Antimalarial Medications

Article Author:
Stephen Hill
Article Editor:
Gyanendra Sharma
Updated:
12/6/2017 2:37:07 PM
PubMed Link:
Antimalarial Medications

Indications

When treating patients who are suspected to have malaria, it is important that treatment is not initiated until the diagnosis of malaria has been established. To guide malaria treatment appropriately, it is important to identify three factors: (1) the infecting Plasmodium species, (2) the clinical status of the patient, and (3) the drug susceptibility of the infecting parasites (the geographic area from where the infection was acquired from and any previous antimalarial medications). The obvious exception in waiting for confirmation to treat suspected malaria is if the patient shows signs of severe malaria and clinical suspicion for malaria is high.

By identifying the infecting Plasmodium species, the healthcare practitioner can identify which infections will progress to severe manifestations and which will not. Also, some infections can remain dormant in the liver as hypnozoites and can lead to a relapse. The clinical status of a patient can be categorized into two main categories: uncomplicated malaria or severe malaria. The main difference in treatment is that uncomplicated malaria is treated with oral antimalarials, while severe malaria is treated with parenteral antimalarials. Last, by determining the drug susceptibility of the infecting Plasmodium species, healthcare practitioners can select an appropriate treatment course. Practitioners can do this by looking at where the patient was when they acquired the infection and if they have received any previous treatment with antimalarials.

Mechanism of Action

Chloroquine phosphate is the preferred agent if the infection is considered uncomplicated and is caused by chloroquine sensitive P.falciparum and works by inhibiting parasite growth by concentrating within the parasite acid vesicles thereby raising internal pH. Hydroxychloroquine is also an acceptable first-line treatment of chloroquine-sensitive P. falciparum and has a similar mechanism of action as chloroquine phosphate.

Primaquine phosphate is utilized as an add-on agent to either chloroquine phosphate or hydroxychloroquine when infections are caused by P. vivax or P. ovale with chloroquine sensitivity. This medication works by eliminating the hypnozoites that remain dormant in the patient’s liver, which reduces the risk of relapse in a patient.

Atovaquone-proguanil is utilized in infections caused by P. falciparum with chloroquine resistance. This combination product acts as an antimalarial as atovaquone selectively inhibits parasite mitochondrial electron transport and proguanil inhibits dihydrofolate reductase disrupting deoxythymidylate synthesis.

Artemether-lumefantrine is an alternative first-line option for the treatment of malaria caused by chloroquine-resistant P. falciparum. The proposed mechanism of action for both agents is to inhibit nucleic acid and protein synthesis.  

Quinine sulfate plus doxycycline, tetracycline, or clindamycin can be used as a second-line option for the treatment of malaria caused by chloroquine-resistant P. falciparum. Quinine intercalates into DNA, disrupting the parasites replication and transcription to exert its antimalarial effects.

For the treatment of uncomplicated chloroquine-resistant P. vivax, there are three options considered to have equal efficacy.

  • Quinine sulfate plus doxycycline or tetracycline plus primaquine phosphate

  • Atovaquone-proguanil plus primaquine phosphate

  • Mefloquine plus primaquine phosphate

    • Mefloquine’s antimalarial effects are similar to quinine sulfate’s effects listed above.

Quinidine gluconate is the drug of choice for suspected severe malaria because it is the only parenterally available antimalarial drug. Severe malaria is characterized by the presence of parasites in the blood and any of the following conditions: altered mental status, seizures, respiratory distress, circulatory collapse, renal failure, anemia, thrombocytopenia, liver failure, and acidosis. The most common causative agent of severe malaria is P. falciparum. Quinidine gluconate acts primarily as an intraerythrocytic schizonticide, with little effect upon sporozoites or upon pre-erythrocytic parasites. Quinidine is gametocidal to P. vivax and P. malariae, but not to P. falciparum. Clindamycin, doxycycline, or tetracycline should be added to quinidine therapy when treating severe malaria in either IV or oral form, depending on the patient's clinical condition.

Administration

Chloroquine phosphate dosing for chloroquine-sensitive P. falciparum is 1000 mg by mouth immediately, followed by 500 mg by mouth at hours 6, 24, and 48 hours. An alternative in chloroquine-sensitive infections is to use Hydroxychloroquine 800 mg by mouth immediately, followed by 400 mg by orally at hours 6, 24, 48 hours. Other malaria infections that would follow the same protocol would be P. malariae or P. knowlesi.

