02-28-2008, 08:42 AM
9.
Of the following, which is unlikely to be associated with receptors bound to plasma membranes, their interaction with ligands, and the biologic response to this interaction?
A.
Structurally, these receptors have hydrophobic amino acid domains, which are in contact with the membrane, and hydrophilic regions, which extend into the extracellular fluid and the cytoplasm
B.
Chemical interactions of ligands with these receptors may involve the formation of many types of bonds, including ionic, hydrogen, van der Waals', and covalent
C.
Ligand-receptor interactions are often stereospecific (i.e., one stereoisomer is usually more potent than the other)
D.
In some cases, a ligand that acts as an agonist at membrane-bound receptors increases the activity of an intracellular second messenger
E.
Activation of membrane-bound receptors and subsequent intracellular events elicit a biologic response through the transcription of DNA
The answer is: E
Based upon the molecular mechanisms with which receptors transduce signals, four major classes of receptors have been identified: (1) ion channel receptors, (2) receptors that interact with G proteins, (3) receptors with tyrosine kinase activity, and (4) nuclear receptors. The first three types of receptors are complex membrane-bound proteins with hydrophilic regions located within the lipoid cell membrane and hydrophilic portions found protruding into the cytoplasm of the cell and the extracellular milieu; when activated, all of these receptors transmit (or transduce) information presented at the extracellular surface into ionic or biochemical signals within the cell (i.e., second messengers). Nuclear receptors are found in the nucleus of the cell, not bound to plasma membranes.
In addition, these receptors do not transduce information by second-messenger systems; rather, they bind to nuclear chromatin and elicit a biologic response through the transcription of DNA and alterations in the formation of cellular proteins. Ligand binding to all types of receptors may involve the formation of ionic, hydrogen, hydrophobic, van der Waals', and covalent bonds. In most cases, ligand-receptor interactions are stereospecific; for example, natural (“)-epinephrine is 1000 times more potent than (+)-epinephrine.
10.
Of the following, which is unlikely to be associated with the binding of drugs to plasma proteins?
A.
Acidic drugs generally bind to plasma albumin; basic drugs preferentially bind to 1-acidic glycoprotein
B.
Plasma protein binding is a reversible process
C.
Binding sites on plasma proteins are nonselective, and drugs with similar physicochemical characteristics compete for these limited sites
D.
The fraction of the drug in the plasma that is bound is inactive and generally unavailable for systemic distribution
E.
Plasma protein binding generally limits renal tubular secretion and biotransformation
The answer is: E
Because only the free (unbound) fraction of a drug can cross biologic membranes, binding to plasma proteins limits a drug's concentration in tissues and, therefore, decreases the apparent Vd of the drug. Plasma protein binding will also reduce glomerular filtration of the drug because this process is highly dependent on the free drug fraction. Renal tubular secretion and biotransformation of drugs are generally not limited by plasma protein binding because these processes reduce the free drug concentration in the plasma. If a drug is avidly transported through the tubule by the secretion process or is rapidly biotransformed, the rates of these processes may exceed the rate of dissociation of the drug-protein complex (in order to restore the free:bound drug ratio in plasma) and, thus, become the rate-limiting factor for drug elimination. This assumes that equilibrium conditions exist and that other influences (e.g., changes in pH or the presence of other drugs) do not occur.
11.
Of the following, which is unlikely to be associated with drug distribution into and out of the central nervous system (CNS)?
A.
The blood-brain barrier, which involves drug movement through glial cell membranes as well as capillary membranes, is the main hindrance to drug distribution to the CNS
B.
Most drugs enter the CNS by simple diffusion at rates that are proportional to the lipid solubility of the nonionized form of the drug
C.
Receptor-mediated transport allows certain peptides to gain access to the brain
D.
Strongly ionized drugs freely enter the CNS through carrier-mediated transport systems
E.
