Introduction to drug classification lecture

Introduction

This chapter will introduce the topic of drug classification in the context of the responsibilities nurses have to both UK law and the Nursing and Midwifery Council (NMC). The naming system of drugs and common drug classification systems will be explained, in the context of UK practice.  The differences between controlled and non-controlled drugs will be introduced, and examples will be used to illustrate the ways in which the rules regarding the use of drugs are implemented and adhered to in everyday nursing practice.  Finally, advice will be given on how to apply this knowledge to your everyday nursing practice. 

Learning objectives for this chapter

By the end of this chapter, we would like you to:

- Understand how and why drugs have chemical, generic and trade names and the implications of this.

- Understand how drugs are generally classified by their structure, or by their function (physiological or therapeutic effects) and be able to apply this understanding.

-Understand how prescribed drugs are regulated in the UK by law and by regulatory bodies such as the NMC.

-Appreciate how a good understanding of drug classification can enhance nursing practice and patient safety.

-Understand why some drugs are classified as requiring special care when prescribing, especially in specific patient populations such as pregnant or breastfeeding women.

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Drug Naming

Pharmacology may be defined as "the study of the effects of drugs on the function of living systems" (Rang et al., 2014, p.1), with the aim of enhancing health and correcting the physiological changes in the body caused by disease.  Drugs have a chemical name (relating to the molecular structure of the active region of the molecule), a generic name and a trade name under which it is sold. To write these correctly, a drug's trade name is capitalised, however the generic and chemical names are not.  One of the reasons why drugs may be sold under trade names rather than simply as generic preparations is that the cost of developing a drug, testing it through preclinical and clinical trials and bringing it to market is a very expensive process, with estimates ranging from US$161 million to US$2billion per drug (Sertkaya et al., 2016, p.117).  By protecting production of the drug via a patent for the first few years of its use, the company who developed the drug can recoup the development cost by selling the drug under a trade name.  After this time, other companies can make the drug (under other trade names or as a generic copy), allowing the drug to be available at a lower price to healthcare organisations.  This ensures that the need for the pharmaceutical company to receive the financial benefits of selling the drug is balanced with the need to control prices and ensure that healthcare funds are not exploited.  An example of the different names that one drug could be referred to by is below:

Example:

How could the drug generically known as amoxicillin be known?

Chemical name:
(2S,5R,6R)-6-{[(2R)-2-amino-2-(4-hydroxyphenyl)-acetyl]amino}-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-24-carboxylic acid

Generic name:
amoxicillin

Trade name examples:
Amoxil®, Amix®, Amoram® and Rimoxallin®

Drugs Are Classified by Their Chemical Family, Physiological or Therapeutic Effect

Medicinal drugs can firstly be classified into prescription drugs, or non-prescription drugs - commonly referred to as over the counter (OTC) drugs.  OTC drugs can include remedies for common ailments, or drugs in a lower dosage than would be prescribed by a doctor or nurse practitioner (for example, paracetamol and ibuprofen).  These are generally considered to be safe when used correctly and it is not usually necessary for their use to be monitored by healthcare professionals.  On the other hand, prescription-only drugs are generally intended to treat more significant conditions, and legally require an appropriately qualified healthcare professional (for example, a doctor or nurse practitioner) to make a diagnostic decision, and then a decision about which drug is most suitable for use in that circumstance.

Drugs are generally classified by family (the group of drugs they are chemically similar to) or by the physiological effects they can cause.  Table 1 shows the two ways that drugs can be described; for example, the angiotensin converting enzyme (ACE) inhibitor drug ramipril can be described either by its family (ACE inhibitors) or by its therapeutic effect (an antihypertensive drug).  The effects can either be physiological (i.e. its effects on the body's systems) or therapeutic (i.e. its medicinal use).  For example, the drug citalopram could be described by its physiological effect as a selective serotonin-reuptake inhibitor (SSRI), or by its therapeutic action as an antidepressant.  There is therefore often overlap between drug classification systems. 

