How the Body Inactivates Drugs
As far as the body is concerned, drugs - whether natural or man made, are foreign substances that need to be inactivated or detoxified and eliminated. These chemicals can not be allowed to accumulate in the body. If they do accumulate they increase the toxic burden in the body. The accumulation of toxic substances in the body is now considered to be one of the main reasons behind the development of disease (Miller 1997).
The body does the drug detoxification and elimination mainly via the liver and kidneys (and out in the urine).
Some drugs are eliminated unchanged in the urine. The kidneys have a number of specialized processes that remove substances from the blood and pass them out in urine.
Some fat-soluble drugs are removed from the blood quickly as they tend to concentrate in the fat stores of the body. Such drugs can stay in those fat stores for some time and gradually leak out into the blood and are excreted through the kidneys and into the urine. It should not be assumed that these drugs are harmless as when they are stored in the fat tissue - they can cause problems while they are there! Cannabis is an example of a drug that is stored in fat tissue. It can persist in the fat stores of the body for several weeks after a single dose. It leaks out of the fat and is excreted in the urine.
The most important means of inactivating drugs is by metabolism - using enzymes to convert them to harmless products (though sometimes these products are not so harmless and can cause other damage in the body). Much of this drug metabolism takes place in the liver - which has many drug metabolising enzymes. The liver receives the blood that comes from the intestines - the gut, before the blood moves around the rest of the body. It can therefore remove toxic chemicals that are absorbed from the diet before they can do harm in other parts of the body. Drugs are also inactivated by one or more enzymes and are excreted from the liver either into the gut to be passed out in faeces or by the kidneys in urine.
Many drugs are given repeatedly for long periods of time and the liver and kidneys are called upon on a daily basis to eliminate the chemicals. The liver and kidneys are exposed to high concentrations of drugs. It is not surprising that the liver and kidneys are most vulnerable to drug-induced damage. This can be serious and life threatening. The metabolism of drugs in the liver can also produce toxic chemicals.
For example:
Paracetamol, a commonly used analgesic, is broken down or inactivated in the liver to produce a liver-damaging chemical. This can have life threatening consequences.
There are genetic variations in how people respond to and detoxify various drugs. There are people who lack some drug detoxifying enzymes. Some of these enzymes are involved in the detoxification and elimination of about 1/4 of all drugs. This means that these people are unable to effectively deal with the drugs.
Medical and others drugs place a strain on the detoxification capacity of the body. The liver and kidneys are particularly responsible for the detoxification and they can become overloaded. Toxins cause problems for the body on their way in, when they move around the body, when they are stored and when they are on their way out of the body. They irritate tissues, cause cells to breakdown and mutagenic changes to occur. This means that the body has to deal with these problems as well as trying to break down the toxins and eliminate them.
References
Goyen, M. 2000, Guide to Medications: Including Prescription and Non-prescription Drugs. Watermark Press.
Iversen, L. 2001, Drugs. Oxford Press.
Miller, C.S. 1997, Toxicant-Induced Loss of Tolerance - An Emerging Theory of Disease? Environmental Health Perspectives, Vol. 105, Supplement 2, March 1997
Society of Hospital Pharmacists of Australia. 2002, Pharmacology and Drug Information for Nurses. Saunders.
12.08.2007. 18:23
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