A 7-year-old boy is brought to the Emergency Department during an acute asthma exacerbation. He is tachypnoeic, using his accessory muscles, and has a peak expiratory flow of 40% predicted. After initiating oxygen therapy, the medical team administers a bronchodilator via a nebuliser for rapid relief of bronchoconstriction. This nebulised drug most directly belongs to which class of medications?

A researcher is studying the molecular pharmacology of drugs used in obstructive airways disease. She is investigating a common reliever medication that acts on a specific G-protein coupled receptor. Activation of which receptor by this drug primarily mediates its therapeutic bronchodilator effect?

A medical student is revising the cellular actions of asthma medications. They note that one key reliever drug works by increasing the intracellular concentration of a specific second messenger within airway smooth muscle cells. Which second messenger is increased as the direct result of this drug's action on its receptor?

A 58-year-old man with chronic obstructive pulmonary disease (COPD) is reviewed in clinic. He experiences daily breathlessness and wheeze. His current medication includes tiotropium. The consultant advises adding an inhaler for immediate relief of breakthrough symptoms. Which of the following is the most appropriate addition for this purpose?

A 19-year-old university student with asthma is seen in A&E with a severe exacerbation. He is anxious, tremulous, and tachycardic. He admits to overusing his reliever inhaler excessively over the past 24 hours due to severe symptoms before coming to hospital. Which of the following adverse effects is most directly attributable to the systemic absorption of his reliever medication?

A 45-year-old patient with severe asthma is being reviewed in a specialist respiratory clinic. Their symptoms are not fully controlled on a moderate-dose inhaled corticosteroid alone. The consultant decides to initiate a maintenance bronchodilator that has both a long duration of action and a relatively rapid onset. Which of the following long-acting beta-2 agonists (LABAs) is the consultant most likely to add to the regimen?

A practice nurse is counselling a patient on their new combination inhaler for asthma. She explains that the inhaler contains two medicines: one to reduce background inflammation daily and another to provide sustained relaxation of the airway muscles for 12 hours. The bronchodilator component in this combination inhaler belongs to which class of drugs?

During a pharmacology tutorial, students discuss maintenance therapies for COPD. One drug is highlighted for its role in preventing breathlessness by continuously stimulating receptors on bronchial smooth muscle. What is the primary molecular target through which this drug exerts its prolonged bronchodilator effect?

A patient with COPD is stable on a combination inhaler containing formoterol and budesonide. The GP explains that the formoterol component works by initiating a signalling cascade inside the airway muscle cells that leads to relaxation. What is the key intracellular event that directly follows formoterol binding to its receptor, leading to muscle relaxation?

A 35-year-old woman with asthma suffers nocturnal symptoms and exercise-induced breathlessness despite using a standard-dose inhaled corticosteroid. Her asthma control test score is 17. The consultant decides to add a long-acting bronchodilator to her regimen. In which of the following forms is formoterol most appropriately initiated for this patient's asthma?

A 60-year-old man with COPD is started on a formoterol-containing inhaler. At his follow-up appointment, he reports feeling a slight shaking in his hands shortly after taking his morning dose, which tends to settle within an hour. He is otherwise well. Which of the following is the most likely cause of this patient's reported symptom?

A 52-year-old woman with moderate persistent asthma is being stepped up from a reliever and low-dose steroid inhaler. Her consultant prescribes a new maintenance inhaler to be used twice daily, which contains a steroid and a long-acting bronchodilator with a slow onset of action. Which long-acting beta-2 agonist is most likely contained in this combination inhaler?

A practice pharmacist is reconciling a patient's medications for COPD. The patient uses a "preventer" inhaler morning and night that the pharmacist notes contains two active ingredients to reduce exacerbations and improve lung function. In this combination inhaler, which class does the long-lasting bronchodilator component belong to?

In a pharmacology practical, students use isolated bronchial smooth muscle to study the effects of different drugs. Adding salmeterol causes a prolonged relaxation. This effect is completely blocked by pre-treating the tissue with another compound. Which type of drug, if applied first, would most likely block the relaxant effect of salmeterol?

A research scientist explains that the prolonged duration of action of salmeterol is due to its unique pharmacokinetic property. Unlike its endogenous counterpart adrenaline, it does not get rapidly taken up into nerve terminals. What property of salmeterol's structure primarily accounts for its long duration of action in the airways?