Drug classifications by family (or active ingredient)

Drug classification by physiological effect

Drug classification by therapeutic effect

ACE inhibitors

Diuretics

Antihypertensives

Barbiturates

Selective serotonin-reuptake inhibitors (SSRIs)

Antidepressants

Opioids

CNS depressant

Analgesics

Penicillin

Antibiotics

Antimicrobial

Heparin (and mimetics)

Anti-coagulants

Antithrombotics

Table 1: Examples of drug classifications by family or active ingredient or by effect

Example:

The drug morphine sulphate could be classified as follows:

Chemical classification:
Morphine sulphate is based on the active ingredient of opium.

Physiological classification:
Central nervous system depressant.

Therapeutic classification:
Morphine sulphate is a powerful analgesic that can also cause respiratory depression.  It is therefore classified as an opioid analgesic. 

In addition to this, there are also other classification systems in operation for specific uses, such as according to the relative safety of the drug in pregnant women, whether or not athletes would be permitted to compete while taking the drug (for example, the lists held and reviewed by the World Anti-Doping Agency (WADA, 2016)), or whether prescription of a drug should be controlled to prevent harm or misuse.  Controlled drugs are discussed in greater detail in the later sections of this chapter. 

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Reflection

Drugs usually have three types of names; a chemical name, a generic name and trade names(s).

Drugs can be classified by their chemical structure, and the physiological or therapeutic effects they can cause.  There is often overlap between these categories depending on the way in which you are looking to describe that particular drug. 

- How could this cause confusion in prescribing in the hospital environment? 

- How can this be prevented?

- Should prescribers use the chemical, generic or a trade name?  Why?

The Nursing and Midwifery Council and Drugs

Drugs are potentially powerful tools for use in combating disease.  However, incorrect administration of drugs may cause harm to patients, or even death.  It is therefore essential that the administration of drugs is carefully regulated.  In the UK, this is primarily carried out by government legislation and policy, however the professional bodies that represent each type of healthcare professional also have their own guidelines to guide their professionals in the particular way in which they are involved in the drug administration process in accordance with their particular profession.  For nurses, drug administration guidance is given by the NMC - specifically, the NMC Standards for Medicine Management (NMC, 2016).  These guidelines not only describe safe and effective drug administration practice, but also encourage nurses to follow local and national policies for drug administration, as most institutions will have specific guidelines for their nurses to follow. This is discussed in more detail in Chapter 3. 

Reflection Questions

Consider the following questions:

1. Patient A has been taking 20mg fluoxetine daily for the past 6 months to treat his depression.  He usually receives his medication from the chemist under the name Prozac.  When collecting his repeat prescription, he has noticed that the box does not say "Prozac", but "20mg fluoxetine".  Patient A is concerned that he has been given the wrong medication and has asked you to help him.  Which of the following statements are correct?

a. "Prozac is a trade name of the drug fluoxetine.  Your new prescription is essentially the same medication as your previous prescriptions"

b. "Different trade names reflect the quality of the preparation of medication"

c. "Different trade names exist because the company who discovered the drug patent it in order to recoup the cost of developing the drug.  After a few years, other companies can make cheaper versions"

d. "You are more likely to have side effects from the generic version of a drug than a branded version like Prozac"

e. "Choosing between brands or a generic (unbranded) version of the medication allows the pharmacist to choose the cheapest option and to save the NHS money"

f. "Fluoxetine sold under the trade name Prozac may be more effective than other preparations, for example Sarafem"

2. The classification "antihypertensive" is which of the following:

a. A therapeutic classification

b. A physiological classification

c. A chemical classification

3.  Which of the following is a physiological drug classification?

a. Antithrombotic

b. Benzodiazepines

c. SSRIs

d. All of the above

Controlled and Non-Controlled Drugs

All drugs can be classified as either controlled or non-controlled drugs.  Controlled drugs require additional care in their prescription and administration, as these drugs have the capability to either cause significant harm to patients if taken incorrectly, or have the potential to be abused.  Harm can be characterised as physiological damage (e.g. liver toxicity from the abuse of analgesics), mental harm (e.g. depression associated with abuse of hypnotic drugs), or by causing psychological and physiological dependence.  Dependence on the abuse of controlled drugs can have very negative effects; for example, the individual may experience an overwhelming desire to use the drug, even committing crimes to obtain it, and may experience physical withdrawal symptoms when it is not used, such as abdominal cramps or tremors.  Addiction can have many harmful effects on society and on the patient's physical and mental wellbeing.  By implementing and enforcing procedures and policies to restrict the use of these drugs, the safety of patients, the public and healthcare professionals can be ensured.  The guidelines for the use of controlled drugs cover every step of the drug's life - from its production to its storage, prescription, administration and even wastage if unused.  This will be covered in more detail in Chapters 2 and 3. 

