Safe Prescribing Practice Questions

Q: A 28-year-old man with newly diagnosed epilepsy is started on sodium valproate. What is the single most important baseline investigation that must be performed before starting sodium valproate?

Full blood count and liver function tests. ***Full blood count and liver function tests*** - **Sodium valproate** is associated with rare but severe **hepatotoxicity**, making baseline **liver function tests (LFTs)** mandatory to identify pre-existing hepatic disease. - It can also cause **thrombocytopenia** and other blood dyscrasias, necessitating a baseline **Full Blood Count (FBC)** for subsequent monitoring. *Serum ammonia levels* - **Hyperammonemia** is a known side effect of valproate, but levels are typically only measured if the patient develops signs of **encephalopathy**. - It is not a standard baseline investigation as it does not reliably predict the development of future **valproate-induced toxicity**. *Electroencephalogram (EEG)* - An **EEG** is vital for the **diagnosis and classification** of epilepsy syndromes, but it is not a safety-related prerequisite for starting medication. - The decision to treat is based on clinical diagnosis; the EEG helps guide drug choice but does not monitor for **drug adverse effects**. *Pregnancy test if female of childbearing potential* - While the **Valproate Pregnancy Prevention Programme** makes this crucial for females due to **teratogenicity**, the patient in this scenario is a **28-year-old man**. - For a male patient, this investigation is irrelevant and does not form part of his mandatory **pre-treatment safety screening**. *Genetic testing for mitochondrial disorders* - This is indicated primarily in children with suspected **Alpers-Huttenlocher syndrome** due to the high risk of **acute liver failure** with valproate. - It is not a routine baseline requirement for an **adult male** unless there is a specific family history or clinical suspicion of a **mitochondrial disorder**.

Q: A 82-year-old woman with atrial fibrillation is on warfarin with stable INR of 2.5. She develops a urinary tract infection and the GP prescribes a 7-day course of antibiotics. Which antibiotic would be most likely to significantly increase her INR?

Trimethoprim 200mg twice daily. ***Trimethoprim 200mg twice daily*** - **Trimethoprim** is a potent inhibitor of the **CYP2C9** enzyme, which is primarily responsible for the metabolism of **S-warfarin**, the more active isomer. - This inhibition significantly reduces **warfarin clearance**, leading to a rapid and substantial increase in **INR** and a high risk of bleeding. *Nitrofurantoin 100mg twice daily* - **Nitrofurantoin** has minimal interaction with the cytochrome P450 system and is not known to inhibit warfarin metabolism. - It is generally considered a **safer antibiotic** choice for patients on warfarin, with a low risk of significant INR fluctuations. *Cefalexin 500mg three times daily* - **Cefalexin**, a **cephalosporin**, does not inhibit the enzymes responsible for warfarin metabolism and usually has a **negligible effect** on INR. - Significant clinical interactions are rare unless a patient has a severe pre-existing **vitamin K deficiency**. *Amoxicillin 500mg three times daily* - **Amoxicillin** is not a known enzyme inhibitor and does not significantly interfere with the **pharmacokinetics** of warfarin. - It is frequently used for infections in warfarinized patients with **stable INR** profiles and typically requires no dose adjustments. *Fosfomycin 3g single dose* - A single dose of **fosfomycin** has a very short duration of action and no known interaction with the **cytochrome P450 system**. - Its lack of systemic metabolic interference makes it an **excellent alternative** for treating uncomplicated UTIs in patients on therapeutic anticoagulation.

Q: A 58-year-old man is started on direct oral anticoagulant (DOAC) therapy following a diagnosis of atrial fibrillation. His CHA₂DS₂-VASc score is 3. He has normal renal function (eGFR 78ml/min/1.73m²) and normal liver function. Which of the following statements about DOAC monitoring is correct?