A 40-year-old man with asthma reports frequent nocturnal waking due to breathlessness and needs his salbutamol inhaler 3-4 times per day. He is currently on a moderate-dose beclometasone inhaler. According to BTS/SIGN guidelines, what is the recommended next step? Which therapeutic regimen is most appropriate to improve this patient's control?

A patient with severe COPD is admitted with acute breathlessness and tachycardia. He is found to be overusing his salmeterol/fluticasone inhaler due to anxiety about his symptoms. ECG shows sinus tachycardia and occasional ventricular ectopics. Which of the following adverse effects is most directly related to excessive systemic absorption of the LABA component of his inhaler?

A 68-year-old man with a 40-pack-year smoking history presents with progressive exertional dyspnoea and a chronic productive cough. Spirometry confirms a post-bronchodilator FEV1/FVC ratio of 0.58. He is started on a maintenance inhaler to be used once daily. Which of the following once-daily inhalers is most appropriate as a first-line maintenance bronchodilator for his condition?

A 72-year-old woman with COPD and a history of cardiac disease is reviewed. She is currently using a salbutamol inhaler but remains breathless. To reduce her exacerbation frequency and improve exercise tolerance, a consultant prescribes a new dry-powder inhaler that works via a different mechanism to her current reliever. The newly prescribed drug most likely belongs to which class?

A pharmacology student is studying drugs that cause bronchodilation by interfering with the parasympathetic nervous system's control of airway tone. Antagonism of which specific receptor subtype on airway smooth muscle is primarily responsible for the therapeutic effect of tiotropium?

A patient with COPD asks how their new tiotropium inhaler works differently from their old salbutamol inhaler. The doctor explains it blocks a natural chemical messenger in the lungs. What is the primary intracellular consequence of this drug blocking its target receptor on airway smooth muscle?

A 65-year-old man with stable COPD (GOLD Group B) continues to experience significant breathlessness affecting his daily activities despite smoking cessation and pulmonary rehabilitation. He currently uses salbutamol as needed. According to GOLD guidelines, what is the most appropriate initial regular maintenance therapy to improve his symptoms?

An 80-year-old man with severe COPD is started on tiotropium. At his 4-week review, he reports a persistently dry mouth and has recently been troubled by difficulty initiating urination. He has a history of benign prostatic hyperplasia. Which of the following is the most likely class-wide explanation for these new symptoms?

A 55-year-old man with COPD presents to the Emergency Department with an acute exacerbation. He is wheezy and tachycardic. Alongside oxygen and corticosteroids, the medical team administers a nebulised bronchodilator that works by a different mechanism to salbutamol. Which drug, often combined with salbutamol in a nebuliser for acute exacerbations, is the team most likely using?

A practice nurse is teaching a patient about their new inhaler for COPD. She explains that this inhaler works by blocking the effect of a specific neurotransmitter in the lungs, leading to airway relaxation. It is used four times a day for maintenance. This medication belongs to which class of bronchodilators?

A patient with COPD is prescribed ipratropium. They ask their GP how it works, and the GP explains it blocks the action of the body's own "rest and digest" nervous system on the lung muscles. Which receptor, normally stimulated by acetylcholine from the vagus nerve, does ipratropium primarily block to cause bronchodilation?

In a pharmacology lab, a researcher adds ipratropium to a sample of bronchial smooth muscle that has been pre-treated with methacholine, a muscarinic agonist that causes contraction. What is the primary molecular mechanism by which ipratropium reverses this contraction?

A 70-year-old woman with severe COPD and ischemic heart disease is admitted with an exacerbation. She is very tachycardic, and the team is cautious about using standard first-line bronchodilators due to potential cardiac side effects. Which of the following is a key indication for choosing nebulised ipratropium in this clinical scenario?

An elderly patient with COPD complains of a very dry mouth and a bitter metallic taste since starting a new ipratropium inhaler. On review, his inhaler technique is poor, and he does not use a spacer device. What is the most likely pharmacological cause of these symptoms?

A 58-year-old man with severe COPD requires triple therapy but has poor inhaler technique. His consultant considers an oral maintenance medication that requires careful dose monitoring due to a narrow therapeutic index. Which oral methylxanthine drug is the consultant considering?

