NURS 6521 PHARMACOLOGY MIDTERMS STUDYGUIDES

NURS 6521 PHARMACOLOGY MIDTERMS STUDYGUIDES

Pharmacokinetics:

•  Understand the implications of changing renal function on creatinine and drug dosing.

Renal disease interacts with drugs in three main ways. Firstly, patients with renal disease may be more vulnerable to a given drug effect (patient susceptibility). Secondly, a drug effect may be exaggerated or attenuated in patients with renal disease (pharmacodynamic change). Thirdly, and most importantly, some drugs have higher steady-state concentrations when given at usual doses to patients with renal disease (pharmacokinetic changes).

Serum creatinine is the most commonly used analyte in the evaluation of renal function, and equations using serum creatinine concentration are the basis of most estimates of GFR

•  What is the impact of the following on drug levels and dosing:

o  Cirrhosis The liver is the main organ for metabolism and detoxification of endogenous and exogenous substances. Several pathophysiological changes that occur in liver cirrhosis influence this detoxification of exogenous substances, that is, drug pharmacokinetics.

o  Protein binding Drugs can form reversible bonds with various proteins in the body. Of all the proteins with which drugs can bind, plasma albumin is the most important. Like other proteins, albumin is a large molecule. Because of its size, albumin is too large to leave the bloodstream.

Even though a drug can bind albumin, only some molecules will be bound at any moment. The percentage of drug molecules that are

bound is determined by the strength of the attraction between albumin and the drug

An important consequence of protein binding is restriction of drug distribution. Because albumin is too large to leave the bloodstream, drug molecules that are bound to albumin cannot leave either. As a result, bound molecules cannot reach their sites of action or undergo metabolism or excretion until the drug-protein bond is broken so that the drug is free to leave the circulation. In addition to restricting drug distribution, protein binding can be a source of drug interactions.

Each molecule of albumin has only a few sites to which drug molecules can bind. Because the number of binding sites is limited, drugs with the ability to bind albumin will compete with one another for those sites. As a result, one drug can displace another from albumin, causing the free concentration of the displaced drug to rise, thus increasing the intensity of drug responses. If plasma drug levels rise sufficiently, toxicity can result

o  Drug interactions Drug-drug interactions can occur whenever a patient takes two or more drugs. Some interactions are both intended and desired, as when we combine drugs to treat hypertension. In contrast, some interactions are both unintended and undesired.

Consequences of Drug-Drug Interactions When two drugs interact, there are three possible outcomes:

(1)   one drug may intensify the effects of the other,

(2)   one drug may reduce the effects of the other, or

(3)   the combination may produce a new response not seen with either drug alone.

Half-life - Drug half-life is defined as the time required for the amount of drug in the body to decrease by 50%. A few drugs have half-lives that are extremely short—on the order of