Renal function should be checked at least annually. ***Renal function should be checked at least annually*** - For patients on **Direct Oral Anticoagulants (DOACs)** with a stable **eGFR >60 ml/min**, clinical guidelines recommend monitoring renal function at least **once every 12 months**. - More frequent monitoring is necessary if renal function declines, as DOAC clearance is heavily dependent on **renal excretion**, increasing the risk of toxicity. *INR monitoring is required monthly while on apixaban* - Unlike warfarin, DOACs like **apixaban** have a predictable effect and do not require **INR monitoring** or regular titration. - Using **INR** to monitor DOACs is clinically inappropriate as these drugs do not affect the **International Normalized Ratio** in a consistent or reliable way. *Full blood count monitoring is required every 3 months* - While a baseline **Full Blood Count (FBC)** is essential to screen for anemia, routine **three-monthly monitoring** is not a standard requirement for stable patients. - FBC is typically repeated **annually** or if clinical signs of **occult bleeding** or procedural needs arise. *Liver function tests are only needed if symptoms develop* - Guidelines state that **Liver Function Tests (LFTs)** should be checked at **baseline** and then at least **annually** for patients on chronic DOAC therapy. - Many DOACs, particularly **rivaroxaban** and **apixaban**, undergo significant **hepatic metabolism**, making regular assessment of liver health necessary for safe prescribing. *Anti-Xa levels should be checked before each dose adjustment* - **Anti-Xa assays** are not used for routine dose adjustments; dosing for DOACs is strictly based on clinical criteria like **age, weight, and creatinine clearance**. - Measurement of drug levels is reserved for **emergency situations**, such as major bleeding, suspected overdose, or before **urgent surgery**.

Q: A 72-year-old man is started on digoxin for rate control in atrial fibrillation. Which of the following factors would require a dose reduction of digoxin?

eGFR of 35ml/min/1.73m². ***eGFR of 35ml/min/1.73m²*** - **Digoxin** is primarily excreted by the **kidneys**; therefore, patients with **renal impairment** (eGFR < 50ml/min) require a dose reduction to avoid accumulation and toxicity. - An eGFR of 35ml/min/1.73m² (CKD stage 3b) significantly increases the risk of **digitalis toxicity**, which can result in life-threatening **arrhythmias**, nausea, and visual changes. *Body weight of 95kg* - Digoxin has a large **volume of distribution** and primarily distributes to **lean muscle mass**, so a higher total body weight does not typically necessitate a dose reduction. - Dose adjustments are usually only considered for patients with a very **low body mass** (e.g., <50kg) to avoid high serum concentrations. *Concurrent use of bisoprolol* - While both drugs have **negative chronotropic** effects and offer additive **rate control**, bisoprolol does not alter the **pharmacokinetics** (metabolism or excretion) of digoxin. - **Drug-drug interactions** that would require dose reduction include those with **amiodarone**, verapamil, or quinidine, which increase digoxin plasma levels. *History of hypertension* - Hypertension is a common comorbidity in patients with **atrial fibrillation** but does not independently affect the **clearance** or mechanism of action of digoxin. - Dosing is primarily driven by **renal function** and serum electrolyte levels (e.g., potassium) rather than blood pressure status. *Age over 70 years alone* - While **elderly patients** often have lower renal reserves, age alone is not a definitive indication for dose reduction if the **renal function** is otherwise normal. - Dosing should be based on a calculated **creatinine clearance** or eGFR rather than age as a stand-alone factor.

Q: A 45-year-old woman with type 1 diabetes mellitus is admitted with diabetic ketoacidosis. After initial resuscitation with intravenous fluids and insulin infusion, her blood glucose drops from 28mmol/L to 14mmol/L within 2 hours. Her pH is 7.18 and ketones remain elevated at 4.2mmol/L. What is the most appropriate next step in insulin management?

