Repeto
Which hormone's receptor-mediated renal action does spironolactone antagonize?
Aldosterone's action, increasing sodium and water excretion while conserving potassium.
Pharmacology: Mechanisms of Action
273 questions on drug targets and mechanisms of action. Foundational pharmacology in English.
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How does sugammadex's mechanism differ from pyridostigmine's?
Sugammadex binds selected neuromuscular blockers; pyridostigmine inhibits acetylcholine breakdown.
How does tranexamic acid reduce fibrin breakdown?
It occupies lysine-binding sites on plasminogen and interferes with plasminogen and plasmin interactions with fibrin.
Which catecholamine-metabolizing enzyme does entacapone reversibly inhibit?
Catechol-O-methyltransferase, or COMT.
How does cinacalcet lower parathyroid hormone secretion?
It increases the calcium-sensing receptor's sensitivity to extracellular calcium on parathyroid chief cells.
Which fungal membrane sterol does amphotericin B bind?
Ergosterol.
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Question Answer
How does cinacalcet lower parathyroid hormone secretion? It increases the calcium-sensing receptor's sensitivity to extracellular calcium on parathyroid chief cells.
Which fungal membrane sterol does amphotericin B bind? Ergosterol.
How does tamsulosin reduce the dynamic component of bladder outlet obstruction? It blocks alpha-1 receptors in the prostate and bladder neck, relaxing smooth muscle.
Which hormone's receptor-mediated renal action does spironolactone antagonize? Aldosterone's action, increasing sodium and water excretion while conserving potassium.
Which host-cell receptor does maraviroc bind to block HIV entry? CCR5, preventing the required interaction with HIV-1 gp120.
Which two adrenergic receptor families does epinephrine activate? Alpha and beta adrenergic receptors.
How does sugammadex's mechanism differ from pyridostigmine's? Sugammadex binds selected neuromuscular blockers; pyridostigmine inhibits acetylcholine breakdown.
What actions does buprenorphine have at mu- and kappa-opioid receptors? It is a partial agonist at mu receptors and an antagonist at kappa receptors.
How does doxorubicin physically interact with DNA? It intercalates between DNA base pairs.
Which neuronal ion-channel action has been demonstrated for carbamazepine in electrophysiologic studies? Inhibition of voltage-gated sodium channels.
How does tranexamic acid reduce fibrin breakdown? It occupies lysine-binding sites on plasminogen and interferes with plasminogen and plasmin interactions with fibrin.
Which terminal peptide motif in cell-wall precursors is bound by vancomycin? D-alanyl-D-alanine, often abbreviated D-Ala-D-Ala.
How does blocking PCSK9 increase LDL clearance? It reduces PCSK9-mediated LDL-receptor degradation, leaving more hepatic receptors available to remove LDL from blood.
Which serotonin receptor subtypes does sumatriptan activate? 5-HT1B and 5-HT1D receptors.
What chemical activation step contributes to metronidazole's activity in susceptible anaerobic bacteria? Reduction of its nitro group forms reactive intermediates that may damage DNA; the precise mechanism is not fully established.
How can adenosine interrupt an atrioventricular-node-dependent re-entry circuit? It slows conduction through the atrioventricular node.
Which enzyme does mycophenolic acid inhibit to reduce de novo guanosine nucleotide synthesis? Inosine monophosphate dehydrogenase, or IMPDH.
How does insulin lower circulating glucose through its effects on tissues and liver? It increases peripheral glucose uptake, especially in muscle and fat, and suppresses hepatic glucose production.
Which catecholamine-metabolizing enzyme does entacapone reversibly inhibit? Catechol-O-methyltransferase, or COMT.
Which leukotriene receptor does montelukast block? The cysteinyl leukotriene type 1 receptor, CysLT1.
Why does inhibiting SARS-CoV-2 Mpro interfere with viral replication? The enzyme can no longer process viral polyproteins into functional products.
Is linezolid uniformly bactericidal against all susceptible Gram-positive organisms? No. Time-kill studies found it bacteriostatic against enterococci and staphylococci, but bactericidal against most tested streptococcal isolates.
How does blocking RANKL affect osteoclasts? It inhibits their formation, function, and survival, reducing bone resorption.
What action does valsartan add to neprilysin inhibition in sacubitril–valsartan? It blocks AT1 receptors, reducing angiotensin II signaling and angiotensin II-dependent aldosterone release.
Which serotonin receptor does ondansetron selectively antagonize? 5-HT3 receptors.
Which vasopressin receptor does tolvaptan selectively antagonize? The V2 receptor.
Which bacterial synthetic process is inhibited by aztreonam? Bacterial cell-wall synthesis.
In which conduction system is flecainide's slowing effect especially pronounced? The His–Purkinje system.
Which protein does evolocumab bind to lower LDL cholesterol? PCSK9.
