Chemistry Reference
In-Depth Information
The most significant behavioral effects of caffeine occur after consumption
of low to moderate doses and include increased alertness, energy feelings and
ability to concentrate. In contrast, higher doses of caffeine may induce negative
effects such as anxiety, restlessness, insomnia, and tachycardia.
Caffeine is considered an overall safe compound, it is not classified as a drug
of dependence in the DSM-IV (APA, 1994) and the only restriction to its use
refers to the IOC regulations. For these reasons, different kinds of dietary
products containing caffeine are marketed to both adolescents and adults and
moderate caffeine consumption rarely leads to health risks. Nevertheless, a
health risk associated with caffeine consumption originates from the recently
established habit of teenagers to mix energy drinks with alcoholic beverages
(Malinauskas et al 2007). Furthermore, adverse effects have been reported,
including cardiac arrest, after high doses of caffeine taken from energy drinks
in combination with other substances (i.e. taurine) (Berger and Alford 2009).
Over the years, the scientific literature on caffeine has generated an enormous
amount of data which deal with caffeine from many points of view and, as far
as the pharmacological properties of caffeine are concerned, besides the studies
on the peripheral effects of caffeine, the research on its central properties
covers a great number of fields which range from its psychomotor stimulant
properties, to its role in cognition, in synaptic plasticity modulation and to its
neuroprotective properties in neurodegenerative diseases. At the basis of the
central effects of caffeine is the ability to modulate adenosine transmission
and, indirectly, to affect the release of neurotransmitters such as DA, ACh and
serotonin. Based on these premises, the present chapter aims to provide an
overview of the literature on the effects of caffeine in the brain with particular
emphasis on its central effects related to its psychomotor stimulant, arousing
and neuroprotective properties.
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14.2 Pharmacokinetic and Pharmacodynamic of Caffeine
Following its oral administration caffeine is adsorbed rapidly (y45 minutes)
and almost completely (y99%) by the stomach and the small intestine.
Concentrations of caffeine rise in plasma within 30 to 120 minutes as a
function of dose and other factors related to the nature of the beverage or the
food. Caffeine is a lipophilic molecule that easily penetrates biologic
membranes and distributes to body tissues. The elimination half-life of
caffeine in humans is in the range of 2.5 to 4.5 hours but it can be lowered by
30-50% in smokers as a consequence of smoke-elicited enzymatic induction.
The metabolism of caffeine takes place mostly by the action of the isozyme
CYP1A2 which converts it into paraxanthine (1,7-dimethylxanthine), although
also theophylline, theobromine and the urinary metabolites, 1-methylxantine
and 1-methyluric acid, must be taken into account. The four main molecular
mechanisms responsible for central effects of caffeine are blockade of
adenosine receptors, inhibition of phosphodiesterases, blockade of GABA
A
receptors and translocation of intracellular calcium. These effects are highly
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