Clinical Pharmacology and Toxicology question bank

Pharmacology

Clinical pharmacology relates to the study of drugs in humans. The discipline studies the ways in which drugs alter biological systems in an attempt to improve health and stop disease.

Clinical toxicology is also concerned about the impact of drugs and other chemicals on humans. But is more focussed around the investigation, diagnosis and management of suspected poisoning.

Our multiple choice question bank for Clinical Pharmacology and Toxicology has been designed to give you examples of the kinds of questions you may get in your medical student exams.

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Overdose with paracetamol and anorexia

A nineteen year old presents to accident and emergency following a witnessed overdose of 18 paracetamol tablets two hours prior to her admission to hospital. She suffers from anorexia nervosa and has a BMI of 15. Which of the following is true?

  • She will definitely not require the antidote
  • She will definitely will require the antidote
  • She needs an immediate blood test and then a decision requiring antidote therapy
  • She can be safely discharged
  • None of the other answers are correct

Treatment of paracetamol overdose following a single ingested dose of paracetamol at one time is guided in general by a paracetamol level taken at least 4 hours post the time of the overdose. Clearly here a 2 hour level may give a false reassurance if the level appears to be “quite low”. Patients are often referred to be as being “above” or “below” the treatment line. There is a graph in the BNF suggesting levels above which patients should be treated depending on their “levels”

I.E. FOR EXAM PURPOSES DO A FOUR HOUR LEVEL

SHE IS “HIGH RISK”

EXTREME care should be taken in paracetamol overdose questions in the exam. Staggered overdoses (e.g. 4 tablets last night 16 this morning and 10tablets 5 hours ago) is trouble as you cannot safely rely on levels.

The patient stays in A&E and has a 4 hour paracetamol level taken (4 hours after the overdose). The nurse says she’s below the “normal” treatment line and therefore does not require the antidote. Which of the following statements is correct?

Please select 2 answers:

  • She may require treatment because she may have ingested 4 units of alcohol already that day
  • She may require treatment if she has also taken aspirin tablets
  • She may require treatment if she drinks >80 units of alcohol per week
  • She may require treatment because she is anorexic
  • She should be treated irrespective of her paracetamol level until a repeat blood test is done
  • She will require treatment if she normally takes citalopram
  • She will require treatment if she normally takes fluoxetine

Patients with any of the following conditions may require treatment a separate treatment line (a high risk treatment line).

Low BMI / malnourished (HIV anorexia etc)
Taking “enzyme inducers” e.g. rifampicin
St Johns wort

e.g. 4 hour treatment line for treatment high risk= approx 100mg/l paracetamol
e.g. 4 hour treatment line for treatment “normal” risk= approx 200mg/l paracetamol

Phenytoin side effects

A 26 year old hairdresser develops has a single tonic clonic fit whilst at work, unrelated to any substance misuse or head injury. She is sexually active. She takes the oral contraceptive pill. Which of the following statements are true?

Please select UP TO 2 answers.

Antiepileptic medicine (assuming no obvious contraindications) is always advised following a fit in these circumstances
Phenytoin will reduce the efficacy of her contraception
Phenytoin will increase the efficacy of her contraception
Phenytoin will have no effect on the the efficacy of her contraception
Phenytoin is potentially tetratogenic
She will be legally unable to drive for the next six months only
In common with most other drugs phenytoin is metabolised by “first order metabolism”


Phenytoin is an enzyme inducer and will therefore affect her oral contraceptive pill making it potentially less effective.

Most antiepileptics are p[potentially tetratogenic. You can’t Drive (DVLA) for 1 year after an unprovoked seizure or “first fit”.

After a “first fit” antiepileptic medication is not always indicated. Many physicians prefer to adopt a “watch and wait” approach pending the investigations etc. If no underlying precipitant is found, general advice and follow up can be undertaken.

Phenytoin like alcohol is metabolised by zero order kinetics. This will be dealt with in a separate question.