Primaquine phosphate 26.3 mg is added to the above therapy at a dose of two tablets by mouth once a day for 14 days for chloroquine-sensitive P. vivax or P. ovale infections. Primaquine should be given with meals to decrease GI adverse effects (abdominal cramps, nausea, vomiting). If the patient vomits within 30 minutes of taking a dose, then they should repeat the dose.

Atovaquone-proguanil 250 mg/100 mg dosing is administered as four tablets once a day for three days. The other first-line treatment for malaria caused by chloroquine-resistant P. falciparum is artemether-lumefantrine 20 mg/120 mg dosed as four tablets immediately and at 8 hours, followed by four tablets twice daily on days 2 and 3. It should be taken with a meal or milky drink to increase absorption as the rate of absorption of atovaquone is dependant on the amount administered with dietary fat.

When treating chloroquine-resistant P. vivax or P. falciparumuinine, sulfate is given as 650 mg by mouth three times a day for 3 or 7 days with the 7-day regimen used for infections acquired in Southeast Asia.  The addition of doxycycline, tetracycline, and clindamycin is given as a 7-day course as well.

Mefloquine is administered as 750 mg by initial mouth dose followed by 500 mg by mouth, given 6 to 12 hours after the initial dose. Mefloquine should be administered with food and at least 8 ounces of water. If vomiting occurs within 30 minutes after the dose, an additional full dose should be given; if it occurs within 30 to 60 minutes after the dose, an additional half-dose should be given. This agent can be used as a third-line option for the treatment of malaria caused by chloroquine-resistant P. falciparum or a first line option for the treatment of uncomplicated chloroquine-resistant P. vivax.

Quinine gluconate, used as the only IV option for severe malaria treatment is given as a loading dose of 10mg/kg IV over one to two hours followed by a continuous infusion of 0.02 mg/kg/minute for at least 24 hours. Patients may alternatively receive a 24 mg/kg loading dose infused over four hours followed by 12 mg/kg over four hours dosed every eight hours. IV quinidine should be continued until the parasite density is less than 1% and the patient can tolerate oral medications. Once IV quinine is discontinued, the patient should be switched to oral quinine for the remainder of treatment. Renal adjustments do not need to be made when calculating loading doses of IV quinidine gluconate. If a patient has a creatinine clearance less than or equal to 1 mL/minute, the maintenance dose should be reduced by 25%. The addition of doxycycline, tetracycline, or clindamycin to intravenous (IV)  quinidine is given as a 7-day course as well.

Adverse Effects

Many patients will experience gastrointestinal upset (GI), headache, blurred vision, and insomnia when taking chloroquine. It rarely has been shown to cause QT interval prolongation. It should be used with caution in patients with a previous history of GI disorders, conduction abnormalities, or patients taking QT-prolonging drugs.  Side effects of hydroxychloroquine are similar to chloroquine although hydroxychloroquine is most commonly used as an alternative for patients who cannot tolerate the GI side effects of chloroquine. Both of these drugs have been reported to cause psoriatic exacerbations.

Primaquine is known to cause hemolytic anemia in patients with G6PD deficiency. A G6PD level should be taken before administration of primaquine to determine if the patient can receive this medication. The common side effect of primaquine is mainly limited to GI disturbances such as abdominal pain, nausea, and vomiting.

Common side effects of atovaquone-proguanil are abdominal pain, nausea, vomiting, headache, and increased serum transaminases (AST/ALT). Vomiting is of particular note because absorption may be decreased in patients with diarrhea or vomiting. Healthcare providers should consider the use of an antiemetic in patients with vomiting or diarrhea that may impact the absorption of their medication. Atovaquone-proguanil may also enhance the anticoagulant effect of warfarin. Patients taking both medications should be monitored closely for increased bleeding episodes.

The most common side effects of artemether-lumefantrine include a headache, fever, dizziness, fatigue, nausea and vomiting, and anorexia. Of note, for this medication, muscular effects are common and usually manifest as weakness and/or myalgia. The most serious side effect associated with this agent is QT prolongation, especially in concomitant use with other medications that can prolong the QT interval.

