Safe Prescribing — MCQs

A 62-year-old man with type 2 diabetes is admitted with hyperosmolar hyperglycaemic state (HHS). His blood glucose is 48.6 mmol/L, serum osmolality 358 mOsm/kg, and he is significantly dehydrated. Intravenous fluid resuscitation is commenced. According to the Joint British Diabetes Societies guidelines for HHS management, at what rate should the blood glucose be lowered initially?

Q154

A 53-year-old woman with epilepsy has been taking phenytoin 300mg daily for 10 years with good seizure control. Her phenytoin level 6 months ago was 12 mg/L (therapeutic range 10-20 mg/L). She now reports episodes of ataxia, nystagmus, and slurred speech. A repeat phenytoin level is 28 mg/L. She has not changed her dose and denies taking any new medications. Which of the following best explains her phenytoin toxicity?

Q155

A 59-year-old man is being considered for dabigatran therapy for stroke prevention in atrial fibrillation. He has a CHA₂DS₂-VASc score of 3. His renal function shows eGFR of 42 ml/min/1.73m². According to current licensing and guidance, what is the appropriate dose of dabigatran for this patient?

Q156

A 41-year-old man with type 1 diabetes presents to the emergency department with a 24-hour history of vomiting and abdominal pain. He has continued his usual insulin doses. Blood tests show: glucose 22.4 mmol/L, pH 7.28, bicarbonate 14 mmol/L, ketones 4.2 mmol/L. He is diagnosed with diabetic ketoacidosis. According to the Joint British Diabetes Societies guidelines, what is the recommended initial fixed-rate intravenous insulin infusion rate for this patient weighing 80 kg?

Q157

A 75-year-old woman with atrial fibrillation has been on warfarin for 5 years with consistently stable INR values between 2.0-3.0, checked every 8 weeks. She is now diagnosed with recurrent urinary tract infections requiring frequent antibiotic courses. Over the past 3 months, she has required 3 courses of antibiotics (trimethoprim, nitrofurantoin, and cefalexin). What is the most appropriate modification to her anticoagulation management?

Q158

A 32-year-old woman with type 1 diabetes is 24 weeks pregnant. She is on insulin aspart before meals and insulin detemir at bedtime. Her HbA1c is 48 mmol/mol (6.5%). She reports frequent hypoglycaemic episodes (glucose <3.5 mmol/L) occurring 2-3 times weekly, particularly in the afternoon. She is concerned about the effect on her baby. According to current guidance, what is the most appropriate management approach?

Q159

A 68-year-old man with non-valvular atrial fibrillation has been taking apixaban 5mg twice daily for 2 years. He now presents with acute cholecystitis requiring emergency cholecystectomy. His last dose of apixaban was 8 hours ago. He has normal renal function (eGFR >80 ml/min/1.73m²). According to perioperative anticoagulation guidelines, what is the most appropriate management of his apixaban for surgery scheduled in 6 hours?

Q160

A 47-year-old woman with rheumatoid arthritis has been taking methotrexate 20mg weekly for 3 years with good disease control. She presents to her GP with a 4-day history of cough, fever, and shortness of breath. Chest examination reveals bilateral crepitations. Her oxygen saturation is 92% on room air. Blood tests show: white cell count 3.2 × 10⁹/L (neutrophils 1.8 × 10⁹/L), platelets 165 × 10⁹/L. Chest X-ray shows bilateral interstitial infiltrates. What is the most important immediate action regarding her methotrexate?

Safe Prescribing UK Medical PG Practice Questions and MCQs

Question 151: Which of the following insulin types has the longest duration of action and is classified as an ultra-long-acting basal insulin analogue?