Which channel effect is thought to help phenytoin reduce sustained high-frequency neuronal firing? Voltage-dependent blockade of membrane sodium channels.
Which steroidogenic enzyme does abiraterone inhibit? CYP17, which has 17-alpha-hydroxylase and C17,20-lyase activities required for androgen synthesis.
How does omalizumab interfere with IgE signaling? It binds IgE and prevents its binding to high-affinity Fc-epsilon-RI receptors, with subsequent receptor downregulation.
Which potassium-sparing drug acts independently of aldosterone: amiloride or spironolactone? Amiloride. It inhibits distal sodium reabsorption without acting as an aldosterone antagonist.
Which receptor family mediates norepinephrine's direct positive inotropic action? Beta adrenergic receptors.
How does digoxin's indirect parasympathetic action affect atrioventricular nodal conduction? It slows conduction through the atrioventricular node.
Which step in HIV DNA integration does dolutegravir inhibit? Integrase-mediated strand transfer.
Does amphotericin B bind exclusively to fungal sterols? No. It prefers ergosterol but can also bind mammalian membrane cholesterol, contributing to cytotoxicity.
Does pioglitazone primarily increase insulin secretion or increase responsiveness to insulin? It increases responsiveness to insulin; it is not an insulin secretagogue.
Does monoamine oxidase inhibition alone fully explain phenelzine's clinical effects? No. Its label leaves uncertain the contributions of MAO inhibition, other pharmacologic actions, and their interaction.
Which activated coagulation factor does apixaban directly inhibit? Factor Xa.
Which enzyme inhibition is proposed to explain hydroxyurea's rapid inhibition of DNA synthesis? Ribonucleotide reductase inhibition; its complete antineoplastic mechanism is not established.
Does methotrexate's antifolate mechanism fully establish how it works in rheumatoid arthritis? No. The label describes its rheumatoid arthritis mechanism as unknown.
Despite both binding FKBP-12, how do sirolimus and tacrolimus differ in their main downstream targets? Sirolimus inhibits mTOR; tacrolimus inhibits calcineurin.
How does efavirenz's reverse-transcriptase inhibition differ from emtricitabine's? Efavirenz inhibits noncompetitively; emtricitabine's active nucleotide competes with substrate and terminates DNA after incorporation.
Which intracellular enzyme family is inhibited by tofacitinib? Janus kinases, or JAKs.
Which second messenger increases downstream of beta-adrenergic stimulation by albuterol? Cyclic AMP, formed through activation of adenylate cyclase.
What receptor class does dexamethasone bind as part of its anti-inflammatory action? Intracellular steroid receptors, including nuclear glucocorticoid receptors.
How does aspirin inhibit platelet thromboxane production? It irreversibly inhibits platelet cyclooxygenase, reducing thromboxane A2 synthesis.
Which enzyme does sacubitril's active metabolite inhibit? Neprilysin, an enzyme that degrades peptides including natriuretic peptides.
Does apixaban require antithrombin for its anticoagulant action, as heparin does? No. Apixaban directly inhibits factor Xa without requiring antithrombin.
Does gabapentin's structural similarity to GABA mean it directly changes GABA binding, uptake, or degradation? No. Gabapentin has no effect on those processes in the described mechanism studies.
Which cytokine does adalimumab bind and prevent from activating its cell-surface receptors? TNF-alpha.
Which of lisinopril and losartan inhibits the enzyme that also degrades bradykinin? Lisinopril. ACE is also kininase II; losartan blocks AT1 receptors without inhibiting ACE.
What types of DNA cross-links can cisplatin form? Both intrastrand and interstrand cross-links, interfering with transcription and DNA replication.
How can dipyridamole's inhibition of adenosine uptake inhibit platelets? It raises local adenosine, which stimulates platelet A2 receptors and increases cyclic AMP.
Which enzyme complex is the principal target implicated in warfarin's action? Vitamin K epoxide reductase, particularly its VKORC1 subunit, reducing vitamin K recycling.
What type of NMDA-receptor antagonism is proposed to mediate memantine's effect? Low-to-moderate-affinity uncompetitive, or open-channel, antagonism.
Which adrenergic receptor subtype does albuterol preferentially stimulate to relax bronchial smooth muscle? Beta-2 adrenergic receptors.
Which acetylcholine receptor family does atropine competitively antagonize? Muscarinic receptors.
Which enzyme does lisinopril inhibit? Angiotensin-converting enzyme, which converts angiotensin I to angiotensin II.
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What broad action is thought to underlie mesalamine's effect in the colon? A topical anti-inflammatory action on colonic epithelial cells; the precise mechanism is not fully understood.
What does it mean that atropine's muscarinic antagonism is surmountable? Increasing acetylcholine at the receptor can overcome the competitive antagonism.
