A 34-year-old man comes to the emergency department due to recurrent fevers, chills, and excessive sweating. The symptoms began a few days ago and seem to occur every 48 hours. The patient recently returned from a trip to India. Temperature is 38.6 C (101.5 F). Physical examination is otherwise unrevealing. Laboratory studies are notable for anemia and thrombocytopenia. A blood smear with Giemsa staining demonstrates red blood cell inclusions. The patient is prescribed chloroquine and primaquine. The addition of primaquine to the treatment regimen is most likely to have which of the following effects?

Question

A 34-year-old man comes to the emergency department due to recurrent fevers, chills, and excessive sweating.  The symptoms began a few days ago and seem to occur every 48 hours.  The patient recently returned from a trip to India.  Temperature is 38.6 C (101.5 F).  Physical examination is otherwise unrevealing.  Laboratory studies are notable for anemia and thrombocytopenia.  A blood smear with Giemsa staining demonstrates red blood cell inclusions.  The patient is prescribed chloroquine and primaquine.  The addition of primaquine to the treatment regimen is most likely to have which of the following effects?

Quizplus · Accepted Answer

This patient has fever, chills, sweats, and red blood cell inclusions on Giemsa smear that developed following travel to a tropical geographic region (areas including South America, Africa, India, and Southeast Asia). Together, these findings support a diagnosis of malaria. Fever and sweating that occur every 48 hours (tertian malaria) are especially characteristic of Plasmodium vivax, P ovale, or P falciparum infection. All species of malaria-causing organisms share a similar life cycle. Organisms are first inoculated into the human host by the Anopheles mosquito and then travel to the liver, where they infect hepatocytes and replicate. Lysis of infected hepatocytes releases merozoites into the bloodstream. Merozoites go on to infect erythrocytes, and it is the resultant erythrocyte lysis that causes relapsing fevers and sweating. P vivax and P ovale are unique in that they also establish a latent hepatic infection (exo-erythrocytic cycle) in the form of hypnozoites, responsible for relapses. Chloroquine is effective in eradicating chloroquine-sensitive plasmodia from the bloodstream, but it has no activity against the latent hepatic infections established by P vivax and P ovale. Primaquine must be added to the regimen to completely eradicate the hypnozoites. (Choice A) Retinopathy is the most serious long-term adverse effect related to chloroquine use. It occurs only rarely and is related to prolonged use. Primaquine has no influence on the occurrence of chloroquine retinopathy. (Choices B and E) Primaquine has limited therapeutic activity against the erythrocytic forms of plasmodia, including trophozoites. Primaquine is not effective in treating chloroquine-resistant strains, which can be managed with mefloquine or quinine, among others. (Choice D) No antimalarial agent specifically acts to prevent hemolysis. Primaquine is contraindicated in patients with glucose-6-phosphate dehydrogenase deficiency as the medication can cause hemolysis. Educational objective: Chloroquine is the treatment of choice for uncomplicated malaria contracted in a chloroquine-sensitive geographic region. It eliminates susceptible erythrocytic forms of all Plasmodium species. Primaquine is added in the treatment of infections with P vivax and P ovale to eradicate the intrahepatic stages (hypnozoites) of these malarial species, which are responsible for relapses.

A 34-Year-Old Man Comes to the Emergency Department Due to Recurrent