A. Insulin glargine U100 (Lantus)
B. Insulin detemir (Levemir)
C. Insulin degludec (Tresiba) (Correct Answer)
D. Insulin glargine U300 (Toujeo)
E. NPH insulin (isophane insulin)

Explanation: ***Insulin degludec (Tresiba)*** - Classified as an **ultra-long-acting** basal insulin, it forms multi-hexamer strings in subcutaneous tissue, resulting in a **duration of action exceeding 42 hours**. - It provides a very stable, **peakless profile** which is associated with a lower risk of nocturnal **hypoglycaemia** and allows for greater dosing flexibility. *Insulin glargine U100 (Lantus)* - This is a standard **long-acting** insulin analogue typically providing a **24-hour** duration of action. - While it provides a relatively flat basal rate, it does not reach the ultra-long duration seen with **degludec**. *Insulin detemir (Levemir)* - A long-acting analogue that binds to **albumin**, its duration of action is **dose-dependent**, typically ranging from **12 to 24 hours**. - It often requires **twice-daily dosing** in patients with type 1 diabetes to maintain adequate basal coverage. *Insulin glargine U300 (Toujeo)* - A **concentrated** form of glargine that lasts longer than U100 (approximately **36 hours**), but is generally considered shorter-acting than degludec. - It has a **flatter and more prolonged** pharmacokinetic profile than U100 but remains categorized below the ultra-long duration of Tresiba. *NPH insulin (isophane insulin)* - Classified as an **intermediate-acting** insulin with a duration of only **12 to 18 hours**. - It has a distinct **peak of action** (4-12 hours), which increases the clinical risk of **hypoglycaemia** compared to basal analogues.

Question 152: A 59-year-old man with atrial fibrillation is prescribed warfarin. According to the British National Formulary, what is the standard loading dose regimen for initiating warfarin therapy in a patient without hepatic impairment or other risk factors?

A. 5mg daily for 2 days, then adjust dose according to INR
B. 10mg on day 1, 10mg on day 2, then adjust dose according to INR
C. 10mg on day 1, 5mg on day 2, then adjust dose according to INR (Correct Answer)
D. 2.5mg daily for 2 days, then adjust dose according to INR
E. 7.5mg daily for 2 days, then adjust dose according to INR

Explanation: ***10mg on day 1, 5mg on day 2, then adjust dose according to INR*** - The **British National Formulary (BNF)** recommends this regimen as the standard loading dose for **warfarin initiation** in adults without specific risk factors like advanced age or hepatic impairment. - This approach aims to achieve a therapeutic **International Normalized Ratio (INR)** quickly and safely, with subsequent doses adjusted based on the measured INR response, typically on day 3. *5mg daily for 2 days, then adjust dose according to INR* - A lower induction dose of **5mg daily** is usually reserved for patients with increased **bleeding risk**, such as those over 75 years old, with hepatic impairment, or on interacting medications. - For a healthy 59-year-old, this dose would likely prolong the time taken to reach the desired **therapeutic INR range**, delaying effective anticoagulation. *10mg on day 1, 10mg on day 2, then adjust dose according to INR* - Administering **10mg for two consecutive days** is generally considered an aggressive loading regimen and significantly increases the risk of **over-anticoagulation** and bleeding complications. - Such a high initial dose can lead to a rapid depletion of **Protein C**, potentially causing a transient **prothrombotic state** or skin necrosis before other vitamin K-dependent clotting factors are reduced. *2.5mg daily for 2 days, then adjust dose according to INR* - This dose is typically too low to serve as an effective **loading dose** for most adult patients initiating warfarin therapy. - It would lead to a considerably delayed achievement of the **therapeutic INR**, leaving the patient sub-optimally anticoagulated and at increased risk of thromboembolic events. *7.5mg daily for 2 days, then adjust dose according to INR* - This particular loading dose regimen is **not a standard recommendation** outlined by major drug formularies like the BNF for typical warfarin initiation. - Following non-standard protocols can lead to unpredictable **INR responses** and potential challenges in achieving and maintaining therapeutic anticoagulation.

Question 153: A 62-year-old man with type 2 diabetes is admitted with hyperosmolar hyperglycaemic state (HHS). His blood glucose is 48.6 mmol/L, serum osmolality 358 mOsm/kg, and he is significantly dehydrated. Intravenous fluid resuscitation is commenced. According to the Joint British Diabetes Societies guidelines for HHS management, at what rate should the blood glucose be lowered initially?

