Caffeine and Related Nonprescription Sympathomimetics

There are three methylxanthine alkaloids: theobromine, theophylline, and caffeine. Cocoa and chocolate contain theobromine and some caffeine. Tea contain caffeine and some theophylline. Coffee and many cola-flavored beverages are rich sources of caffeine.
Theophylline and caffeine are used in drug therapy. Methylxanthines stimulate the CNS, induce diuresis, relax smooth muscle ( bronchial muscle), and stimulate cardiac functions. Caffeine also augment the analgesic properties of salicylates and is contained in many analgesic products, migraine treatments, and products promoting alertness.
Nonprescription sympathomimetics such as ephedrine, phenylpropanolamine, and phenylephrine have been abused for their stimulant effects and are commonly found in cold preparations
Pharmacokinetics:
In adults Caffeine is metabolized to theophylline by the cytochrome P-450 enzyme system with approximately 1 % excreted unchanged in the urine. However, in neonates approximately 85 % of a dose is excreted unchanged in the urine. Decreased elimination and a prolonged half-life may increase caffeine toxicity in neonates and premature infants. The metabolism of a child approaches that of an adult at the approximate age of 8 months.
Phenylpropanolamine is a weak base that is readily absorbed in the small intestine. Maximum concentrations occur approximately 1.5 hours after ingestion. High per cent of a given dose of phenylpropanolamine will be excreted unchanged in the urine. Approximately 8–20 per cent of a dose of ephedrine undergoes N-demethylation to phenylpropanolamine. Phenylephrine has a bioavailability of 38 per cent. most of a given dose is excreted unchanged in the urine.