The Misuse of Drugs Act 1971 sub-classifies controlled drugs by their potential to cause harm when misused.  As well as prescription drugs, this also includes drugs of abuse that do not have a medicinal use, for example lysergide (LSD).  These are shown in Table 2.  Harm can be caused by abuse of these medications in the form of addiction, and organisations such as The Royal College of General Practitioners (RCGP) recognise the responsibility of prescribers to consider this risk (and to ensure that the need for the drug outweighs this risk) when prescribing these medications to patients in their care.  However, it should be remembered that despite this, where a clinical need for a controlled drug is indicated, such as the use of morphine in the palliative care of cancer patients experiencing pain, it is not recommended by NICE to restrict the use of controlled drugs through fear of creating dependence.  In this case, the risk of creating a dependence is considered to be far outweighed by the necessity of controlling the patient's pain. 

Drug Class

Example

Class A

Cocaine, diamorphine (heroin), alfentanil, lysergide (aka "LSD"), methadone, dipipanone, morphine, pethidine, opium, MDMA (aka "ecstasy"), remifentanil, phencyclidine, and any class B drug prepared for administration by injection

Class B

Cannabis, barbiturates, amphetamines, codeine, ketamine, ethylmorphine, glutethimide, nabilone, pholcodine, phenmetrazine and pentazocine

Class C

Benzfetamine, buprenorphine, chlorphentermine, mazindol, pipradrol, pemoline, meprobamate, tramadol, most benzodiazepine drugs, zopiclone, zolpidem, zaleplon, anabolic and androgenic steroids, human chorionic gonadotrophin (HCG), non-human chorionic gonadotrophin, clenbuterol, somatotropin, somatropin and somatrem

Table 2: Classifications of controlled drugs into classes A-C by the potential harm that abuse of the drug can cause (BNF, 2016c)

Reflection

Controlled drugs are classified in accordance with the risk they pose to patient health and wellbeing, or to prevent their abuse.

Controlled drugs require specific production, storage, prescription, administration and wastage procedures.

Nurses have an obligation to operate in accordance with the NMC Code and the NMC Standards for Medicine Management for the administration of both controlled and non-controlled drugs.

Classification of drugs by potential risk to patient health

The MHRA is the agency of the Department of Health responsible for the safety of medicines (and medical devices) in the UK and was first formed in 2003.  It can review the classification of drugs based on new evidence, for example, reclassifying the statin Simvastatin to OTC from prescription only on the basis of the collection of extensive safety data, or the classification of new biological or chemical medicinal agents. 

Most drugs are known to have potential adverse effects in patients, usually identified during the drug development and clinical trial stage, or in the UK, through the Yellow Card reporting system monitored by the Medicines and Healthcare Products Regulatory Agency (MHRA) (BNF, 2016b).  These may include observed adverse effects, interactions with other drugs, vaccines or even complementary and herbal medicines.  Adverse effects can be relatively minor (e.g. headaches, dry mouth or rashes) or very severe (e.g. cardiac arrhythmia or seizure).  Furthermore, some drugs, for example anticancer drugs, can themselves cause severe illness such as cardiac dysfunction.  It is important that these risks are understood by prescribers, and a careful analysis should be undertaken of the potential cost to the patient of taking the drug in comparison with the potential benefits they may receive.  If the patient is fully informed of the risks, and the healthcare team feel that a drug with known risks is still in the patient's best interest, then informed consent can be taken from the patient and the drug prescribed.  A common example of this is the cytotoxic anticancer drug trastuzumab, which is associated with a significant risk of congestive heart failure, with reported incidence from clinical trials in between 2% and 16% of patients (Popat and Smith, 2008, p.325).   However, as trastuzumab has been shown to be an effective treatment for HER2 positive breast cancer, its use is still recommended, although careful patient monitoring and cessation of treatment in the event of cardiac toxicity is recommended by NICE (NICE, 2010).  Put simply, if an otherwise healthy patient develops HER2+ breast cancer, the potential benefit of taking trastuzumab and treating the cancer may be considered to outweigh the potential risk of cardiotoxicity.  However, for a less life threatening condition such as depression, the potential risk of cardiotoxicity may far outweigh the potential benefit to the patient - particularly when other drug alternatives with lower risk profiles are available.  In order to manage the risk of cytotoxic drugs to patients, drugs classified as cytotoxic (i.e. that may cause harm to some systems as well as treating tumours) require special handling. For example, they should only be prepared by trained personnel in designated pharmacy areas.  Healthcare professionals handling these drugs should wear protective clothing (gloves, masks and gowns), and local procedures for the control of spillages and disposal of waste should be followed (BNF, 2016a). 

