<p>Caution is necessary when giving choroquine to patients with porphyria who also have hepatic dysfunction or cirrhosis as the drug may precipitate severe constitutional symptoms and an increase in the amount of porphyrins excreted in the urine. This reaction is especially apparent in alcoholics. Patients receiving choloquine continuously at higher dose levels for a period longer than 12 months or at weekly intervals for a period of more than 3 years as prophylactic against malaria (or the consumption exceeds 1.6 g/Kg) should undergo ophthalmic examination at three months interval.</p>