• dietary sources – coffee, tea, cola, chocolate
• mechanism of action not clear but could block adenosine receptors; enhance calcium permeability in sarcoplasmic reticulum; inhibit enzymes  accumulation of cyclic AMP)
• in CNS, small doses  decrease fatigue, increase alertness, increase capacity for prolonged intellectual activity; in large doses  nervousness, insomnia and tremors.
• high does stimulate heart and promote vasodilation in peripheral vessels; diuretic effects on kidney
• clinical indications – apnoea in infants; promoting wakefulness

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