Drugs may also be classified by the potential risk they pose when administered during pregnancy.  Some drugs, such as diethylstilboestrol (thalidomide), have the potential to cause congenital malformation (teratogenesis) when administered in the first trimester. Similarly, some can affect the development of the foetus or its growth, particularly when administered in the second and third trimesters, which may be linked with congenital abnormalities such as cleft palate, heart defects or low birth weight, although evidence for this link is mixed (Nezvalová-Henriksen et al., 2013). Ibuprofen is one example of such a drug. Finally, other drugs, such as pethidine, may have adverse effects (in this case respiratory depression) on the foetus if administered too close to birth.  Although many drugs are considered to not be harmful in pregnancy, it is difficult to classify these medications as "safe", as ethical considerations prevent the use of clinical trials in pregnant women, therefore evidence tends to be based on reports of complications following usage.  In general, prescribers are advised to only prescribe drugs when the benefits to the mother outweigh the potential risk to the foetus.  This risk can range from evidence obtained from animal studies of teratogenicity, or evidence from studies or reported examples of teratogenicity in humans.  Some medications may be contraindicated by both human and animal model evidence.  However, risk should still be balanced with the overall benefit to mother and child.  For example, salbutamol is not thought to be harmful during pregnancy, although this cannot be empirically proven in a clinical trial.  However, salbutamol would still be recommended for use in pregnant asthmatic women, as the potential risk to the mother (and therefore the foetus) from an uncontrolled asthma attack far outweighs the small possibility of risk to the foetus from the exposure to salbutamol.  Prescribers may also have similar concerns when prescribing to breastfeeding women, as there is a possibility that the drug may enter the breast milk and therefore be passed to the infant, however the potential risk of this is dependent on the pharmacokinetics of the drug (how it acts and is metabolised in the body), the rate of absorption and elimination of the drug by both mother and infant, and the potential effects of any drug (or drug metabolites) on the infant.  In the UK, previously the BNF contained a table classifying the potential harmfulness of drugs during pregnancy, however in recent editions this has been replaced with recommendations for use in pregnant or breastfeeding women under each individual drug entry, with the general recommendation that drugs should only be prescribed to pregnant women if the benefit to the mother outweighs any potential risk.  Institutions may have local recommendations for drug choices in pregnant women, or have produced their own formularies. For example, there is good evidence that paracetamol is not harmful in pregnancy, and only enters breast milk in such small amounts that it is not considered to be harmful in lactating women.  SSRIs such as citalopram take more consideration to prescribe to pregnant women, as there is limited evidence to suggest a correlation between taking the drug in pregnancy and withdrawal symptoms in the neonate, for example tremors and irritability.  There is also limited evidence to support a link with heart defects in the foetus.  However, the social and psychological risks of untreated depression to mother and child are significant in terms of issues with bonding and anxiety in both mother and child.  Therefore, although citalopram itself may be discouraged during pregnancy, there are other SSRIs such as sertraline which are thought to provide a safer alternative and a doctor may discuss changing to this medication with the expectant mother. 

The Food and Drugs Agency (FDA) in the USA has also made similar changes, moving from a classification system for drug risk in pregnancy (where risk is rated from A to D based on the amount of evidence for a risk through to category X, which was a list of drugs contraindicated in pregnancy) to the Pregnancy and Lactation Labelling Rule (PLLR).  This system entails the risk during pregnancy and lactation being printed on the medication label itself, and encouraging prescribers to discuss risks with women so that they can make an informed decision under the Physician Labelling Rule (PLR) (FDA, 2016).   

