Individual Variation in Drug Response & Pharmacogenetics Flashcards
A patient with cancer is receiving morphine for pain control. The patient calls the nurse to report that the morphine is no longer controlling his pain. What is the most appropriate response by the nurse?
“You have developed a tolerance to morphine and will need a higher dose.”
“Increasing the dose of morphine will make you so sleepy that you will not be able to function.”
“It is recommended that we wait to increase the morphine until the pain is more severe.”
“This means that you have developed a psychologic addiction to morphine.”
“You have developed a tolerance to morphine and will need a higher dose.”
Tolerance is a decreased responsiveness to a drug as a result of repeated drug administration. Patients who become tolerant to a drug require higher doses to produce effects equivalent to those that could be achieved with lower doses before the tolerance developed.
The nurse is preparing to administer warfarin [Coumadin] to a patient. The nurse notes that the patient has altered CYP2D6 genes. It is most important for the nurse to do which of the following?
Observe the patient’s legs for symptoms of a blood clot.
Examine the patient’s stools for the presence of blood.
Monitor for ST-segment elevation or depression.
Check for signs of a transient ischemic attack.
Examine the patient’s stools for the presence of blood.
Variants in the gene that codes for CYP2C9 can increase the risk of toxicity (ie, bleeding) when taking warfarin [Coumadin], an anticoagulant with a narrow therapeutic index. The nurse should assess the patient for the presence of bleeding.
A patient was discharged from the hospital with instructions to take an antibiotic for 7 days to treat a bladder infection. Twelve days later, a home care nurse visits the patient and finds that the symptoms have not resolved. What is the most important question for the nurse to ask?
“How much water have you been drinking each day?”
“Do you think you have another bladder infection?”
“Have you taken all of the antibiotics as directed?”
“What antibiotic do you usually take to treat an infection?”
“Have you taken all of the antibiotics as directed?”
The failure to take medications as directed is a common cause of persistent infection.
A nurse administers the same medication in the same preparation in the same dose to several patients and notes that some patients have a better response to the drug than others. What is the most likely explanation for this phenomenon?
Patient compliance with the therapeutic regimen
Altered bioavailability of the drug
Placebo effects enhancing expectations of drug efficacy
Pharmacogenomic differences among individuals
Pharmacogenomic differences among individuals
Each patient’s genetic makeup can determine how that patient responds to drugs quantitatively and qualitatively, and this is the most likely cause of individual variation when the same drug is given at the same dose. The bioavailability of a drug is determined by the drug’s composition and varies across formulations of the drug. The patients in this example were given the same drug. The nurse was administering the medication to the patients, so compliance is not an issue. Nothing in this example indicates that a placebo effect was in play.
The U.S. Food and Drug Administration (FDA) recommends genetic testing of patients receiving certain medications. Genetic testing helps prescribers:
produce a drug that is tailored to an individual patient’s genetic makeup.
identify racial characteristics that affect psychosocial variation in drug response.
determine whether a patient is a rapid or slow metabolizer of the drug.
better establish a drug’s therapeutic index.
determine whether a patient is a rapid or slow metabolizer of the drug.
Pharmacogenomics is the study of the ways genetic variations affect individual responses to drugs through alterations in genes that code for drug-metabolizing enzymes and drug receptors. For some drugs, the FDA requires genetic testing, and for others, this testing is recommended but not required. Genetic testing does not determine a drug’s therapeutic index; this is a measure of a drug’s safety based on statistics of the drug’s use in the general population (see Chapter 5). Any distinct physiologic differences in drug response among various racial populations are related to genetic differences and do not affect psychosocial differences in drug responses. Genetic testing is recommended to identify how a patient will respond to a drug and not to design a drug specific to an individual.
A patient asks a nurse why a friend who is taking the same drug responds differently to that drug. The nurse knows that the most common variation in drug response is due to differences in each patient’s:
psychosocial response.
hypersensitivity potential.
drug receptor sites.
metabolism of drugs.
metabolism of drugs.
The most common source of genetic variation in drug response is related to alterations in drug metabolism and is determined by genetic codes for various drug-metabolizing isoenzymes. There are known genetic differences in codes for drug target sites, but these are not as numerous as those for metabolic isoenzymes. Hypersensitivity potential is also genetically determined, but variations produce differences in adverse reactions to drugs and not in drug effectiveness. Psychosocial responses vary for many less measurable reasons, such as individual personalities and variations in cultures.
A patient has been taking narcotic analgesics for chronic pain for several months. The nurse caring for this patient notes that the prescribed dose is higher than the recommended dose. The patient has normal vital signs, is awake and alert, and reports mild pain. What does the nurse recognize about this patient?
This patient produces higher than normal hepatic enzymes as a result of prolonged exposure to the drug.
This patient has developed a reaction known as tachyphylaxis because of repeated exposure to the drug.
This patient exhibits a negative placebo effect with a reduced response to the drug.
This patient has developed pharmacodynamic tolerance, which has increased the minimal effective concentration (MEC) needed for analgesic effect.
This patient has developed pharmacodynamic tolerance, which has increased the minimal effective concentration (MEC) needed for analgesic effect.
Pharmacodynamic tolerance results when a patient takes a drug over a period of time. Adaptive processes occur in response to chronic receptor occupation. The result is that the body requires increased drug, or an increased MEC, to achieve the same effect. This patient is getting adequate pain relief, so there is no negative placebo effect. Tachyphylaxis is a form of tolerance that can be defined as a reduction in drug responsiveness brought on by repeated dosing over a short time; this occurs over several months. Barbiturates induce synthesis of hepatic enzymes that cause increased metabolism of the drug, but it does not increase the MEC.
Which groups of people are especially sensitive to medication effects? (Select all that apply.)
Minorities
Older adults
Infants
Caucasians
Women
Older adults & Infants
Older adults and infants are the two groups most sensitive to drugs because of differences in organs that absorb, metabolize, and excrete drugs. In the older adult, organ degeneration accounts for these differences, whereas in infants the differences are related to organ immaturity. Racial and gender differences tend to be related to genetic differences and not race and gender per se. These groups are more sensitive to drug effects in some cases and less sensitive in other cases.
A nurse is teaching a group of women about medications. The women want to know why so many drugs have unpredictable effects in women. The nurse will tell them that:
most known drug effects are based on drug trials in men.
women metabolize drugs more slowly.
drugs usually have more toxic effects in women.
women have varying responses to drugs during menstrual cycles.
most known drug effects are based on drug trials in men.
Until 1997, almost all clinical drug trials were performed in men. Women may have more toxic effects with some drugs and fewer toxic effects with others. Not all drugs are influenced by hormonal changes. Women metabolize some drugs more slowly and other drugs more quickly. Unless drug trials are performed in both women and men, the effects of drugs in women will not be clear.