Continue the insulin infusion at the same rate and add 10% glucose. ***Continue the insulin infusion at the same rate and add 10% glucose***- In **Diabetic Ketoacidosis (DKA)**, the primary goal is the suppression of ketogenesis and correction of acidosis; insulin must be maintained to achieve **ketone clearance** even if glucose levels drop.- When blood glucose falls below **14 mmol/L**, 10% glucose should be started to prevent **hypoglycemia** while the fixed-rate insulin continues to treat the underlying ketosis.*Stop the insulin infusion until ketones normalize*- Stopping insulin represents a critical error as it allows **ketogenesis** to resume, worsening the metabolic acidosis.- High **ketone levels (4.2 mmol/L)** and low **pH (7.18)** indicate the DKA is not yet resolved, necessitating continuous insulin therapy.*Reduce the insulin infusion rate by half and continue monitoring*- Fixed-rate intravenous insulin infusion (FRIII) should generally be maintained at **0.1 units/kg/hour** to ensure adequate suppression of ketone production.- Reducing the rate prematurely can delay the resolution of **acidosis** and lead to a rebound in ketone levels.*Switch from intravenous to subcutaneous insulin immediately*- The criteria for switching to **subcutaneous insulin** include a pH >7.3, bicarbonate >15 mmol/L, and ketones <0.6 mmol/L, none of which are met here.- Switching before **DKA resolution** can lead to a rapid relapse into ketoacidosis due to the short half-life of IV insulin.*Increase the insulin infusion rate to clear ketones more rapidly*- The insulin rate is typically fixed based on weight; increasing it beyond the standard protocol increases the risk of **cerebral edema** and severe **hypokalemia**.- Rapid shifts in **osmolarity** should be avoided; adding glucose is the standard method to allow continued insulin action safely.

Question 1

A 42-year-old woman with type 2 diabetes on insulin presents to the emergency department following accidental administration of 50 units of rapid-acting insulin (insulin aspart) instead of her usual 10 units. This was given 30 minutes ago. Her current blood glucose is 8.2mmol/L and she is asymptomatic. What is the most appropriate immediate management strategy?

Accepted Answer

Give 100ml of 20% glucose intravenously followed by 10% glucose infusion with close monitoring for at least 12 hours

Answer

Administer 50ml of 50% glucose intravenously immediately

Answer

Observe for 2 hours with blood glucose monitoring every 15 minutes and treat hypoglycemia if it develops

Answer

Administer intramuscular glucagon 1mg and discharge with advice

Answer

Give oral glucose 20g and recheck blood glucose in 15 minutes

Question 2

A 65-year-old woman with mechanical mitral valve replacement is on warfarin with target INR 2.5-3.5. She is scheduled for dental extraction in 2 weeks. Her current INR is 3.0. What is the most appropriate peri-procedural anticoagulation management?

Accepted Answer

Continue warfarin without interruption as dental procedures are low-bleeding risk

Answer

Stop warfarin 5 days before procedure, bridge with therapeutic LMWH, restart warfarin post-procedure

Answer

Stop warfarin 3 days before procedure, no bridging required, restart warfarin evening of procedure

Answer

Switch to DOAC 2 weeks before procedure for easier management

Answer

Stop warfarin 5 days before, start IV heparin infusion, stop 4 hours before procedure

Question 3

A 28-year-old man with newly diagnosed epilepsy is started on sodium valproate. What is the single most important baseline investigation that must be performed before starting sodium valproate?

Accepted Answer

Full blood count and liver function tests

Answer

Serum ammonia levels

Answer

Genetic testing for mitochondrial disorders

Answer

Electroencephalogram (EEG)

Answer

Pregnancy test if female of childbearing potential

Question 4

A 82-year-old woman with atrial fibrillation is on warfarin with stable INR of 2.5. She develops a urinary tract infection and the GP prescribes a 7-day course of antibiotics. Which antibiotic would be most likely to significantly increase her INR?