A. Aim for blood glucose reduction of 10 mmol/L/hour
B. Aim for blood glucose reduction of 5 mmol/L/hour
C. Aim for blood glucose reduction of 3-5 mmol/L/hour (Correct Answer)
D. Aim for blood glucose reduction of 1-3 mmol/L/hour
E. Aim to normalize blood glucose within 6 hours

Explanation: ***Aim for blood glucose reduction of 3-5 mmol/L/hour*** - According to the **Joint British Diabetes Societies (JBDS) guidelines** for HHS management, the target rate for initial blood glucose reduction is **3-5 mmol/L/hour**. - This gradual reduction helps prevent rapid osmotic shifts, which can lead to complications such as **cerebral oedema** due to the movement of water into brain cells.*Aim for blood glucose reduction of 10 mmol/L/hour* - This rate is **too rapid** and significantly increases the risk of **cerebral oedema** and dangerous osmotic shifts. - A fast drop in blood glucose can cause a steep decline in **serum osmolality**, potentially leading to severe neurological complications.*Aim for blood glucose reduction of 5 mmol/L/hour* - While 5 mmol/L/hour is at the higher end of the recommended range, the guideline specifies a **range of 3-5 mmol/L/hour**, not a single fixed rate. - Adhering to the specified range allows for appropriate clinical judgment and adjustment based on the patient's individual response to **fluid resuscitation**.*Aim for blood glucose reduction of 1-3 mmol/L/hour* - This rate is considered **too slow** for the initial management of HHS and may unnecessarily prolong the patient's **hyperosmolar state** and dehydration. - A slower reduction might delay the resolution of severe hyperglycemia and its associated metabolic derangements.*Aim to normalize blood glucose within 6 hours* - Normalizing blood glucose within 6 hours is **dangerously fast** and highly discouraged in HHS management, which typically takes **24-72 hours** for full resolution. - Such rapid correction significantly increases the risk of **cerebral oedema**, central pontine myelinolysis, and cardiovascular instability due to drastic fluid and electrolyte shifts.

Question 154: A 53-year-old woman with epilepsy has been taking phenytoin 300mg daily for 10 years with good seizure control. Her phenytoin level 6 months ago was 12 mg/L (therapeutic range 10-20 mg/L). She now reports episodes of ataxia, nystagmus, and slurred speech. A repeat phenytoin level is 28 mg/L. She has not changed her dose and denies taking any new medications. Which of the following best explains her phenytoin toxicity?

A. Phenytoin exhibits first-order kinetics so small dose increases cause proportional level increases
B. Phenytoin exhibits zero-order kinetics so saturation of metabolism causes disproportionate level increases (Correct Answer)
C. Phenytoin undergoes extensive first-pass metabolism which decreases with age
D. Phenytoin is highly protein-bound and total levels increase with age due to increased albumin
E. Phenytoin auto-induces its own metabolism leading to accumulation over time

Explanation: ***Phenytoin exhibits zero-order kinetics so saturation of metabolism causes disproportionate level increases*** - Phenytoin follows **Michaelis-Menten kinetics**, meaning its metabolism shifts from **first-order to zero-order (non-linear)** kinetics once the hepatic enzyme systems become saturated, typically at therapeutic concentrations. - Once these enzymes are saturated, the drug is eliminated at a fixed rate, so even minor changes in dose or metabolic capacity can cause a **disproportionate and rapid rise** in serum levels, leading to characteristic signs of toxicity such as **ataxia, nystagmus, and slurred speech**. *Phenytoin exhibits first-order kinetics so small dose increases cause proportional level increases* - In **first-order kinetics**, a constant **fraction** of the drug is eliminated per unit of time, which means plasma levels increase proportionally with dose increases. - This mechanism does not explain the sudden, sharp increase in phenytoin levels from 12 mg/L to 28 mg/L in this patient on a stable dose, indicating a shift away from proportional elimination. *Phenytoin undergoes extensive first-pass metabolism which decreases with age* - Phenytoin has good oral bioavailability and does not undergo significant **first-pass metabolism**; its elimination is primarily via hepatic metabolism. - While hepatic metabolism can be affected by age, the primary explanation for the toxicity here is the **saturation kinetics** of phenytoin, rather than changes in first-pass effect. *Phenytoin is highly protein-bound and total levels increase with age due to increased albumin* - Phenytoin is indeed **highly protein-bound**, mainly to albumin, but **albumin levels** typically **decrease** or remain stable with age or chronic illness, rather than increase. - A decrease in albumin would increase the **free (unbound) fraction** of phenytoin, potentially causing toxicity, but it would not explain such a significant increase in the **total serum level** itself. *Phenytoin auto-induces its own metabolism leading to accumulation over time* - Phenytoin is a known **inducer** of hepatic cytochrome P450 enzymes, which means it generally **increases** the metabolism of other drugs and, to some extent, its own. - Auto-induction would lead to **lower serum concentrations** over time due to faster clearance, not accumulation and toxicity as observed in this case.

