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Quinine and Quinidine

Drugs obtained from Alkaloids 
Quinine Alkaloids from Cinchona

Two drugs are obtained:

  1. Quinine
  2. Quinidine
Source & History

Chief alkaloid of cinchona bark (known as ‘Fever Bark’), a tree found in South America (Peru).

a. Jesuit’s Bark

b. Cardinal’s Bark

It was discovered as a cure for malaria in 1633 and has a colourful history of more than 350 years. In 1667 it was established that it was effective in tertian malaria. In 1820, two scientists extracted quinine and quinidine from cinchona bark.

Even today, Quinine is obtained entirely from the natural sources due the difficulties in synthesizing the complex molecule.

Quinine and Quinidine

Quinidine is as potent as quinine but due to high toxicity, quinidine is not recommended.

Mechanism of action

Mechanism is somewhat similar as chloroquine, which involves:

i.      Getting incorporated in DNA strand

ii.      Inhibiting replication

iii.      Hence RNA transcription is inhibited

Chloroquine Quinine
Has to be trapped inside food vacuole not required
Pharmacological Actions

1. Anti malarial action

Intercalation into DNA, inhibiting metabolic process, producing anti-malarial effects.

2. CVS

  1. depression of cardiac conduction,
  2. hypotension (severe),
  3. QRS lengthening

3. Insulin – releasing action

Therefore, in severe hypoglycemia administration of glucose is recommended along with quinine.

4. GIT

Anti muscarinic effect is produced (anti-cholinergic) causing:

  1. Severe dryness of mouth
  2. Constipation
  3. Blurring of vision

5. Oxytocic Effect

Uterine contractions with use. Gravid uterus is much sensitive to effects in which excessive uterine contractions occur. Chances of abortion esp. during last trimester of pregnancy.

6. Curare – like action

Muscle relaxation (NMJ blockage)

Therapeutic Uses

1.      Effective anti malarials

  • Used as blood schizonticides.
  • Also used in regions where chloroquine resistance is seen
  • Gametocidal against P. vivax and ovale but not for P. falciparum
  • Also used in severe cerebral malarial condition

2.      Babesiosis

Tick like parasite is involved, may have some role when used in combination with Clindamycin

3.      Previously used for nocturnal leg cramps relief, now FDA has withdrawn it.

Pharmacokinetics
  • Readily/rapidly absorbed when given orally or I/M
  • Peak plasma concentrations are achieved within 1 – 3 hours after oral dose
  • Most absorption occurs from upper part of small intestine
  • Plasma half-life is about 11 hours.
  • High PPB
  • Widely distributed & metabolised
  • Excretion in urine, alkaline so acidic medium facilitates elimination
  • In acute malaria, the volume of distribution of Quinine contracts and clearance is reduced, and the elimination half-life increases (up to 18 hours) in proportion to the severity of the illness. Still adverse effects are not seen in acute malaria as quinine binding to plasma proteins is increased and clearance is reduced.
Quinine – Adverse Effects

1.      Cinchonism

In form of specific triad called Cinchonism.

  • Rhinitis
  • Angioedema
  • Tinnitus
  • Vertigo
  • Dizziness
  • Fatigue
  • Hot sweaty skin
  • Fever
  • Rash
  • Blurring of vision
  • Dizziness
  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal pain
  • Headache
  • Impaired hearing

Excessive toxicity occurs by massive doses, thus dose adjustments are done, characterized by:

  • Confusion
  • Seizures
  • Blindness
  • Deafness

2. CNS

  • Dizziness
  • Headache

3. CVS

  • Depressed cardiac conduction
  • Severe hypotension
  • QRS widening

4. GIT

  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal pain

5. Antimuscarinic action

  • Blurring of vision
  • Constipation
  • Dryness of mouth

6. Hypoglycemia
7. Abortion
8. Hypersensitivity reactions
9. Blood dyscrasias

Hemolytic anemia and thrombocytopenia (G6PD deficiency) 

10. Black-water fever

In severe cases on I/V administration hemolysis occurs, resulting in:

  • Hemoglobinurea.
  • Urine and feces turn dark
  • Anuria
  • Excessive coagulation
  • Renal failure
  • Uremia occur
  • Damage to 8th nerve also occurs
  • Retinal artery stenosis
  • Ischemia
  • Diplopia
  • Blurring of vision
  • Night blindness
  • Visual field impairment
  • Mydriasis
  • Even blindness can occur on excessive doses
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