[TDM] Drug monitoring

Question 1

Hydroxychloroquine - when starting medication

Answer 1

Check visual acuity and fundoscopy - may result in a severe and permanent retinopathy

Question 2

How should you check tacrolimus levels?

Answer 2

Measuring a trough level before the morning or evening dose is the correct way to check a tacrolimus level.

After a transplant, the optimal level might be 6–10 ng/mL.

Question 3

What does the initial dose of ramipril depend on?

Answer 3

Renal function

Renal function and electrolytes should be checked before starting ACE inhibitors (or increasing the dose) and monitored during treatment (more frequently if side effects mentioned are present).

Question 4

What should predose ‘trough’ concentrations of vancomycin be?

Answer 4

10–15 mg/L

Question 5

If ferrous sulphate 1 tablet daily is not tolerated, what should you do?

Answer 5

Reduced if not tolerated to 1 tablet once daily on alternate days.

Question 6

How long should iron replacement (e.g. with ferrous sulphate) be given for?

Answer 6

Monitor haemoglobin concentration within the first 4 weeks of treatment, then regularly thereafter to assess response (e.g. every 4 weeks).

Once haemoglobin is within the normal range, treatment should be continued for around a further 3 months to replenish the iron stores.

Question 7

What will provide the most accurate plasma-digoxin concentration?

Answer 7

Level taken at least 6 hours post dose

Question 8

What is important to monitor when phenytoin is given IV?

Answer 8

ECG - associated with cardiac arrhythmias!

Question 9

When a patient is on aminophylline, what level is monitored and when?

Answer 9

The ideal level for theophylline is 10–20 mg/L.

Aminophylline is monitored therapeutically in terms of plasma-theophylline concentrations; a blood sample should be taken 4–6 hours after starting treatment.

It is worth noting that it is not an ‘aminophylline’ level that is checked, but a ‘theophylline’ level. Aminophylline is a simply a stable mixture of combined theophylline and ethylenediamine.

Question 10

How should aminophylline be given?

Answer 10

Over at least 20 minutes (by very slow IV infusion)

Question 11

What should be monitored by a GP when a patient takes fluoxetine?

Answer 11

The presence of a rash

Question 12

How is the dose of enoxaparin determined?

Answer 12

dose-adjusted in low eGFRs (<30 mL/min) but also in adults under 50 kg to prevent excessive anticoagulation

Note that patients under 50 kg should also have lower dose paracetamol to prevent hepatotoxicity.

Question 13

In a patient at risk of hypercapnic respiratory failure, what should be monitored?

Answer 13

ABG

Ventilation (non-invasive or invasive) may be required if this patient develops hypercapnic respiratory failure.

Peripheral oxygen saturations should be monitored continuously, however, will not detect a rise in carbon dioxide levels.

Question 14

What to check 15 mins after starting a blood transfusion to detect risk of acute tranfusion reaction>

Answer 14

Heart rate, blood pressure and temperature

Question 15

What should be monitored when enoxaparin is given?

Answer 15

Platelet counts should be measured just before treatment with unfractionated or low molecular weight heparin, and regular monitoring of platelet counts may be required if given for longer than 4 days.

ALSO: potassium

Can cause heparin-induced thrombocytopenia.

Question 16

Which electrolyte should be monitored in patients taking enoxaparin?

Answer 16

Potassium

This is because enoxaparin and unfractioned heparin can inhibit aldosterone, therefore causing a rise in serum potassium. An increased risk of hyperkalaemia is seen in chronic renal failure, acidosis, diabetes mellitus and those with a high starting potassium.

Question 17

When is anti-factor Xa activity indicated in patients taking heparin?

Answer 17

Increased risk of bleeding (e.g. in renal impairment and those who are underweight or overweight).

Question 18

Frequency of monitoring of FBC with clozapine use

Answer 18

Every week for the first 18 weeks and every second week up to 1 year

Question 19

How often should lithium levels be checked?

Answer 19

Serum lithium level should be re-checked one week after every dose change and then weekly until levels are stable. Following stabilisation of lithium levels, they can be monitored every 3 months. Lithium levels are usually checked 12 hours post-dose. Toxicity occurs at serum levels above 1.5mmol/L.

Urea & electrolytes should be checked at least every 6 months. If there is a decline in renal function, then monitoring should occur more regularly.

Serum calcium level should be checked at least every 6 months. Lithium can cause hyperparathyroidism and hypercalcaemia.

