6: Pharmacology

Section 6 Pharmacology

6.1: Drugs and the law

6.2: Medicines management

6.3: Nurse prescribing

6.4: Pharmacology in practice

6.5: Classification of drugs

6.1 Drugs and the law

There are two main Acts of Parliament that control the prescription and administration of many drugs. These are The Medicines Act 1968 and The Misuse of Drugs Act 1971.

The Medicines Act 1968

This was the first comprehensive legislation on medicines in the UK and the act regulated the manufacture, distribution and importation of all medicines for human or animal use. European Community (EC) legislation now takes precedence over the 1968 Act which is amended from time to time to fall in line with new EC requirements.

The Medicines and Healthcare Regulatory Agency (MHRA) was set up in 2003 to ensure that medicines and medical devises work and are safe. They have a website at www.mhra.gov.uk. They assess the quality and safety of medicines and authorize their sale in the UK.

The Misuse of Drugs Act 1971

The act relates to drugs which are liable to cause dependence if misused. These drugs are referred to as ‘Controlled Drugs’ and known as CDs. Accurate records of all purchases, amounts of drug issued and dosages given have to be kept. There must be special labels on the containers of these drugs to make them clearly recognizable.

The Controlled Drugs (Supervision of Management and Use) Regulations 2006 were introduced in response to the Shipman Inquiry which found that ineffective monitoring had allowed Dr Harold Shipman to use diamorphine to kill at least 15 patients and possibly many, many more, over a period of time, without being detected.

The Care Quality Commission (CQC) is now responsible for ensuring that healthcare providers are creating a safer environment for the management of controlled drugs and further information is available on their website at www.cqc.org.uk.

In hospitals there are regulations controlling these drugs:

They are stored in a double-locked cupboard of their own.

The key must be carried by the nurse in charge.

There is a special Controlled Drugs Order Book for those drugs in frequent use which can be kept as stock. The sister in charge must sign each order.

Each administration of these drugs has to be recorded in the Controlled Drug Book with the patient’s name, the dose of the drug, the time it was given and the signature of the nurse who administers the drug and another who has checked all these details.

The content of the CD cupboard is checked regularly by the pharmacist against the contents of the CD Book and any discrepancies are fully investigated.

The Misuse of Drugs Regulations 1985 divides drugs into five schedules, each with its own requirements governing supply, prescribing and record keeping.

Schedule 1 are drugs that are not used medicinally and possession and supply are prohibited. An example would be lysergic acid diethylamide (LSD).

Schedule 2 includes drugs subject to full controlled drug requirements. Examples include:

diamorphine (heroin) morphine

pethidine methadone

amphetamine cocaine

fentanyl remifentanil

Schedule 3 drugs are subject to the same special prescription requirements (except phenobarbital), but not to the safe custody requirements (except buprenorphine and diethylpropion). They do not need a special register but invoices must be retained for 2 years. Examples include buprenorphine.

Schedule 4 drugs are subject to minimal control and include 34 benzodiazepines, examples being diazepam and temazepam.

Schedule 5 includes those drugs which, because of their strength, are exempt from virtually all CD regulations other than retention of invoices for 2 years. An example would be low doses of codeine present in combined preparations.

6.2 Medicines management

Medicines management is defined as ‘the clinical, cost-effective and safe use of medicines to ensure that patients get the maximum benefit from the medicines they need, while at the same time minimising the potential harm’ (MHRA 2004).

In 2007, The Nursing and Midwifery Council (NMC) published their ‘Standards for Medicines Management’. These have been updated in 2010 and are available on the NMC website (www.nmc-uk.org). The standards replaced the NMC’s ‘Guidelines for the Administration of Medicines’ (2004), but do continue to emphasize the importance of the trained nurse using thought and professional judgement when administering medication and so going beyond the mechanistic delivery of the prescribed dose on the treatment sheet. They describe the importance of using local expertise regarding medicines management and refer to the importance of the pharmacist in the role of advisor.

