Laridox

Treatment of Acute Malaria

Laridox (sulfadoxine and pyrimethamine) is indicated for the treatment of acute, uncomplicated P. falciparum malaria for those patients in whom chloroquine resistance is suspected. However, strains of P. falciparum (see CLINICAL PHARMACOLOGY: Microbiology) may be encountered which have developed resistance to Laridox (sulfadoxine and pyrimethamine) , in which case alternative treatment should be administered.

Prevention of Malaria

Malaria prophylaxis with Laridox (sulfadoxine and pyrimethamine) is not routinely recommended and should only be considered for travelers to areas where chloroquine-resistant P. falciparum malaria is endemic and sensitive to Laridox (sulfadoxine and pyrimethamine) , and when alternative drugs are not available or are contraindicated (see CONTRAINDICATIONS). However, strains of P. falciparum may be encountered which have developed resistance to Laridox (sulfadoxine and pyrimethamine).

(See INDICATIONS AND USAGE)

The dosage should be swallowed whole, and not chewed, with plenty of fluids after a meal.

Treatment of Acute Malaria

Prevention of Malaria

The malaria risk must be carefully weighed against the risk of serious adverse drug reactions (see INDICATIONS AND USAGE). If Laridox (sulfadoxine and pyrimethamine) is prescribed for prophylaxis, it is important that the physician inquires about sulfonamide intolerance and points out the risk and the need for immediate drug withdrawal if skin reactions do occur.

The first dose of Laridox (sulfadoxine and pyrimethamine) should be taken 1 or 2 days before arrival in an endemic area; administration should be continued during the stay and for 4 to 6 weeks after return.

Prophylaxis with Laridox (sulfadoxine and pyrimethamine) should not be continued for more than two years, since no experience of more prolonged administration is available to date.

• Repeated prophylactic (prolonged) use of Laridox (sulfadoxine and pyrimethamine) is contraindicated in patients with renal or hepatic failure or with blood dyscrasias;
• Hypersensitivity to pyrimethamine, sulfonamides, or any other ingredient of Laridox (sulfadoxine and pyrimethamine) ;
• Patients with documented megaloblastic anemia due to folate deficiency;
• Infants less than 2 months of age;
• Prophylactic use of Laridox (sulfadoxine and pyrimethamine) in pregnancy at term and during the nursing period.

WARNINGS

FATALITIES ASSOCIATED WITH THE ADMINISTRATION OF Laridox (sulfadoxine and pyrimethamine) HAVE OCCURRED DUE TO SEVERE REACTIONS, INCLUDING STEVENS-JOHNSON SYNDROME AND TOXIC EPIDERMAL NECROLYSIS. Laridox (sulfadoxine and pyrimethamine) PROPHYLAXIS MUST BE DISCONTINUED AT THE FIRST APPEARANCE OF SKIN RASH, IF A SIGNIFICANT REDUCTION IN THE COUNT OF ANY FORMED BLOOD ELEMENTS IS NOTED, OR UPON THE OCCURRENCE OF ACTIVE BACTERIAL OR FUNGAL INFECTIONS.

Fatalities associated with the administration of sulfonamides, although rare, have occurred due to severe reactions, including fulminant hepatic necrosis, agranulocytosis, aplastic anemia and other blood dyscrasias. Laridox (sulfadoxine and pyrimethamine) prophylactic regimen has been reported to cause leukopenia during a treatment of 2 months or longer. This leukopenia is generally mild and reversible.

PRECAUTIONS

General

Oral Laridox (sulfadoxine and pyrimethamine) has not been evaluated for the treatment of cerebral malaria or other severe manifestations of complicated malaria, including hyperparasitemia, pulmonary edema or renal failure. Patients with severe malaria are not candidates for oral therapy. In the event of recrudescent P. falciparum infections after treatment with Laridox (sulfadoxine and pyrimethamine) or failure of chemoprophylaxis with Laridox (sulfadoxine and pyrimethamine) , patients should be treated with a different blood schizonticide.

Laridox (sulfadoxine and pyrimethamine) should be given with caution to patients with impaired renal or hepatic function, to those with possible folate deficiency and to those with severe allergy or bronchial asthma. As with some sulfonamide drugs, in glucose-6-phosphate dehydrogenase-deficient individuals, hemolysis may occur. Urinalysis with microscopic examination and renal function tests should be performed during therapy of those patients who have impaired renal function. Excessive sun exposure should be avoided.

