|
General Medication Information |   |
 |
There are
a wide variety of patient circumstances that can necessitate the modification
of recommended dosage or frequency of medications administered to
pulmonary patients. Following administration, most drugs go through
several steps in a well-defined sequence before being excreted from
the body, including:
|
Metabolism, also known as biotransformation, is the step in which a drug circulating in the bloodstream is transformed from its original active form to a less active form. While other organs participate to a limited degree in the metabolism process, the liver is the principal site of drug metabolism. Drugs absorbed through the mucous membrane of the stomach or intestines, enter the bloodstream via the portal vein. Before this vein empties into the general circulation system, it passes through the liver where the drugs carried by the vein are exposed immediately to metabolism by liver enzymes.
Because the liver plays such a key role in the metabolism of most drugs, a decreased rate of drug metabolism can occur in patients with liver diseases or hepatitis. Drug dosages for these patients need to be adjusted in order to avoid toxicity, and to compensate for the prolonged pharmacologic action of unmetabolized drug in the blood stream.
The kidney is the principal organ involved in the excretion of drugs from the body. Poor renal function can significantly prolong the effects of some drugs, and altered pH levels can inactivate some drugs, such as bronchodilators. Since mechanical ventilation can affect kidney function by decreasing perfusion pressure, drug dosages may need to be modified for patients on ventilation.
Also, since many patients are being treated with more than one drug at a time, drug interaction and synergism needs to be taken into account when setting dosages and administration frequencies. All of these factors contribute to making the task of prescribing proper dosage of medications for respiratory patients a more complex undertaking.