Which medications are contraindicated in patients with glucose‑6‑phosphate dehydrogenase (G6PD) deficiency and what safer alternatives can be used?

Medications Contraindicated in G6PD Deficiency

Five medications are absolutely contraindicated in G6PD deficiency: rasburicase, primaquine, tafenoquine, dapsone, and methylene blue (methylthioninium chloride), as these potent oxidants can trigger life-threatening hemolysis. 1, 2

Absolutely Contraindicated Medications

High-Risk Oxidant Drugs

• Rasburicase is contraindicated in all G6PD-deficient patients regardless of variant severity, and should never be used for tumor lysis syndrome management in these individuals. 1
• Methylene blue is absolutely contraindicated because it paradoxically worsens methemoglobinemia in G6PD deficiency—the enzyme deficiency prevents conversion of methylene blue to its active reduced form, and high doses act as an oxidant causing Heinz-body hemolytic anemia. 2, 3
• Dapsone is a potent oxidant that causes both methemoglobinemia and severe red blood cell hemolysis by overwhelming the reduced antioxidant capacity in G6PD-deficient erythrocytes, and must be avoided completely. 2
• Primaquine is contraindicated in severe G6PD deficiency (enzyme activity <30% of normal), though it may be considered at reduced dosing (45 mg once weekly for 8 weeks) only in mild-to-moderate deficiency (30-70% activity) with intensive hematological monitoring. 2
• Tafenoquine is contraindicated in individuals with G6PD activity <70% because it triggers severe hemolysis, particularly in Mediterranean variants. 2

Variant-Specific Risk Stratification

• The Mediterranean G6PD variant (B⁻) carries very high risk of severe, potentially life-threatening hemolysis requiring strict avoidance of all oxidant medications, whereas the African variant (A⁻) typically produces milder, self-limited hemolysis. 2, 4
• Patients of Mediterranean, African, Indian, or Southeast Asian descent should undergo G6PD screening before starting any oxidant drug therapy. 2

Safer Alternative Medications

For Malaria Treatment and Prophylaxis

• Artemisinin-based combination therapies (ACTs)—including artesunate, artemether-lumefantrine, and dihydroartemisinin-piperaquine—are safe for malaria treatment in G6PD-deficient patients. 2
• Chloroquine and hydroxychloroquine at standard doses are relatively safe for most G6PD-deficient patients and can be used during pregnancy. 2

For Pneumocystis Prophylaxis

• Atovaquone or inhaled pentamidine should replace dapsone for Pneumocystis prophylaxis in G6PD-deficient patients. 3

For Dermatologic Conditions

• Mycophenolate, azathioprine, or methotrexate are appropriate alternative immunosuppressants when dapsone would otherwise be indicated for dermatologic conditions. 3

For Methemoglobinemia Treatment

• High-dose ascorbic acid (0.5-10 g) is the treatment of choice for methemoglobinemia when methylene blue is contraindicated, though these doses exceed FDA recommendations and carry hemolysis risk requiring close monitoring. 2, 3
• Exchange transfusion should be considered for severe methemoglobinemia or hemolytic crises when pharmacologic options are unsafe. 2, 3

Medications Requiring Caution

Moderate-Risk Drugs

• NSAIDs including ibuprofen present moderate hemolysis risk and should be used cautiously with close hemoglobin monitoring. 4
• Aspirin is explicitly contraindicated as it can overwhelm reduced antioxidant capacity in G6PD-deficient red blood cells. 4

Safe Analgesics and Anesthetics

• Benzodiazepines, codeine/codeine derivatives, propofol, fentanyl, and ketamine have not been shown to cause hemolytic crises and are safe for perioperative pain and anxiety management. 5
• Penicillins including amoxicillin are not contraindicated and can be used in normal therapeutic doses. 4

Critical Screening and Testing Recommendations

Pre-Treatment Screening

• Quantitative G6PD testing is mandatory before initiating primaquine, tafenoquine, dapsone, rasburicase, or methylene blue in at-risk populations. 2, 3
• Calculate the percentage of normal G6PD activity by dividing the patient's level by the laboratory upper limit of normal and multiplying by 100—values <30% indicate severe deficiency with absolute contraindications. 3

Testing Timing Pitfalls

• Never test during or immediately after acute hemolytic episodes, as reticulocytes and young RBCs contain near-normal enzyme levels that mask true deficiency. 3
• Wait at least 50-120 days after RBC transfusion before performing enzyme assays, as donor RBC contamination of 6-12% causes false-negative results. 3
• Qualitative fluorescent spot tests work well for males and homozygous females with severe deficiency, but quantitative assays are necessary for heterozygous females and borderline cases. 3

Management of Acute Hemolytic Crisis

Recognition of Hemolysis

• Patients should be educated to recognize early signs: dark urine, sudden fatigue or pallor, jaundice, and abdominal or back pain typically appearing 24-72 hours after oxidant exposure. 2, 6

Acute Management

• Immediately discontinue the offending oxidant medication upon recognition of hemolysis. 3
• Provide aggressive intravenous hydration maintaining urine output ≥100 mL/hour in adults (≥3 mL/kg/hour for patients <40 kg) to prevent hemoglobin-induced acute kidney injury. 2
• Monitor vital signs every 4-6 hours during the initial 24-48 hours to detect tachycardia or hypotension. 2

Transfusion Thresholds

• Transfusion is not indicated for asymptomatic patients with hemoglobin ≈8.6 g/dL; supportive care and observation are sufficient. 2
• Initiate red-cell transfusion when hemoglobin falls below 7 g/dL or when signs of severe anemia develop (dyspnea, chest pain, altered mental status, hemodynamic instability) regardless of absolute hemoglobin value. 2
• Consider discontinuing hemolysis-inducing drugs when hemoglobin drops below 8.5 g/dL. 2

Supportive Care

• Folic acid supplementation (1 mg daily) is recommended for all G6PD-deficient patients. 4
• Continuously monitor for acute kidney injury from hemoglobinuria during hemolytic crises. 2