derived from the bark of the cinchona trees, originally found in high altitudes of South America. These trees remain the only economically practical source of quinine and they are also found in great number in Java. Infusions of cinchona bark have been used for the treatment of malaria since the 1630s.
Quinine was isolated in 1820 and remained the antimalarial drug of choice until the 1940s, when other drugs, that have fewer adverse effects, replaced it. The first use in dermatology was in 1894 by Payne, to treat discoid lesions in patients with lupus erythematosus.
Chloroquine phosphate (CQ) was synthesized in 1934, and introduced into clinical practice in 1947 for the prophylactic treatment of malaria. Hydroxychloroquine sulfate (HCQ) was synthesized in 1946. Mepacrine, or quinacrine in the US, was synthesized in 1930: it is another antimalarial drug, first used for lupus in 1951 by Page, but it is not commercially available in many countries, so it will not be covered in detail here.
Antimalarials are rapidly and completely absorbed from the gastrointestinal tract following oral administration. Various dosage regimens for HCQ and CQ yield nearly identical plasma level curves with peaks at 4 and 5 hours, respectively.
These two drugs bind avidly to tissue proteins and distribution in tissues are qualitatively similar; the lowest concentrations are found in bone, skin, fat, and brain, and greater concentrations (in ascending order) in muscle, eye (iris and choroid, reaching levels 480000 times that of plasma), heart, kidney, liver, lung, spleen, and adrenal glands.
The extensive tissue uptake and slow release into circulation lead to half-lives of 40–50 days. A steady-state concentration is achieved in 3–4 months, so it may take up to 4-6 months for the appearance of an adequate therapeutic effect. Overall, about 50% of a daily dose of the drug undergoes renal excretion.
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