Quinine (Cinchona Quinoline Alkaloid · Antimalarial · Historical Pharmaceutical · Informational)

Compound	Quinine
Chemical class	Alkaloid — Quinoline (Cinchona bark primary alkaloid)
CAS	130-95-0
Primary source	Cinchona officinalis, Cinchona pubescens (Cinchona bark), Cinchona succirubra
Key applications	Pharmaceutical antimalarial (historical); nocturnal leg cramps (OTC); informational reference
Claim strength	High (as pharmaceutical antimalarial and leg cramps); informational only (supplement)
Typical form	Pharmaceutical tablet; tonic water (trace doses); not a dietary supplement active
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Name origin: From quina or kina — the Quechua (Andean indigenous) name for Cinchona bark (“bark of barks” / “holy bark”). Quinine is the primary quinoline alkaloid of Cinchona bark — a complex molecule with both quinoline and quinuclidine ring systems linked by a secondary alcohol. Historical significance: Quinine is one of the most historically important pharmaceutical compounds ever discovered. Cinchona bark was introduced to Europe from Peru in the 1630s–1640s as a treatment for malaria (then called “ague”). The pure compound quinine was isolated in 1820 by Pierre-Joseph Pelletier and Joseph Caventou. For centuries quinine was the only effective antimalarial, responsible for enabling European colonial expansion into tropical regions and saving millions of lives. The synthesis of quinine by Robert Woodward and William von Doering (1944) was a landmark in organic synthesis. Current status: Quinine remains WHO Essential Medicine for severe malaria (IV formulation) and for nocturnal leg cramps (FDA-approved in the US, withdrew OTC approval in 1994 due to risk; retained as prescription drug Qualaquin). Tonic water contains quinine at approximately 83 mg/L (sub-therapeutic for malaria). Supplement status: Quinine cannot be marketed for therapeutic claims as a dietary supplement; the FDA has specifically warned against quinine supplements for leg cramps.

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Quinine — Pharmaceutical and Historical Context

Antimalarial mechanism — haemozoin inhibition: Quinine accumulates in the acidic food vacuole of Plasmodium falciparum parasites and inhibits haematin polymerisation (the conversion of toxic haem released from haemoglobin digestion into insoluble haemozoin). This causes toxic haem accumulation and parasite death. Quinine remains effective against most malaria species but is now largely replaced by artemisinin-based combination therapies (ACTs) as first-line treatment due to better tolerability. Pharmaceutical evidence: High.

Nocturnal leg cramps (historical pharmaceutical): Quinine was approved and widely used for nocturnal leg cramps (idiopathic, drug-induced). Multiple RCTs confirmed significant reduction in leg cramp frequency. The FDA withdrew OTC quinine for leg cramps in 1994 due to reports of rare but serious adverse effects (haemolytic uraemic syndrome, thrombocytopaenia, cardiac arrhythmia, hypersensitivity) at over-the-counter doses, retaining it as a prescription drug only for this indication. Pharmaceutical evidence: High.

Cardiac channel effects (proarrhythmic risk): Quinine is a Class Ia antiarrhythmic (sodium and potassium channel blocker) — the same class as quinidine. It prolongs the QT interval, creating a risk of torsades de pointes at therapeutic doses. This is the primary safety concern that led to restriction of OTC quinine availability. Critical safety reference.

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Frequently Asked Questions — Quinine

Is tonic water a meaningful source of quinine?
Commercial tonic water contains approximately 83 mg quinine per litre (EU maximum is 100 mg/L; US uses a similar limit). The antimalarial therapeutic dose of quinine is 600–650 mg three times daily. One litre of tonic water provides approximately 1/20th of the minimum antimalarial dose — not medically meaningful. For leg cramps, the FDA prescription dose is 324 mg once daily; tonic water provides approximately 1/4 of this per litre consumed — somewhat closer to a low therapeutic range but still sub-therapeutic in typical beverage amounts. The risk of tonic water for cardiac arrhythmia at beverage doses is very low; the risk of therapeutic quinine preparations is meaningful.

Why did quinine become the basis for synthetic antimalarials?
The quinoline ring system of quinine was identified as the pharmacophore responsible for antimalarial activity. Synthetic quinoline antimalarials (chloroquine, hydroxychloroquine, mefloquine) were developed by modifying the quinine scaffold to improve tolerability, oral bioavailability, and pharmacokinetics. Chloroquine was developed by German chemists in 1934, became the dominant antimalarial through the 1950s–80s, and is now limited by widespread Plasmodium falciparum resistance. Hydroxychloroquine (a hydroxylated chloroquine) retains use for autoimmune conditions (lupus, rheumatoid arthritis) where it was repurposed.

Can quinine in tonic water cause health problems?
At tonic water beverage concentrations, serious adverse effects are extremely rare. Cases of quinine-induced haemolytic uraemic syndrome (HUS) and thrombocytopaenia have been reported even at tonic water doses in hypersensitive individuals — these are idiosyncratic reactions unrelated to dose. For most people, tonic water is safe in reasonable amounts. Individuals with G6PD deficiency should avoid quinine entirely (haemolytic risk). QT-prolonging effect is negligible at tonic water concentrations.

What is quinidine and how does it differ from quinine?
Quinidine is the diastereoisomer of quinine (same molecular formula, different stereochemistry at C-8 and C-9). Despite the structural similarity, quinidine has predominantly antiarrhythmic uses (Class Ia, approved for atrial fibrillation) and weaker antimalarial activity than quinine. Both have QT-prolonging effects and serious cardiac risk profiles that limit their clinical use.

Related compounds: Quinidine, Cinchonine, Chloroquine, Camptothecin

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Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.

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