There are 26 Standards in 10 Sections, covering all aspects of medicines management, including supplying, dispensing, storage, transportation, administration, assessment of the patient, delegation, reporting adverse reactions and administration of controlled drugs.

The administration of medicines

As a registered nurse, the administration of medicines is an important aspect of your professional practice.

Safety is of prime importance in the administration of medicines and the effects of any medication should be assessed and evaluated. Any side-effects should be reported to the medical team without delay.

The ‘five rights’ act as a simple and basic reminder of some of the essential points of care:

Who can administer medicines in a hospital setting?

The NMC Standards state that prescribed medications should only be administered by registered practitioners who are competent for the purpose and aware of their personal accountability. If the registrant delegates any part of the administration, they are accountable to ensure that the patient, carer or care assistant is competent to carry out the task. Students must never administer or supply medicinal products without direct supervision.

Two registrants should check drugs to be administered intravenously and one of those two registrants should administer the drug.

Important points

The nurse should never administer a medication without knowing its therapeutic use, normal dosage, side-effects, precautions and contra-indications. There should always be a copy of the British National Formulary (BNF) available when medicines are administered so that any unfamiliar drugs can be looked up.

The nurse must be certain of the identity of the patient to whom the medication is to be administered and should also have knowledge of his planned care.

Always check that the patient is not allergic to the medicine before administration.

The prescription must be very clear and legible. Doctors are asked to print the drug name and in hospital must always use the generic name of the medication and not the trade name. The label on the medicine dispensed should be clear and unambiguous.

The expiry date of the medicine (if available) should be checked.

If there is any ambiguity or query regarding the drug, the dose or the route of administration, which should all be very clear on the prescription sheet, the nurse must refuse to administer the medication and should contact the prescriber.

If any contraindications to the prescribed medicine are discovered or where the patient develops a reaction the prescriber should be contacted without delay.

When a medication has been administered, this must be recorded at the time in a clear and accurate manner and with a signature which is legible. If the patient refuses his medication this should also be recorded and the nurse in charge should assess the situation and contact the prescriber.

A medicine must never be charted before it is given. When you sign for that drug you are saying that the client has actually taken it.

Always check that the client understands the medication that s/he is receiving and is aware of any important side-effects. Emphasize the importance of the treatment and explain its mode of action in simple terms.

If an error is made in the administration of a medicine, this should immediately be reported to the nurse in charge, who will inform the prescriber.

Evaluate the action of the prescribed medication and record any positive or negative effects, informing the prescriber of these.

6.3 Nurse prescribing

The Medicines Act of 1968 allowed only doctors, dentists and veterinary surgeons to prescribe, but this has been rapidly changing within the NHS in recent years. Non-medical prescribing is rapidly expanding in the UK and nurse prescribing has been extremely successful.

Prescribing by certain groups of nurses began in October 1994 and permitted some nurses with a health visiting and district nursing qualification to prescribe certain drugs and dressings from a nurse prescribers’ formulary. The primary legislation allowing nurse prescribing was set out in the Medicinal Products: Prescription by Nurses Act of 1992.

In 2002 registered nurses and midwives with additional training were allowed to prescribe from the Nurse Prescribers’ Extended Formulary, a limited list that included over 120 prescription-only medications.

From May 2006, independent prescribing for nurses from a full formulary was permitted by legislation. Independent nurse prescribers can prescribe any medicine for any condition within their competence. Thirteen controlled drugs are also included for specific conditions. Pharmacist Independent Prescribers are not currently able to prescribe any controlled drugs. The nurse prescribers must be first-level registered nurses or midwives and have passed the appropriate University course in order to meet the ‘Standards of Proficiency for Nurse Prescribers’ first produced by the NMC in 2006.

6.4 Pharmacology in practice

Pharmacology is the study of drugs and their actions. It includes absorption, metabolism and elimination of the drug as well as the mode of action of the drug. Drug absorption will vary depending on the route of administration.

Drug administration

The aims of administration are:

To establish optimal drug concentration at the target site.

To maintain optimal concentration for the required period of time.