A patient with difficult-to-control asthma is reviewed in a specialist clinic. They are already on high-dose ICS/LABA. The consultant discusses adding an oral drug that works by inhibiting a specific intracellular enzyme to provide an additional bronchodilator and anti-inflammatory effect. This proposed add-on therapy belongs to which class of drugs?

A patient stable on theophylline for COPD is started on ciprofloxacin for a chest infection. One week later, they present with nausea, vomiting, and palpitations. Blood tests reveal a significantly elevated theophylline level. What is the primary pharmacokinetic mechanism for this dangerous interaction?

Theophylline has multiple proposed mechanisms contributing to its effect in airways disease. While its precise primary mechanism is debated, a key pharmacological action is well-established. Which of the following is a recognised mechanism contributing to theophylline's bronchodilator effect?

A patient with chronic, severe, irreversible airways obstruction remains symptomatic despite maximal inhaled therapy (including LAMA/LABA/ICS) and pulmonary rehabilitation. In which of the following scenarios might oral theophylline be considered as an add-on treatment?

A patient on maintenance theophylline presents to the Emergency Department with a two-day history of worsening nausea, vomiting, agitation, and sinus tachycardia. They recently started a new medication for heartburn. Which of the following sets of symptoms is most suggestive of theophylline toxicity?

A 9-year-old boy with asthma and concomitant allergic rhinitis is struggling with adherence to his inhaled corticosteroid. His mother reports he often forgets to use his inhaler. The GP considers adding an oral, once-daily, leukotriene receptor antagonist to his regimen. Which of the following medications is the GP most likely to prescribe?

A teenager with exercise-induced asthma finds her salbutamol inhaler helpful but wants a preventive treatment she can take before sports. She is prescribed a non-steroidal tablet that works by blocking inflammatory mediators released from mast cells and eosinophils. This preventive tablet belongs to which class of anti-asthma drugs?

A researcher is investigating the inflammatory pathway targeted by montelukast. The drug prevents a specific group of lipid mediators from binding to their G-protein coupled receptor on airway smooth muscle and inflammatory cells. Which inflammatory mediators are specifically antagonised by montelukast?

A patient with aspirin-exacerbated respiratory disease (AERD) is prescribed montelukast. The doctor explains that in this condition, taking aspirin leads to an overproduction of certain chemicals that cause bronchospasm, and this drug blocks their effect. By blocking leukotriene receptors, what is the primary physiological effect of montelukast in the airways?

A 35-year-old woman with mild persistent asthma, which is worse during the spring pollen season, experiences predominantly cough and nocturnal symptoms. She is reluctant to start an inhaled corticosteroid. According to guidelines, which of the following is an appropriate use of montelukast for this patient?

Following the initiation of montelukast for asthma in a 12-year-old boy, his parents contact the GP as they are concerned about changes in his mood, including new-onset nightmares and irritability. Which of the following is a recognised, though uncommon, neuropsychiatric adverse effect associated with montelukast?

A 16-year-old girl with newly diagnosed asthma is started on a regular preventer inhaler. She is prescribed a metered-dose inhaler containing a drug that is a synthetic glucocorticoid. The GP emphasises the importance of rinsing her mouth after use. Which of the following inhaled corticosteroids is she most likely to have been prescribed as a common first-line option?

A patient with moderate persistent asthma is using a brown-coloured inhaler twice daily. The practice nurse explains that this medication works by reducing the underlying inflammation in the airways over time, making them less sensitive to triggers. The medication in this brown inhaler belongs to which fundamental class of asthma preventer drugs?

A pharmacology student is studying the mechanism of anti-inflammatory drugs in asthma. They learn that beclometasone, after being activated in the lungs, enters airway cells and binds to a specific intracellular receptor. Binding to which receptor mediates the vast majority of beclometasone's genomic anti-inflammatory effects?

A patient asks how their regular beclometasone inhaler actually prevents asthma attacks. The doctor explains it works inside the cells of the airway lining to switch off multiple inflammatory pathways. Which of the following is a key genomic action of beclometasone that contributes to its preventive effect in asthma?

A 25-year-old man with asthma reports using his salbutamol reliever inhaler 3-4 times per week for daytime symptoms and occasionally at night. He has no symptoms currently. Spirometry is normal. According to the BTS/SIGN stepwise approach, what is the most appropriate initial regular treatment to improve his asthma control?