Question 155: A 59-year-old man is being considered for dabigatran therapy for stroke prevention in atrial fibrillation. He has a CHA₂DS₂-VASc score of 3. His renal function shows eGFR of 42 ml/min/1.73m². According to current licensing and guidance, what is the appropriate dose of dabigatran for this patient?

A. Dabigatran 150mg twice daily
B. Dabigatran 110mg twice daily (Correct Answer)
C. Dabigatran 75mg twice daily
D. Dabigatran is contraindicated; use alternative anticoagulant
E. Dabigatran 150mg once daily

Explanation: ***Dabigatran 110mg twice daily***- Patients with **moderate renal impairment** (eGFR 30–49 ml/min) require a dose reduction to **110mg twice daily** to prevent drug accumulation and minimize bleeding risk.- Per guidelines (e.g., NICE and SMPC), this lower dose is indicated because **dabigatran** is approximately **80% renally excreted**.*Dabigatran 150mg twice daily*- This is the **standard dose** for patients with good renal function (eGFR ≥50 ml/min) who are under 80 years of age.- Administering this dose to a patient with an **eGFR of 42 ml/min** would significantly increase the **risk of major hemorrhage**.*Dabigatran 75mg twice daily*- The **75mg twice daily** dose is primarily used in the USA for **severe renal impairment** (CrCl 15–30 ml/min) but is not the licensed dose for AF in several other jurisdictions like the UK.- At an eGFR of 42 ml/min, this dose would be **sub-therapeutic** for stroke prevention in atrial fibrillation.*Dabigatran is contraindicated; use alternative anticoagulant*- Dabigatran is only **contraindicated** when the eGFR or CrCl falls **below 30 ml/min** (or 15 ml/min depending on specific local guidelines).- Since this patient’s renal function is **42 ml/min**, it is safe to use provided the **dose is adjusted** appropriately.*Dabigatran 150mg once daily*- Dabigatran is not licensed for **once-daily administration** for the prevention of stroke in patients with atrial fibrillation.- **Twice-daily dosing** is required due to the **pharmacokinetic profile** and half-life of the medication to maintain stable plasma concentrations.

Question 156: A 41-year-old man with type 1 diabetes presents to the emergency department with a 24-hour history of vomiting and abdominal pain. He has continued his usual insulin doses. Blood tests show: glucose 22.4 mmol/L, pH 7.28, bicarbonate 14 mmol/L, ketones 4.2 mmol/L. He is diagnosed with diabetic ketoacidosis. According to the Joint British Diabetes Societies guidelines, what is the recommended initial fixed-rate intravenous insulin infusion rate for this patient weighing 80 kg?

A. 0.05 units/kg/hour (4 units/hour)
B. 0.1 units/kg/hour (8 units/hour) (Correct Answer)
C. 0.15 units/kg/hour (12 units/hour)
D. 0.2 units/kg/hour (16 units/hour)
E. 10 units/hour regardless of weight

