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Am Fam Physician. 1999;59(3):539-540

to the editor: I would like to congratulate Dr. Dick for his thorough, succinct review of the preventive medicine recommendations for travelers.1

However, I feel that it is important to clarify the issue of malaria chemoprophylaxis. Chloroquine, mefloquine or doxycycline alone does not provide complete protection from the disease. While all four Plasmodium species exhibit both a hepatic stage and an erythrocytic stage, those of P. falciparum and P. malariae are transient, while both P. vivax and P. ovale may remain dormant for years in an intrahepatic form.2,3 Primaquine is the only drug available that can eliminate intrahepatic parasites.2 Thus, active malaria may develop years after the occurrence of an infective bite, despite strict adherence to chemoprophylaxis, if the regimen used lacks primaquine.

Primaquine is only used for “terminal prophylaxis” of disease, and it must be used in addition to a primary chemoprophylactic agent.2 Primaquine should be administered at the doses listed in the article once a day for 14 days after leaving the country of risk. It may be taken during the first two weeks or the second two weeks in conjunction with the primary chemoprophylactic agent, or alone following the completion of such therapy.

The Centers for Disease Control and Prevention currently only recommends terminal prophylaxis with primaquine for certain individuals, such as missionaries or Peace Corps workers, who have prolonged exposure to malaria.4 The definition of prolonged exposure, however, is unclear, and other prescribing references do not include this modifier, recommending terminal prophylaxis for all persons traveling to at-risk regions.2 Note that those who are G6PD deficient are at great risk for developing hemolytic anemia after taking primaquine.

Dr. Dick presents the key aspects of preventive travel medicine in an organized and concise review. The information provided here is intended to clarify one issue in an otherwise excellent review.

to the editor: The article, “Travel Medicine: Helping Patients Prepare for Trips Abroad,” by Dr. Dick1 is a very well-written, well-organized discussion. The article lists drugs for the prophylaxis and treatment of travelers' diarrhea. However, none of these drugs is appropriate for children. I hoped that Dr. Dick would further discuss this issue and make some recommendations for children who are also at risk for “Montezuma's revenge” while traveling.

in reply: Dr. Jordan provides an excellent review of the indications and actions of primaquine. Use of primaquine as a “radical cure” for the liver stages of Plasmodium vivax and Plasmodium ovale infection has been advocated for asymptomatic persons with “prolonged exposure” in malarious endemic areas.1 The Centers for Disease Control and Prevention (CDC) does not define “prolonged,” but other authors have suggested a definition of more than two to three months of continued exposure to malaria.2

Another option is a “wait-and-watch” approach, treating patients for malaria and giving the “radical cure” only if symptoms develop and the diagnosis is made.3 P. vivax infections may become symptomatic months and, rarely, even one to two years after the initial infection.4 Since healthy persons rarely die of P. vivax malaria, some persons may opt for the wait-and-watch approach, especially in areas of low malaria transmission. Finally, readers should know that in Oceania, Somalia and some parts of southeast Asia, some strains of P. vivax require a doubling of the usual oral daily dose of primaquine to 30 mg base for 14 days, because of a relative resistance.3 The CDC malaria hot-line number for physicians is 770-488-7788.

Dr. Dubik correctly notes the absence of drug therapy for the treatment of travelers' diarrhea in children. The mainstay of treating diarrhea in children remains oral rehydration therapy. Various premade and homemade oral rehydration solutions are available, each with its own advantages. When dysentery or moderate to severe diarrhea is present in children, furazolidone, trimethoprim-sulfamethoxazole and azithromycin are treatment options.

All three of these medications are available in suspensions. Furazolidone acts against Escherichia coli, salmonella, shigella, Campylobacter, Vibrio species and giardia. Azithromycin has activity against Campylobacter and other common gastrointestinal pathogens. Trimethoprim-sulfamethoxazole is the least preferred as a single treatment agent because of the nearly worldwide resistance of salmonella, shigella and Campylobacter in varying degrees. Dosing and further details on travelers' diarrhea in children are provided elsewhere.3,5

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This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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