Although it may seem to be incredible, drugs like caffeine that have the aptitude to transform mood and change behavioral patterns of an individual are actually able to accomplish the task by influencing as many as 50 billion nerve cells in our brain! In order to start working in the brain, these drugs first need to assimilate into the bloodstream and this is accomplished by absorption. In fact, the absorption of such drugs into the bloodstream is done by two primary ways - the enteral or enteric administration and the parenteral (drugs taken into the body in a manner other than through the digestive canal) administration. When caffeine is absorbed by the body through the enteral or enteric administration if follows a simple path in the gastrointestinal tract - the mouth, gullet, stomach, intestines and the rectum.
As mentioned above, when caffeine is taken through parenteral administration, the chemical compound sidesteps the gastrointestinal route. As an alternative, caffeine is administered into the body through the lungs, ear, skin, and vagina or by means of injection shots. The injections may be shot expressly into a muscle, an artery or vein, the spinal cord or some other places in the body - the skin or in the region of the intestines. Although these routes of administering caffeine are not common, there are numerous instances when the parenteral administration has to be followed.
While injecting caffeine directly into the bloodstream is the easiest, fastest and most simple route, this occasionally proves to be the most unsafe method. It may be mentioned here that a number of medications, such as insulin, are not administered enterally as they may be rendered ineffective by substances present in the gastrointenstinal route. On the contrary, other medications, such as a number of barbiturates, usually are unable to go through the gastrointestinal tract and enter the blood vessels of the stomach and the intestines. Hence, such medications are not governed through the enteral administration. In fact, drugs like cocaine and heroin are also not effectual when given through enteral administration as they usually are soaked up by the blood vessels in the stomach and the intestine before they go to the liver and eventually to the brain. While in the liver, these drugs are broken up into different chemical compounds and, thus are not very effective when administered internally.
The blood vessels present in the wall or lining of the stomach and intestines eagerly take up caffeine since this chemical compound is not broken down into newer products by the acids present in the stomach. Approximately 1/6 of any dose of caffeine is soaked up by the stomach walls, while most of the remaining amount is taken up by the lining on the duodenum, which comprises the first part of the small intestine. Apart from these, the liver also metabolizes caffeine, but comparatively at a much slow pace. All these aspects of caffeine make the drug most suitable for administration internally. In addition, the rapidity with which ingested caffeine transfers from the mouth to the bloodstream is dependent on several aspects. For instance, the absorption of caffeine by the body is relatively slow when the stomach is full or after a long period of fasting. However, it has been observed that under normal circumstances, a single dose of caffeine passes into the bloodstream in just 36 minutes after the drug is administrated.
After absorbing caffeine from the gastrointestinal system, the blood containing the chemical compound gets to the liver and, from there, to the heart. Once the blood containing caffeine reaches the heart, it is swiftly circulated to different parts of the body by a process called distribution of caffeine. In an adult male, caffeine is distributed to all parts of the body where water is present and this includes approximately the entire 42 liters present in the body comprising about 62 per cent of the body weight. Interestingly, of the approximately 42 liters of water present in an adult male body, only six liters is in blood. Of the remaining amount of water in the body, most, approximately 28 liters, is present in the different cells of the body that compose the muscles, tissues and the brain. The residual amount of water in the body remains between the cells.
It may be mentioned here that the consequences of the amount of any drug taken by a person or an animal largely depends on the weight of the organism receiving the drug. This is primarily because the heavier the body, the more amount of water it will contain. Hence, it will water down the effect of a dosage drug administered further. Consequently, the blood will contain a lower concentration of caffeine when it reaches the brain and other organs of the body where the chemical substance has an influence. In fact, it is the intensity of caffeine present in the blood that actually determines the potency of the effect it will have on certain parts of the body. In addition, every time blood containing caffeine goes through the liver, a little amount of the caffeine is metabolized into metabolites that are eventually discharged by the body by means of urination. As the caffeine content is eliminated from the blood, it is immediately restored by the chemical substance coming from other fluids present in the body. This is a continuous process and goes on until all the caffeine is metabolized by the liver and eventually removed from the body.
In fact, the assimilation of caffeine is a very composite procedure that entails over a dozen metabolites or new products created during metabolism. Only recently have the scientists come to comprehend the process completely. This has been possible owing to the introduction of new and potent paraphernalia that are able to differentiate intimately associated chemicals and also owing to the progress made in attaining advanced procedures to label parts of the caffeine molecule as well as map out their outcome in the human body.
