The Merck Manual estimates that worldwide, malaria infects between 300 million and 500 million people, killing one to two million annually. Malaria spreads when mosquitoes infected with certain species of the Plasmodium protozoa inject the parasite into the bloodstream. Several drugs, including primaquine and chloroquine, can prevent malaria among travelers headed for malaria-prone areas.
Use
Chloroquine and primaquine both can be used to prevent and treat malaria. Primaquine also prevents relapse in people infected with P.vivax and P. ovale. For malaria prevention, travelers take chloroquine once per week for one to two weeks before their trip, once weekly all during their trip, and once weekly for four weeks following their trip. Travelers would take primaquine daily, starting on the day before their trip and continuing for three to seven days following their trip. For malaria prevention, adults take 500 mg of chloroquine once per week or 30 mg of primaquine once per day.
Benefits
Because of the different dosing regimens, the timing and duration of the trip might favor one malaria-preventative over the other. Travelers leaving on short notice or those planning short trips might favor primaquine's quick start and end timetable, while travelers going on extended trips might prefer chloroquine's once weekly dosing schedule. Unlike other malaria prophylactics, pregnant women can take chloroquine safely all though pregnancy.
Drawbacks
People with a condition called glucose-6-phosphatase-dehydrogenase (G6PD) deficiency and those who have not been tested for it cannot take primaquine. Primaquine is not safe for women who are pregnant, or for nursing mothers unless the baby tests negative for G6PD deficiency. Chloroquine cannot be used in areas of the world where Plasmodium strains have developed chloroquine resistance. Chloroquine can worsen the skin condition psoriasis.
Effectiveness
The Merck Manual says that some studies show that primaquine is less effective against P. vivax than P. falciparum, and lists it as a less preferred "alternate" drug for malaria prophylaxis in areas where P.falciparum is resistant to chloroquine. However, the CDC says that primaquine is the most effective drug available against P. vivax and recommends its use by travelers going to areas where more than 90 percent of malaria cases result from P. vivax infection. The Merck Manual lists chloroquine as the "drug of choice" for travelers to areas with chloroquine-sensitive P. falciparum. The CDC warns that no drug can completely prevent malaria, so travelers must also take precautions against mosquito bites.
Mechanism
Primaquine prevents and treats malaria by eliminating forms of P. falciparum from the blood. Primaquine disrupts the parasite's energy-producing organelle, the mitochondria, and binds to Plasmodium DNA to prevent protein synthesis. Chloroquine damages cell membranes of Plasmodium and inhibits the polymerase enzymes that build DNA and RNA, ultimately shutting down protein synthesis. Levels of chloroquine build up inside Plasmodium cells, raising the pH, which inhibits cell growth.