What is pyrazinamide's major active metabolite? Pyrazinoic acid; the label does not establish the full antibacterial mechanism.
Which fungal enzyme does fluconazole inhibit? Lanosterol 14-alpha-demethylase, a step in ergosterol synthesis.
What active phosphorylated form of tenofovir inhibits viral reverse transcriptase? Tenofovir diphosphate.
Which influenza enzyme is inhibited by oseltamivir carboxylate? Neuraminidase, interfering with release of viral particles.
Which COX isoenzyme is the principal target of celecoxib, distinguishing it from ibuprofen? COX-2. Ibuprofen inhibits both COX-1 and COX-2.
How does tenofovir diphosphate inhibit HIV-1 and HBV reverse transcriptases? It competes with a natural nucleotide substrate and terminates DNA elongation after incorporation.
Which receptor actions distinguish carvedilol from a beta-1-selective blocker? Carvedilol combines nonselective beta blockade with alpha-1 blockade.
Which electrophysiologic effect supports classifying amiodarone as a class III antiarrhythmic? Prolongation of the cardiac action potential and refractoriness, associated with potassium-channel blockade.
At which receptor site does midazolam bind to enhance GABAergic neurotransmission? The benzodiazepine site of the GABA-A receptor.
Which shared cytokine subunit does ustekinumab target? The p40 subunit shared by IL-12 and IL-23.
Which cholinergic effects predominate with bethanechol: muscarinic or nicotinic? Muscarinic effects, including increased bladder detrusor tone and gastrointestinal motility.
Which cotransporter does hydrochlorothiazide inhibit in its distal tubular action? The sodium–chloride cotransporter.
Does propylthiouracil inactivate thyroid hormone that is already stored or circulating? No. It inhibits synthesis and peripheral conversion rather than inactivating preformed hormone.
How does reduced distal sodium reabsorption with amiloride reduce potassium secretion? It makes the tubular lumen less negative, reducing the electrical drive for potassium secretion.
How does albendazole disrupt parasite microtubules? It binds beta-tubulin and inhibits polymerization into microtubules.
How does efavirenz inhibit HIV-1 reverse transcriptase? Predominantly through noncompetitive inhibition, as a non-nucleoside reverse-transcriptase inhibitor.
What type of monoamine oxidase inhibition is produced by phenelzine? Irreversible, nonselective MAO inhibition, reducing monoamine breakdown.
Which monoamine oxidase subtype is preferentially and irreversibly inhibited by selegiline at selective exposure? MAO-B, reducing a pathway involved in catecholamine metabolism.
Does hydralazine preferentially dilate arterioles or veins? Arterioles, through direct vascular smooth muscle relaxation; its precise molecular mechanism is not fully understood.
Which substrate does sulfamethoxazole compete with during bacterial folate synthesis? Para-aminobenzoic acid, or PABA.
Does metformin lower glucose primarily by increasing insulin secretion? No. It reduces hepatic glucose production and improves insulin sensitivity while insulin secretion remains unchanged.
How can bacterial beta-lactamases inactivate amoxicillin? They cleave its beta-lactam ring.
Why are bethanechol's effects more prolonged than those of acetylcholine? Bethanechol is not destroyed by cholinesterase.
Which enzyme does methotrexate inhibit in its antifolate action? Dihydrofolate reductase.
Is metoprolol's beta-1 selectivity absolute? No. At higher plasma concentrations, it also blocks beta-2 receptors.
Which membrane enzyme does digoxin inhibit? Na+/K+-ATPase, the sodium–potassium pump.
Which surface antigen is targeted by rituximab? CD20 on pre-B and mature B lymphocytes.
How does blocking PD-1 affect inhibitory signaling in T cells? It prevents PD-L1 and PD-L2 from engaging PD-1, releasing an inhibitory influence on T-cell immune responses.
Why can a ribosomal modification cause cross-resistance between azithromycin and clindamycin? Their binding sites involve overlapping regions of bacterial 23S ribosomal RNA.
How do omeprazole and famotidine act at different points in gastric acid secretion? Omeprazole inhibits the final proton-pump step; famotidine blocks histamine H2 receptor signaling.
Which enzymatic process is inhibited by cytarabine's active nucleotide triphosphate? DNA polymerase activity.
Why does empagliflozin increase urinary glucose excretion? SGLT2 inhibition reduces renal glucose reabsorption and lowers the renal threshold for glucose.
Which two neurotransmitters' reuptake is inhibited by venlafaxine? Serotonin and norepinephrine, an action thought to contribute to its therapeutic effects.
How does propranolol reduce catecholamine-driven myocardial oxygen demand? It limits increases in heart rate, blood pressure, and myocardial contractility through beta blockade.
How does sugammadex reverse rocuronium- or vecuronium-induced neuromuscular blockade? It forms complexes with those drugs, reducing the free drug available to bind nicotinic receptors at the neuromuscular junction.