Reflection

As well as being classified by their chemical structure (or family), physiological and therapeutic actions, drugs are also classified by the specific risks they pose to:

- The general patient population

- Specific patient populations (e.g. pregnant and breastfeeding women)

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Example:

The correct prescribing decision can differ between patients depending on their individual circumstances.  Think about how you would feel administering the prescribed drug in each of the following circumstances, would you question the decision or be confident that administering the drug was in the patient's best interests?

- Patient A is overweight and has a previous history of deep vein thrombosis.  She has recently found out she is pregnant.  The BNF shows that heparin is associated with a risk of stillbirth and low birth rate.  Her doctor has instructed her to keep taking the heparin.

- Patient B is taking the SSRI, citalopram.  She is pregnant and wants to stop taking the drug as she is worried about the limited evidence of foetal cardiac defects.  The prescribing doctor has advised you that the risk of adverse effects to both mother and child from untreated depression are significant.  How do you approach this discussion with Patient B?  Please also consider informed consent. 

- Patient C has terminal pancreatic cancer.  He is in a great deal of pain and has been prescribed morphine, a controlled drug.  His family are concerned about him developing an addiction to morphine.  How do you advise them? 

- Patient D is scheduled to start a course of chemotherapy for non-Hodgkin's lymphoma that includes the drug rituximab.  Patient D is concerned, as the patient information leaflet states there is a risk of cardiotoxicity with this drug.  How would you help him analyse the costs and benefits of this treatment?

Implications of Drug Classification Systems for Nurses

It is important that nurses have a good understanding of the way in which drugs are named, as confusion between the names could cause medication errors which could affect patient safety, as some trade names are fairly similar. For example, the trade name of the antiepileptic drug lamotrigine is Lamictal, which is similar to the drug name Lamisil (generic name terbinafine), which is a topical antifungal agent.  Nurses should therefore be familiar with both generic and trade names of drugs, and check any names they are unfamiliar with. The British National Formulary (BNF) publishes a regularly updated guide to every prescription medication used in Britain that aids healthcare practitioners in safely prescribing the most suitable medication, whilst considering cost implications.  As many prescriptions are handwritten, misspellings or unclear writing could cause similar trade names to be confused.  However, it should be remembered that the nurse administering the medication has a legal and ethical responsibility to ensure that the right drug has been prescribed, and that the right drug is administered, therefore the nurse would be responsible for querying any unfamiliar or hard to read instructions.  In general, drugs are therefore prescribed by their generic name, which gives the pharmacist the ability to choose to dispense a particular trade name or generic preparation of that drug on the basis of their current drug supply, or to minimise costs to the National Health Service (NHS).  Finally, the nurse should consider any patient-specific risks to administering any prescribed medication, such as pregnancy, and should always check if there is any doubt that this has been considered.  Although it may be difficult to question a prescribing doctor's decision owing to the historical imbalance between the professions, raising a question in a respectful and open manner should not be seen as a negative - especially when it is in the interests of patient safety and wellbeing.  Conflict management and assertive communication strategies may help to increase the student nurse's confidence with this. 

Final Reflection

Nurses should understand the common drug classification systems in order to:

- Guide patients in making informed decisions about their care.

- Ensure that a patient has been prescribed a drug with the necessary consideration of that patient's personal situation and individual risk factors / history.

- To help prevent and to identify errors in prescribing in order to protect patient safety

Conclusion

Drug classification is an important concept for nurses to be familiar with. This is so that you can understand the potential risks of any medications you are asked to administer, and so that you can ensure that your patients have the necessary information to give informed consent for their treatment.  You should also be able to solve any confusion caused to the patient by the differing names of their prescription medication.  By understanding how drugs are commonly named and classified, you should be able to understand why it is advisable to use a drug's generic name rather than trade names where possible, and understand how confusion can occur between trade names and how this may cause prescribing errors.  This should help you to identify prescribing errors in your future nursing practice, which will enhance the safety of your patients and the quality of care you can offer them.  Finally, you should now be aware of the reason why controlled drugs are classified as such, and why they should be treated differently to non-controlled drugs.  You should also now understand that some patient populations, such as pregnant women, are at particular risk from certain classifications of drug and be confident in advising them accordingly. 

References list

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Sertkaya, A., Wong, H.-H., Jessup, A. and Beleche, T. (2016). Key cost drivers of pharmaceutical clinical trials in the United States. Clinical Trials, 13 (2), pp.117-126.

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