primaquine phosphate

Action

Unknown. Thought to disrupt parasitic mitochondria and bind to native DNA, leading to structural changes that disrupt metabolic processes and to inhibition of gametocyte and erythrocyte forms. Destroys some gametocytes and makes others incapable of undergoing maturation division.

Availability

Tablets: 26.3 mg (15 mg base)

Indications and dosages

➣ To prevent or treat relapse of malaria caused by Plasmodium vivax

Adults: 15 mg base P.O. daily for 14 days

Children: 0.3 mg base/kg/day P.O. for 14 days, to a maximum of 15 mg base daily

Off-label uses

• Pneumocystis jiroveci pneumonia

Contraindications

• Hypersensitivity to drug

• Concurrent use of quinacrine, other hemolytic drugs, or myelosuppressants

• Bone marrow depression

• Systemic disease with history of or tendency to granulocytopenia (such as lupus erythematosus or rheumatoid arthritis)

Precautions

Use cautiously in:

• porphyria, methemoglobinemia, methemoglobin reductase deficiency, hemolytic anemia in G6PD deficiency (particularly in Blacks, Asians, and persons of Mediterranean descent), iodine deficiency, anemia

• pregnant patients.

Administration

See Before giving, check prescription to see if dosage is written as mg or mg base.

• Start therapy during last 2 weeks of suppression course with chloroquine or comparable drug, or after suppression course ends.

Adverse reactions

CNS: headache, dizziness, asthenia

CV: hypertension

EENT: blurred vision, difficulty focusing

GI: nausea, vomiting, diarrhea, constipation, abdominal pain, epigastric distress

Hematologic: mild anemia, leukocytosis, hemolytic anemia, methemoglobinemia

Skin: pruritus, skin eruptions, pallor

Interactions

Drug-drug. Aluminum and magnesium salts: decreased GI absorption of primaquine

Quinacrine: increased risk of primaquine toxicity

Drug-diagnostic tests. Hemoglobin, red blood cells: decreased levels White blood cells: increased or decreased count

Patient monitoring

See Monitor CBC. Watch for evidence of blood dyscrasias or hemolytic reaction (dark urine, chills, fever, chest pain, bluish skin). Stop drug and notify prescriber at once if these occur.

• Monitor blood pressure.

Patient teaching

• Advise patient to take with food to minimize GI upset.

See Teach patient to recognize and immediately report signs and symptoms of hemolytic reactions.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration, vision, and alertness.

• Instruct patient to complete entire course of therapy as prescribed, even after symptoms improve.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.