Amodiaquine

BRAND NAMES

Amodiaquine is an antimalarial drug frequently administered alongside Artesunate for the treatment of uncomplicated Plasmodium falciparum malaria. Popular brand names include Camoquin, Basoquin, Flavoquine, and Eriquin. It is also commonly available in fixed-dose combinations with artesunate (ASAQ), such as Coarsucam.

MECHANISM OF ACTION

Amodiaquine exerts its antimalarial effect by accumulating in the parasite’s food vacuole within red blood cells and inhibiting the conversion of toxic heme into inert hemozoin. This causes a buildup of free heme, which damages the parasite’s membranes and leads to its death. When combined with Artesunate, amodiaquine acts synergistically to enhance parasite clearance and reduce the risk of drug resistance.

PHARMACOKINETICS

Absorption:
Amodiaquine is rapidly absorbed after oral administration, with good bioavailability. Maximum plasma levels are usually achieved within 1 to 2 hours after administration.

Distribution:
The volume of distribution (Vd) of Amodiaquine is approximately 10–20 L/kg, reflecting extensive distribution into body tissues, especially the liver, spleen, and red blood cells. Its active metabolite, desethylamodiaquine, also has a large Vd, contributing to prolonged antimalarial effects.

Metabolism:
Amodiaquine is extensively metabolized in the liver, primarily by cytochrome P450 enzymes (mainly CYP2C8), into its active metabolite, desethylamodiaquine, which contributes significantly to its antimalarial activity.

Excretion:
The drug and its metabolites are primarily eliminated via the urine, with a relatively long half-life of the active metabolite, allowing sustained antimalarial activity.

PHARMACODYNAMICS

Amodiaquine, a 4-aminoquinoline structurally and functionally similar to Chloroquine, has been used for over 40 years as both an antimalarial and an anti-inflammatory agent. It demonstrates efficacy comparable to chloroquine and remains active against certain chloroquine-resistant strains, although cases of amodiaquine resistance have been reported. The precise mechanism by which amodiaquine acts is still not fully understood. Like other 4-aminoquinolines, it can depress cardiac muscle function, impair electrical conduction in the heart, and cause vasodilation leading to hypotension, while also potentially affecting respiration and causing side effects such as diplopia, dizziness, and nausea.

ADMINISTRATION

Amodiaquine is administered orally, usually in tablet form, and can be taken with or without food. It is most effective when given at the onset of malaria symptoms, typically as part of a combination therapy with Artesunate.

DOSAGE AND STRENGTH

Amodiaquine is commonly available in tablet form of 153 mg (base) or 200 mg (salt) per tablet. For the treatment of uncomplicated Plasmodium falciparum malaria, the usual adult dose is 10 mg/kg of body weight per day (base) for three consecutive days. Pediatric dosing is weight-based, typically 10 mg/kg/day, also for three days. When used in combination with Artesunate (as ASAQ), the dosing is adjusted according to fixed-dose combination formulations to ensure both drugs are given at effective therapeutic levels.

DRUG INTERACTIONS

Amodiaquine is primarily metabolized by the liver enzyme CYP2C8. Drugs that inhibit this enzyme, such as gemfibrozil, can increase amodiaquine levels, raising the risk of toxicity. It may also interact with other antimalarial drugs like chloroquine or mefloquine, increasing the likelihood of liver damage or hematologic side effects. Additionally, concurrent use with medications that prolong the QT interval, such as certain antiarrhythmics or antipsychotics, can increase the risk of dangerous cardiac arrhythmias.

FOOD INTERACTIONS

Food does not significantly affect the absorption of amodiaquine, but taking it with meals can reduce gastrointestinal discomfort, such as nausea or abdominal pain. Alcohol should be avoided during therapy, as it can increase the risk of liver toxicity.

CONTRAINDICATIONS

Amodiaquine is contraindicated in patients with a known hypersensitivity to amodiaquine or other 4-aminoquinoline compounds, including chloroquine. It should not be used in individuals with severe liver disease, a history of blood disorders like agranulocytosis or aplastic anemia, or known QT prolongation and serious cardiac arrhythmias. Use in pregnancy, especially the first trimester, and breastfeeding should generally be avoided unless no safer alternatives are available.

SIDE EFFECTS

Common side effects of amodiaquine include nausea, vomiting, diarrhea, abdominal pain, headache, and itching (pruritus). Serious but rare side effects include liver toxicity, potentially leading to jaundice or liver failure, severe blood disorders such as agranulocytosis, skin reactions like Stevens-Johnson syndrome, and cardiac arrhythmias, particularly in cases of overdose.

OVER DOSE

Symptoms of amodiaquine overdose include severe vomiting, diarrhea, low blood pressure, seizures, liver dysfunction, and life-threatening cardiac arrhythmias. Management is supportive, with hospitalization recommended. Early ingestion may be treated with activated charcoal, and continuous cardiac monitoring may be necessary for severe cases.

TOXICITY

The most concerning toxic effects of amodiaquine are hepatotoxicity and blood dyscrasias. Prolonged or high-dose use can lead to liver failure or severe neutropenia. Cardiac toxicity, including QT prolongation and torsades de pointes, is rare but possible, especially in overdose or when combined with other QT-prolonging medications. Amodiaquine is generally safe when used for a short duration at the recommended dose, but patients with existing liver or blood conditions should be closely monitored.