1. METHYL XANTHINES 20/01/2012

2. Xanthine
A purine base found in most body tissues and fluids, certain plants and some urinary calculi
Crystalline compound formed in the breakdown of nucleic acids (name origin xanthic; Greek, xanthos ‘yellow’)
Is an intermediate in the degradation of adenosine monophosphate to uric acid, being formed by oxidation of hypoxanthine
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3. Xanthine - chemical structure
C5H4N4O2
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4. Methyl xanthines
Methylated xanthine compounds that include caffeine, theobromine, theophylline and their derivatives
The xanthine usually employed in clinical medicine is theophylline (1,3-dimethylxanthine), which can also be used as theophylline ethylenediamine, known as aminophylline.
Caffeine and theophylline produce psychomotor stimulant effects
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5. Methyl Xanthines
The mild central stimulant effects of various beverages, particularly tea, coffee and cocoa, is due to methyl xanthines contained in these drinks
Caffeine and theophylline are the main compounds in these drinks (coffee and tea are the most important source of caffeine)
Nuts of cola plant also contain caffeine, which is present in cola-flavoured soft drinks.
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6. Caffeine – chemical structure-C8H10N4O2
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7. Theophylline – chemical structure-C7H8N4O2
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8. Methyl xanthines – Pharmacological effects
Major pharmacological effects include
CNS stimulation
Diuresis
Stimulation of cardiac muscle
Relaxation of smooth muscle (especially bronchial muscle)
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9. Methly xanthine stimulation of cardiac muscle and relaxation of smooth muscle resemble effects of β-adrenoceptor stimulation; because:
Methyl xanthines, especially theophylline, inhibit phosphodiesterase, responsible for intracellular metabolism of cAMP increasing [cAMP]i and producing effects that mimic those produced by mediators that stimulate adenlyl cyclase (e.g. β2-adrenoceptor agonists)
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10. Methyl xanthines also antagonise many of the effects of adenosine (acting on both A1 and A2 receptors
In the CNS, adenosine generally exerts a pre- and post-synaptic depressant action, reducing motor activity, depressing respiration, inducing sleep and reducing anxiety, all effects opposite of those produced by methyl xanthines
There is some evidence to suggest that antagonism at A2 receptors accounts for part of methyl xanthines CNS stimulant action
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11. For example, transgenic mice lacking function A2 receptors are abnormally active and aggressive and fail to show increased motor activity in response to caffeine
Diuretic effect probably results from vasodilatation of the afferent glomerular arteriole, causing an increased glomerular filtration rate.
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12. Objectively observed effects of caffeine include
Caffeine and theophylline have very similar CNS stimulant effects in human subjects which include:-
Reduction of fatigue, leading to insomnia,
Improved concentration
Clearer flow of thought
Objectively observed effects of caffeine include
Reduction of reaction time and increased speed at which simple calculations are done
Improved performance at motor tasks particularly in fatigued subjects (e.g. typing, simulated driving)
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13. Moderate doses of caffeine (200mg, approx
Moderate doses of caffeine (200mg, approx. 3 cups of coffee) facilitate mental tasks such as syllable-learning but these tasks are impaired by larger doses
Insomnia is common
Unlike amphetamines, methyl xanthines produce less locomotor stimulation and do not induce euphoria, stereotyped behavior patterns or psychotic state
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14. Effects on fatigue and mental function are similar between amphetamines and methyl xanthines
Tolerance and habituation develop to a lesser extent with methyl xanthines and withdrawal effects are slight
Caffeine does not lead to self-administration in animals, and cannot be classified as a dependence producing drug
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15. Clinical Use and Unwanted Effects of Methyl Xanthines
Caffeine is included with aspirin in some preparations for treating headaches and other aches and pain
Caffeine also included with ergotamine in some anti-migraine preparations
The objective of including caffeine in such preparations is to produce a mild sense of alertness
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16. Caffeine has few unwanted effects and is safe even in very large doses
Theophylline is used mainly as a bronchodilator in treating severe asthmatic attacks
Caffeine has few unwanted effects and is safe even in very large doses
However, caffeine has mutagenic effect in vitro and large doses are teratogenic in animals
Even so, epidemiological studies have shown NO evidence of carcinogenic or teratogenic effects of tea or coffee drinking in humans
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17. THANK YOU FOR LISTENING!
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