Commonly Prescribed Medications

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Introduction

In the UK, 1.12 billion prescription items were dispensed in the community in 2019.¹ Of these, just ten medications made up 33% (373 million) of all prescriptions.²

These commonly prescribed medications are frequently encountered in clinical practice and medical exams, including the prescribing safety assessment (PSA) and OSCEs.

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Atorvastatin

Indications

Common indications for atorvastatin include primary and secondary prevention of cardiovascular disease.⁴ Other indications include familial hypercholesteremia.

Mechanism of action

Atorvastatin belongs to a class of drugs called statins. Its primary mechanism of action is to inhibit 5-HMG-CoA reductase, an enzyme used to synthesise cholesterol.³

Dose

Typical drug dosing (oral) for atorvastatin:⁴

• Primary prevention of cardiovascular events: 20mg once daily; atorvastatin can be increased up to 80mg once daily
• Secondary prevention of cardiovascular events: 80mg once daily

Side effects

Side effects of atorvastatin include joint pain (arthralgia), muscle discomfort (myalgia), nausea & vomiting, flatulence, constipation and gastrointestinal discomfort.⁴

Key counselling points

Blood test monitoring is required for statins. Patients should be informed that blood tests will be required before and during treatment:

• Before starting statins: lipid profile, triglyceride concentrations, liver function tests (LFTs), thyroid stimulating hormone (TSH) and renal function
• During treatment: LFTs repeated three monthly and at 12 months. If >3 times the upper limit of normal, stop atorvastatin therapy.

Patients should be counselled on the risk of rhabdomyolysis (breakdown of muscle tissue) and informed to seek medical advice if they develop unexplained muscle pain.

Drug-drug interactions

A significant drug-drug interaction is between statins and macrolide antibiotics (e.g. clarithromycin).

Macrolides inhibit CYP450 enzymes resulting in increased exposure to statins; this could lead to rhabdomyolysis. Consider a different antibiotic or stopping atorvastatin during a course of macrolide antibiotics.

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Levothyroxine

Indications

Levothyroxine is commonly used to treat hypothyroidism. It is also used in hyperthyroidism to replace thyroid hormones when using carbimazole (‘block and replace’).⁵

Mechanism of action

Levothyroxine is a synthetic T4 hormone (thyroxine). It is identical to the natural one the thyroid produces.³

Dose

Typical drug dosing (oral) for levothyroxine:^5,6  

• Primary hypothyroidism (adult): initially 1.6 micrograms/kg once daily; rounding dose to nearest 25 micrograms. This usually works out to be 50-100 micrograms once daily. Adjusted based on response to 100-200 micrograms once daily.
• Primary hypothyroidism (elderly): initially 25-50 micrograms once daily; increase in steps of 25 micrograms every four weeks based on response.

Side effects

Side effects are usually due to excess dosing of levothyroxine which causes symptoms of hyperthyroidism. This includes anxiety, restlessness, flushing/sweating, fine tremors, diarrhoea, nausea & vomiting.⁵

Key counselling points

Advise patients to take levothyroxine in the morning, 30 minutes before breakfast and drinks containing caffeine. Absorption of levothyroxine is reduced by food and caffeine.^5,6

Antacids, calcium, and iron supplements may also affect the absorption of levothyroxine. Patients should be advised to separate drug dosing by at least four hours.^5,6

Monitoring of TSH is required for levothyroxine. TSH is monitored every three months until stable, with dosing adjustment if required. Afterwards, TSH is then monitored once yearly.^5,6

Drug-drug interactions

Most medications which interact affect levothyroxine absorption (e.g. antacids, calcium and iron supplements). 

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Omeprazole

Indications

Omeprazole is commonly prescribed for gastro-oesophageal reflux disease (GORD), prevention of gastric & duodenal ulcers (e.g. concurrent use of NSAIDs or steroids) and indigestion (dyspepsia). It is also used for the treatment of gastric & duodenal ulcers and Helicobacter pylori in combination with other medications.⁷

Mechanism of action

Omeprazole is a proton-pump inhibitor (PPI). It irreversibly binds to the H⁺/K⁺ ATPase pump, inhibiting acid (H⁺) secretion.³

Dose

Typical drug dosing (oral) for omeprazole:³

• Gastro-oesophageal reflux disease (GORD): 20mg once daily for 4 or 8 weeks
• Gastric ulceration: 20mg once daily for eight weeks (if symptoms persist, can be increased to 40mg once daily)
• Duodenal ulceration: 20mg once daily for four weeks (if symptoms persist, can be increased to 40mg once daily)
• Functional dyspepsia: 10 mg once daily for four weeks
• Uninvestigated dyspepsia: 20mg once daily for four weeks

Side effects

The most common side effects of omeprazole are related to the gastrointestinal system. These include nausea & vomiting, stomach pain, constipation and flatulence.^7,8