Anaphylaxis and adrenaline

What is the correct dose in micrograms for the initial treatment of a conscious patients suffering from anaphylaxis?

  • 0.1 ml of adrenaline 1 in 1000
  • 0.5 ml of adrenaline 1 in 1000
  • 10 ml of adrenaline 1 in 10 000
  • 1ml of adrenaline 1 in 10 000
  • 0.1 ml of adrenaline 1 in 10 000

The dose you need to give is 0.5-1mg
This is something you just have to know…

Adrenaline is confusingly found in strengths 1 in 10000 and 1 in 1000.
1 in 1000 means 1 gram in 1000ml
1 in 10000 means 1 gram in 10000 my of dilutent
The dose you need to give is 0.5-1mg
This equates to 1 ml of adrenaline 1 in 1000.

10 ml of 1 in 10000 is 1mg but this strength is primarily reserved for IV use (you would struggle to inject 10ml IM)

Breast feeding

Should you advise patients to avoid Methotrexate whilst breast feeding?

(you can use the BNF to help you answer this question)

You need to refer to the summary of product characteristics: the full summary of product characteristics is not found in the BNF.

This information is not found in either the BNF or the summary of product characteristics, but can be found elsewhere.

For breast feeding: Appendix 5 in the back of the BNF.

See Methotrexate: you’re redirected to cytotoxic drugs and the advice is avoid.

Dosage abbreviations

What do the following dosage abbreviations mean?

  • PO
  • PR
  • INH
  • S/L
  • PRN
  • IV
  • IM
  • PV

Accepted medical abbreviations in many hospitals include the following:
PO = Oral
PR = Per Rectum
INH = Inhaled
S/L = Sub lingual
PRN = As required (pro re nata =as the occassion arises)
IV = INtravenous
IM = intramuscular
PV = Per Vagina

Other notes:
Statins are usually given at night, Atorvastatin can be given at any time of day.
Methotrexate is once a week
GTN spray is for angina
Diazepam PR is often scripted for care homes who look after patients with epilepsy who will not have IV access or medical practitioners on site to insert it
Digoxin dose is in Microgramms
Enoxaparin S/C is one of a number of low molecular weight heparin (LMWH) drugs used in deep vein thrombosis (DVT) prophylaxis

Dose entries

Calculate the following dose entries:

  • Dose of aspirin for acute myocardial infaction
  • Dose of diazepam in patient having epileptic seivure (i.v.)
  • Dose of furosemide IV for initial treatment of pulmonary oedema
  • Treatment dose of enoxaparin once daily in pulmonary embolism daily in a 80kg man
  • Initial dose of diamorphine for acute pain in a patient with a suspected myocardial infarction

Dose of aspirin for acute myocardial infaction

Suspected MI / Acute coronary syndrome for exams the following drugs and doses can be used:
Aspirin 300mg PO
Oxygen high flow (e.g. 15/l min rebreathe mask)
Nitrate (e.g. 2 puffs GTN)
Clopirdogel 300mg PO
Diamorphine 2.5-5mg
LMWH S/c e.g. enoxaparin 1mg/kg

Dose of diazepam in patient having epileptic seivure (i.v.)

The equivalent dose of lorazepam is 2-4mg. Diazepam can be given IV or PR at the same dose. It has a short half life. Benzodiazepine effect can be reversed by flumazenil but extreme caution should be used because of the risk of seizure following administration.

Dose of furosemide IV for initial treatment of pulmonary oedema

IV furosemide is given at a dose of 40-100mg initially. It comes in 50mg vials. Therefore prefer to prescibe either 50 or 100mg IV. Higher doses are needed for renal failure. Caution in hypostensive patients (e.g. Systolic BP <100mmhg). Furosemide effect is not simply from diuresis it has effects on the pulmonary vascular bed.