Some drugs leave the CNS by passing from the cerebrospinal fluid into the dural blood sinuses through the arachnoid villi
The answer is: D
Drugs can enter the brain from the circulation by passing through the blood-brain barrier. This boundary consists of several membranes, including those of the capillary wall, the glial cells closely surrounding the capillary, and the neuron. In most cases, lipid-soluble drugs diffuse through these membranes at rates that are related to their lipid-to-water partition coefficients. Therefore, the greater the lipid solubility of the nonionized fraction of a weak acid or base, the more freely permeable the drug is to the brain. Some drugs enter the CNS through specific carrier-mediated or receptor-mediated transport processes. Carrier-mediated systems appear to be involved predominantly in the transport of a variety of nutrients through the blood-brain barrier; however, the thyroid hormone 3,5,3'-triiodothyronine and drugs such as levodopa and methyldopa, which are structural derivatives of phenylalanine, cross the blood-brain barrier via carrier-mediated transport.
Receptor-mediated transport functions to permit a peptide (e.g., insulin) to enter the CNS; therefore, some peptide-like drugs are believed to gain access to the brain by this mechanism. Regardless of the process by which drugs can enter the CNS, strongly ionized drugs (e.g., quaternary amines) are unable to enter the CNS from the blood.
The exit of drugs from the CNS can involve (1) diffusion across the blood-brain barrier in the reverse direction at rates determined by the lipid solubility and degree of ionization of the drug, (2) drainage from the cerebrospinal fluid (CSF) into the dural blood sinuses by flowing through the wide channels of the arachnoid villi, and (3) active transport of certain organic anions and cations from the CSF to blood across the choroid plexuses.
12.
A 19-year-old male being treated for leukemia develops fever. You give agents that will cover bacterial, viral, and fungal infections. Two days later, he develops acute renal failure. Which drug was most likely responsible?
A.
Vancomycin
B.
Ceftazidime
C.
Amphotericin B
D.
Acyclovir
The answer is: C
Amphotericin B may alter kidney function by decreasing creatinine clearance; if this occurs, the dose must be reduced. It also commonly increases potassium (K+) clearance, leading to hypokalemia, and causes anemia and neurologic symptoms. A liposomal preparation may reduce the incidence of renal and neurologic toxicity. Vancomycin is less likely to cause kidney damage; if it does, the damage is less severe.
13.
Which of the following is the quinolone derivative that is most effective against Pseudomonas aeruginosa?
A.
Norfloxacin
B.
Ciprofloxacin
C.
Ofloxacin
D.
Enoxacin
E.
Lomefloxacin
The answer is: B
Ciprofloxacin is a fluorinated quinolone derivative highly effective against P. aeruginosa. Other derivatives in this class have less activity toward this organism, although they are effective against other common Gram-negative organisms.
14.
A 19-year-old woman is diagnosed with tuberculosis (TB). Before prescribing a drug regimen, you take a careful medication history because one of the drugs commonly used to treat TB induces microsomal cytochrome P450 enzymes in the liver. Which drug is this?
A.
Isoniazid
B.
Rifampin
C.
Pyrazinamide
D.
Ethambutol
E.
Vitamin B6
The answer is: B
Rifampin induces cytochrome P450 enzymes, which causes a significant increase in elimination of drugs, such as oral contraceptives, anticoagulants, ketoconazole, cyclosporine, and chloramphenicol. It also promotes urinary excretion of methadone, which may precipitate withdrawal.
15.
The elimination half-life of which of the following tetracyclines remains unchanged when the drug is administered to an anuric patient?
A.
Methacycline
B.
Oxytetracycline
C.
Doxycycline
D.
Tetracycline
E.
None of the above
The answer is: C
All tetracyclines can produce negative nitrogen balance and increased blood urea nitrogen (BUN) levels. This is of clinical importance in patients with impaired renal function. With the exception of doxycycline, tetracyclines should not be used in patients that are anuric. Doxycycline is excreted by the GI tract under these conditions, and it will not accumulate in the serum of patients with renal insufficiency.
16.
In patients with hepatic coma, decreases in the production and absorption of ammonia from the gastrointestinal (GI) tract will be beneficial. Which of the following is the antibiotic of choice in this situation?
A.
Neomycin
B.
Tetracycline
C.
Penicillin G
D.
Chloramphenicol
E.
