Agriculture Reference
In-Depth Information
fissured with an exfoliating cork, and bearing whitish, green, or gray lichens or mosses, more or
less rough, with or without reddish warts. It has a pale yellowish-brown to brown inner surface with
fine-to-coarse longitudinal striations. The fracture is fibrous, the taste is bitter and astringent, and
the odor is very characteristic but faint. The microscopic characteristics of
Cinchona
are described
in
African Pharmacopoeia
.
436
The genus
Cinchona
consists of about 40 species, occurring as shrubs or medium-size trees,
growing up to 30 m in height. The leaves of
C. succirubra
(ca. 20-25 cm long) are hairy below,
elliptic to obovate-lanceolate, simple, entire, and evergreen with prominent midrib and lateral veins.
The flowers are borne in terminal panicles, are pinkish or whitish and fragrant; they are tubular
with a 5-flaring capsule, which splits open at the base when ripe to reveal 40 to 50 flat, slender,
winged seeds.
Habitat and Distribution —
Cinchona
is native to the mountainous regions of tropical America
from where it has been introduced to Africa. The plant is cultivated in Cameroon, Congo, Rwanda,
and Tanzania.
Ethnomedicinal Uses —
Cinchona
yields up to 16% of quinolone alkaloids, consisting
mainly of quinine, quinidine, cinchonine, and cinchonidine and their epimers and hydroxyderiva-
tives. The plant also contains other alkaloids, such as cinchonamine, quinamie, and the tannin
conjugates of these alkaloids known as cinchotannic acids. Tannins, resins, and waxes co-occur
with these alkaloids.
Pharmacological Studies —
The Peruvian bark
Cinchona
has been recognized as a potent
antimalarial agent since the seventeenth century. The drug is antiplasmodial, febrifuge, orexigenic,
spasmolytic, astringent, and tonic. Quinine and quinidine are the most clinically important of the
Cinchona
alkaloids; quinine is the most potent of the alkaloids as an antimalarial, whereas quini-
dine has stronger cardiac depressant activity. Quinine is used clinically for the treatment of malaria,
especially in infections by parasites that are resistant to the newer synthetic drugs.
Quinine —
Quinine, C
20
H
24
N
2
O
2
, (8S, 9R)-6′-methoxycinchonana-9 ol; (αR)-α-(6-methoxy-4-
quinoyl)-α-[(2S, 4S, 5R)-(5-vinylquinuclidin-20yl)] methanol, is the most important alkaloid occur-
ring in
Cinchona
. The compound was first isolated in 1820 by Pelletier and Caventou. It is available
as the bisulfate, dihydrochloride, and sulfate. Quinine sulfate is a colorless or white, odorless, fine
acicular crystal or a white or almost white crystalline powder that darkens on exposure to light; the
hydrochloric occurs as colorless, fine, silky, acicular crystals, and the dihydrochloride is a white
or almost white odorless or almost odorless powder. Quinine salts have differential solubility; the
hydrochloric is soluble in a ratio of 1:23 in water, freely soluble in alcohol and chloroform, and very
slightly soluble in ether. The dihydrochloride is soluble in a ratio of 1:0.5 in water and 1:14 in alco-
hol; the sulfate is soluble in a ratio of 1:500 in water and 1:20 in alcohol.
Pharmacological and Clinical Properties —
Quinine is a rapidly acting blood schizonticide
used orally for the treatment of malaria. It has activity against the blood schizonts of
Plasmodium
falciparum, P. malariae, P. vivax,
and
P. ovale
and the gametocytes of
P. malariae
and
P. vivax
,
but is not active against
P. falciparum
gametocytes. The compound has no activity against the exo-
erythrocytic forms of the infection and therefore does not produce a radical cure in malaria due to
P. vivax
or
P. ovale.
Quinine, its congeners, and salts are readily absorbed when given orally or intramuscularly. In
the treatment of uncomplicated attacks of falciparum malaria due to chloroquine- or multidrug-
resistant strains, quinine is given by mouth at dose of 1.8 to 2 g in three divided doses for at least
7 days. Following oral administration, over 80% of the drug is absorbed mainly from the upper
small intestine, and peak plasma concentrations are achieved within 1 to 3 h. The dosage is adjusted
according to the salt used, and corresponding lower doses are indicated for children. In complicated
or severe cases of malaria for which it may not be suitable to give the drug orally, quinine is admin-
istered by the parenteral route, usually as a slow intravenous infusion. About 90% of plasma quinine