Accepted Answer

Trimethoprim 200mg twice daily

Answer

Nitrofurantoin 100mg twice daily

Answer

Cefalexin 500mg three times daily

Answer

Amoxicillin 500mg three times daily

Answer

Fosfomycin 3g single dose

Question 5

A 76-year-old man is prescribed lithium carbonate for bipolar affective disorder. Which of the following is the most appropriate monitoring schedule for lithium therapy?

Accepted Answer

Lithium levels at 12 hours post-dose weekly until stable, then every 3 months with 6-monthly renal and thyroid function

Answer

Lithium levels weekly for first month, then monthly thereafter

Answer

Lithium levels and full blood count monthly for first year

Answer

Lithium levels daily for first week, then weekly for 3 months

Answer

Lithium levels every 6 months with annual renal function tests

Question 6

A 34-year-old woman with type 1 diabetes is 10 weeks pregnant. She is currently on a basal-bolus insulin regimen with insulin glargine 20 units at night and insulin aspart with meals. Her HbA1c is 7.8% (62mmol/mol). What is the most appropriate modification to her diabetes management?

Accepted Answer

Increase insulin doses to aim for pre-meal glucose 3.5-5.9mmol/L and 1-hour post-meal <7.8mmol/L

Answer

Switch to oral hypoglycemic agents as insulin crosses the placenta

Answer

Reduce insulin doses by 50% to minimize risk of hypoglycemia

Answer

Switch to twice-daily mixed insulin for simplicity

Answer

Continue current regimen as HbA1c is acceptable in pregnancy

Question 7

A 58-year-old man is started on direct oral anticoagulant (DOAC) therapy following a diagnosis of atrial fibrillation. His CHA₂DS₂-VASc score is 3. He has normal renal function (eGFR 78ml/min/1.73m²) and normal liver function. Which of the following statements about DOAC monitoring is correct?

Accepted Answer

Renal function should be checked at least annually

Answer

INR monitoring is required monthly while on apixaban

Answer

Full blood count monitoring is required every 3 months

Answer

Liver function tests are only needed if symptoms develop

Answer

Anti-Xa levels should be checked before each dose adjustment

Question 8

A 55-year-old woman with rheumatoid arthritis on methotrexate 15mg weekly presents to the emergency department with a 3-day history of mouth ulcers, sore throat, and fever. Her full blood count shows: Hb 118g/L, WCC 1.2×10⁹/L, neutrophils 0.3×10⁹/L, platelets 245×10⁹/L. What is the most critical immediate action?

Accepted Answer

Stop methotrexate and start broad-spectrum antibiotics immediately

Answer

Prescribe oral folinic acid 15mg daily for 3 days

Answer

Stop methotrexate permanently and avoid restarting

Answer

Reduce methotrexate dose to 10mg weekly and continue monitoring

Answer

Continue methotrexate but add prophylactic co-trimoxazole

Question 9

A 72-year-old man is started on digoxin for rate control in atrial fibrillation. Which of the following factors would require a dose reduction of digoxin?

Accepted Answer

eGFR of 35ml/min/1.73m²

Answer

Body weight of 95kg

Answer

Concurrent use of bisoprolol

Answer

History of hypertension

Answer

Age over 70 years alone

Question 10

A 45-year-old woman with type 1 diabetes mellitus is admitted with diabetic ketoacidosis. After initial resuscitation with intravenous fluids and insulin infusion, her blood glucose drops from 28mmol/L to 14mmol/L within 2 hours. Her pH is 7.18 and ketones remain elevated at 4.2mmol/L. What is the most appropriate next step in insulin management?

Accepted Answer

Continue the insulin infusion at the same rate and add 10% glucose

Answer

Stop the insulin infusion until ketones normalize

Answer

Reduce the insulin infusion rate by half and continue monitoring

Answer

Switch from intravenous to subcutaneous insulin immediately

Answer

Increase the insulin infusion rate to clear ketones more rapidly

Safe Prescribing — MCQs

Safe Prescribing — MCQs

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