Cephalothin
The answer is: A
Neomycin, an aminoglycoside, is not significantly absorbed from the GI tract. After oral administration, the intestinal flora is suppressed or modified and the drug is excreted in the feces. This effect of neomycin is used in hepatic coma to decrease the coliform flora, thus decreasing the production of ammonia that causes the levels of free nitrogen to decrease in the bloodstream. Other antimicrobial agents (e.g., tetracycline, penicillin G, chloramphenicol, and cephalothin) do not have the potency of neomycin in causing this effect.
17.
Which of the following is the most active aminoglycoside against Mycobacterium tuberculosis?
A.
Streptomycin
B.
Amikacin
C.
Neomycin
D.
Tobramycin
E.
Kanamycin
The answer is: A
The activity of streptomycin is bactericidal for the tubercle bacillus organism. Other aminoglycosides (e.g., gentamicin, tobramycin, neomycin, amikacin, and kanamycin) have activity against this organism but are seldom used clinically because of toxicity or development of resistance.
18.
Chronic candidiasis infections of the GI tract and oral cavity are treated with which agent in pill form?
A.
Amphotericin B
B.
Nystatin
C.
Miconazole
D.
Fluconazole
E.
Clotrimazole
The answer is: D
Mucocutaneous infections, most commonly Candida albicans, involve the moist skin and mucous membranes. Agents used topically include amphotericin B, nystatin, miconazole, and clotrimazole. Ketoconazole and fluconazole are administered orally in pill form for treatment of chronic infections.
19.
Drug X is an antimycobacterial agent that inhibits other bacteria as well as poxviruses. However, it should not be used as a single agent because resistant mutants frequently form. The responsible mutation may alter the site of action of drug X [i.e., the deoxyribonucleic acid (DNA)“dependent ribonucleic acid (RNA) polymerase]. What is drug X?
A.
INH
B.
Rifampin
C.
Pyrazinamide
D.
Ethambutol
The answer is: B
Rifampin inhibits RNA synthesis in bacteria, mycobacteria, and chlamydiae by binding to the DNA-dependent RNA polymerase; it also inhibits assembly of poxvirus particles. Rifampin is used as a single prophylactic agent for contacts of people with meningococcal or H. influenzae type b infections. Otherwise, it is not used alone because 1 in 10 organisms in a population exposed to rifampin will become resistant, possibly because of mutation or a barrier against rifampin's entry into cells.
20.
For the treatment of a patient with Legionella pneumophila, which of the following is the drug of choice?
A.
Penicillin G
B.
Chloramphenicol
C.
Erythromycin
D.
Streptomycin
E.
Lincomycin
The answer is: C
Erythromycin, a macrolide antibiotic, was initially designed to be used in penicillin-sensitive patients with streptococcal or pneumococcal infections. Erythromycin has become the drug of choice for the treatment of pneumonia caused by Mycoplasma and Legionella.
21.
The mechanism of action by which pyrantel pamoate is effective for the treatment of Necator americanus (hookworm) disease is
A.
Interference with cell-wall synthesis
B.
Interference with cell division
C.
Inhibition of neuromuscular transmission
D.
Interference with protein synthesis
E.
Depletion of membrane lipoproteins
The answer is: C
Pyrantel pamoate is an antihelminthic that acts primarily as a depolarizing neuromuscular blocker. In certain worms, a spastic neuromuscular paralysis occurs, resulting in the expulsion of the worms from the intestinal tract of the host. Pyrantel also exerts its effect against parasites via release of acetylcholine and inhibition of cholinesterase.
22.
Amantadine, a synthetic antiviral agent used prophylactically against influenza A2, is thought to act by
A.
Preventing production of viral capsid protein
B.
Preventing virion release
C.
Preventing penetration of the virus into the host cell
D.
Preventing uncoating of viral DNA
E.
Causing lysis of infected host cells by release of intracellular lysosomal enzymes
The answer is: D
Amantadine's mechanism of action involves inhibition of uncoating of the influenza A viral DNA. The primary target is the membrane M2 protein. The drug does not affect penetration and DNA-dependent RNA polymerase activity. Amantadine both reduces the frequency of illness and diminishes the serologic response to influenza infection. The drug has no action, however, on influenza B. As a weak base, amantadine buffers the pH of endosomes, thus blocking the fusion of the viral envelope with the membrane of the endosome.
