CHLOROQUINE PHOSPHATE (chloroquine phosphate 500 mg) Dailymed

For Malaria and Extraintestinal Amebiasis

Rx only

Description

Chloroquine phosphate, USP is a 4-aminoquinoline compound for oral administration. It is a white crystalline powder, odorless, has a bitter taste, and is discolored slowly on exposure to light. It is freely soluble in water, practically insoluble in alcohol, in chloroform and in ether.
Chloroquine phosphate, USP is an antimalarial and amebicidal drug.
Chemically, it is 7-chloro-4-[[4-(diethylamino)-1-methylbutyl]amino]quinoline phosphate (1:2) and has the following structural formula:
C₁₈H₂₆CIN₃.2H₃P0₄ Molecular Weight: 515.86
Each tablet contains 500 mg of chloroquine phosphate USP, equivalent to 300 mg chloroquine base.
Inactive ingredients: colloidal silicon dioxide, corn starch, hypromellose, magnesium stearate, microcrystalline cellulose, polyethylene glycol 400, polyethylene glycol 3350, polysorbate 80, povidone, sodium starch glycolate, talc, and titanium dioxide.

Clinical Pharmacology

Chloroquine is rapidly and almost completely absorbed from the gastrointestinal tract, and only a small proportion of the administered dose is found in the stools. Approximately 55% of the drug in the plasma is bound to nondiffusible plasma constituents. Excretion of chloroquine is quite slow, but is increased by acidification of the urine. Chloroquine is deposited in the tissues in considerable amounts. In animals, from 200 to 700 times the plasma concentration may be found in the liver, spleen, kidney, and lung; leukocytes also concentrate the drug. The brain and spinal cord, in contrast, contain only 10 to 30 times the amount present in plasma.
Chloroquine undergoes appreciable degradation in the body. The main metabolite is desethylchloroquine, which accounts for one fourth of the total material appearing in the urine; bisdesethylchloroquine, a carboxylic acid derivative, and other metabolic products as yet uncharacterized are found in small amounts. Slightly more than half of the urinary drug products can be accounted for as unchanged chloroquine.

Microbiology

Mechanism of Action: Chloroquine is an antimalarial agent. While the drug can inhibit certain enzymes, its effect is believed to result, at least in part, from its interaction with DNA. However, the mechanism of plasmodicidal action of chloroquine is not completely certain.
Activity in vitro and in vivo: Chloroquine is active against the erythrocytic forms of Plasmodium vivax, Plasmodium malariae, and susceptible strains of Plasmodium falciparum (but not the gametocytes of P. falciparum). It is not effective against exoerythrocytic forms of the parasite.
In vitro studies with trophozoites of Entamoeba histolytica have demonstrated that chloroquine also possesses amebicidal activity comparable to that of emetine.
Drug Resistance: Resistance of Plasmodium falciparum to chloroquine is widespread and cases of Plasmodium vivax resistance have been reported.

Indications And Usage

Chloroquine phosphate tablets are indicated for the suppressive treatment and for acute attacks of malaria due to P. vivax, P.malariae, P. ovale, and susceptible strains of P. falciparum. The drug is also indicated for the treatment of extraintestinal amebiasis.
Chloroquine phosphate tablets does not prevent relapses in patients with vivax or malariae malaria because it is not effective against exoerythrocytic forms of the parasite, nor will it prevent vivax or malariae infection when administered as a prophylactic. It is highly effective as a suppressive agent in patients with vivax or malariae malaria, in terminating acute attacks, and significantly lengthening the interval between treatment and relapse. In patients with falciparum malaria it abolishes the acute attack and effects complete cure of the infection, unless due to a resistant strain of P. falciparum.

Contraindications

Use of this drug is contraindicated in the presence of retinal or visual field changes either attributable to 4-aminoquinoline compounds or to any other etiology, and in patients with known hypersensitivity to 4-aminoquinoline compounds. However, in the treatment of acute attacks of malaria caused by susceptible strains of plasmodia, the physician may elect to use this drug after carefully weighing the possible benefits and risks to the patient.

Warnings

It has been found that certain strains of P. falciparum have become resistant to 4- aminoquinoline compounds (including chloroquine and hydroxychloroquine). Chloroquine resistance is widespread and, at present, is particularly prominent in various parts of the world including sub-Saharan Africa, Southeast Asia, the Indian subcontinent, and over large portions of South America, including the Amazon basin¹.
Before using chloroquine for prophylaxis, it should be ascertained whether chloroquine is appropriate for use in the region to be visited by the traveler. Chloroquine should not be used for treatment of P. falciparum infections acquired in areas of chloroquine resistance or malaria occurring in patients where chloroquine prophylaxis has failed.
Patients infected with a resistant strain of plasmodia as shown by the fact that normally adequate doses have failed to prevent or cure clinical malaria or parasliia should be treated with another form of antimalarial therapy.
Retinopathy/maculopathy, as well as macular degeneration have been reported (see ADVERSE REACTIONS), and irreversible retinal damage has been observed in some patients who had received long-term or high-dosage 4-aminoquinoline therapy. Retinopathy has been reported to be dose related. Risk factors for the development of retinopathy include age, duration of treatment, high daily and/or cumulated doses.
When prolonged therapy with any antimalarial compound is contemplated, initial (base line) and periodic ophthalmologic examinations (including visual acuity, expert slit-lamp, funduscopic, and visual field tests) should be performed.
If there is any indication (past or present) of abnormality in the visual acuity, visual field, or retinal macular areas (such as pigmentary changes, loss of foveal reflex), or any visual symptoms (such as light flashes and streaks) which are not fully explainable by difficulties of accommodation or corneal opacities, the drug should be discontinued immediately and the patient closely observed for possible progression. Retinal changes (and visual disturbances) may progress even after cessation of therapy.
Acute extrapyramidal disorders may occur with chloroquine (see ADVERSE REACTIONS and OVERDOSE). These adverse reactions usually resolve after treatment discontinuation and/or symptomatic treatment.
All patients on long-term therapy with this preparation should be questioned and examined periodically, including testing knee and ankle reflexes, to detect any evidence of muscular weakness. If weakness occurs, discontinue the drug.
A number of fatalities have been reported following the accidental ingestion of chloroquine, sometimes in relatively small doses (0.75 g or 1 g chloroquine phosphate in one 3-year-old child). Patients should be strongly warned to keep this drug out of the reach of children because they are especially sensitive to the 4-aminoquinoline compounds.
Use of chloroquine phosphate in patients with psoriasis may precipitate a severe attack of psoriasis. When used in patients with porphyria the condition may be exacerbated. The drug should not be used in these conditions unless in the judgment of the physician the benefit to the patient outweighs the potential risks.
Usage in Pregnancy: Radioactively tagged chloroquine administered intravenously to pregnant pigmented CBA mice passed rapidly across the placenta and accumulated selectively in the melanin structures of the fetal eyes. It was retained in the ocular tissues for five months after the drug had been eliminated from the rest of the body². There are no adequate and well-controlled studies evaluating the safety and efficacy of chloroquine in pregnant women. Usage of chloroquine during pregnancy should be avoided except in the suppression or treatment of malaria when in the judgment of the physician the benefit outweighs the potential risk to the fetus.