To minimize adverse drug reactions due to general distribution.

Routes of administration

Oral

This is usually the most convenient route. Medication for oral administration may come in several forms:

Tablets. The drug has been diluted, powdered and compressed by a tabletting machine into a shape that will be easy to swallow. Tablets are often coated with sugar or some colouring material.

Some tablets have an enteric coating (EC), which is usually shiny in nature and is an acid-resistant layer to prevent dissolution in the stomach. This is used for drugs that may be irritant to the stomach lining.

Some oral medications may be specially formulated for slow release and will have SR after their name.

Capsules. These usually contain oily or nauseous preparations in an envelope made of gelatine or a similar substance. Examples are ampicillin and cod liver oil. The medication is liberated when the outer capsule is digested in the stomach or intestine.

Mixtures. These are liquid preparations in water or other solvent base which usually contain a number of ingredients. An example is magnesium trisilicate mixture, which is used as an antacid. Bottles containing mixtures should be shaken before administration as ingredients may separate out during storage.

Linctus. Used as a cough suppressant and made with a strong syrup base and flavouring agents. An example is linctus codeine.

Oral drug absorption. This is the passage of the drug from the gut lumen, through the gut mucosa and into the bloodstream. Although some absorption takes place in the stomach, the surface area here is much less than the small intestine, where most of the absorption takes place.

The absorption of oral medication is influenced by many factors.

Food in the stomach. Drugs are usually absorbed more quickly if the stomach is empty and in the case of most antibiotics, the client is instructed to take the medication 1 hour before food for this reason.

Drugs which may irritate the stomach should be given with or after food and this instruction will usually be on the container. An example is aspirin.

Interactions with other drugs. Drugs that inhibit gastric emptying, e.g. atropine, amphetamine, morphine, may reduce the rate of absorption of other drugs.

Diseases of the gastrointestinal tract, e.g. ulcerative colitis, may lead to poor absorption of the medication.

Transit time. The time taken for passage through the small intestine. The longer the medication is in the gut, the more of it will usually be absorbed.

Gastrointestinal movement aids the absorption of a drug and as the drug passes through the intestine, it is fragmented and dissolved. If there is excessive peristalsis, as in diarrhoea, the drug will not have time to be absorbed.

Laxatives also decrease absorption.

Acid in the stomach. This will destroy some drugs, e.g. acid-sensitive penicillins, so they have to be given by injection.

Enzymes. These will break down proteins and amino acids such as insulin, which therefore has to be given by injection.

Metal ions and tetracycline. Tetracycline forms a complex with either calcium or iron and if either of these is given with tetracycline a large molecule is formed that cannot be absorbed and the patient will not get the benefit of either drug. As there is calcium in milk, tetracycline should not be taken with a drink of milk. Magnesium and aluminium also complex and may be found in antacids.

The concentration of a drug in the intestine depends on the:

Amount ingested.

Rate with which it is released from the formulation.

Volume of gastrointestinal contents with which it is mixed.

Sublingual/buccal

The drug is administered under the tongue or sprayed into the mouth. This route is used for drugs that are destroyed rapidly by the liver, e.g. glyceryl trinitrate (GTN). If GTN is taken orally and swallowed it is absorbed and passes into the hepatic portal vein, reaching the liver and being metabolized before it can have any vasodilatory action. When given sublingually it is absorbed directly into the systemic circulation, thus bypassing the liver.

This route is also useful if the patient is not allowed fluids or feels sick. Examples include the analgesic buprenorphine which may given sublingually and the antiemetic prochlorperazine given buccally.

Rectal

Drugs may be given rectally for local or systemic action. For local action a suppository or an enema may be given when the patient is constipated to promote a bowel action. Glycerin suppositories are the most common. Glycerol is a mild irritant to the rectal mucosa and thus stimulates the defecation reflex.

Steroid enemas are administered for local action on an inflamed bowel in ulcerative colitis.

Normally the rectum is empty and a suppository will melt and be absorbed via the rectal mucosa into the bloodstream, making this a good route for systemic drug administration.