Key counselling points

Patients should be made aware of the long-term side effects of taking omeprazole. These include an increased risk of osteoporosis, Clostridium difficile infection, hypomagnesaemia and vitamin B₁₂ deficiency.^7,8

Drug-drug interactions

Omeprazole is relatively safe. However, there are several important drug-drug interactions to be aware of:^7,8 

• Selective serotonin reuptake inhibitors (e.g. citalopram, escitalopram): omeprazole increases SSRI exposure. The same enzyme metabolises omeprazole and SSRIs (CYP2C19).⁹
• Clopidogrel: omeprazole reduces effectiveness of clopidogrel. Omeprazole and clopidogrel are metabolised by the same enzyme (CYP2C19).¹⁰
• Methotrexate: omeprazole increases exposure to methotrexate as it inhibits renal elimination of methotrexate.¹¹

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Lansoprazole

Indications

Like omeprazole, lansoprazole is another type of proton pump inhibitor. The indications are similar, with common indications being gastro-oesophageal reflux disease (GORD), prevention of gastric & duodenal ulcers (e.g. concurrent use of NSAIDs or steroids) and indigestion (dyspepsia).¹⁵

Mechanism of action

Lansoprazole is a PPI. It works by irreversibly binding on to H⁺/K⁺ ATPase pump, inhibiting acid (H⁺) secretion.¹⁵

Dose

Typical drug dosing (oral) for lansoprazole:¹⁵

• GORD: 30mg once daily for four weeks, continued for further four weeks if required (maintenance dose of 15-30 mg once daily, taken in the morning)
• Gastric ulceration: 30mg once daily for eight weeks, taken in the morning
• Duodenal ulceration: 30mg once daily for four weeks, taken in the morning (maintenance dose of 15mg once daily)
• Functional dyspepsia: 15mg once daily for four weeks
• Uninvestigated dyspepsia: 30mg once daily for four weeks

Side effects and key counselling points

As both lansoprazole and omeprazole belong to the same class of medications. Side effects and counselling points are the same.

Drug-drug interactions

Like omeprazole, lansoprazole also interacts with SSRIs and methotrexate. However, lansoprazole does not interact with clopidogrel.^15,16

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Amlodipine

Indications

Amlodipine is used for hypertension and angina.¹²

Mechanism of action

Amlodipine belongs to a class of medications known as dihydropyridine calcium channel blockers (CCBs).

As the name suggests, it acts on calcium channels and inhibits calcium influx in vascular smooth muscle. This results in reduced contractility and vasodilation.³

Dose

Typical drug dosing (oral) for amlodipine is initially 5mg once daily (can be increased to 10mg once daily).¹²

Side effects

The common side effects of amlodipine are associated with its mechanism of action (vasodilation of blood vessels).¹²

These include dizziness, flushing, palpitations, headaches, peripheral oedema (usually leg swelling) and headaches.

Key counselling points

Inform patients that amlodipine may make them feel dizzy. If this occurs, they should not operate heavy machinery or tools (e.g. cars).¹²

Patients should also know that blood pressure monitoring will be required during treatment.

Drug-drug interactions

Amlodipine and other CCBs used in treating hypertension and angina (dihydropyridines CCBs) interact with diltiazem and verapamil (non-dihydropyridine CCBs).

As these medications act on similar receptors, taking both simultaneously increases the risk of side effects and arrhythmias. Therefore, they should be carefully monitored when used together.

Amlodipine is known to interact with simvastatin. Both amlodipine and simvastatin are inhibitors of CYP3A4. This results in increased levels of simvastatin and an increased risk of rhabdomyolysis. It is recommended that patients on amlodipine only have simvastatin at a maximum dose of 20mg daily (or are switched to an alternative statin).

CCBs are commonly used with other anti-hypertensive medications (e.g. ramipril). This may cause hypotension. Patients should be carefully monitored for hypotensive symptoms.

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Ramipril

Indications

The most common use of ramipril is for hypertension. Other uses include heart failure, following myocardial infarction and proteinuric renal disease.¹⁴

Mechanism of action

Ramipril belongs to a class of medications known as ACE (angiotensin-converting enzyme) inhibitors. They act on the renin aldosterone system (RAA) by preventing the conversion of angiotensin I to angiotensin II, a vasoconstrictor. ACE inhibitors result in arterial smooth muscle vasodilation leading to lower blood pressure.³

Dose

Typical drug dosing (oral) for ramipril is an initial dose of 1.25 – 2.5mg once daily. It can be increased up to 10mg once daily. The dose is increased in intervals of 2-4 weeks.¹⁴

Side effects

A dry cough is a common side effect due to the accumulation of bradykinin.