Explanation: ***0.1 units/kg/hour (8 units/hour)*** - According to the **Joint British Diabetes Societies (JBDS)** guidelines, the recommended initial **fixed-rate intravenous insulin infusion (FRIII)** for DKA is **0.1 units/kg/hour**. - For a patient weighing **80 kg**, this calculation (0.1 x 80) equals **8 units/hour**, which is the standardized rate to suppress ketogenesis and resolve acidosis. *0.05 units/kg/hour (4 units/hour)* - This dose is generally too low to effectively switch off **ketone production** in the initial stages of DKA management. - A lower rate like this might be considered only in specific scenarios where **insulin sensitivity** is extremely high to avoid rapid metabolic shifts, but it is not the standard starting dose. *0.15 units/kg/hour (12 units/hour)* - Using a rate higher than 0.1 units/kg/hour increases the risk of **hypokalaemia** and a too-rapid fall in blood glucose levels. - Rapid shifts in **osmolarity** caused by higher insulin rates can theoretically increase the risk of **cerebral oedema**, especially in younger patients. *0.2 units/kg/hour (16 units/hour)* - This dosage is double the recommended guideline and significantly increases the risk of **iatrogenic complications** like severe hypoglycaemia. - Guidelines moved away from such high doses because **0.1 units/kg/hour** is sufficient to saturate insulin receptors and achieve maximal metabolic effect. *10 units/hour regardless of weight* - Modern DKA management emphasizes a **weight-based approach** to tailor therapy to the individual's metabolic needs. - A fixed **non-weight-based** dose of 10 units/hour would be an overdose for a small person and an underdose for a very large person, leading to inconsistent clinical outcomes.

Question 157: A 75-year-old woman with atrial fibrillation has been on warfarin for 5 years with consistently stable INR values between 2.0-3.0, checked every 8 weeks. She is now diagnosed with recurrent urinary tract infections requiring frequent antibiotic courses. Over the past 3 months, she has required 3 courses of antibiotics (trimethoprim, nitrofurantoin, and cefalexin). What is the most appropriate modification to her anticoagulation management?

A. Continue warfarin with more frequent INR monitoring during antibiotic courses
B. Switch to a direct oral anticoagulant to avoid INR monitoring (Correct Answer)
C. Continue warfarin but increase target INR range to 2.5-3.5
D. Stop anticoagulation during antibiotic courses then restart
E. Switch to aspirin monotherapy to avoid drug interactions

Explanation: ***Switch to a direct oral anticoagulant to avoid INR monitoring*** - **Direct oral anticoagulants (DOACs)** like apixaban or rivaroxaban are preferred here because they provide stable anticoagulation without the need for frequent **INR monitoring** or risk of drug-drug interactions with most antibiotics. - Frequent antibiotic courses significantly destabilize **warfarin** levels by inhibiting **CYP450 enzymes** or altering **gut flora**, making DOACs a safer and more convenient alternative for this patient. *Continue warfarin with more frequent INR monitoring during antibiotic courses* - While technically possible, this approach is **burdensome** for the patient and increases the risk of **sub-therapeutic or supratherapeutic INR** levels between checks. - Frequent monitoring does not eliminate the inherent **instability** of warfarin therapy caused by repeated antibiotic exposure. *Continue warfarin but increase target INR range to 2.5-3.5* - Raising the **target INR** is clinically inappropriate and significantly increases the **risk of major hemorrhage**, especially in an elderly patient. - A higher target range does not address the underlying issue of **pharmacokinetic interactions** between antibiotics and warfarin. *Stop anticoagulation during antibiotic courses then restart* - Suspending anticoagulation leaves the patient at high risk for **embolic stroke** or systemic embolism, even during short antibiotic courses. - The transient nature of the infection does not justify exposing the patient to the **pro-thrombotic risk** of stopping therapy. *Switch to aspirin monotherapy to avoid drug interactions* - **Aspirin monotherapy** is significantly less effective than anticoagulation for stroke prevention in **atrial fibrillation** and is no longer recommended for this purpose. - While aspirin has fewer interactions, it would provide **inadequate protection** (only ~20% risk reduction) compared to the ~64% reduction provided by anticoagulants.

Question 158: A 32-year-old woman with type 1 diabetes is 24 weeks pregnant. She is on insulin aspart before meals and insulin detemir at bedtime. Her HbA1c is 48 mmol/mol (6.5%). She reports frequent hypoglycaemic episodes (glucose <3.5 mmol/L) occurring 2-3 times weekly, particularly in the afternoon. She is concerned about the effect on her baby. According to current guidance, what is the most appropriate management approach?

