Hemolytic anemia and G6PD deficiency

Due to the risk of hemolytic anemia in patients with G6PD deficiency, G6PD testing has to be performed before using primaquine. Due to the limitations of G6PD tests, physicians need to be aware of residual risk of hemolysis and adequate medical support and follow-up to manage hemolytic risk should be available.

Primaquine should not be prescribed for patients with severe G6PD deficiency (see CONTRAINDICATIONS).

In case of mild to moderate G6PD deficiency, a decision to prescribe primaquine must be based on an assessment of the risks and benefits of using primaquine. If primaquine administration is considered, baseline hematocrit and hemoglobin must be checked before treatment and close hematological monitoring (e.g. at day 3 and 8) is required. Adequate medical support to manage hemolytic risk should be available.

When the G6PD status is unknown and G6PD testing is not available, a decision to prescribe primaquine must be based on an assessment of the risks and benefits of using primaquine. Risk factors for G6PD deficiency or favism must be assessed. Baseline hematocrit and hemoglobin must be checked before treatment and close hematological monitoring (e.g. at day 3 and 8) is required. Adequate medical support to manage hemolytic risk should be available.

Discontinue the use of primaquine phosphate promptly if signs suggestive of hemolytic anemia occur (darkening of the urine, marked fall of hemoglobin or erythrocytic count).

Hemolytic reactions (moderate to severe) may occur in individuals with G6PD deficiency and in individuals with a family or personal history of favism. Areas of high prevalence of G6PD deficiency are Africa, Southern Europe, Mediterranean region, Middle East, South-East Asia, and Oceania. People from these regions have a greater tendency to develop hemolytic anemia (due to a congenital deficiency of erythrocytic G6PD) while receiving primaquine and related drugs.

Usage in Pregnancy

Safe usage of this preparation in pregnancy has not been established. Primaquine is contraindicated in pregnant women. Even if a pregnant woman is G6PD normal, the fetus may not be (see CONTRAINDICATIONS). Animal data show toxicity to reproduction.

Nonclinical data from studies conducted in bacteria and in animals treated with primaquine show evidence of gene mutations and chromosomal/DNA damage, teratogenicity, and injury to embryos and developing fetuses when primaquine is administered to pregnant animals. Patients must be informed of the potential for adverse genetic and reproductive effects associated with primaquine treatment (see PRECAUTIONS, Carcinogenesis, Mutagenesis, and Impairment of Fertility and Animal Pharmacology and/or Animal Toxicology).

Use in Females and Males of Reproductive Potential

Lactation

It is not known whether primaquine is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants from primaquine, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Blood Monitoring

Since anemia, methemoglobinemia, and leukopenia have been observed following administration of large doses of primaquine, the adult dosage of 1 tablet (= 15 mg base) daily for fourteen days should not be exceeded. In G6PD normal patients it is also advisable to perform routine blood examinations (particularly blood cell counts and hemoglobin determinations) during therapy.

If primaquine phosphate is prescribed for an individual who has shown a previous idiosyncratic reaction to primaquine phosphate as manifested by hemolytic anemia, methemoglobinemia, or leukopenia; an individual with a family or personal history of hemolytic anemia or nicotinamide adenine dinucleotide (NADH) methemoglobin reductase deficiency, the person should be observed closely. In all patients, the drug should be discontinued immediately if marked darkening of the urine or sudden decrease in hemoglobin concentration or leukocyte count occurs.

Potential Prolongation of QT Interval

Due to potential for QT interval prolongation, monitor ECG when using primaquine in patients with cardiac disease, long QT syndrome, a history of ventricular arrhythmias, uncorrected hypokalemia and/or hypomagnesemia, or bradycardia (<50 bpm), and during concomitant administration with QT interval prolonging agents (see PRECAUTIONS, Drug Interactions, ADVERSE REACTIONS, and OVERDOSAGE).

Carcinogenesis, Mutagenesis, Impairment of Fertility

No carcinogenicity studies have been conducted with primaquine. No fertility studies have been conducted with primaquine. Primaquine is reported in the literature to be a weak genotoxic agent which elicits both gene mutations,1 chromosomal damage and DNA strand breaks.2 The publications reported positive results in the in vitro reverse gene mutation assays using bacteria (Ames test)3,4 and in the in vivo studies using rodents (mouse bone marrow cell sister chromatid exchange, mouse bone marrow cell chromosome abnormality, and rat DNA strand breaks in multiple organs).2,5 The genotoxicity data obtained in vitro and in rodent models are suggestive of a human risk for genotoxicity with primaquine administration (see WARNINGS, Usage in Pregnancy).

Animal Pharmacology and/or Animal Toxicology

Literature data on reproductive toxicology identified embryo-fetal development toxicity. In studies in rats, teratogenic effects on fetus were observed (see WARNINGS, Usage in Pregnancy).

In the first reproductive toxicity study,6 primaquine was administered orally to rats between gestation day (GD) 6 and GD15 at dose levels of 10.3, 30.8 and 61.5 mg/kg/day (as base) (representing approximatively 7, 20 and 40 times the human dose [HD] on a body surface area comparison) when considering a human body weight of 60 kg). High dose levels induced death of pregnant females in almost all cases, while lower dose levels caused maternal toxicity. At cesarean section, embryo resorption, a decrease in fetal survival rate and body size, internal abnormalities (including hydrocephalia, heterotaxia), and an increase in skeletal variations were observed at the mid dose level. There were no fetal abnormalities at the low dose level providing a potential safety margin of at least 7 times the recommended clinical dose.

For the second reproductive toxicity study,7 6 to10 animals per group were used. Dose levels of 0.57, 5.7, 11.4 and 34 mg/kg/day of primaquine (as base) (representing approximatively 0.4, 4, 7 and 22 times the HD on a body surface area comparison) were administered orally to Sprague Dawley rats between GD8 and GD16, or of 57 mg/kg only once on GD13 (representing more than 37 times the HD on a body surface area comparison). A total of 1/7 and 4/6 pregnant females at 34 mg/kg/day and at 57 mg/kg, respectively, died. Primaquine-associated teratogenic malformations (including cleft palate and small chin) were observed in 4/54 fetuses in the 57 mg/kg single-dose group.

Drug Interactions

Caution is advised if primaquine is used concomitantly with other drugs that prolong the QT interval (see PRECAUTIONS, ADVERSE REACTIONS, and OVERDOSAGE).

Geriatric Use

Clinical studies of primaquine 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.

Store at 25°C (77°F); excursions permitted to 15°C–30°C (59°F–86°F) [see USP Controlled Room Temperature]

Dispense in tight, light-resistant container as defined in the USP/NF.