Inclusion Criteria:

1. Ages 18-60 years
2. P. falciparum parasitemia (1,000-100,000 parasites/ul).
3. Clinical syndrome consistent with malaria associated with documented fever (axillary temperature > 38℃) or self-reported history of fever in the last 48 hours with no other cause present
4. Commenced oral quinine ≤ 18 hours prior to scheduled commencement of arginine
5. An indication for hospital admission (eg relative cannot look after/supervise treatment at home but not having any warning signs or severe malaria criteria in "exclusion criteria" below)
6. Informed consent obtained

Exclusion Criteria:

1. Pregnancy or lactation
2. Mixed infection with P. falciparum and P. vivax
3. Warning signs of altered mental state and inability to sit unaided
4. Features of severe/complicated malaria
5. Diabetes
6. Systolic blood pressure (BP) < 100 mmHg
7. Serious underlying disease (cardiac, hepatic, kidney)

8. Initial iSTAT test showing any of the following values:

   • glucose < 4 mmol/L;
   • K+ ≥ 4.2 meq/L;
   • Cl- > 106 meq/L;
   • HCO3- < 20 meq/L.
9. Known allergy to L-arginine

10. Concurrent therapy with any of the following medications:

    • spironolactone;
    • oral nitrates;
    • phosphodiesterase inhibitor (eg sildenafil [Viagra]);
    • alpha-blocking antihypertensive agents (eg prazosin);
    • L-arginine.