A. Reassure that HbA1c is excellent and continue current regimen with glucose monitoring
B. Increase carbohydrate intake in the morning to prevent afternoon hypoglycaemia
C. Reduce morning insulin aspart dose and accept higher HbA1c to reduce hypoglycaemia risk (Correct Answer)
D. Consider continuous subcutaneous insulin infusion (insulin pump) therapy
E. Add metformin to reduce insulin requirements and hypoglycaemia risk

Explanation: ***Reduce morning insulin aspart dose and accept higher HbA1c to reduce hypoglycaemia risk*** - The frequent **afternoon hypoglycaemic episodes** suggest that the **morning (breakfast) insulin aspart dose** is too high for her current physiological needs, especially given the increased insulin sensitivity that can occur in the second trimester of pregnancy. - While maintaining a low HbA1c is important in pregnancy to reduce fetal risks, preventing **severe maternal hypoglycaemia** is paramount. It is appropriate to slightly relax the HbA1c target to ensure maternal safety and well-being. *Reassure that HbA1c is excellent and continue current regimen with glucose monitoring* - Although an **HbA1c of 48 mmol/mol (6.5%)** is within an acceptable range for pregnancy, it does not negate the significant risk posed by frequent and symptomatic **hypoglycaemia**. - Continuing an insulin regimen that causes frequent hypoglycemia is unsafe and could lead to severe adverse events for the mother, which must be prioritized. *Increase carbohydrate intake in the morning to prevent afternoon hypoglycaemia* - While increased carbohydrate intake might temporarily raise glucose, it is a reactive measure and does not address the underlying mismatch between **insulin dose** and need. - This approach can lead to **post-prandial hyperglycemia** and complicate overall glycemic control, making it harder to manage long-term. *Consider continuous subcutaneous insulin infusion (insulin pump) therapy* - While an **insulin pump** can offer more precise insulin delivery and potentially reduce hypoglycaemia, it is a more advanced intervention that is usually considered after optimizing a multiple daily injection regimen. - Simple dose adjustments, particularly reducing the specific insulin dose causing the hypoglycemia, should be the initial approach before escalating to pump therapy. *Add metformin to reduce insulin requirements and hypoglycaemia risk* - **Metformin** is generally not recommended as a primary treatment for **type 1 diabetes** in pregnancy, especially not to manage insulin-induced hypoglycaemia. - Its main role in diabetes management is to reduce **hepatic glucose production** and improve **insulin sensitivity**, which is not the direct solution for an over-dosed rapid-acting insulin causing hypoglycemia.

Question 159: A 68-year-old man with non-valvular atrial fibrillation has been taking apixaban 5mg twice daily for 2 years. He now presents with acute cholecystitis requiring emergency cholecystectomy. His last dose of apixaban was 8 hours ago. He has normal renal function (eGFR >80 ml/min/1.73m²). According to perioperative anticoagulation guidelines, what is the most appropriate management of his apixaban for surgery scheduled in 6 hours?

A. Proceed with surgery as planned; apixaban can be omitted for one dose (Correct Answer)
B. Delay surgery for 24 hours after last dose of apixaban
C. Give 2000 units of four-factor prothrombin complex concentrate and proceed
D. Delay surgery for 48 hours after last dose of apixaban
E. Give idarucizumab to reverse anticoagulation and proceed immediately

