Parenteral Routes of Drug Administration
The parenteral route introduces drugs directly across the body's barrier defenses into the systemic circulation or other vascular tissue. Parenteral administration is used for drugs that are poorly absorbed from the GI tract (for example heparin) and for agents that are unstable in the GI tract (for example, insulin).
Intravenous (IV): Injection is the most common parenteral route. For drugs that are not absorbed orally, such as the neuromuscular blocker atracurium, there is often no other choice.
In IV administration, the drug avoids the GI tract and therefore, first-pass metabolism by the liver. Intravenous delivery permits a rapid effect and a maximal degree of control over the circulating levels of the drug. However, unlike drugs in the GI tract, those that are injected cannot be recalled by strategies such as emesis or by binding to activated charcoal. Intravenous injection may inadvertently introduce bacteria through contamination at the site of injection. IV injection may also induce hemolysis or cause other adverse reactions by the too-rapid delivery of high concentrations of drug to the plasma and tissues. Therefore, the rate of infusion must be carefully controlled. Similar concerns apply to intra-arterially injected drugs.
Subcutaneous (SC): This route of administration, like that of Intra Muscular injection, requires absorption and is somewhat slower than the IV route. Subcutaneous injection minimizes the risks associated with intravascular injection. Other examples of drugs utilizing Subcutaneous administration include solids, such as a single rod containing the contraceptive etonogestrel that is implanted for long-term activity , and also programmable mechanical pumps that can be implanted to deliver insulin in diabetic patients.
Intramuscular (IM): Drugs administered IM can be aqueous solutions or specialized preparation often a suspension of drug in a non-aqueous vehicle such as polyethylene glycol.
Absorption of drugs in an aqueous solution is fast, whereas that from depot preparations is slow. As the vehicle diffuses out of the muscle, the drug precipitates at the site of injection. The drug then dissolves slowly, providing a sustained dose over an extended period of time. An example is sustained-release haloperidol decanoate , which slowly diffuses from the muscle and produces an extended neuroleptic effect.
Intravenous (IV): Injection is the most common parenteral route. For drugs that are not absorbed orally, such as the neuromuscular blocker atracurium, there is often no other choice.
In IV administration, the drug avoids the GI tract and therefore, first-pass metabolism by the liver. Intravenous delivery permits a rapid effect and a maximal degree of control over the circulating levels of the drug. However, unlike drugs in the GI tract, those that are injected cannot be recalled by strategies such as emesis or by binding to activated charcoal. Intravenous injection may inadvertently introduce bacteria through contamination at the site of injection. IV injection may also induce hemolysis or cause other adverse reactions by the too-rapid delivery of high concentrations of drug to the plasma and tissues. Therefore, the rate of infusion must be carefully controlled. Similar concerns apply to intra-arterially injected drugs.
Subcutaneous (SC): This route of administration, like that of Intra Muscular injection, requires absorption and is somewhat slower than the IV route. Subcutaneous injection minimizes the risks associated with intravascular injection. Other examples of drugs utilizing Subcutaneous administration include solids, such as a single rod containing the contraceptive etonogestrel that is implanted for long-term activity , and also programmable mechanical pumps that can be implanted to deliver insulin in diabetic patients.
Intramuscular (IM): Drugs administered IM can be aqueous solutions or specialized preparation often a suspension of drug in a non-aqueous vehicle such as polyethylene glycol.
Absorption of drugs in an aqueous solution is fast, whereas that from depot preparations is slow. As the vehicle diffuses out of the muscle, the drug precipitates at the site of injection. The drug then dissolves slowly, providing a sustained dose over an extended period of time. An example is sustained-release haloperidol decanoate , which slowly diffuses from the muscle and produces an extended neuroleptic effect.
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