The rectal route is especially useful when:

A drug is irritant to the stomach mucosa.

The patient is vomiting or nauseated.

There is difficulty in swallowing.

The patient is drowsy or unconscious.

Examples of drugs given rectally are:

Diazepam – for convulsions.

Transdermal (via the skin)

Usually in the form of a patch that releases the drug through a rate-controlling membrane. The drug is absorbed through the skin and into the blood supply. Hormone replacement therapy, fentanyl (an opioid) and glyceryl trinitrate may be administered this way.

Topical application

This is for local effect on the skin and mucous membranes:

Creams – these are emulsions of oil and water that are well absorbed into the skin and may be used for dry and scaly skin or as the base for other drugs, such as steroids in eczema.

Eye drops – sterile preparations for instillation into the eye. This could be for an infection, e.g. chloramphenicol drops, or to have an effect on the pupil or the drainage system.

Ear drops – these are for application to the external auditory meatus, e.g. Cerumol® which helps to dissolve wax in the ear.

Vaginal pessaries or cream – for local action.

An advantage of topical application is that a high local concentration can be achieved, usually without a systemic effect. A disadvantage is that absorption can occasionally occur with serious effects.

Inhalation

This route is used for drugs that are absorbed via the respiratory mucosa for systemic action, e.g. volatile anaesthetics, and for drugs acting on the respiratory system.

The drug may be administered as:

A gas, as in anaesthetics.

An aerosol, as in salbutamol inhalers used to treat asthma. Aerosols contain particles dispersed in a gas and small enough to remain suspended for a long time.

A powder dispensed from a rotary inhaler as in sodium cromoglicate (Intal) for the treatment of asthma.

A nebulizer – the machine converts a solution of the drug into an aerosol. These are used in respiratory conditions, e.g. salbutamol for asthma.

Injection

Injections may be given:

Intradermally – into the skin. Used for allergy testing and diagnostic tests. Less than 0.1 ml may be given.

Subcutaneously – under the skin. Used for insulin and heparin administration where slow and steady release is needed. Up to 2 ml may be administered. Sites for subcutaneous injection are shown in Figure 6.1. Absorption of the drug does depend on local blood supply and may be more rapid with exercise. The needle was traditionally inserted at a 45º angle but with the advent of shorter specialist needles the recommendation for insulin injection is an angle of 90º.

Intramuscularly – into a muscle. Up to 4 ml may be given into well-developed muscle. The sites used are shown in Figure 6.2 and detailed below. Again, absorption is variable dependent on the site and the state of the circulatory system.

Intravenously – into the venous circulation. This route may only be used by doctors and registered nurses who have done a course in intravenous drug administration.

Intrathecally – into the spinal theca.

Intraosseous – into the bone marrow cavity. A route more commonly used in paediatrics but also in adults when intravenous access cannot be obtained.

Into various body cavities, e.g. the peritoneum and the pleura.

Fig. 6.1 Sites used for subcutaneous injection. A. Anterior aspect. B. Posterior aspect.

From Jamieson/Clinical Nursing Practices, 3rd edn, reproduced with permission.

Fig. 6.2 Sites used for intramuscular injection. A. Deltoid region of the arm. B. Ventrogluteal site. C. Dorsogluteal site. D. Vastus lateralis site.

Adapted from Rodger MA, King L (2000), with permission. Original illustration by Alison Tingle.

The administration of any injection is an aseptic procedure and great care should be taken with hand-washing technique.

Care must also be taken to avoid needlestick injury to yourself as there is a danger of transmitting bloodborne viruses such as hepatitis B and HIV.

Some advantages of intravenous administration

The drug is delivered into the bloodstream and so is able to act immediately.

There is no reliance on absorption and the whole dose of the drug reaches the bloodstream, enabling better calculation of the amount the patient actually receives.

A continuous infusion allows the rate of administration to be controlled and the action of the drug thus modified.

Some disadvantages of intravenous administration

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Jun 15, 2016 | Posted by admin in NURSING | Comments Off

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