ACE inhibitors can cause hyperkalemia as a result of reduced aldosterone synthesis. Monitoring potassium when starting treatment with ramipril or increasing the dose is important. 

Angioedema is a serious side effect of ACE inhibitors. Angioedema may compromise the airway, and patients should stop ACE inhibitors immediately. This side-effect is thought to be due to the accumulation of bradykinin.^3,14

Key counselling points

Patients should be informed of the side effects of ramipril (dry cough and risk of angioedema).¹⁴

Blood test monitoring is required for ramipril to check renal function and electrolytes (particularly potassium). Blood pressure will be monitored, and doses of ramipril will be adjusted accordingly.

Drug-drug interactions

Ramipril can interact with non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. Taking both together can reduce renal function and increase the risk of hyperkalaemia.¹⁴

Ramipril interacts with lithium, a mood stabiliser with a narrow therapeutic range. Lithium is excreted in the kidney, and ramipril interferes with lithium excretion resulting in an increased lithium concentration.

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Bisoprolol

Indications

Bisoprolol is commonly used in hypertension, angina and heart failure. It is also used in atrial fibrillation and following myocardial infarction.¹⁷

Mechanism of action

Bisoprolol belongs to a class of medications known as beta-blockers. They exert their effect by antagonising (blocking) β₁ receptors of the autonomic nervous system.

This results in a slowing of the heart rate (negative chronotropic effect) and reduced contractility of the heart (negative inotropic effect).

Dose

Typical drug dosing (oral) for bisporolol:¹⁷

• Hypertension or angina: initially 5mg once daily (usual maintenance of 10mg once daily)
• Heart failure (alongside other medications): increased in increments and titrated for effect; doses range between 1.25mg-10mg once daily.

Side effects

Side effects of bisoprolol include coldness of the peripheries, headaches, syncope, erectile dysfunction, dizziness and hypotension.

Beta-blockers are associated with sleep disturbances (e.g. waking up at night and nightmares) as they cross the blood-brain barrier. This is less common among water-soluble beta-blockers (atenolol, celiprolol, nadolol and sotalol) as they are less likely to cross the blood-brain barrier.

Although uncommon, beta-blockers can cause bronchospasm. This is due to cross-reactivity with β₂ receptors responsible for bronchodilation. Therefore, it is generally advised to avoid prescribing beta blockers to patients with asthma.

Beta-blockers can also mask hypoglycemia symptoms due to suppressing autonomic responses of hypoglycemia (e.g. tachycardia, palpitations and tremor).

Key counselling points

When starting bisoprolol, advise patients on the side effects described above.¹⁸

Drug-drug interactions

Bisoprolol should not be prescribed with non-dihydropyridine CCBs (e.g. verapamil and diltiazem). Use of both concurrently may result in complete heart block.

Bisoprolol can be used with dihydropyridine CCBs (e.g. amlodipine, lercanidipine and felodipine) commonly used to treat hypertension.

Bisoprolol should not be given with amiodarone, an anti-arrhythmic. Use of both concurrently may result in complete heart block.

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Colecalciferol

Indications

Colecalciferol is used to treat and prevent vitamin D deficiency.¹⁹

Mechanism of action

Colecalciferol is a vitamin D₃ analogue. Vitamin D₃ is normally made in the skin through exposure to sunlight (UV radiation). It increases calcium levels in the blood.

Effects of vitamin D include increasing bone turnover (osteoclastic activity), calcium resorption in the kidney and calcium absorption in the gut.¹⁹

Dose

Typical drug dosing (oral) of colecalciferol:¹⁹

• Prevention of vitamin D deficiency: 400 units daily
• Treatment of vitamin D deficiency: loading dose (50,000 units) once weekly for six weeks) then maintenance dose (800-2000 units daily)

Side effects

Colecalciferol is usually well tolerated with minimal side effects.

Side effects are associated with increased calcium absorption due to the effects of vitamin D. This includes abdominal pain and nausea.¹⁹

Excess intake of colecalciferol may cause vitamin D toxicity and hypercalcemia.  

Key counselling points

Loading and treatment doses may be confusing to patients. It is important to provide appropriate counselling on how to take colecalciferol.¹⁹

Monitoring is required when treating vitamin D deficiency. Calcium levels should be checked within one month of the last loading dose or after starting the maintenance dose.

Drug-drug interactions

As colecalciferol is a vitamin D₃ analogue, there are no significant drug-drug interactions.¹⁹

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Metformin

Indications

Metformin is commonly used for the treatment of type 2 diabetes. Other uses include the treatment of polycystic ovary syndrome.²⁰

Mechanism of action

The mechanism of action of metformin is not fully understood.

Mechanisms may include reducing hepatic glucose production (gluconeogenesis) and increasing glucose uptake in skeletal muscle by increasing insulin sensitivity. These mechanisms help drive glucose out of the bloodstream.³

Dose

Typical drug dosing (oral) of metformin is initially 500mg once daily and increased gradually to 2 grams once daily.

