The purpose of this study is to determine the highest tolerable dose of primaquine within 0.75 mg/kg. A tolerable dose is defined as one in which:

• Two or fewer participants (< 30%) experience hemolysis;
• No participant experiences a drug-related serious adverse event; and
• No participant requires a blood transfusion.

Purpose: The purpose of this study is to determine the highest tolerable dose of primaquine within 0.75 mg/kg. A tolerable dose is defined as one in which:

• Two or fewer participants (< 30%) experience hemolysis;
• No participant experiences a drug-related serious adverse event; and
• No participant requires a blood transfusion.

Design:

• This is an open-label, phase 2, dose-adjustment study.
• The initial primaquine dose will be 0.40 mg/kg. Subsequent dose groups will be selected depending on the occurrence of adverse events in the previous dose group. Once the highest tolerable dose in G6PD-deficient (G6PDd) individuals is established, a control group of G6PD normal malaria-free men will be enrolled and evaluated under the highest tolerable dose of primaquine.

Study Population:

• Malian men aged 18-50 years without malaria infection.
• The majority of study participants will be G6PDd.

Study Size: This study will enroll 7 participants per dose group. If all dose groups are tested, this study will enroll approximately 28 participants.

Study visit and duration:

• Each participant will be followed for 28 days.
• Participants will be evaluated for hemolysis and adverse events on Days 1-10, 14, and 28 following their assigned primaquine dose.

Primary objective:

To measure the change in hemoglobin among G6PD deficient west-African men following a single low-dose of primaquine not to exceed 0.75 mg/kg.

Secondary objectives:

1. To measure the occurrence of adverse events, graded by severity, at each primaquine dose among G6PD deficient men

2. To measure the occurrence of markers of acute hemolytic anemia (AHA), at each primaquine dose among G6PD deficient men. AHA markers will include:

   • Absolute and fractional change in hemoglobin on day 7 vs. baseline
   • Urine color
   • Reticulocyte count
   • Bilirubin (both total and direct)
   • Methemoglobin concentration
   • Development of physical signs or symptoms of hemolytic anemia

3. To compare the change in hemoglobin, frequency and severity of adverse events, and occurrence of markers of AHA between G6PD deficient and non-deficient participants receiving the highest tolerable primaquine dose

4. To measure G6PD enzyme activity (semiquantitative testing, U / gHb)

5. To measure the pharmacokinetics of primaquine, carboxyprimaquine, and other metabolites according to plasma concentrations.

6. To genotype participant blood samples for cytochrome P450 2D6 (CYP2D6) single nucleotide polymorphisms (SNPs), to determine if potential hemolysis in G6PDd individuals is affected by CYP2D6 metabolizer status (e.g. weak metabolizers and/or intermediate metabolizers)

Inclusion Criteria:

• Males ages 18- 50 (inclusive)
• Ability to swallow oral medication
• Informed consent
• Willing and able to participate in the study for 28 days

For the G6PDd participants:

• G6PDd defined by Carestart 3 rapid diagnostic test or
• The OSMMR2000 G6PD qualitative test

For the G6PDn participants:

• G6PDn defined by Carestart 3 rapid diagnostic test or
• The OSMMR2000 G6PD qualitative test

Exclusion Criteria:

• Moderate to severe anemia (Hb < 10 g/dL)
• Malaria infection by blood smear
• Individuals with known positive HIV test
• Individuals with known positive hepatitis B test.
• Known allergy to study drugs
• Current use of medication (for tuberculosis, HIV, or any drugs that have hemolytic potential in G6PDd individuals including sulphonamides, dapsone, nitrofurantoin, nalidixic acid, ciprofloxacin, methylene blue, toluidine blue, phenazopyridine, and co-trimoxazole)
• The individual is unwilling to abstain from the ingestion of grapefruit-containing products from 72 hours prior to the start of dosing until the study is complete
• Use of antimalarials within 2 weeks before contact with the study team as reported by the patient
• History of blood transfusion or a bleed of > 500 mLs within the last 3 months, as reported by the patient
• Reported history of high alcohol intake (> 14 units per week, each unit is equivalent to 10 g of alcohol (1 glass of wine or 1 bottle of beer or one shot of distilled spirits), within 6 months of study as reported by the patient
• Reported use of illicit drugs (marijuana, heroin, cocaine, methamphetamine) or dependence within 6 months of study, as reported by the patient
• Participants who vomit within 1 hour after administration of primaquine (will be removed from the analysis and will not count towards the total sample size, though they will be followed as any other enrolled individual)
• Already enrolled in this study.