An elderly patient with COPD on high-dose beclometasone via a metered-dose inhaler presents with a hoarse voice and painful white patches on the oral mucosa and tongue. They do not use a spacer and rarely rinse their mouth after inhalation. What is the most likely cause of these local adverse effects?

A 42-year-old patient with severe eosinophilic asthma is being considered for add-on biologic therapy. Their current high-dose maintenance therapy includes an inhaled corticosteroid known for its high potency and strong receptor binding affinity. Which of the following high-potency inhaled corticosteroids is commonly used in such severe asthma regimens before stepping up to biologics?

A patient with allergic rhinitis is prescribed a nasal spray to use regularly throughout the pollen season. The pharmacist explains it contains a steroid that works locally to reduce inflammation in the nasal passages. The active ingredient in this nasal spray belongs to which class of medication?

Fluticasone is a highly lipophilic drug designed for topical activity in the lungs. Its structure ensures it has a strong affinity for its target after it is inhaled and absorbed into airway cells. What is the primary intracellular target that mediates fluticasone's anti-inflammatory effects?

A student is comparing the mechanisms of different asthma drugs. They note that while salbutamol provides rapid relief, fluticasone works more slowly by altering gene expression in inflammatory cells. What is a key anti-inflammatory genomic action of fluticasone in asthma pathogenesis?

A patient with COPD and a history of frequent exacerbations (≥2 per year) remains breathless and exacerbates despite being on a long-acting bronchodilator (LAMA or LABA). According to GOLD guidelines, in which of the following regimens would fluticasone most appropriately be used for this patient?

An elderly patient with severe COPD on long-term high-dose fluticasone/salmeterol presents with generalised fatigue, easy bruising, and proximal muscle weakness. Blood tests show a low morning cortisol level. What is the most likely systemic adverse effect of fluticasone in this context?

A 65-year-old man is brought to A&E with a suspected organophosphate insecticide poisoning. He is bradycardic, salivating excessively, and has pinpoint pupils. The medical team prepares an antidote derived from the deadly nightshade plant. Which anticholinergic drug is the definitive antidote for this type of poisoning?

Prior to an ophthalmic procedure, an elderly patient is given eye drops that cause pupillary dilation (mydriasis) and paralysis of accommodation (cycloplegia). This prevents the lens from changing shape during surgery. The eye drops used belong to which class of drugs?

A patient receives a large dose of atropine during resuscitation for bradyasystolic cardiac arrest. The drug works by blocking the effects of the parasympathetic neurotransmitter on specific receptors in the heart. Blockade of which receptor subtype on the sinoatrial (SA) node is primarily responsible for the increase in heart rate?

During a simulation, an anaesthetist administers atropine before induction to prevent a reflex bradycardia that can occur with certain drugs. A student asks how it prevents this reflex. What is the fundamental pharmacological action of atropine at a molecular level?

A 50-year-old man is scheduled for elective surgery. As part of the premedication, the anaesthetist prescribes an intramuscular injection to be given shortly before theatre. What is a classic indication for pre-operative atropine?

A child is brought to A&E after accidentally ingesting berries from a garden plant. On examination, he is agitated, has a flushed, dry skin, widely dilated pupils, and a heart rate of 140 bpm. His temperature is elevated. Which of the following best describes this classic toxidrome?

A 58-year-old man with hypertension and a history of exercise-induced angina is started on a new medication. The GP chooses a once-daily, water-soluble beta-blocker that is relatively cardioselective and is often used in patients who may be prone to bronchospasm with non-selective agents. Which of the following beta-blockers fits this description?

A 45-year-old woman presents with symptoms of hyperthyroidism, including palpitations and tremor. While definitive treatment is arranged, the endocrinologist prescribes an oral medication to provide rapid symptomatic control of her tachycardia and anxiety. Which class of drugs is commonly used for this symptomatic purpose in thyrotoxicosis?

A patient with stable angina is prescribed atenolol. The cardiologist explains that the drug works by blocking receptors in the heart, which reduces its workload and oxygen demand. Antagonism of which adrenergic receptor subtype is primarily responsible for the beneficial cardiac effects of atenolol in angina?

A medical student is revising how beta-blockers lower blood pressure. They understand that atenolol's effect is not primarily vasodilatory but involves a reduction in cardiac output. By blocking cardiac beta-1 receptors, what is the primary haemodynamic change through which atenolol lowers blood pressure?