23.
Streptomycin and other aminoglycosides inhibit bacterial protein synthesis by binding which of the following?
A.
Peptidoglycan units in the cell wall
B.
Messenger RNA (mRNA)
C.
DNA
D.
30S ribosomal particles
E.
RNA polymerase
The answer is: D
The bactericidal activity of streptomycin and other aminoglycosides involves a direct action on the 30S ribosomal subunit, the site at which these agents both inhibit protein synthesis and diminish the accuracy of translation of the genetic code. Proteins containing improper sequences of amino acids (known as nonsense proteins) are often nonfunctional.
24.
A patient with AIDS is treated with a combination of agents, which includes zidovudine. What is the mechanism of action of zidovudine?
A.
Inhibition of RNA synthesis
B.
Inhibition of viral particle assembly
C.
Inhibition of viral proteases
D.
Inhibition of nucleoside reverse transcriptase
E.
Inhibition of nonnucleoside reverse transcriptase
The answer is: D
Zidovudine competitively inhibits HIV-1 nucleoside reverse transcriptase. It is also incorporated in the growing viral DNA chain to cause termination. Each action requires activation via phosphorylation of cellular enzymes. Zidovudine decreases the rate of clinical disease progression and prolongs survival in HIV-infected patients.
25.
A 39-year-old male with aortic insufficiency and a history of no drug allergies is given an intravenous dose of antibiotic as a prophylaxis preceding the insertion of a valve prosthesis. As the antibiotic is being infused, the patient becomes flushed over most of his body. What antibiotic was given?
A.
Vancomycin
B.
Gentamicin
C.
Erythromycin
D.
Penicillin G
E.
Tetracycline
The answer is: A
The "red man" syndrome is associated with vancomycin, thought to be caused by histamine release. Prevention consists of a slower infusion rate and pretreatment with antihistamines.
Of the following, which is unlikely to be associated with receptors bound to plasma membranes, their interaction with ligands, and the biologic response to this interaction?
A.
Structurally, these receptors have hydrophobic amino acid domains, which are in contact with the membrane, and hydrophilic regions, which extend into the extracellular fluid and the cytoplasm
B.
Chemical interactions of ligands with these receptors may involve the formation of many types of bonds, including ionic, hydrogen, van der Waals', and covalent
C.
Ligand-receptor interactions are often stereospecific (i.e., one stereoisomer is usually more potent than the other)
D.
In some cases, a ligand that acts as an agonist at membrane-bound receptors increases the activity of an intracellular second messenger
E.
Activation of membrane-bound receptors and subsequent intracellular events elicit a biologic response through the transcription of DNA
The answer is: E
Based upon the molecular mechanisms with which receptors transduce signals, four major classes of receptors have been identified: (1) ion channel receptors, (2) receptors that interact with G proteins, (3) receptors with tyrosine kinase activity, and (4) nuclear receptors. The first three types of receptors are complex membrane-bound proteins with hydrophilic regions located within the lipoid cell membrane and hydrophilic portions found protruding into the cytoplasm of the cell and the extracellular milieu; when activated, all of these receptors transmit (or transduce) information presented at the extracellular surface into ionic or biochemical signals within the cell (i.e., second messengers). Nuclear receptors are found in the nucleus of the cell, not bound to plasma membranes.
In addition, these receptors do not transduce information by second-messenger systems; rather, they bind to nuclear chromatin and elicit a biologic response through the transcription of DNA and alterations in the formation of cellular proteins. Ligand binding to all types of receptors may involve the formation of ionic, hydrogen, hydrophobic, van der Waals', and covalent bonds. In most cases, ligand-receptor interactions are stereospecific; for example, natural (“)-epinephrine is 1000 times more potent than (+)-epinephrine.
10.
Of the following, which is unlikely to be associated with the binding of drugs to plasma proteins?
A.
