- A pharmacist should be alerted if a patient with severe chronic kidney disease (CKD) receives a prescription for metformin. The primary risk associated with using metformin in this patient population is:
Answer: Lactic acidosis
Metformin is eliminated from the body by the kidneys. In patients with severe renal impairment, the drug is not cleared effectively and can accumulate to toxic levels. This accumulation increases the risk of lactic acidosis, a rare but very serious metabolic complication with a high mortality rate.
- A patient brings in a new prescription for sildenafil. The technician checks the patient's profile and sees an active prescription for nitroglycerin. This combination is absolutely contraindicated due to the risk of what severe adverse effect?
Answer: Severe hypotension
Both sildenafil (a PDE-5 inhibitor) and nitroglycerin (a nitrate) are potent vasodilators. When used together, they can cause a synergistic effect, leading to a profound and life-threatening drop in blood pressure (severe hypotension).
- A patient receiving a prescription for phenelzine should be counseled to avoid foods rich in tyramine, such as aged cheeses and cured meats. Consuming these foods while taking this medication can cause what type of adverse reaction?
Answer: Hypertensive crisis
Phenelzine is a Monoamine Oxidase Inhibitor (MAOI). MAOIs prevent the breakdown of tyramine. An excess of tyramine can cause a massive release of catecholamines, leading to a rapid and dangerous increase in blood pressure known as a hypertensive crisis.
- A medication order for lisinopril is being filled for a patient who also buys over-the-counter potassium chloride supplements. The combination of these two products can lead to a dangerously high level of potassium in the blood, a condition known as:
Answer: Hyperkalemia
ACE inhibitors like lisinopril can increase potassium levels. Taking them with potassium supplements can lead to hyperkalemia (high potassium), which can cause serious cardiac arrhythmias. Hypokalemia is low potassium, while hyponatremia and hypernatremia refer to sodium levels.
- A patient stabilized on warfarin is started on amiodarone for an arrhythmia. Why must the patient's warfarin therapy be closely monitored and likely adjusted?
Answer: Amiodarone inhibits the metabolism of warfarin, increasing its effect.
Amiodarone is a potent inhibitor of several cytochrome P450 enzymes, including CYP2C9, which is the primary enzyme that metabolizes the S-isomer of warfarin. This inhibition slows down the clearance of warfarin, leading to higher blood levels and an increased INR, which elevates the risk of bleeding. The warfarin dose typically needs to be reduced.
- A patient prescribed spironolactone for heart failure mentions using a salt substitute that contains potassium chloride. This combination should be flagged for the pharmacist because it increases the risk of:
Answer: Hyperkalemia
Spironolactone is a potassium-sparing diuretic, which works by blocking aldosterone and causing the body to retain potassium. Salt substitutes often replace sodium chloride with potassium chloride. Combining these two sources of potassium can lead to dangerously high blood potassium levels (hyperkalemia), which can cause life-threatening heart rhythm problems.
- A patient is taking both digoxin and furosemide. Furosemide can deplete potassium levels in the body. How does low potassium (hypokalemia) affect the patient taking digoxin?
Answer: It increases the risk of digoxin toxicity.
Digoxin exerts its effect by binding to the Na+/K+ ATPase pump in heart muscle cells, a site where potassium also binds. When potassium levels are low (hypokalemia), there is less competition for these binding sites, allowing more digoxin to bind. This enhances digoxin's effects and greatly increases the risk of toxicity, even at therapeutic drug levels.
- A patient mentions she has started taking St. John's wort, an over-the-counter herbal supplement for mood. Her medication profile includes an oral contraceptive. What is the most significant potential interaction the technician should recognize?
Answer: Decreased effectiveness of the oral contraceptive.
St. John's wort is a potent inducer of the CYP3A4 enzyme system. This enzyme metabolizes the hormones in oral contraceptives. By inducing the enzyme, St. John's wort speeds up the breakdown of the hormones, lowering their blood levels and potentially leading to unintended pregnancy.
- A patient with a history of uncontrolled hypertension asks to purchase an over-the-counter cold medication containing pseudoephedrine. Why is this a concern?
Answer: Pseudoephedrine can increase blood pressure.
Pseudoephedrine is a sympathomimetic agent that acts as a vasoconstrictor, meaning it narrows blood vessels. This action can lead to a significant increase in both systolic and diastolic blood pressure, which is particularly dangerous for individuals with pre-existing or uncontrolled hypertension.
- A patient with a known history of asthma is prescribed propranolol for migraine prevention. This is a potential drug-disease interaction because non-selective beta-blockers like propranolol can cause:
Answer: Bronchoconstriction
Non-selective beta-blockers block both beta-1 (in the heart) and beta-2 (in the lungs) receptors. Blocking beta-2 receptors can cause the airways to narrow (bronchoconstriction), which can trigger a severe, potentially fatal asthma attack in susceptible individuals.