How do aripiprazole's actions differ at 5-HT1A and 5-HT2A receptors? It is a partial agonist at 5-HT1A receptors and an antagonist at 5-HT2A receptors.
Which adrenergic receptor subtype does metoprolol preferentially block? Beta-1 adrenergic receptors.
What membrane process does verapamil inhibit in arterial smooth muscle and cardiac cells? Calcium influx through slow calcium channels.
How does enoxaparin's balance of anti-Xa to anti-IIa activity compare with unfractionated heparin's? Enoxaparin has a higher ratio of anti-Xa to anti-IIa activity.
How does paclitaxel disrupt microtubule function? It promotes microtubule assembly and stabilizes microtubules against depolymerization, preventing normal dynamic reorganization.
What renal transport effect underlies furosemide's diuresis? Reduced tubular sodium and chloride reabsorption, with a major action in the loop of Henle.
What initial receptor effect explains the fasciculations that can precede succinylcholine-induced paralysis? Depolarization of the motor end plate.
Which ribosomal component does azithromycin bind? 23S ribosomal RNA in the bacterial 50S subunit.
Which receptor family mediates norepinephrine's peripheral vasoconstrictor action? Alpha adrenergic receptors.
Which mycobacterial enzyme family is targeted by ethambutol to disrupt cell-wall arabinan synthesis? Arabinosyltransferases.
How does amphotericin B binding alter fungal membranes? It forms transmembrane channels, increasing permeability and allowing ion leakage.
Is propranolol's mechanism for migraine prevention established? No. Its migraine-preventive mechanism has not been established.
How does acyclovir triphosphate interfere with herpesviral DNA synthesis? It inhibits viral DNA polymerase and can terminate the growing viral DNA chain after incorporation.
How does donepezil increase acetylcholine availability? It reversibly inhibits acetylcholinesterase-mediated acetylcholine breakdown.
Does heparin directly dissolve an existing fibrin clot? No. It inhibits coagulation but has no fibrinolytic activity.
Does pramipexole's greater D3 affinity establish D3 binding as the explanation for its benefit in Parkinson's disease? No. The relevance of D3 binding to its clinical effect is unknown.
Which overexpressed receptor characterizes tumor cells targeted by trastuzumab? HER2.
Which intracellular protein binds tacrolimus before calcineurin inhibition? FKBP-12.
How does lidocaine's action on neuronal membranes produce local anesthesia? It inhibits ionic fluxes needed to initiate and conduct nerve impulses.
Which bacterial structure's synthesis does ceftriaxone inhibit? The bacterial cell wall.
Which carbamazepine metabolite has demonstrated anticonvulsant activity in animal models? Carbamazepine-10,11-epoxide. Its contribution to clinical efficacy and safety is not established in the label.
How does semaglutide change insulin and glucagon secretion when blood glucose is high? It increases insulin secretion and suppresses glucagon secretion in a glucose-dependent manner.
Why does ACE inhibition by lisinopril tend to reduce aldosterone secretion? It reduces angiotensin II, a stimulus for adrenal aldosterone secretion.
Which peripheral thyroid hormone conversion does propylthiouracil inhibit in addition to thyroid hormone synthesis? Conversion of T4 to T3.
Which step in bacterial protein synthesis does linezolid prevent after binding the 50S subunit? Formation of the functional 70S initiation complex.
Which intracellular second messenger rises when nitroglycerin-derived nitric oxide activates guanylate cyclase? Cyclic GMP, promoting vascular smooth muscle relaxation.
What characteristic electrical activity associated with absence seizures does ethosuximide suppress? Paroxysmal three-cycle-per-second spike-and-wave activity.
How does doxorubicin's topoisomerase II action promote DNA damage? It stabilizes the cleaved enzyme–DNA complex and interferes with rejoining broken DNA strands.
Which conversion is prevented when dabigatran inhibits thrombin? The conversion of fibrinogen to fibrin.
Which thyroid enzyme-related process does methimazole inhibit? Thyroid-peroxidase-mediated iodination of thyroglobulin, reducing T3 and T4 synthesis.
Which hormone receptor does semaglutide activate? The GLP-1 receptor.
Does erenumab target CGRP itself or its receptor? It binds and antagonizes the CGRP receptor.
Why does the pattern of PTH-like exposure matter for teriparatide's skeletal effect? Intermittent exposure favors bone formation, whereas continuously excessive PTH can favor bone resorption.
How does nitroglycerin's predominant venous dilation reduce cardiac preload? It increases peripheral venous pooling and reduces venous return to the heart.
Does dobutamine primarily stimulate cardiac beta receptors directly or release endogenous norepinephrine? It stimulates cardiac beta receptors directly.
Which ribosomal target mediates clindamycin's inhibition of bacterial protein synthesis? 23S ribosomal RNA in the 50S subunit.