Treatment dose of enoxaparin once daily in pulmonary embolism daily in a 80kg man

DVT and PE treatment doses of LMWH= 1.5mg/kg = 120mg once daily. Enoxaparin is a LMWH anticoagulant and at this dose will have a similar therapeutic effect to a warfarinised patinet with an INR of approximately 2-3.[Unstable angina\: enoxaparin dose is different- 1mg kg BD].

Initial dose of diamorphine for acute pain in a patient with a suspected myocardial infarction

For exam purposes for a typical patient not currently taking morphine: Acute pain relief with diamorphine for severe pain is 2.5-5mg initially.

Match drugs and side effects

What are the commoner side effects of the following drugs?

  • Beta blockers
  • Digoxin
  • Calcium channel blockers
  • Spirinolactone
  • Statins
  • Corticosteroids

Beta blockers block both beta 1 and beta 2 receptors so their side effects as well as acting on the heart are seen elsewhere e.g. in the form of bronchospasm, bradycardia etc.

Digoxin toxicity can occur in patients on a stable dose of digoxin who develop another problem e.g. overdose/ acute renal impairment (part of digoxin is renally excreted).

Calcium channel blockers commonly cause peripheral oedema.

Spirinolactone is one of a numebr of causes of gynecomastia including oestrogen therapy, cannabis, chronic liver disease etc.

Statins classically cause muscle cramps and in extreme cases rhabdomyolysis.

Corticosteroids e.g. prednisolone have side effects including those listed along with fluid retention, weight gain, thin skin, hypertension etc.

Match drugs with contraindication

What is the specific relative contraindication of each of these drugs?

  • Septrin
  • NSAIDs
  • Haloperidol
  • Metformin

Septrin contains trimethoprim and sulfamethoxazole [1 part trimethoprim to 5 parts sulfamethoxazole]. Betablockers and Verapamil can cause complete heart block and should not be prescribed without specialist supervision.

NSAIDs can precipitate asthma.

Haloperidol can cause extra pyramidal side effects i.e. parkonsonian symptoms, dystonia, akathisia and tardive dyskinesia. Its therfore not reccomended with parkinsons disease.

Metformin is a Biguanide used in the treatment of type 2 diabetes. Metformin can cause a metabolic acidosis and is essentially contraindicated in patients with a creatinine of >150. It should also be omitted prior to angiography because of the risks of contrast nephropathy.

Nebuliser question

A 26 year old fit and well asthmatic present with wheeze and is diagnosed as having an acute asthma attack.

Assuming she have no other co morbidities what is the preferred route of delivery for the salbutamol?

  • Nebulised via air
  • Nebulised via oxygen high flow
  • Inhaler
  • Inhaler with spacer
  • Intravenous

The correct answer is nebulised via Oxygen.

You can nebulise via medical “air”: air in a medical cylinder. This is useful in some forms of chronic obstructive pulmonary disease.

A nebuliser is more effective at delivering the salbutamol locally. Although IV salbutamol can be used it should be only be directed by a seniour medical doctor under close supervision.

However in acute asthma you want to deliver oxygen and salbutamol at the same time: you can mix ipratropium and salbutamol in the nebuliser and then “drive” the nebuliser by turning up the oxygen.

Paracetamol “antidote”

Which of the following is the “antidote” used in paracetamol?

  • N acetylcysteine
  • 5 amino Salicylate
  • Acetylcholinesterase
  • Pabrinex
  • Haemofiltration

N acetylcysteine.

Do not confuse N acetylcysteine (parvolex) with pabrinex.

Treatment is given over a set of quite complex infusion schedules over 24 hours. There is advice given on the calculation of doses in the BNF.

Paracetamol overdose

A healthy female is treated with NAC for a paracetamol overdose.

The patient goes on to have an infusion of 6g acetylcysteine.

10 minutes later you are called to her with the following set of observations.

  • RR36
  • Sats 89% Air
  • BP 80/40
  • There is no lip or tongue swelling. She is wheezy. She has chest tightness.