Doxycycline and tetracycline are usually well tolerated, but some GI upset can be seen and, less commonly, ultraviolet photosensitivity. Patients should apply sunscreen liberally to avoid the photosensitivity. Patients also may have a side effect of Candida vaginitis, so it is recommended to offer women antifungal self-treatment for management. Clindamycin most commonly causes GI disturbances, most notably diarrhea, and is the most common antibiotic associated with C. difficileFq infections post-treatment.

Mefloquine side effects to be aware of are GI upset, lightheadedness, headache, difficulty concentrating, mood swings, and strange dreams. A US box warning is that mefloquine can cause neuropsychiatric effects even after discontinuation. Symptoms to monitor include anxiety, depression, nightmares, hallucinations, dizziness, and paranoia. Severe neuropsychiatric reactions involve seizures, suicidal ideation, and psychosis.

A baseline EKG is recommended before using quinidine gluconate or oral quinine due to their potential to cause QTc prolongation. Once quinidine is initiated, continuous telemetry monitoring is recommended. A patient’s infusion should be stopped or slowed if any of the following occur: an increase in the QRS complex by more than 50%, increase in QTc interval by more than 0.6 seconds, QTc prolongation of more than 25% from baseline, or hypotension that is unresponsive to fluid challenge. Other serious side effects associated with quinine and quinidine include central nervous system disturbances such as dizziness, confusion, and headache as well as serious skin conditions from bullous dermatitis to Steven-Johnson syndrome and toxic epidermal necrolysis.

Contraindications

Chloroquine and hydroxychloroquine have few contraindications. Either a previous hypersensitivity to any 4-aminoquinoline compounds or the underlying presence of retinopathy are the only absolute exclusions to these medications. Patients also should be tested for a G6PD deficiency before starting chloroquine or hydroxychloroquine. Patients with a G6PD deficiency are at increased risk for hemolysis when given these drugs. Both chloroquine and hydroxychloroquine are safe to use throughout pregnancy.

Primaquine is contraindicated in pregnancy and breastfeeding as well as in patients with severe G6PD deficiency and acutely ill patients with a tendency to develop granulocytopenia (rheumatoid arthritis, SLE, etc.).  Use also is strongly discouraged in conjunction with medications that can cause hemolytic anemia or myeloid bone marrow suppression.

Atovaquone-proguanil is not intended for use in patients less than 5 kg or women who are pregnant or breastfeeding. It should not be used in patients with severe renal impairment (CrCl < 30 mL/min) because proguanil is excreted in the urine.

Artemether-lumefantrine is contraindicated only if a patient has a previous hypersensitivity reaction to either medication or in the concurrent use with strong CYP3A4 inducers such as rifampin, carbamazepine, or phenytoin.  

Contraindications for doxycycline and tetracycline include pregnant women, children less than eight years of age, or previous hypersensitivity to any of the tetracycline antibiotics. Clindamycin’s only true contraindications are a previous history of hypersensitivity reactions to it or lincomycin and to avoid use when less toxic antibiotics are appropriate due to the increased risk of severe and possibly fatal colitis.

Contraindications for mefloquine use include known hypersensitivity to the drug, history of seizures or major psychiatric disorder, and a recent history of depression or anxiety. Mefloquine has been associated with sinus bradycardia and QT interval prolongations. It should be used with caution in patients with cardiac conduction disorders or using antiarrhythmic agents. Mefloquine can be safely administered during all trimesters of pregnancy.

Contraindications for both quinine and quinidine include thrombocytopenia, thrombocytopenic purpura, myasthenia gravis, any heart block greater than first degree, QT prolongation, or in combination with medications that can also cause QT prolongation.  

Monitoring

Due to the short duration of treatment for most regimens of antimalarial treatment, the following are the only monitoring parameters necessary for these medications.

  • G6PD screening is recommended if the patient will be started on chloroquine, hydroxychloroquine, and primaquine. If the patient has known mild to moderate G6PD deficiency or unknown status and is placed on any of these three medications, then it is recommended to obtain a baseline CBC as well as a CBC at day 3 and day 8 of therapy.  

  • A baseline ECG is recommended with primaquine, artemether-lumefantrine, mefloquine, quinine, and quinidine. Continuous telemetry monitoring for hypotension and cardiac conduction changes is recommended while patients are on IV quinidine. Also, periodic blood glucose monitoring to check for hypoglycemia should be performed while on IV therapy.

  • A negative pregnancy test for women of childbearing age should be performed prior to starting primaquine.