Which calcium-channel component binds gabapentin with high affinity in vitro? The alpha-2-delta subunit of voltage-activated calcium channels; the label does not establish how this binding produces its therapeutic effects.
Which fluorouracil metabolite inhibits thymidylate synthase? FdUMP, or 5-fluoro-2′-deoxyuridine monophosphate.
How does ipratropium oppose acetylcholine-mediated bronchial smooth muscle contraction? It antagonizes muscarinic receptors, limiting the associated rise in intracellular calcium.
Which cholesterol-synthesis enzyme does atorvastatin competitively inhibit? HMG-CoA reductase, which produces mevalonate.
Which two activated coagulation factors are particularly inhibited by the heparin–antithrombin interaction? Factor Xa and thrombin, factor IIa.
Which immune checkpoint receptor does pembrolizumab block? PD-1.
Why can entacapone prolong levodopa exposure when levodopa is combined with a decarboxylase inhibitor? It inhibits COMT-mediated levodopa metabolism, making plasma levodopa levels greater and more sustained.
Which bacterial proteins does meropenem bind to inhibit cell-wall synthesis? Penicillin-binding proteins, or PBPs.
How do tranexamic acid and alteplase differ in their effects on fibrin breakdown? Tranexamic acid inhibits fibrin breakdown; alteplase promotes it by generating plasmin.
What GABA-related mechanism has been proposed for valproate's antiseizure activity? Increased brain GABA concentrations. The mechanisms responsible for its therapeutic effects have not been established.
Which enzyme does acetazolamide inhibit? Carbonic anhydrase.
What intracellular change links digoxin's sodium-pump inhibition to stronger myocardial contraction? Increased intracellular calcium availability.
Why is ritonavir paired with nirmatrelvir? Ritonavir inhibits CYP3A-mediated nirmatrelvir metabolism, increasing nirmatrelvir exposure.
How does carbidopa increase the amount of levodopa available to enter the brain? It inhibits peripheral levodopa decarboxylation without crossing the blood–brain barrier.
What major hepatic process is reduced by metformin? Hepatic glucose production.
Which phosphatase is inhibited by the tacrolimus–FKBP complex? Calcineurin, limiting activation of transcription factors involved in T-cell activation.
How does ivermectin-induced chloride permeability affect susceptible parasite nerve and muscle cells? It hyperpolarizes them, causing paralysis and contributing to parasite death.
Which active metabolite is formed from mycophenolate mofetil? Mycophenolic acid.
Which receptor site does flumazenil competitively block? The benzodiazepine recognition site on the GABA-A receptor complex.
How does propranolol's beta-receptor selectivity differ from metoprolol's? Propranolol is a nonselective beta blocker; metoprolol preferentially blocks beta-1 receptors.
Which ergosterol-pathway enzyme does terbinafine inhibit? Squalene epoxidase.
What effect does metoclopramide have on upper gastrointestinal motility? It increases coordinated upper gastrointestinal motility and accelerates gastric emptying; its full prokinetic mechanism is unclear.
Which viral enzyme performs acyclovir's first phosphorylation step in susceptible herpesviruses? Viral thymidine kinase.
How do thyroid hormone receptors alter cell function? They regulate DNA transcription and subsequent protein synthesis.
Which parasite process does atovaquone inhibit? Mitochondrial electron transport.
During which cell-cycle phase is cytarabine's cytotoxicity especially prominent? S phase, when cells synthesize DNA.
Does tamsulosin's described mechanism directly shrink the prostate or reduce smooth muscle tone? It reduces smooth muscle tone in the prostate and bladder neck.
Which ionotropic glutamate receptor does ketamine antagonize? The NMDA receptor, through noncompetitive antagonism.
Which bacterial ribosomal subunit contains a demonstrated gentamicin-binding site? The 30S subunit.
Why is potassium-channel blockade alone an incomplete description of amiodarone? It also has sodium-channel, calcium-channel, and antisympathetic actions.
Which procoagulant factors require vitamin K-dependent modification and are affected by warfarin? Factors II, VII, IX, and X.
Which fungal cell-wall polymer has its synthesis inhibited by caspofungin? Beta-(1,3)-D-glucan.
Which voltage-gated ion channels are blocked by flecainide? Voltage-gated sodium channels.
What change in adrenal steroid production can accompany CYP17 inhibition by abiraterone? Increased mineralocorticoid production.
Which synaptic vesicle protein binds levetiracetam and may contribute to its antiseizure activity? SV2A. The precise therapeutic mechanism and significance of this binding remain incompletely understood.
How does loperamide reduce propulsive intestinal peristalsis? It binds opioid receptors in the gut wall, inhibiting release of acetylcholine and prostaglandins.
Which transcription-factor family loses JAK-mediated phosphorylation and activation during tofacitinib exposure? Signal transducers and activators of transcription, or STATs.
