Administration route blood supply

The route of administration is an important factor in determining the rate and extent of absorption. For example, absorption after an oral dose can be relatively slow and erratic, whilst absorption from the lungs is usually fast because of the good blood supply. Most drugs are administered orally, and an understanding of the mechanism of absorption by this route is by far the most important for the toxicologist. 

An intramuscular (IM) injection is the administration of a drug into a muscle (see Pig. 2-5C). Dru that are irritating to SC tissue can be given via IM injection. Dru given by this route are absorbed more rapidly than dru given by the SC route because of the rich blood supply in the muscla In addition, a larger volume (1-3 inL) can be given at one site. 

Due to the rich blood and lymph supply to rectum the unionised and lipid soluble substances are readily absorbed from the rectum. The advantages of this route are that gastric irritation is avoided and easy administration by the patient himself. 

Intravenous route is the most rapidly effective and the desired blood concentration can be obtained with a definite dose but at the same time it is the most dangerous route of administration. For once the drug is injected there is no retreat. So, intravenous injection must usually be performed slowly and with constant monitoring of the patient. This route is usually reserved for emergencies when a rapid action is required and infusion of large amounts of fluids to overcome dehydration or to supply nutrition to patients who can not take food/fluids orally. 

The cardiac output or flow of blood normally is so rapid that the distribution of a drug or poison throughout the body is complete within a short period of time. An entire 6 liter supply of blood is pumped through the body at the rate of about once per minute. Some organs and tissues are more highly perfused with blood than others, such as the brain, heart, liver, and kidneys. Adipose (fat) tissue is not as richly endowed. Should a person be in shock or have suffered a myocardial infarction (heart attack), however, the cardiac output can be sharply diminished and a route of drug administration normally used may be circumvented because of poor... 

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