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Chloroquine phosphate.
Anti-malarial, amoebicidal, anti-inflammatory, and used in collagen diseases.
Studies in volunteers using single doses of chloroquine phosphate equivalent to 300mg base have found peak plasma levels to be achieved within one to six hours. These levels are in the region of 54 to 102 microgram/litre, the concentration in erythrocytes being some 4.8 times higher. The elimination half-life of chloroquine is dose dependent and is approximately 100 hours. Following a single dose, chloroquine may be detected in plasma for more than four weeks. Mean bioavailability from tablets of chloroquine phosphate is 89%. Chloroquine is widely distributed in body tissues such as the eyes, kidneys, liver and lungs where retention is prolonged.
The principal metabolite is monodesethylchloroquine, which reaches a peak concentration of 10-20 microgram /litre within a few hours. Mean urinary recovery, within 3-13 weeks, is approximately 50% of the administered dose, most being unchanged medicine and the remainder as metabolite. Chloroquine may be detected in urine for several months.
Suppression and treatment of malaria; amoebic hepatitis; in certain phases of lupus erythematosus, rheumatoid arthritis and related collagen diseases.
The use of chloroquine is contraindicated
Chlorquin should be used with caution in patients with a history of epilepsy, as seizures have been reported.
Blurring of vision, corneal changes and retinal damage have been reported, particularly after prolonged therapy. Irreversible retinal damage may occur in patients receiving prolonged therapy. Regular examination for ocular disturbances should be carried out in patients receiving long courses of treatment.
Care is necessary for administering Chlorquin to patients with impaired liver or renal function, or with porphyria (as there is the possibility of the occurrence of acute episodes) or psoriasis (there is a possibility of exacerbation of lesions). Reactions are more common in alcoholics. Chlorquin may temporarily affect visual accommodation, and patients undergoing treatment should not take charge of vehicles or machinery until these effects are no longer evident.
Patients with glucose-6-phosphate dehydrogenase deficiency should be observed for haemolytic anaemia during chloroquine treatment and for acute renal failure.
Complete blood cell counts should be performed periodically in patients receiving prolonged therapy with chloroquine. Chloroquine should be discontinued if there is evidence of adverse haematological effects that are severe and not attributable to the disease being treated.
Patients receiving prolonged therapy with chloroquine should be questioned and examined periodically for evidence of muscular weakness; knee and ankle reflexes should be tested. If muscular weakness occurs during therapy with chloroquine, the drug should be discontinued.
Considerable caution is needed in the use of Chlorquin for long-term high dosage therapy and such use should only be considered when no other medicine is available.
Patients expected to receive Chlorquin continuously at higher dose levels for periods longer than 12 months should undergo opthalmic examination before treatment and at intervals of three months thereafter to exclude early keratopathy and retinopathy. This also applies to patients receiving Chlorquin at weekly intervals for a period of more than 3 years as a prophylactic against malarial attacks, or if the total consumption exceeds 1.6g/kg.
Resistance of Plasmodium Falciparum to chloroquine is well documented. Therefore, epidemiological data should be considered before starting therapy with chloroquine.
Overdoses may be fatal, especially in children.
The use of antimalarials in the treatment of malaria is accepted because the small risk to the fetus is outweighed by the benefits to the mother and fetus. Prophylaxis in high risk situations is also justified.
Chloroquine and related substances may cause neurological disturbances and interference with hearing, balance and vision in the fetus. The use of higher doses in the treatment of malaria and in the second line treatment of hepatic amoebiasis is accepted because the lifesaving benefits of the treatment to the mother and fetus outweigh the risk. However, wherever possible, women taking chloroquine should avoid becoming pregnant.
Although chloroquine is excreted in breast milk, the amount is insufficient to confer any benefit on the infant. Separate chemoprophylaxis for the infant is required.
Antacids or kaolin can reduce the absorption of chloroquine and it is recommended that they be taken at least 4 hours apart.