Which adrenergic receptor subtype does phenylephrine activate? Alpha-1 adrenergic receptors.
Which signaling ligand does denosumab bind? RANKL, preventing activation of RANK on osteoclasts and their precursors.
Which fluorouracil metabolite can be incorporated into RNA? FUTP, or fluorouridine triphosphate.
Which nuclear receptor does pioglitazone activate? PPAR-gamma, altering transcription of genes involved in glucose and lipid metabolism.
Which reactive species contribute to doxorubicin's cytotoxic effects and toxicity? Oxygen free radicals, which can damage membrane lipids.
Which endogenous anticoagulant protein mediates heparin's inhibition of activated coagulation factors? Antithrombin, whose inhibitory activity is enhanced by heparin binding.
Which active metabolite mediates emtricitabine's reverse-transcriptase inhibition? Emtricitabine triphosphate, a cytidine analogue that can terminate viral DNA chains.
Which bacterial cellular structure does gentamicin bind to inhibit protein synthesis? The prokaryotic ribosome.
How does methotrexate's inhibition of tetrahydrofolate formation impair DNA synthesis? It limits one-carbon transfer reactions needed to synthesize purine nucleotides and thymidylate.
How does amlodipine lower peripheral vascular resistance? It inhibits calcium entry into vascular smooth muscle and promotes arterial relaxation. Its effect is greater on vascular smooth muscle than on cardiac muscle.
How does succinylcholine initiate neuromuscular blockade? It activates cholinergic receptors at the motor end plate and produces depolarization; transmission then remains inhibited while enough drug remains at the receptor.
Which enzyme is inhibited by proguanil's metabolite cycloguanil? Plasmodium dihydrofolate reductase, disrupting deoxythymidylate synthesis.
Which receptor antagonism is associated with metoclopramide's antiemetic effect? Central and peripheral dopamine receptor antagonism.
How does insulin affect lipolysis and proteolysis? It inhibits both, while promoting protein synthesis.
Why does acetazolamide tend to alkalinize urine? Carbonic anhydrase inhibition increases renal bicarbonate loss.
Which integrin does vedolizumab bind? Alpha-4-beta-7 integrin.
What receptor blockade is associated with prazosin's vasodilator action? Blockade of postsynaptic alpha adrenergic receptors. The label does not describe the complete hypotensive mechanism as established.
What off-target current effect may explain luminous visual phenomena with ivabradine? Inhibition of the retinal Ih current involved in responses to changing light intensity.
Which bacterial ribosomal subunit does doxycycline bind? The 30S subunit, inhibiting protein synthesis.
Which bacterial synthetic process does amoxicillin inhibit? Cell-wall biosynthesis in susceptible, actively multiplying bacteria.
Which substrate accumulates when terbinafine blocks squalene epoxidase? Squalene; its accumulation contributes to increased fungal membrane permeability.
What immediate membrane effect follows daptomycin binding to susceptible bacteria? Rapid depolarization of the bacterial cell membrane.
How do caffeine and theophylline affect adenosine's action? They competitively antagonize it.
Which intestinal sterol transporter does ezetimibe inhibit? NPC1L1, reducing intestinal cholesterol absorption.
Which angiotensin receptor do losartan and its active metabolite block? The angiotensin II type 1 receptor, AT1.
How can a GnRH agonist such as leuprolide eventually suppress gonadal steroid production? After initial stimulation, continuous exposure suppresses gonadotropin secretion and gonadal steroidogenesis.
How do paclitaxel and vincristine differ in their effects on microtubules? Paclitaxel stabilizes assembled microtubules; vincristine inhibits microtubule formation.
Which enzyme does anastrozole inhibit to reduce estrogen production? Aromatase, which converts androgens into estrogens.
Which endogenous anticoagulant proteins are also affected by warfarin's inhibition of vitamin K-dependent synthesis? Proteins C and S.
Which histamine receptor does cetirizine selectively inhibit? Peripheral H1 receptors.
How does administered T4 provide much of its physiologic thyroid hormone activity? Peripheral deiodination converts T4 to T3, which mediates most thyroid hormone actions.
Which bacterial enzyme does rifampin inhibit? DNA-dependent RNA polymerase.
How does naloxone oppose opioid effects? It competes for opioid receptor sites as an antagonist.
Which invertebrate channels are the main targets of ivermectin? Glutamate-gated chloride channels in nerve and muscle cells.
What cardiac mechanical effect is central to dobutamine's action? Increased myocardial contractility, which can increase stroke volume and cardiac output.
Which neurotransmitter uptake processes does amitriptyline inhibit? Norepinephrine and serotonin uptake. How this produces its full antidepressant effect is not established.
Which cotransporter family is inhibited by furosemide? Sodium–potassium–chloride cotransporters.