As discussed earlier, 1,5 dimethylxanthine (paraxanthine) is the primary metabolite produced during the metabolism of caffeine. However, when paraxanthine passes through the liver it is metabolized producing newer chemicals, including 1-methylxanthine. In fact, when caffeine is eliminated from the body through urination, 1-methylxanthine is the main metabolite of this chemical compound.
It may be underlined here that the potency of the consequences of ingesting caffeine on the body to a great extent depends on the intensity of the chemical compound present in the blood circulating through the brain. The concentration of caffeine in the blood circulating through the brain reaches the peak sometime between 30 minutes and 60 minutes of taking the drug orally. This intervening period, the caffeine travels from the mouth to the gastrointestinal tract, where the chemical compound is absorbed, but before considerable amount of the drug is metabolized in the liver.
As long as even some amount of a caffeine dosage remains in the bloodstream, it will continue to have an impact on the body. The metabolic activity of substances in the liver, called enzymes, form the vital aspect in this regard. When the pace of caffeine metabolism by the liver is slow, it means that the drug remains inside the body for longer periods and, hence its effects too last longer. It may be noted that even the half-life of caffeine, i.e. the time taken by the liver to remove half the dosage of caffeine ingested, also differs from one person to another. The normal half-life of caffeine in adults is something between 2.5 hours and 10 hours with an average of four hours. And in most cases, the entire caffeine dosage ingested is eliminated from the body within 12 hours of taking the drug. In fact, men and women as well as people belonging to all age groups are inclined to have identical mean rates of caffeine metabolism in the liver. As the liver is mainly responsible for caffeine metabolism, the caffeine half-life is increased in people who suffer from different liver ailments that are associated with alcohol abuse.
In addition, concurrent use of other drugs also has a notable influence on the rate of caffeine metabolism by the liver. Generally, smokers have a caffeine half-life of three hours and are able to metabolize this chemical substance at least 50 per cent more rapidly compared to people who do not smoke. As a result, when smokers consume a cup of coffee, they experience the impact of caffeine for a much shorter duration compared to people who do not smoke. Moreover, nicotine as well as caffeine has conflicting influences on the neurotransmitter adenosine. It is believed that this could be one reason why smokers drink more coffee than the non-smokers. By consuming more coffee, they seem to make up for the short duration of caffeine in their body.
On the other hand, some inconsistencies in the pace of metabolism of caffeine by the liver are said to be inherited. For instance, caffeine metabolism in the Asians appears to be different as well as slow compared to the Caucasians. In addition, some changes in the rate of caffeine metabolism are also believed to be owing to an individual's understanding with the chemical compound. Although this theory is yet to be established, it is believed that people who use caffeine on a regular basis are able to metabolize the drug more rapidly. It needs to be noted that the pace of caffeine metabolism reduces significantly among pregnant women, especially during the last few weeks of pregnancy. However, the rate of caffeine metabolism returns to usual levels after they have delivered the baby.
Newborn babies or infants do not possess majority of the enzymes responsible for caffeine metabolism in their liver. As a result, the caffeine present in their bloodstream is eliminated from the body by means of urination. However, this is a very slow process and the half-life of caffeine in the new born babies is as high as 85 hours. However, as they grow up, their liver starts producing the enzymes resulting in the gradual decrease of the drug's half-life. By the time they are around two months old, the half-life of caffeine decreases to around 27 hours and when they are four months old is approximately 14 hours. When they are six months old, their caffeine half-life reduces to two to three hours below the half-life of caffeine in the adults. The half-life of caffeine remains under the level of the adults till their teenage years.
It is a known fact that caffeine passes on into the breast milk of lactating mothers. In addition, caffeine also secretes from the blood into the saliva and even semen. While the intensity of caffeine present in the saliva is around 75 per cent in an individual, the semen of a male contains approximately 100 per cent of the chemical compound as is present in the individual's bloodstream.
Barring the instances of newborn babies, excretion of unchanged caffeine remains the same in people of all other age groups. While only a little quantity of caffeine that has not been metabolized in the liver is eliminates along with feces and other fluids present in the body, except urine. In fact, urine contains not more than three per cent of unchanged caffeine. The reason for this is that most of the caffeine ingested by an individual is excreted through urine in the form of different metabolites of the chemical substance. In fact, the kidneys are responsible for this action, as the rate of flow of blood through the kidneys is directly related to the amount of urine produced and excreted by the body. It needs to be mentioned that while only a small amount of the caffeine consumed is present in urine, on an average, the intensity of caffeine present in urine is comparatively high - about 40 per cent more than what is found in the bloodstream. The reason behind this is easy to understand, as the actual volume of urine is much less in comparison to the volume of blood in the body.