Chloroquine is given in high loading dose because of:

Pharmacokinetics :Oral absorption of chloroquine is excellent. About 50% gets bound in the plasma. It has high affinity for melanin and nuclear chromatin: gets tightly bound to these tissue constituents and is concentrated in liver, spleen, kidney, lungs (several hundred-fold), skin, leucocytes and some other tissues. Its selective accumulation in retina is responsible for the ocular toxicity seen with prolonged use. Absorption after i.m. injection is also good. Chloroquine is paly metabolized by liver and slowly excreted in urine. The early plasma tYz varies from 3-10 days. Because of tight tissue binding, small amounts persist in the body with a terminal Ph of 1-2 months. ESSENTIALS OF PHARMACOLOGY page no 822