Explanation: ***Proceed with surgery as planned; apixaban can be omitted for one dose*** - For urgent surgeries like **cholecystectomy** in a patient with normal renal function, a direct oral anticoagulant (**DOAC**) like apixaban can often be safely managed by omitting doses and ensuring a sufficient time interval. - With the last dose 8 hours ago and surgery scheduled in 6 hours, there will be a **14-hour gap** since the last dose, which is generally considered safe for urgent procedures with low-moderate bleeding risk in patients with normal kidney function. *Delay surgery for 24 hours after last dose of apixaban* - While a 24-hour delay is often appropriate for **elective procedures** or those with a higher bleeding risk, it is too long for an **urgent cholecystectomy**. - Delaying surgery for acute cholecystitis increases the risk of complications such as **gallbladder perforation**, empyema, or sepsis. *Give 2000 units of four-factor prothrombin complex concentrate and proceed* - **Four-factor prothrombin complex concentrate (4F-PCC)** is primarily used for rapid reversal in **life-threatening bleeding** or for emergency major surgeries when a DOAC has been taken very recently. - Given the 14-hour interval between the last apixaban dose and scheduled surgery, the anticoagulant effect is already significantly reduced, making 4F-PCC unnecessary and potentially prothrombotic. *Delay surgery for 48 hours after last dose of apixaban* - A 48-hour delay is typically reserved for **high-bleeding-risk elective surgeries** or for patients with **renal impairment** where DOACs are cleared more slowly. - This duration is excessive and unsafe for an urgent procedure like cholecystectomy, which requires timely intervention to prevent further complications. *Give idarucizumab to reverse anticoagulation and proceed immediately* - **Idarucizumab** is a specific reversal agent for **dabigatran** (a direct thrombin inhibitor), not for apixaban, which is a Factor Xa inhibitor. - The specific reversal agent for apixaban is **andexanet alfa**, but its use is generally reserved for severe or life-threatening bleeding or very high-risk emergency surgeries where immediate complete reversal is critical.

Question 160: A 47-year-old woman with rheumatoid arthritis has been taking methotrexate 20mg weekly for 3 years with good disease control. She presents to her GP with a 4-day history of cough, fever, and shortness of breath. Chest examination reveals bilateral crepitations. Her oxygen saturation is 92% on room air. Blood tests show: white cell count 3.2 × 10⁹/L (neutrophils 1.8 × 10⁹/L), platelets 165 × 10⁹/L. Chest X-ray shows bilateral interstitial infiltrates. What is the most important immediate action regarding her methotrexate?

A. Continue methotrexate but add folic acid 5mg daily
B. Reduce methotrexate dose to 15mg weekly
C. Stop methotrexate immediately and consider differential diagnosis including methotrexate pneumonitis (Correct Answer)
D. Continue methotrexate but prescribe prophylactic co-trimoxazole
E. Switch from weekly methotrexate to daily low-dose methotrexate

Explanation: ***Stop methotrexate immediately and consider differential diagnosis including methotrexate pneumonitis*** - This patient presents with a triad of **fever, cough, and dyspnoea**, which alongside **bilateral interstitial infiltrates** and **hypoxia**, suggests either **methotrexate-induced pneumonitis** or an **opportunistic infection**. - Immediate **cessation of methotrexate** is the most critical step, as the drug is either the direct cause of the lung injury or a contributor to **immunosuppression** during a severe infection. *Continue methotrexate but add folic acid 5mg daily* - Adding **folic acid** is standard to reduce chronic GI side effects or macrocytosis, but it will not treat or stop the progression of acute **methotrexate pneumonitis**. - Continuing an **immunosuppressant** in a patient with active respiratory distress and **interstitial changes** is dangerous and medically inappropriate. *Reduce methotrexate dose to 15mg weekly* - **Dose reduction** is insufficient for managing severe adverse reactions; the drug must be stopped entirely to prevent further pulmonary damage or worsening of **bone marrow suppression**. - The current presentation indicates a life-threatening complication that requires **total withdrawal** of the offending agent. *Continue methotrexate but prescribe prophylactic co-trimoxazole* - While **co-trimoxazole** treats bacterial infections like **Pneumocystis jirovecii**, it does not address the potential direct toxicity of methotrexate on lung tissue. - **Methotrexate** and **co-trimoxazole** interact to increase the risk of severe **pancytopenia** through additive anti-folate effects, making this combination hazardous here. *Switch from weekly methotrexate to daily low-dose methotrexate* - Methotrexate for rheumatoid arthritis must **always be given weekly**; switching to daily dosing is a prescribing error that leads to fatal **toxicity**. - Daily dosing would worsen the patient's existing **neutropenia** and pulmonary inflammation by providing constant, rather than pulsed, folate antagonism.

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