Laboratory Tests

Regularly scheduled complete blood counts, liver enzyme tests and analysis of urine for crystalluria should be performed whenever Laridox (sulfadoxine and pyrimethamine) is administered for more than three months.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Pyrimethamine was not found carcinogenic in female mice or in male and female rats. The carcinogenic potential of pyrimethamine in male mice could not be assessed from the study because of markedly reduced life-span. Pyrimethamine was found to be mutagenic in laboratory animals and also in human bone marrow following 3 or 4 consecutive daily doses totaling 200 mg to 300 mg. Pyrimethamine was not found mutagenic in the Ames test. Testicular changes have been observed in rats treated with 105 mg/kg/day of Laridox (sulfadoxine and pyrimethamine) and with 15 mg/kg/day of pyrimethamine alone. Fertility of male rats and the ability of male or female rats to mate were not adversely affected at dosages of up to 210 mg/kg/day of Laridox (sulfadoxine and pyrimethamine). The pregnancy rate of female rats was not affected following their treatment with 10.5 mg/kg/day, but was significantly reduced at dosages of 31.5 mg/kg/day or higher, a dosage approximately 30 times the weekly human prophylactic dose or higher.

Pregnancy

Teratogenic Effects: Pregnancy Category C

Laridox (sulfadoxine and pyrimethamine) has been shown to be teratogenic in rats when given in weekly doses approximately 12 times the weekly human prophylactic dose. Teratology studies with pyrimethamine plus sulfadoxine (1:20) in rats showed the minimum oral teratogenic dose to be approximately 0.9 mg/kg pyrimethamine plus 18 mg/kg sulfadoxine. In rabbits, no teratogenic effects were noted at oral doses as high as 20 mg/kg pyrimethamine plus 400 mg/kg sulfadoxine.

There are no adequate and well-controlled studies in pregnant women. However, due to the teratogenic effect shown in animals and because pyrimethamine plus sulfadoxine may interfere with folic acid metabolism, Laridox (sulfadoxine and pyrimethamine) therapy should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Women of childbearing potential who are traveling to areas where malaria is endemic should be warned against becoming pregnant, and should be advised to practice contraception during prophylaxis with Laridox (sulfadoxine and pyrimethamine) and for three months after the last dose.

Nonteratogenic Effects

See CONTRAINDICATIONS.

Nursing Mothers

See CONTRAINDICATIONS.

Pediatric Use

Laridox (sulfadoxine and pyrimethamine) should not be given to infants less than 2 months of age because of inadequate development of the glucuronide-forming enzyme system.

Geriatric Use

Clinical studies of Laridox (sulfadoxine and pyrimethamine) did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal or cardiac function, and of concomitant disease or other drug therapy. This drug is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function.

For completeness, all major reactions to sulfonamides and to pyrimethamine are included below, even though they may not have been reported with Laridox (see WARNINGS and PRECAUTIONS: Information For The Patient).

Hematological Changes

Agranulocytosis, aplastic anemia, megaloblastic anemia, thrombocytopenia, leukopenia, hemolytic anemia, purpura, hypoprothrombinemia, methemoglobinemia, and eosinophilia.

Skin and Miscellaneous Sites Allergic Reactions

Erythema multiforme, Stevens-Johnson syndrome, generalized skin eruptions, toxic epidermal necrolysis, urticaria, serum sickness, pruritus, exfoliative dermatitis, anaphylactoid reactions, periorbital edema, conjunctival and scleral injection, photosensitization, arthralgia, allergic myocarditis, slight hair loss, Lyell's syndrome,

Gastrointestinal Reactions

Glossitis, stomatitis, nausea, emesis, abdominal pains, hepatitis, hepatocellular necrosis, diarrhea, pancreatitis, feeling of fullness, and transient rise of liver enzymes.

Central Nervous System Reactions

Headache, peripheral neuritis, mental depression, convulsions, ataxia, hallucinations, tinnitus, vertigo, insomnia, apathy, fatigue, muscle weakness, nervousness, and polyneuritis.

Respiratory Reactions

Pulmonary infiltrates resembling eosinophilic or allergic alveolitis.

Genitourinary

Renal failure, interstitial nephritis, BUN and serum creatinine elevation, toxic nephrosis with oliguria and anuria, and crystalluria.

Miscellaneous Reactions

Drug fever, chills, periarteritis nodosa and LE phenomenon have occurred.

The sulfonamides bear certain chemical similarities to some goitrogens, diuretics (acetazolamide and the thiazides), and oral hypoglycemic agents. Diuresis and hypoglycemia have occurred rarely in patients receiving sulfonamides. Cross-sensitivity may exist with these agents. Rats appear to be especially susceptible to the goitrogenic effects of sulfonamides, and long-term administration has produced thyroid malignancies in the species.

Acute intoxication may be manifested by headache, nausea, anorexia, vomiting and central nervous system stimulation (including convulsions), followed by megaloblastic anemia, leukopenia, thrombocytopenia, glossitis and crystalluria. In acute intoxication, emesis and gastric lavage followed by purges may be of benefit. The patient should be adequately hydrated to prevent renal damage. The renal, hepatic, and hematopoietic systems should be monitored for at least 1 month after an overdosage. If the patient is having convulsions, the use of parenteral diazepam or a barbiturate is indicated. For depressed platelet or white blood cell counts, folinic acid (leucovorin) should be administered in a dosage of 5 mg to 15 mg intramuscularly daily for 3 days or longer.