Acidic drugs generally bind to plasma albumin; basic drugs preferentially bind to 1-acidic glycoprotein
B.
Plasma protein binding is a reversible process
C.
Binding sites on plasma proteins are nonselective, and drugs with similar physicochemical characteristics compete for these limited sites
D.
The fraction of the drug in the plasma that is bound is inactive and generally unavailable for systemic distribution
E.
Plasma protein binding generally limits renal tubular secretion and biotransformation
The answer is: E
Because only the free (unbound) fraction of a drug can cross biologic membranes, binding to plasma proteins limits a drug's concentration in tissues and, therefore, decreases the apparent Vd of the drug. Plasma protein binding will also reduce glomerular filtration of the drug because this process is highly dependent on the free drug fraction. Renal tubular secretion and biotransformation of drugs are generally not limited by plasma protein binding because these processes reduce the free drug concentration in the plasma. If a drug is avidly transported through the tubule by the secretion process or is rapidly biotransformed, the rates of these processes may exceed the rate of dissociation of the drug-protein complex (in order to restore the free:bound drug ratio in plasma) and, thus, become the rate-limiting factor for drug elimination. This assumes that equilibrium conditions exist and that other influences (e.g., changes in pH or the presence of other drugs) do not occur.
11.
Of the following, which is unlikely to be associated with drug distribution into and out of the central nervous system (CNS)?
A.
The blood-brain barrier, which involves drug movement through glial cell membranes as well as capillary membranes, is the main hindrance to drug distribution to the CNS
B.
Most drugs enter the CNS by simple diffusion at rates that are proportional to the lipid solubility of the nonionized form of the drug
C.
Receptor-mediated transport allows certain peptides to gain access to the brain
D.
Strongly ionized drugs freely enter the CNS through carrier-mediated transport systems
E.
Some drugs leave the CNS by passing from the cerebrospinal fluid into the dural blood sinuses through the arachnoid villi
The answer is: D
Drugs can enter the brain from the circulation by passing through the blood-brain barrier. This boundary consists of several membranes, including those of the capillary wall, the glial cells closely surrounding the capillary, and the neuron. In most cases, lipid-soluble drugs diffuse through these membranes at rates that are related to their lipid-to-water partition coefficients. Therefore, the greater the lipid solubility of the nonionized fraction of a weak acid or base, the more freely permeable the drug is to the brain. Some drugs enter the CNS through specific carrier-mediated or receptor-mediated transport processes. Carrier-mediated systems appear to be involved predominantly in the transport of a variety of nutrients through the blood-brain barrier; however, the thyroid hormone 3,5,3'-triiodothyronine and drugs such as levodopa and methyldopa, which are structural derivatives of phenylalanine, cross the blood-brain barrier via carrier-mediated transport.
Receptor-mediated transport functions to permit a peptide (e.g., insulin) to enter the CNS; therefore, some peptide-like drugs are believed to gain access to the brain by this mechanism. Regardless of the process by which drugs can enter the CNS, strongly ionized drugs (e.g., quaternary amines) are unable to enter the CNS from the blood.
The exit of drugs from the CNS can involve (1) diffusion across the blood-brain barrier in the reverse direction at rates determined by the lipid solubility and degree of ionization of the drug, (2) drainage from the cerebrospinal fluid (CSF) into the dural blood sinuses by flowing through the wide channels of the arachnoid villi, and (3) active transport of certain organic anions and cations from the CSF to blood across the choroid plexuses.
12.
A 19-year-old male being treated for leukemia develops fever. You give agents that will cover bacterial, viral, and fungal infections. Two days later, he develops acute renal failure. Which drug was most likely responsible?
A.
Vancomycin
B.
Ceftazidime
C.
Amphotericin B
D.
Acyclovir
The answer is: C
Amphotericin B may alter kidney function by decreasing creatinine clearance; if this occurs, the dose must be reduced. It also commonly increases potassium (K+) clearance, leading to hypokalemia, and causes anemia and neurologic symptoms. A liposomal preparation may reduce the incidence of renal and neurologic toxicity. Vancomycin is less likely to cause kidney damage; if it does, the damage is less severe.
