Antimalarials are a group of medications primarily used in the prevention and treatment of malaria, which is caused by Plasmodium spp, a protozoan parasite transmitted by certain Anopheles mosquitoes. In addition, some antimalarials can also be used to treat amebiasis and some autoimmune disorders like systemic lupus erythematosus and rheumatoid arthritis.
The oldest medication of this group is quinine, but its derivative chloroquine is most often used because it has fewer side effects. Other antimalarials include hydroxychloroquine, mefloquine, primaquine, pyrimethamine, and a combination of atovaquone and proguanil. If Plasmodium is resistant to antimalarial therapy, antibiotics like doxycycline, tetracycline, and clindamycin can be used.
Antimalarials are administered orally. Once administered, they work in various ways. Chloroquine, quinine, pyrimethamine, atovaquone, and proguanil all inhibit parasitic DNA synthesis; pyrimethamine, in particular, also inhibits protein synthesis.
Mefloquine and hydroxychloroquine affect the function of lysosomes in the parasitic cell. Finally, primaquine affects the mitochondria of the parasite.
Antimalarials can cause a number of side effects, most commonly of the gastrointestinal tract such as nausea, vomiting, cramps, and anorexia. In addition, clients can develop alopecia, a skin rash, photosensitivity, and hypersensitivity reactions like Stevens-Johnson syndrome and drug reaction with eosinophilia and systemic symptoms or DRESS for short.
Some clients taking antimalarials may also experience neurological side effects, such as headaches, nightmares, and even seizures; and mefloquine has a boxed warning for causing adverse neuropsychiatric reactions like anxiety, depression, hallucinations, and suicidal ideation.
Now, clients on antimalarials can often develop blurred vision and difficulty focusing due to damage to the cornea, while chloroquine and hydroxychloroquine can cause irreversible retinopathy. Quinine, chloroquine, and hydroxychloroquine can cause vertigo, deafness, or tinnitus due to ototoxicity and damage to cranial nerve VIII.
High levels of quinine or primaquine can cause a condition known as cinchonism, which is characterized by nausea, vomiting, tinnitus, and vertigo. On the other hand, pyrimethamine can cause megaloblastic anemia, thrombocytopenia, and leukopenia.
Finally, some antimalarials like mefloquine may also cause cardiovascular side effects, including heart failure, sinus bradycardia, QT prolongation, first degree atrioventricular block, asystole, and torsade de pointes; and quinine can cause dangerous arrhythmias, as well as hemolytic anemia, renal insufficiency, and insulin release leading to hypoglycemia.
When it comes to contraindications, primaquine should not be used in pregnancy and breastfeeding, while other antimalarials should be used with caution.
In addition, antimalarials should be used with caution in clients with hepatic or renal disease, as well as in those with myasthenia gravis, which might be exacerbated. All these medications should also be used cautiously in children, as well as clients with hemolytic anemia, and glucose-6-phosphate dehydrogenase or G6PD deficiency.
Additional precautions should be taken with clients that have eye or skin disorders, as well as in those with neurologic, gastrointestinal, or cardiovascular disease. Mefloquine should also be used with caution in clients with a history of depression.
Regarding interactions, antimalarials should not be combined with any medication that is known to prolong the QT interval, as this can lead to arrhythmias. Also, because pyrimethamine affects folate metabolism, it should not be used with antifolate medications like methotrexate or trimethoprim.
All right, when caring for a client prescribed with the combination medication atovaquone and proguanil for malaria prophylaxis, first ask them about their travel plans, how long they will be in an area where malaria is endemic, and when they plan to return.
Then, perform a focused baseline assessment including vital signs, and review their most recent laboratory test results including CBC, renal, and hepatic function.
Next, explain to your client that atovaquone and proguanil can help prevent malaria by disrupting the parasite’s ability to make DNA, RNA, and proteins. Then, instruct them to take one tablet daily at the same time each day, with food or milk. Let them know that if they vomit within one hour of taking their medication, that they should take another dose.