A 62-year-old man is recovering in hospital following an acute myocardial infarction. His echocardiogram shows reduced left ventricular function. He is already on aspirin, a statin, and an ACE inhibitor. According to post-MI secondary prevention guidelines, which of the following medications should be added to his regimen to reduce mortality and the risk of further infarction, provided he has no contraindications?

A 70-year-old man with COPD (but no active wheeze) and ischemic heart disease is started on atenolol for hypertension. At follow-up, he reports increased breathlessness on exertion and a feeling of generalised fatigue and lethargy. Which of the following is a recognised, mechanism-based adverse effect of atenolol that could explain these symptoms?

A 28-year-old musician suffers from severe performance anxiety, manifesting as tremor, palpitations, and sweating before important concerts. Her psychiatrist prescribes a non-selective beta-blocker to be taken shortly before performances to control these physical symptoms. Which of the following is the classic non-selective beta-blocker used for this indication?

A patient with a history of migraine is started on a daily oral medication for prophylaxis. The GP explains this drug was originally developed for heart conditions but is also effective in reducing the frequency and severity of migraine attacks. This migraine prophylactic belongs to which class of drugs?

A patient with thyrotoxicosis is prescribed propranolol for symptomatic control of tremor and tachycardia. The doctor warns that it will block the body's normal physiological response to hypoglycaemia. Blockade of which receptor subtype is primarily responsible for masking the tachycardia that normally warns of hypoglycaemia?

A patient with portal hypertension secondary to liver cirrhosis is started on propranolol for primary prophylaxis of variceal bleeding. By which combined haemodynamic mechanism does non-selective beta-blockade reduce portal pressure in this context?

A 45-year-old man is referred to cardiology with recurrent episodes of palpitations, anxiety, and headaches. He is diagnosed with a phaeochromocytoma. After initiation of an alpha-blocker (phenoxybenzamine), a second drug is added to control reflex tachycardia. Why must a beta-blocker like propranolol only be started after adequate alpha-blockade in phaeochromocytoma?

A 60-year-old woman with well-controlled hypertension on propranolol presents to her GP feeling increasingly tired and short of breath. She has a history of childhood asthma but has been asymptomatic for decades. On examination, she has a widespread expiratory wheeze. Which of the following is an absolute contraindication to the use of propranolol that has likely been precipitated here?

A 30-year-old woman is stung by a wasp and rapidly develops widespread urticaria, facial swelling, stridor, and hypotension. The emergency team administers a life-saving drug intramuscularly into her anterolateral thigh. Which drug is the first-line, immediate treatment for this anaphylactic reaction?

During a cardiac arrest, a patient in pulseless electrical activity (PEA) is given a drug to increase coronary and cerebral perfusion pressure by causing vasoconstriction and improving the strength of cardiac contractions. This drug, a direct sympathomimetic, belongs to which broad class?

A patient with anaphylaxis receives intramuscular adrenaline. The doctor explains it works on different receptors: one to constrict blood vessels and raise blood pressure, and another to open the airways. Stimulation of which adrenergic receptor subtype is most responsible for the essential vasoconstrictor effect in anaphylaxis?

Adrenaline is administered during a cardiac arrest. A medical student asks how it increases the likelihood of return of spontaneous circulation (ROSC). What is a primary mechanism by which adrenaline improves coronary perfusion during CPR?

A 5-year-old boy with croup is brought to the Emergency Department with marked stridor and intercostal recession. He is agitated and hypoxic. After securing oxygen, the paediatrician decides on a specific pharmacological intervention. Which of the following is a recognised use of nebulised adrenaline in this acute setting?

A healthcare professional accidentally injects a large dose of adrenaline intramuscularly instead of a vaccine. The patient immediately becomes pale, tremulous, and complains of a pounding headache. Their heart rate is 150 bpm and blood pressure is 210/110 mmHg. Which of the following is the most likely explanation for this clinical picture?

A 25-year-old woman suffers from seasonal allergic rhinitis. She wants a non-sedating treatment she can take daily during the pollen season. The GP prescribes a long-acting, over-the-counter antihistamine. Which of the following is a common second-generation, non-sedating antihistamine used for this purpose?

A patient presents with chronic idiopathic urticaria, experiencing daily wheals and pruritus. The dermatologist recommends a regular oral medication that blocks the effects of histamine on blood vessels and sensory nerves. Which class of drugs forms the first-line symptomatic treatment for this condition?

