The chloroquine concentrations in plasma depend on the dose taken and on the kidney and liver functions. Even with constant doses of 250 mg, a strong interindividual (0.2-0.8 |imol/ml) as well as intraindividual variation of approximately 30% can be found. Fifty percent to 70% of chloroquine is bound to plasma proteins. In many organs, the concentrations of chloroquine are much higher than in blood, sometimes up to 1,000 times higher. Owing to the strong affinity of chloroquine to melanin, it accumulates in the iris, chorioidea, and inner ear (concentrations are 80 times higher than in the liver). The concentrations decrease from the liver (highest) over spleen, kidney, lung, heart to muscle and brain. In fatty tissues, however, chloroquine is barely accumulated. This characteristic is important for the dosage. Chloroquine concentrations in the skin are approximately 100-200 times higher than in plasma, whereas the concentration in the epidermis is approximately 3-7 times higher than in the dermis. Chloroquine can be found in the keratinocytes. The concentrations in living epidermis and stratum corneum are the same.

The fictive volume of distribution is high because of this accumulation in deep compartments In blood it reaches a mean±SD value of 115-167±64 l/kg, and in plasma about 800 l/kg. Chloroquine reaches equilibrium between plasma and tissue not before 4 weeks, and hydroxychloroquine not before 6 months.

Quinacrine is widely distributed in the tissues and very slowly liberated. Plasma concentrations increase rapidly during the first week, and 94% equilibrium is attained by the fourth week. Eighty percent to 90% of quinacrine is bound to plasma proteins. The drug accumulates in the same organs as chloroquine (liver: 20 000 times the plasma level; leukocytes, factor 200; erythrocytes, factor 2) and accumulates progressively if chronically administered (Wallace 1989).

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