Which immune mechanisms can contribute to rituximab-mediated B-cell lysis? Complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity.
Which antibody-mediated immune mechanism contributes to trastuzumab's action against HER2-overexpressing cells? Antibody-dependent cellular cytotoxicity.
Which functioning pancreatic cells are needed for glipizide's insulin-releasing effect? Pancreatic islet beta cells.
What can follow incorporation of remdesivir's nucleotide into a growing SARS-CoV-2 RNA chain? Delayed RNA-chain termination, inhibiting viral RNA synthesis.
Which bone cell's activity is inhibited by alendronate? Osteoclast activity, reducing bone resorption.
How does daptomycin-induced loss of membrane potential affect bacterial macromolecule synthesis? It inhibits DNA, RNA, and protein synthesis, contributing to bacterial death.
Which thalamic calcium-current effect has been proposed to contribute to ethosuximide's anti-absence action? Reduction of low-threshold T-type calcium current. Experimental results vary, so this should not be treated as a complete, exclusive explanation of its clinical action.
Which platelet receptor is irreversibly inhibited by clopidogrel's active metabolite? The P2Y12 ADP receptor.
Why does CCR5 blockade by maraviroc not block every HIV-1 variant? CXCR4-tropic and dual-tropic viruses can enter through pathways not blocked by maraviroc.
Which kinase is inhibited by the sirolimus–FKBP-12 complex? The mechanistic target of rapamycin, mTOR.
Which enzyme does trimethoprim inhibit? Bacterial dihydrofolate reductase, reducing tetrahydrofolate production.
Which SARS-CoV-2 protease does nirmatrelvir inhibit? The main protease, Mpro, also called 3CLpro or nsp5.
What immediate effects of praziquantel are described in schistosomes? Rapid contraction associated with altered membrane permeability and damage to the tegument; the label describes the full mechanism as unknown.
Why does flumazenil not reverse every form of GABA-related sedation? It targets the benzodiazepine site, so it does not antagonize drugs acting through other GABA-related sites or mechanisms.
How does anastrozole's mechanism differ from tamoxifen's? Anastrozole inhibits estrogen synthesis; tamoxifen competes for estrogen receptor binding in breast tissue.
How does darunavir prevent production of mature HIV-1 particles? It inhibits HIV-1 protease cleavage of Gag-Pol polyproteins.
How does tamoxifen oppose estrogen signaling in breast tissue? It competes with estrogen for estrogen receptor binding.
What channel change follows sulfonylurea-receptor binding by glipizide in pancreatic beta cells? Closure of ATP-sensitive potassium channels, promoting insulin release.
Which coagulation enzyme does dabigatran directly inhibit? Thrombin, also called factor IIa.
Which two bacterial enzymes does ciprofloxacin inhibit? DNA gyrase, or topoisomerase II, and topoisomerase IV.
Which constitutively active fusion kinase is a principal target of imatinib in Philadelphia chromosome-positive leukemia? BCR-ABL tyrosine kinase.
Which channel is inhibited by amiloride to reduce distal renal sodium reabsorption? The epithelial sodium channel, ENaC.
Which SARS-CoV-2 enzyme is targeted by remdesivir's active triphosphate metabolite? RNA-dependent RNA polymerase.
How does sitagliptin's incretin mechanism differ from semaglutide's? Sitagliptin slows inactivation of endogenous incretins; semaglutide directly activates GLP-1 receptors.
Is morphine a full or partial agonist at opioid receptors? A full agonist, with relative preference for mu-opioid receptors.
Which two receptor tyrosine kinase systems are also inhibited by imatinib? Platelet-derived growth factor receptors and KIT, the stem-cell-factor receptor.
How does acetazolamide lower intraocular pressure? Carbonic anhydrase inhibition reduces aqueous humor secretion.
How does stimulation of brainstem alpha adrenergic receptors by clonidine change sympathetic outflow? It reduces sympathetic outflow from the central nervous system.
Which gastric parietal-cell enzyme is inhibited by omeprazole? H+/K+-ATPase, the gastric proton pump.
Which histamine receptor does famotidine competitively inhibit to reduce gastric secretion? H2 receptors.
Which DNA-associated enzyme interaction is linked to etoposide-induced DNA strand breaks? Interaction with topoisomerase II.
Which cyclooxygenase isoenzymes are inhibited by ibuprofen? COX-1 and COX-2, contributing to reduced prostaglandin synthesis.
How can albendazole-induced microtubule loss deplete a parasite's energy supply? It impairs intestinal glucose uptake and depletes glycogen stores, limiting ATP production.
Which renal glucose transporter does empagliflozin inhibit? SGLT2, reducing reabsorption of filtered glucose.
What DNA effect is thought to contribute to cyclophosphamide's antitumor action? Cross-linking of tumor-cell DNA.
