Pharmacology & Caffeine (Y2)

What is a Drug?
“Any chemical entity or mixture of entities, other than those required for the maintenance of normal health (food), the administration of which alters biological function and possibly structure.” (WHO, 1971)

Is a member of a group of drugs known as xanthine stimulants or the methylxanthines.

There are many methylxanthines, but only tow other, theophylline and theobromine occur naturally and are widely self-administered.

Although methylxanthines occur naturally in many species of plant, the most common sources are tea, coffee and chocolate. They are also found in many over-the-counter painkillers, cold remedies and stimulants.

After drinking tea or coffee, peak levels of caffeine in the blood are reached between 30-60 minutes later. However, there is some evidence that caffeine in cola beverages are absorbed more slowly and reach their peak around two hours later.

The cacao tree, the source of the cocoa bean has long been cultivated by the Mayas, Aztecs and the Incas, where it was a food reserved for the wealthy and powerful.

Commonly believed to be an aphrodisiac, it was used at wedding feasts and by rich noblemen who had many wives.

Following the spanish conquest of central and south america, the roman catholic church banned the use of the drug because of it’s reputation as an aphrodisiac but the ban did not last.

Chocolate was introduced to the Spanish court in 1520. The spanish added vanilla and sugar instead and the sweetened form of chocolate became popular across Europe.

These act on adenosine receptors in the CNS. Adenosine is a neurotransmitter that inhibits the firing of other neurones in the brain.

Methylxanthines compete with adenosine for the receptor sites, consequently, adenosine is prevented from exerting its inhibitory action, resulting in the stimulation of the CNS. Caffeine is a stimulant drug and also a diuretic.

A cup of coffee may contain between 40-176 mg of caffeine.

A cup of tea may contain between 8-91 mg caffeine.

Hot Chocolate
May contain 150-300 mg of caffeine.

Ounce of Chocolate
May contain 75-150 mg.

Physiological effect of Caffiene
The effects on the body include increases of blood pressure and heart rate. Smooth muscle tends to relax, whilst striated muscles (skeletal muscle) are strengthened, reducing fatigue.

Relaxation of smooth muscle causes dilation in the bronchi in the lungs and a subsequent decrease in airway resistance. Consequentally, theophilline is used clinically in the treatment of asthma.

The subjective effects of caffeine include elevated mood, feelings of alertness, the ability to concentrate and the ability to overcome tiredness.

Risks associated with caffeine
People suffering with anxiety disorders may be sensitive to the effects of caffeine, which may exacerbate their symptoms. In children, caffeine may cause hyperactivity.

There have also been concerns with the amount of caffeine you children have been consuming though soft drinks and chocolate.

Tolerance to caffeine
Tolerance to the effects of caffeine may develop over time. There is some evidence that caffeien has a greater effect on non-coffee drinkers than on heavy coffee drinkers. Doses of around 600mg per day may cause dependence after only six to fourteen days.

Lower doses, four to five cups per day, over a long period of time is also sufficient to cause dependence.

Symptoms of caffeine withdrawal include: headache, fatigue, lethargy and agitation which may last up to a week.

There have been at least six deaths recorded due to caffeine overdose. The lethal dose in humans is equivalent to 30-80 cups of coffee. Death results from convulsions and respiratory collapse.

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