13.
Which of the following is the quinolone derivative that is most effective against Pseudomonas aeruginosa?
A.
Norfloxacin
B.
Ciprofloxacin
C.
Ofloxacin
D.
Enoxacin
E.
Lomefloxacin
The answer is: B
Ciprofloxacin is a fluorinated quinolone derivative highly effective against P. aeruginosa. Other derivatives in this class have less activity toward this organism, although they are effective against other common Gram-negative organisms.
14.
A 19-year-old woman is diagnosed with tuberculosis (TB). Before prescribing a drug regimen, you take a careful medication history because one of the drugs commonly used to treat TB induces microsomal cytochrome P450 enzymes in the liver. Which drug is this?
A.
Isoniazid
B.
Rifampin
C.
Pyrazinamide
D.
Ethambutol
E.
Vitamin B6
The answer is: B
Rifampin induces cytochrome P450 enzymes, which causes a significant increase in elimination of drugs, such as oral contraceptives, anticoagulants, ketoconazole, cyclosporine, and chloramphenicol. It also promotes urinary excretion of methadone, which may precipitate withdrawal.
15.
The elimination half-life of which of the following tetracyclines remains unchanged when the drug is administered to an anuric patient?
A.
Methacycline
B.
Oxytetracycline
C.
Doxycycline
D.
Tetracycline
E.
None of the above
The answer is: C
All tetracyclines can produce negative nitrogen balance and increased blood urea nitrogen (BUN) levels. This is of clinical importance in patients with impaired renal function. With the exception of doxycycline, tetracyclines should not be used in patients that are anuric. Doxycycline is excreted by the GI tract under these conditions, and it will not accumulate in the serum of patients with renal insufficiency.
16.
In patients with hepatic coma, decreases in the production and absorption of ammonia from the gastrointestinal (GI) tract will be beneficial. Which of the following is the antibiotic of choice in this situation?
A.
Neomycin
B.
Tetracycline
C.
Penicillin G
D.
Chloramphenicol
E.
Cephalothin
The answer is: A
Neomycin, an aminoglycoside, is not significantly absorbed from the GI tract. After oral administration, the intestinal flora is suppressed or modified and the drug is excreted in the feces. This effect of neomycin is used in hepatic coma to decrease the coliform flora, thus decreasing the production of ammonia that causes the levels of free nitrogen to decrease in the bloodstream. Other antimicrobial agents (e.g., tetracycline, penicillin G, chloramphenicol, and cephalothin) do not have the potency of neomycin in causing this effect.
17.
Which of the following is the most active aminoglycoside against Mycobacterium tuberculosis?
A.
Streptomycin
B.
Amikacin
C.
Neomycin
D.
Tobramycin
E.
Kanamycin
The answer is: A
The activity of streptomycin is bactericidal for the tubercle bacillus organism. Other aminoglycosides (e.g., gentamicin, tobramycin, neomycin, amikacin, and kanamycin) have activity against this organism but are seldom used clinically because of toxicity or development of resistance.
18.
Chronic candidiasis infections of the GI tract and oral cavity are treated with which agent in pill form?
A.
Amphotericin B
B.
Nystatin
C.
Miconazole
D.
Fluconazole
E.
Clotrimazole
The answer is: D
Mucocutaneous infections, most commonly Candida albicans, involve the moist skin and mucous membranes. Agents used topically include amphotericin B, nystatin, miconazole, and clotrimazole. Ketoconazole and fluconazole are administered orally in pill form for treatment of chronic infections.
19.
Drug X is an antimycobacterial agent that inhibits other bacteria as well as poxviruses. However, it should not be used as a single agent because resistant mutants frequently form. The responsible mutation may alter the site of action of drug X [i.e., the deoxyribonucleic acid (DNA)“dependent ribonucleic acid (RNA) polymerase]. What is drug X?
A.
INH
B.
Rifampin
C.
Pyrazinamide
D.