Side effects

Gastrointestinal and taste disturbances (metallic taste) are common when taking metformin. Metformin may cause B₁₂ deficiency.

Metformin causes weight loss, and this may be seen as a benefit.²⁰

Although rare, there is a risk of lactic acidosis when taking metformin.

Key counselling points

Patients should be informed of the risk of lactic acidosis and to seek medical attention if this occurs. Symptoms of lactic acidosis include abdominal pain, nausea, vomiting, shortness of breath and muscle cramps.

Renal function should be monitored before treatment and yearly after starting metformin. Metformin should not be used if eGFR is <30 ml/min/1.37m².

If immediate-release metformin is not well-tolerated (e.g. due to gastrointestinal disturbances), modified-released metformin or other anti-diabetic drugs may be tried.²⁰

For more information, see the Geeky Medics guide to metformin counselling.

Drug-drug interactions

There are no major drug-drug interactions for metformin.²⁰

However, metformin is known to interact with intravenous contrast agents used in radiological investigations. Both can cause renal impairment and increase the risk of lactic acidosis. Withhold metformin for 48 hours before using intravenous contrast agents.

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Salbutamol

Indications

Salbutamol is a bronchodilator used for asthma and chronic obstructive pulmonary disease (COPD).²¹

Mechanism of action

Salbutamol is a selective β₂ agonist. Activation of β₂ receptors results in bronchodilation of bronchioles in the lungs, relieving bronchoconstriction.

Dose

Typical drug dosing (aerosol inhaled) is 1-2 puffs, up to 4 times daily when required.²¹

Side effects

Common side effects of salbutamol are related to the co-activation of β₁ receptors. These include tachycardia, headaches and tremor.²¹

In high doses, salbutamol can cause hypokalemia. This is clinically useful in treating hyperkalemia, where salbutamol nebulisers can be used to reduce potassium levels. 

Key counselling points

Effective inhaler technique is essential to optimising drug delivery and patients should be shown the correct inhaler technique.

Drug-drug interactions

Salbutamol is not known to have any significant drug-drug interactions.²¹

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Editor

Dr Chris Jefferies

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References

1. NHS Business Services Authority. Prescribing Costs for 2019 published. Published in 2020. Available from: [LINK]
2. Mackenna, B. What are the most commonly prescribed medicines? Top 10 prescribed medicines in NHS England primary care for 2019. Published in 2020. Available from: [LINK]
3. Ritter, JM. Flower, RJ. Henderson, G. Loke, YK. MacEwan, D. Rang. H. Rang & Dale’s Pharmacology 9^th 2018.
4. British National Formulary. Atorvastatin. Published in 2023. Available from: [LINK]
5. British National Formulary. Levothyroxine sodium. Published in 2023. Available from: [LINK]
6. NHS UK. Levothyroxine. Published in 2021. Available from: [LINK]
7. British National Formulary. Omeprazole. Published in 2023. Available from: [LINK]
8. NHS UK. Omeprazole. Published in 2021. Available from: [LINK]
9. Interaction Between Omeprazole and Citalopram/Escitalopram. Published in 2014. Available from: [LINK]
10. GOV UK. Clopidogrel and proton pump inhibitors: interaction – updated advice. Published in 2014. Available from: [LINK]
11. Beorlegui, B. Aldaz, A. Oretega, A. Aquerreta, I. Sierrasesumega, L. Giraldez. J. Potential Interaction between methotrexate and omeprazole. Published in 2020. Available from: [LINK]
12. British National Formulary. Amlodipine. Published 2023. Available from: [LINK]
13. GOV UK. Simvastatin: dose limitations with concomitant amlodipine or diltiazem. Published 2014. Available from: [LINK]
14. British National Formulary. Ramipril. Published 2023. Available from: [LINK]
15. British National Formulary. Lansoprazole. Published 2023. Available from: [LINK]
16. Ogilvie, BW. Yerino, P. Kazmi. F. Buckley, DB. Rostami-Hodjegan, A. Paris, BL. Toren, P. Parkinson, A. The proton pump inhibitor, omeprazole, but not lansoprazole or pantoprazole, is a metabolism-dependent inhibitor of CYP2C19: implications for co-administration with clopidogrel. Published 2011. Available from: [LINK]
17. British National Formulary. Bisoprolol Fumarate. Published 2023. Available from: [LINK]
18. NHS UK. Bisoprolol. Published 2021. Available from: [LINK]
19. British National Formulary. Cholecalciferol. Published 2023. Available from: [LINK]
20. British National Formulary. Metformin hydrochloride. Published 2023. Available from: [LINK]
21. British National Formulary. Salbutamol. Published 2023. Available from: [LINK]

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