Her observations had previously been all normal. What is the most likely diagnosis?

  • Acute severe asthma
  • Upper GI bleed
  • Epiglottitis
  • Myocardial infarction
  • Anaphylaxis

Acetlycysteine can commonly cause adverse events including anaphylaxis.

In this situation where a person has been relatively well shortly beforehand this is the most likely diagnosis.

During anaphylaxis common symptoms are syncope/ wheezing/ stridor/ abdominal pain/ collapse/ breathlessness/ rash.

The infusion should be stopped and emergency treatment instigated using the ABC approach.

You assess the patient and correctly identify that she is suffering from anaphylaxis. What is the initial treatment of choice following oxygen/ ABC approach? (IV=intravenous IM =intramuscular)

  • Adrenaline IV
  • Adrenaline IM
  • Hydrocortisone IV
  • Hydrocortisone IM
  • Chlorphenamine IV

Adrenaline IM.

This is important!

It’s anaphylaxis adrenaline is give IM e.g. upper outer quadrant of the thigh.

In anaphylaxis IV adrenaline is not safe for use by practitioners not experienced in its use in extreme conditions. It should only be given by practitioners experienced in its use in a closely monitored environment (e.g. ITU).

IV adrenaline is used in cardiac arrests for a number of indications and this should not be confused when dealing with a conscious patient with anaphylaxis.

Hydrocortisone and chlorphenamine are both important adjuncts but the fast acting treatment of choice is adrenaline. IV hydrocortisone will take >30 minutes to have any appreciable clinical effect.

Pregnant lady prescription

A pregnant lady presents with a productive cough and fever. She is producing green phlegm. Her GP feels she needs antibiotics.

He prescribes the following:

Patient ID
Mrs A Star
1/1/861
Star Street
Starland

Hospital no:334567
Special Instructions
PREGNANT
Allergies
Ciprofloxacin
Name
Amoxycillin

RouteOral

Frequecy
TDS
Dose
500 mg

Comments
Nil
Time given
0800
1400
2200

Which of the following statements is correct?

  • Incorrect route
  • Incorrrect dose
  • Incorrect frequency
  • Correct prescription
  • Contraindicated drug

Contraindicated drug.

Check the BNF appendices at the back for useful information on:

Pregnancy
Renal Impairment
Interactions
Breast feeding

Nothing is ever truly “safe” however common drugs given in pregnancy include paracetamol and amoxycillin.

Prescription analysis

A 54 year old lady is a new patient at her GP surgery having moved house. She has taken methotrexate for several years and told the GP she takes 6 (six) 2.5mg tablets daily.

Patient ID
Mr A Pain
1/1/431
Pain Street
Painland
Hospital no:334867
Special InstructionsAllergies
Nystatin
Name
Methotrexate

Route
oral

Frequency
OD
Dose
15 mg

Comments
Nil
Time given
0800

Which of the following statements is correct?

(You can and should use the BNF to assist you answering this question).

  • Incorrect frequency of medication
  • Incorrect route
  • Incorrect dose of methotrexate (i.e. not 15mg)
  • Correct prescription
  • Contraindicated drug

  1. Incorrect frequency of medication
  2. Incorrect route
  3. Contraindicated drug

OD = once daily
BD = twice daily
TDS = three times a day
QDS = four times a day

But… Methotrexate is given once weekly. This prescribing error has lead the MHRA (Medicines and Healthcare Regulation Agency) to issue strict guidelines on this.

Although it has a short half life (approx 12 hours) if given daily it will rapidly accumulate producing toxicity including:

Marrow suppression and bone marrow failure
Bruising
Hepatitis
Acute renal failure

Prescription error

Look at the following sample prescription (you may use your BNF for this question)

Mr Pan has been bitten by a dog and his family doctor is a little concerned. Having cleaned the wound he gives a course of antibiotics.