Ethambutol
The answer is: B
Rifampin inhibits RNA synthesis in bacteria, mycobacteria, and chlamydiae by binding to the DNA-dependent RNA polymerase; it also inhibits assembly of poxvirus particles. Rifampin is used as a single prophylactic agent for contacts of people with meningococcal or H. influenzae type b infections. Otherwise, it is not used alone because 1 in 10 organisms in a population exposed to rifampin will become resistant, possibly because of mutation or a barrier against rifampin's entry into cells.
20.
For the treatment of a patient with Legionella pneumophila, which of the following is the drug of choice?
A.
Penicillin G
B.
Chloramphenicol
C.
Erythromycin
D.
Streptomycin
E.
Lincomycin
The answer is: C
Erythromycin, a macrolide antibiotic, was initially designed to be used in penicillin-sensitive patients with streptococcal or pneumococcal infections. Erythromycin has become the drug of choice for the treatment of pneumonia caused by Mycoplasma and Legionella.
21.
The mechanism of action by which pyrantel pamoate is effective for the treatment of Necator americanus (hookworm) disease is
A.
Interference with cell-wall synthesis
B.
Interference with cell division
C.
Inhibition of neuromuscular transmission
D.
Interference with protein synthesis
E.
Depletion of membrane lipoproteins
The answer is: C
Pyrantel pamoate is an antihelminthic that acts primarily as a depolarizing neuromuscular blocker. In certain worms, a spastic neuromuscular paralysis occurs, resulting in the expulsion of the worms from the intestinal tract of the host. Pyrantel also exerts its effect against parasites via release of acetylcholine and inhibition of cholinesterase.
22.
Amantadine, a synthetic antiviral agent used prophylactically against influenza A2, is thought to act by
A.
Preventing production of viral capsid protein
B.
Preventing virion release
C.
Preventing penetration of the virus into the host cell
D.
Preventing uncoating of viral DNA
E.
Causing lysis of infected host cells by release of intracellular lysosomal enzymes
The answer is: D
Amantadine's mechanism of action involves inhibition of uncoating of the influenza A viral DNA. The primary target is the membrane M2 protein. The drug does not affect penetration and DNA-dependent RNA polymerase activity. Amantadine both reduces the frequency of illness and diminishes the serologic response to influenza infection. The drug has no action, however, on influenza B. As a weak base, amantadine buffers the pH of endosomes, thus blocking the fusion of the viral envelope with the membrane of the endosome.
23.
Streptomycin and other aminoglycosides inhibit bacterial protein synthesis by binding which of the following?
A.
Peptidoglycan units in the cell wall
B.
Messenger RNA (mRNA)
C.
DNA
D.
30S ribosomal particles
E.
RNA polymerase
The answer is: D
The bactericidal activity of streptomycin and other aminoglycosides involves a direct action on the 30S ribosomal subunit, the site at which these agents both inhibit protein synthesis and diminish the accuracy of translation of the genetic code. Proteins containing improper sequences of amino acids (known as nonsense proteins) are often nonfunctional.
24.
A patient with AIDS is treated with a combination of agents, which includes zidovudine. What is the mechanism of action of zidovudine?
A.
Inhibition of RNA synthesis
B.
Inhibition of viral particle assembly
C.
Inhibition of viral proteases
D.
Inhibition of nucleoside reverse transcriptase
E.
Inhibition of nonnucleoside reverse transcriptase
The answer is: D
Zidovudine competitively inhibits HIV-1 nucleoside reverse transcriptase. It is also incorporated in the growing viral DNA chain to cause termination. Each action requires activation via phosphorylation of cellular enzymes. Zidovudine decreases the rate of clinical disease progression and prolongs survival in HIV-infected patients.
25.
A 39-year-old male with aortic insufficiency and a history of no drug allergies is given an intravenous dose of antibiotic as a prophylaxis preceding the insertion of a valve prosthesis. As the antibiotic is being infused, the patient becomes flushed over most of his body. What antibiotic was given?
A.
Vancomycin
B.
Gentamicin
C.
Erythromycin
D.
Penicillin G
E.
Tetracycline
The answer is: A
The "red man" syndrome is associated with vancomycin, thought to be caused by histamine release. Prevention consists of a slower infusion rate and pretreatment with antihistamines.