- A patient taking azathioprine receives a new prescription for allopurinol. The computer flags a major interaction. What is the consequence of this drug combination if the azathioprine dose is not significantly reduced?
Answer: Increased risk of bone marrow suppression
Allopurinol inhibits xanthine oxidase, an enzyme that is essential for the metabolism of azathioprine. Co-administration without a significant dose reduction of azathioprine (often by 66-75%) can lead to toxic levels of the immunosuppressant, resulting in severe and life-threatening bone marrow suppression.
- When reviewing a medication profile for a patient on warfarin, the technician sees a note that the patient also takes ginkgo biloba supplements. This combination is concerning because it can increase the patient's risk of:
Answer: Bleeding
Warfarin is an anticoagulant that prevents blood clots. Ginkgo biloba is an herbal supplement that can inhibit platelet aggregation, which also impairs clotting. Using them together has an additive effect, increasing the risk of spontaneous or excessive bleeding.
- A prescription for ciprofloxacin is being dispensed. The patient should be advised to avoid taking the antibiotic at the same time as which of the following?
Answer: Milk or yogurt
Fluoroquinolone antibiotics like ciprofloxacin can bind with polyvalent cations, such as the calcium found in dairy products (milk, yogurt, cheese) and calcium-fortified juices. This chelation process forms an insoluble compound, significantly reducing the absorption of the antibiotic and potentially leading to treatment failure.
- A patient who takes sertraline daily receives a new prescription for sumatriptan to be taken as needed for migraines. The pharmacy computer system flags an interaction warning. This combination increases the risk of:
Answer: Serotonin syndrome
Both SSRIs (like sertraline) and triptans (like sumatriptan) increase levels of serotonin in the brain. Using them concurrently can lead to an excessive accumulation of serotonin, causing a potentially life-threatening condition called serotonin syndrome, characterized by agitation, confusion, rapid heart rate, and fever.
- A patient is prescribed doxycycline and is advised to take it one hour before or two hours after taking their daily calcium carbonate antacid. What is the reason for this specific timing instruction?
Answer: Calcium binds to doxycycline, decreasing its absorption.
Polyvalent cations like calcium, magnesium, aluminum, and iron can bind to tetracycline antibiotics (like doxycycline) in the gastrointestinal tract. This process, called chelation, forms an insoluble complex that is not well absorbed, reducing the antibiotic's effectiveness.
- A patient taking levothyroxine for hypothyroidism is instructed to separate the administration of their thyroid medication from their daily iron supplement by at least four hours. This is because iron can:
Answer: Decrease the absorption of levothyroxine.
Iron salts can bind to levothyroxine in the gut, forming a non-absorbable complex. This significantly reduces the amount of levothyroxine that enters the bloodstream, leading to decreased efficacy and potentially uncontrolled hypothyroidism. Similar interactions occur with calcium and aluminum-containing antacids.
- A pharmacy technician notes a high-dose, long-term prescription for ibuprofen for a patient with a diagnosis of chronic kidney disease (CKD). Why should this be brought to the pharmacist's attention?
Answer: NSAIDs can worsen kidney function.
Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen work by inhibiting prostaglandins. Prostaglandins are vital for maintaining adequate blood flow to the kidneys. In patients with compromised renal function, NSAIDs can constrict blood vessels in the kidneys, leading to a further decline in kidney function or acute kidney injury.
- A patient taking atorvastatin for high cholesterol mentions they drink a large glass of grapefruit juice every morning. Why should the pharmacy technician alert the pharmacist to this information?
Answer: Grapefruit juice increases the risk of muscle pain and damage.
Grapefruit juice is a strong inhibitor of the CYP3A4 enzyme, which is responsible for metabolizing atorvastatin. This interaction leads to higher concentrations of the statin in the blood, increasing the risk of adverse effects, including myopathy (muscle pain) and potentially life-threatening rhabdomyolysis (muscle breakdown).
- A technician sees a prescription for hydrochlorothiazide for a patient with a documented history of gout. Why might this be a potential drug-disease interaction?
Answer: Thiazide diuretics can increase uric acid levels.
Thiazide diuretics, such as hydrochlorothiazide, can decrease the kidneys' ability to excrete uric acid. This leads to an increase in uric acid levels in the blood (hyperuricemia). In patients who are already susceptible to gout, this elevated level can trigger a painful acute gout flare.
- A patient's profile shows they are taking warfarin. A new prescription for sulfamethoxazole/trimethoprim is entered. The computer system flags a potential interaction. This interaction increases the risk of which of the following?
Answer: Bleeding
Sulfamethoxazole/trimethoprim can significantly inhibit the metabolism of warfarin, leading to an elevated International Normalized Ratio (INR) and a substantially increased risk of bleeding. The pharmacy technician should always alert the pharmacist to this critical interaction.