Patient ID
Mr Peter Pan
1/1/391
Boat Street
Fairlyand

Hospital no:234567
Special InstructionsAllergies

Penicillin
Name
CO-AMOXICLAV

Route
Oral

Frequecy
QDS
Dose

625 mg

Comments
Time given

0800
1200
1800
2200

What is the most important error on this prescription?

  • Incorrect route
  • Incorrrect dose
  • Incorrect frequency
  • Coamoxiclav is not indicated for this condition
  • Contraindicated drug

Dose etc. are all correct.

The trick here is the penicillin allergy which means Penicillin and its derivatives are all essentially contraindicated until a further allergy history is taken.

Cephalosporins also have a cross reactivity in penicillin allerygy that may approach 10%. Therefore for exam purposes I would also consider these drugs contraindicated (e.g. cefuroxime).

For exam purposes in these instances senior support or microbiological advice is often suggested if no alternative is obvious.

Although co-amoxiclav is normally given 3 times a day, 4 times a day is still within a reasonable dose range.

A further history is taken from Mr Pan about his “penicillin allergy”.

He tells you he has taken penicillin on 3 occasions and completed the course. However he tells you.

On the first occasion after 3 days he vomited and he think the drug made him feel sick (but completed the course).

On the second occasion it was for an infection and he had a rash on his feet but no other ill effects (completed the course).

On the third occasion he had diarrhoea. (Stopped the course after 4 days).

He tells you he spoke to a friend who was a medical student and was told he must be allergic to penicillin. You check his notes and confirm he has received the prescriptions.

Should he be recorded as having a penicillin allergy for the purposes of his notes?

  • Yes but he can probably take penicillin in the future
  • Yes and he should not be given furhter penicillin or its derivatives
  • Not allergic: if needed can safely be prescribed penicillin in the future
  • Not allergic : however should not be prescribed penicillin in the future
  • Should not take penicillin again but can take amoxycillin

HE IS NOT PENICILLIN ALLERGIC ON THE BASIS OF THIS HISTORY!

Adverse drug reactions are common and side effects are common. Each of these symptoms could be considered a side effect but this doesn’t mena that the drug is contraindicated.

There may be a time in the future where withholding penicillin inappropriately could harm the patient.

Review prescription

Look at the following sample prescription (you may use your BNF for this question)

Patient ID
Mr Andres Aardvark
1/1/321
Zoo Street
Timbuktu

Hospital no:123456
Special InstructionsAllergies
NKDA
Name  
Digoxin

Route  
Oral

Frequency 
OD
Dose
125 mcg

Comments
Monitor levels periodically
Time given
0800

What is the most important error on this prescription?

  • Incorrect route
  • Incorrect dose
  • Incorrect frequency
  • You never need to check digoxin levels
  • Contraindicated drug

The dose of digoxin is in MICROGRAMS. DO NOT write microgrammes as mcg it is not acceptable.

DO write microgrammes out in full. In this case a typical dose of digoxin is 125 microgrammes.

What is this diagnosis?

Healthy female treated with NAC for paracetamol overdose
The patient goes on to have the infusion of acetylcysteine.
10 minutes later you are called to her with the following set of observations.

  • RR36
  • Sats 89% Air
  • BP 80/40

There is no lip or tongue swelling. She is wheezy. She has chest tightness.

Her observations had previously been all normal. What is the most likely diagnosis?

  • Acute severe asthma
  • Upper GI bleed
  • Epiglottitis
  • Myocardial infarction
  • Anaphylaxis

Acetlycysteine can commonly cause adverse events including anaphylaxis.
In this situation where a person has been relatively well shortly beforehand this is the most likely diagnosis.
During anaphylaxis common symptoms are:
Syncope/ wheezing/ stridor/ abdominal pain/ collapse/ breathlessness/ rash
The infusion should be stopped and emergency treatment instigated using the ABC approach.