Which important mycobacterial cell-wall components have their synthesis inhibited by isoniazid? Mycolic acids.
Why can epinephrine cause vasodilation at lower exposure but vasoconstriction at higher exposure? Beta-2-mediated vasodilation can predominate at lower exposure; alpha-1-mediated vasoconstriction increasingly dominates at higher exposure.
Why can renin concentration rise while plasma renin activity falls during aliskiren exposure? Loss of angiotensin II feedback can increase renin release, while aliskiren directly inhibits the released enzyme's activity.
Which central dopamine receptor antagonism is thought to contribute to haloperidol's antipsychotic effect? D2 receptor antagonism; the complete therapeutic mechanism remains unclear.
Which pacemaker current does ivabradine inhibit? The If current carried by hyperpolarization-activated cyclic nucleotide-gated channels, with prominent effects in the sinoatrial node.
How does pyridostigmine increase acetylcholine availability at the neuromuscular junction? It inhibits cholinesterase-mediated destruction of acetylcholine.
How does rocuronium block neuromuscular transmission? It competes with acetylcholine for cholinergic receptors at the motor end plate without producing depolarizing blockade.
Which enzyme does sitagliptin inhibit to prolong incretin activity? Dipeptidyl peptidase-4, or DPP-4.
Which digestive enzyme activities does acarbose inhibit to delay carbohydrate absorption? Pancreatic alpha-amylase and intestinal brush-border alpha-glucosidases.
Why can levodopa increase brain dopamine when administered dopamine cannot do so effectively? Levodopa crosses the blood–brain barrier and can be converted to dopamine in the brain; dopamine does not cross it effectively.
Which inhibitory receptor system is positively modulated by propofol? The GABA-A receptor system. This is thought to contribute to its sedative and anesthetic effects, whose full mechanism is incompletely understood.
Which neurotransmitter reuptake actions distinguish bupropion from a serotonin reuptake inhibitor? Bupropion weakly inhibits norepinephrine and dopamine reuptake without inhibiting serotonin reuptake.
Which neurotransmitter's neuronal reuptake does fluoxetine inhibit? Serotonin. Its therapeutic effects are presumed to be related to this action, but the exact mechanism is unknown.
Does donepezil's cholinergic mechanism establish that it changes the underlying dementing process? No. The label states that there is no evidence it alters that underlying process.
How does vedolizumab reduce memory T-cell migration into inflamed gastrointestinal tissue? It blocks alpha-4-beta-7 integrin binding to MAdCAM-1 on gut endothelium.
How does metoprolol affect sinus rate and atrioventricular nodal conduction? It slows sinus rate and reduces atrioventricular nodal conduction.
Which step of the renin–angiotensin pathway does aliskiren directly inhibit? Renin-mediated conversion of angiotensinogen to angiotensin I.
Which two incretin hormones have their active lifetimes prolonged by sitagliptin? GLP-1 and GIP.
How does ticagrelor's interaction with P2Y12 differ from that of clopidogrel's active metabolite? Ticagrelor binds reversibly; clopidogrel's active metabolite binds irreversibly.
How does vincristine interfere with the mitotic spindle? It inhibits microtubule formation, leading to metaphase arrest.
Why is trimethoprim–sulfamethoxazole described as sequential folate-pathway blockade? Sulfamethoxazole inhibits dihydrofolate synthesis, while trimethoprim inhibits its subsequent conversion to tetrahydrofolate.
Which bacterial biosynthetic process is primarily inhibited by vancomycin? Cell-wall biosynthesis.
How does acarbose reduce the post-meal rise in blood glucose? It delays carbohydrate breakdown into absorbable monosaccharides, delaying glucose absorption.
What distinguishes tolvaptan-induced aquaresis from a primarily natriuretic effect? It increases free-water excretion without a significant increase in urinary sodium or potassium excretion.
What renal electrolyte effect underlies hydrochlorothiazide's diuresis? Reduced distal tubular sodium and chloride reabsorption, increasing their urinary excretion.
Which steroid receptor activity predominates in budesonide's anti-inflammatory action? Glucocorticoid activity; its mineralocorticoid activity is weak.
At which dopamine receptor does aripiprazole have partial agonist activity? D2 receptors. Its therapeutic effects may reflect this activity together with serotonin receptor actions.
What conversion does alteplase catalyze to initiate fibrinolysis? Conversion of plasminogen to plasmin, enhanced by fibrin.
Which dopamine receptor family does pramipexole activate? The D2 receptor subfamily, with greater in vitro affinity for D3 than for D2 or D4 receptors.
Is the connection between omalizumab's IgE effects and improvement in chronic spontaneous urticaria fully established? No. That connection remains unknown in the label.
Which voltage-gated ion channels does lidocaine block to inhibit nerve impulse conduction? Voltage-gated sodium channels.
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