Cimetidine and chloroquine should be used with caution as cimetidine can significantly reduce the metabolism and elimination of chloroquine and increase its volume of distribution.
The activity of chloroquine may be affected when it is administered with other antimalarials.
Other anti-infective agents that might interact with chloroquine include metronidazole, acute dystonic reactions have been reported in patients receiving concomitant therapy.
Chloroquine may reduce the gastro-intestinal absorption of ampicillin.
Concurrent antimalarial prophylaxis with chloroquine has been reported to reduce the antibody response to human diploid rabies vaccine.
Chlorquin is well tolerated at the standard dosage regimens recommended for the control of malaria. Minor side effects such as headache and gastrointestinal disturbances such as nausea, vomiting, diarrhoea, epigastric discomfort, anorexia, abdominal cramps and slight weight loss may occur.
Where prolonged high dose therapy is indicated, e.g. in the treatment of lupus erythematosus and rheumatoid arthritis, side effects can be of greater severity and patients may develop skin eruptions, occasional depigmentation or loss of hair, difficulty in accommodation, blurring of vision, corneal opacities, and less often, retinal degeneration. Corneal opacities disappear completely when the drug is stopped. The serious adverse effect of prolonged high dose therapy is the occasional development of irreversible retinal damage. For this reason, considerable caution is required in prolonged high dose therapy and such use should only be considered when no other effective drug is available.
Discard ½ tablets if not consumed immediately.
ADULTS:
2 tablets (310 mg base) taken on the same day each week, commencing two weeks before exposure and continuing for 4 weeks after exposure is over.
CHILDREN :
1 to 4 years: 1/2 tablet
4 to 8 years: 1 tablet
over 8 years: adult dose
Initial dose of 4 tablets for adults, followed by 2 tablets eight hours later, 2 tablets in a single dose each day for two days, then 2 tablets weekly for four weeks.
4 tablets daily in divided doses for two days, then 1 tablet twice daily for two to three weeks.
Average adult dose, 1 tablet twice daily for one to two weeks, followed by maintenance dose of 1 tablet daily.
1 tablet one to two times daily with meals for four to twelve weeks. Prolonged courses are sometimes necessary as response may not appear for one to three months after treatment commences and maximum benefit until much later. If side effects appear, withdraw drug until they disappear, reinstate treatment with 1/2 tablet daily and if well tolerated increase to 1 tablet. Usual maintenance dose is 1 tablet daily.
Chloroquine is rapidly absorbed and is highly toxic in overdose. Children are particularly susceptible. The main symptoms of overdosage include circulatory collapse due to potent cardiotoxic effect, respiratory arrest. Symptoms may progress rapidly after initial headache, drowsiness, visual disturbances, nausea, vomiting and dizziness. Visual disturbances may be dramatic with a sudden loss of vision. Death may result from circulatory or respiratory failure or cardiac dysrhythmia.
In the event of gross overdosage, prompt measures will be required to counteract the depressant effect of the drug on the cardiovascular and respiratory systems. Vomiting should be induced or gastric lavage carried out as soon as possible, followed by appropriate resuscitative measures, such as tracheal intubation with artificial respiration and the administration of vasopressor agents or intravenous fluids. Intravenous molar sodium lactate solution 30 to 50 mL has been used to counteract the quinidine-like action of chloroquine on the myocardium. To promote excretion of the drug, the administration of enteric-coated ammonium chloride tablets 0.5 g every 8 hours is also recommended. Chloroquine is excreted very slowly therefore cases of overdosage require observation for several days.
Since acute overdosage with chloroquine may be rapidly lethal, patients must be promptly hospitalized, preferably in an intensive care unit and intensive and supportive treatment, including monitoring, instituted immediately.
Tablets
250 mg (=155 mg base), (white, scored) 100's.
Store below 30°C. Protect from light.
Prescription Medicine
CHLORQUIN has provisional consent under Section 23 of the Medicines Act 1981. This consent expires on 13 October 2007.
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1 November 2005