Primaquine resistance in Plasmodium vivax.

Reports have appeared calling attention to what has been termed primaquine resistance in Plasmodium vivax in several geographic areas. The possibility exists that primaquine tolerant strains (often referred to as the tropical zone type from the South Pacific and Southeast Asian regions characterized by early and frequent relapses) may have become widely disseminated to areas where they had not previously existed through the widespread population mobility that has characterized the last 50 years. The appearance in the relatively recent past of strains of P. vivax, particularly from the South Pacific area, that are resistant to the 4-aminoquinolines has added a new dimension to the resistance problem. While there seems to be little evidence to date of the existence of acquired primaquine resistance in P. vivax, the possibility of its emergence in the future can certainly not be ruled out, and its timely detection and confirmation will be most important, albeit quite difficult because of the relatively covert sites of drug effect. The occurrence of relapses in P. vivax after primaquine therapy would be assumed to be the most reliable indication of resistance. Reports of the sporontocidal or gametocytocidal activity of primaquine when used alone (i.e., without concomitant administration of an effective suppressive) against a P. vivax infection have been few and inconclusive. The establishment of baselines of this activity in P. vivax might be useful in detecting and evaluating primaquine resistance in this species.