Understanding Drug Administration and Absorption

PHA 6840

Assignment #3

1. Administration is the route by which the drug or chemical enters the body. Routes of administration are classified as oral, topical, parenteral, rectal, or through inhalation. Absorption of drugs is dependent on how they are administered. Drugs that are taken orally have a slower onset of action compared to drugs taken parenterally (i.e. intravascular, intramuscular, or subcutaneous). Drugs of abuse that are taken by intravascular route such as cocaine or heroin, are absorbed within seconds of injection and result in immediate high. Drugs that are taken by oral route such as phenobarbital will have to be absorbed by the small intestines before effects of drug are seen.

Distribution is the termed used to describe

Barbiturates fall into the class of sedative-hypnotics. Some of the medical uses include: short-acting barbiturates that can be used for anesthesia induction, while the long acting barbiturates are utilized in anti-convulsant therapy. Barbiturates attach to the β subunit of the GABAA receptor. Stimulation of this inhibitory receptor causes an influx of chloride into cell membranes, which affects the threshold potential of the postsynaptic terminal. Barbiturates at high doses can actually cause direct opening of the chloride channel, essentially mimicking GABA without the actual presence of GABA. Barbiturates also have the ability to suppress depolarization, which is induced by glutamate, an excitatory neurotransmitter within the CNS. These drugs are highly effective at causing neuronal inhibition within the CNS. Barbiturates have a very narrow therapeutic window, which can result in life threatening side effects if not monitored properly. Some of the serious side effects corresponding to the cardiovascular system include: hypotension, decreased cardiac contractility, decreased cardiac output and decreased cerebral blood flow. In long-term barbiturate use cytochrome P450 enzymes are induced which can rapidly metabolize and affect other drugs utilizing this pathway. Tolerance to the depressant effects is common amongst chronic users. Barbiturates have both a tissue specific tolerance and metabolic tolerance. Tissue specific tolerance occurs in the reticular activating

Barbiturates have the ability to cause severe respiratory depression and possibly death with their ability to induce GABA receptors on their own. Today, some long acting barbiturates such as phenobarbital are still used in both human and veterinary medicine. Today, there are safer and more effective drugs such as benzodiazepines that have replaced the use of barbiturates.

4. Both benzodiazepines and alcohol effectively suppress neuronal excitability in the CNS through the GABA receptor. Alcohol also has the ability to suppress the excitatory neurotransmitter glutamate at the NDMA receptor. This drug combination can have a synergistic effect at the GABA receptor, resulting in an increase sedation and significant respiratory depression to the point where abuser stops breathing and loses consciousness. There is also an increased risk of accidents (i.e vehicle) due to cognitive