Thyroid function tests should be checked every 6 months due to the risk of thyrotoxicosis.

An electrocardiogram should be performed prior to commencing lithium therapy.

Question 20

Follow up checks for COCP use?

Answer 20

Weight + Blood pressure

All women who are on combined oral contraceptive pills should have their weight and blood pressure recorded before beginning therapy and as part of their follow-up. This is because women who are on the pill are at increased risk of developing hypertension and therefore are at increased risk of myocardial infarction and haemorrhagic stroke. There has been debate as to whether the pill causes significant weight gain, with some studies finding only a small percentage increase in some participants’ weight. However, weight should be checked routinely, as if a patient’s BMI is 35 or greater, they should be on a more suitable form of contraception.

Question 21

Most appropriate set of blood tests to monitor for the risk of adverse effects associated with methotrexate therapy.

Answer 21

FBC, U&Es, LFTs

Patients on methotrexate are at risk of blood dyscrasias. This includes severe anaemia, leukopenia, and thrombocytopenia. Therefore, a full blood count is required. Additionally, methotrexate can lead to liver cirrhosis and so LFTs must also be checked. These blood tests should be checked every 1-2 weeks until therapy is stabilised. After this, patients can have their blood checked every 2-3 months.

Patients on methotrexate should be advised to let their GP know of any signs of infection, for example, sore throat, fever, shortness of breath or fatigue.

Question 22

When using insulin-glucose infusion for hyperkalaemia, what should be monitored?

Answer 22

Capillary blood glucose should be monitored throughout the insulin-glucose infusion due to the risk of hypoglycaemia. The Renal Association guidelines on the management of hyperkalaemia advise blood glucose levels should be monitored at regular intervals up to 12 hours following the administration of an insulin-glucose infusion.

Question 23

Conditions in which target INR of 2.5 is recommended?

Answer 23

• mitral valve replacement
• deep-vein thrombosis or pulmonary embolism
• atrial fibrillation
• cardioversion
• dilated cardiomyopathy
• mitral stenosis or regurgitation in patients with either atrial fibrillation, a history of systemic embolism, a left atrial thrombus, or an enlarged left atrium
• acute arterial embolism requiring embolectomy

Question 24

Levothyroxine - TSH requirements?

Answer 24

Consider measuring thyroid stimulating hormone (TSH) level every three months until stabilised (two similar measurements within the reference range, 3 months apart), then yearly thereafter.

Question 25

Investigations to perform before starting amiodarone

Answer 25

CXR, ECG, U&Es, TFTs, LFTs

Question 26

Most appropriate option to monitor for the adverse effects of atorvastatin after 3 months of treatment.

Answer 26

Liver function tests should be repeated within 3 months of starting treatment and again at 12 months according to NICE guidelines. Use of statins can cause liver injury and hepatotoxicity, although liver failure is rare.

Question 27

Monitoring for rivaroxaban

Answer 27

Patient-reported symptoms

Patients should be monitored for signs of bleeding or anaemia; treatment should be stopped if severe bleeding occurs.

No routine anticoagulant monitoring required (INR tests are unreliable).

Question 28

What should be checked before changing the dose of ACE inhibitors?

Answer 28

Renal function and electrolytes should be checked before starting ACE inhibitors (or increasing the dose) and monitored during treatment (more frequently if side effects mentioned are present).

Question 29

What are the most appropriate investigations which should be checked after 6 months of treatment to monitor for adverse effects of lithium therapy?

Answer 29

BMI, U&Es, TFTs

According to the BNF, patients on lithium therapy should have their TFTs and U&Es checked before beginning therapy. If the patient has cardiovascular disease or risk factors for it, they should also have an ECG performed.

Every 6 months, patients on lithium should have their BMI, U&Es (including eGFR), and TFTs checked. They should have them checked over a shorter interval if there is any evidence of impaired renal or thyroid function or raised calcium levels.

Rationale for monitoring:
* BMI is monitored as lithium is associated with weight gain.
* U&Es are monitored because lithium is associated with electrolyte disturbances and renal impairment.
* TFTs are monitored as lithium can cause hypothyroidism.
* ECGs are recommended in some patients due to the association of lithium and atrioventricular block as well as cardiomyopathy.

Question 30

Gentamicin multiple daily dosing - changing interval vs dose?

Answer 30

Trough high= Increase interval

Peak high= Decrease dose