The Effects of Hypoxia on Infections with Plasmodium Cathemerium

The minimal "curative" (or suppressive) dosage of Primaquine for canaries infected by Plasmodium cathemerium in normal air, at slightly over 800 ft altitude, must be increased approximately tenfold for similarly infected canaries which have been maintained in an atmosphere deficient in oxygen (75 mm Hg partial pressure) for a period of 3 or 4 days. In other words, hypoxia markedly reduces the effectiveness of antimalarial agents. The marked decrease in effectiveness of the drug in conditions of hypoxia occurs quickly and adaptation to this environment is very slow (over 16 days). However, removal of birds from the oxygen-deficient environment to normal air causes a very prompt recovery from the harmful effects of hypoxia. The course of infection with P. cathemerium in canaries which have been subjected to simulated altitudes of 19,000 to 20,000 ft bears a considerable similarity to the course of infection of birds receiving daily injections of cortisone (100 mg/kg). Administration of cortisone, previous to infection, reduces the effectivity of Primaquine but this effect is not as marked as that obtained with the reduction of the tension of oxygen as employed in these experiments.