A pharmacology student is studying the mechanism of action of common allergy medications. They note that loratadine works by binding to a specific receptor without activating it, preventing a key inflammatory mediator from having its effect. Which receptor does loratadine competitively antagonise to produce its therapeutic effects?

A patient asks why their new loratadine tablet doesn't make them drowsy like an old allergy pill they used to take. The GP explains it's due to differences in how the drug interacts with the body. What is the key property of loratadine that minimises central nervous system side effects like sedation?

A 10-year-old boy with eczema experiences intense pruritus, especially at night, which exacerbates his skin condition through scratching. His dermatologist recommends a regular oral medication to help control the itch. Which of the following is a primary indication for using a non-sedating antihistamine like loratadine in this context?

A patient starts taking loratadine for hay fever. They report it is effective and does not cause drowsiness. However, they have read online about potential side effects and ask the GP what to look out for. Which of the following is a recognised, though generally mild, potential side effect of loratadine?

A patient with chronic spontaneous urticaria is looking for a more effective alternative to their current over-the-counter antihistamine. Their dermatologist suggests switching to a second-generation H1-antagonist that is known for its potent anti-itch effects and may have mild anti-inflammatory properties. Which of the following second-generation antihistamines is the dermatologist most likely to recommend?

During the spring pollen season, a patient presents with rhinorrhoea, sneezing, and itchy eyes. They want a daily tablet that won't make them drowsy at work. The GP prescribes a medication that blocks the action of histamine. To which class of anti-allergy drugs does this prescribed tablet belong?

A researcher is developing a new drug for allergies. They use cetirizine as a reference compound because it is known to bind tightly and selectively to a specific receptor subtype, preventing its natural agonist from causing symptoms. Cetirizine exerts its therapeutic effect primarily through competitive antagonism at which receptor?

A patient asks why cetirizine helps their hives. The doctor explains it stops histamine, a chemical released during an allergic reaction, from working on the small blood vessels and nerves in the skin. Blocking histamine at the H1 receptor most directly prevents which of the following pathophysiological effects?

A 40-year-old woman presents with a 6-week history of recurrent, intensely itchy wheals that appear daily and resolve within 24 hours without scarring. A diagnosis of chronic spontaneous urticaria is made. What is the recommended first-line pharmacological treatment for this condition?

A patient starts taking cetirizine 10mg daily for hay fever. While it controls his symptoms effectively, he mentions feeling slightly more drowsy than usual in the afternoons, though he is still able to function at work. Which of the following is a recognised difference in the side effect profile of cetirizine compared to some other second-generation antihistamines like loratadine or fexofenadine?

A 6-year-old boy is brought to the Emergency Department with acute urticaria and angioedema following a suspected food allergy. After administering adrenaline, the doctor prescribes an antihistamine injection to provide further symptomatic relief. Which first-generation, sedating antihistamine is commonly available in an intramuscular or intravenous formulation for use in acute allergic reactions in a hospital setting?

A patient presents to their GP with a severe cold, complaining of a runny nose and sneezing. The GP prescribes a combination over-the-counter preparation that contains paracetamol, a decongestant, and an agent to reduce rhinorrhoea. The agent that reduces rhinorrhoea in many cold remedies is most likely from which drug class?

A pharmacology student is revising the side effects of older medications. They note that chlorphenamine can cause dry mouth, blurred vision, and urinary retention, effects not typically seen with newer antihistamines. These additional side effects occur because chlorphenamine also has significant antagonistic activity at which other receptor type?

A patient with an acute allergic rash is given chlorphenamine. The doctor explains it works by blocking histamine, the chemical causing the itch and swelling. How does chlorphenamine achieve this blockade at a molecular level?

An elderly patient with severe pruritus due to cholestatic liver disease is struggling to sleep at night due to constant itching. The dermatologist considers a pharmacological option to relieve the itch and promote sleep. Why might a first-generation antihistamine like chlorphenamine be chosen over a second-generation agent in this specific palliative context?

An 80-year-old man with benign prostatic hyperplasia (BPH) is given chlorphenamine for a viral upper respiratory tract infection. Two days later, he presents to A&E in acute urinary retention. What property of chlorphenamine is the most likely cause of this acute complication?