Prescribing, adherence and information about medicines

About 80% of medicines are prescribed in general practice (primary medical care). On average, men visit their general practitioners three to four times each year and women visit five times. About two-thirds of consultations end with the issuing of a prescription. Prescribing is particularly frequent for elderly people, who are likely to continue treatment for long periods of time. For these reasons, regular review of prescribed treatment should take place to determine whether it is still appropriate or necessary, and to ensure that important drug interactions and unwanted effects are not overlooked. Some drugs also require regular monitoring of efficacy (e.g. warfarin, antihypertensive treatment), of blood concentrations (e.g. lithium) or for biochemical effects (e.g. amiodarone, thiazide diuretics).

Duties of the prescriber

There are certain legal requirements that must be met when a medicine is prescribed. The information to be recorded is:

the name of the person for whom the drug is prescribed (surname and initial) and address; in the case of children up to 12 years, the person's age must be specified,

drug name (without abbreviation),

dose,

route of administration (usually given on the manufacturer's product information rather than the prescription),

frequency of administration (with minimum dose-interval for preparations to be taken ‘as required’),

either the quantity to be supplied or the duration of therapy,

prescriber's name, address and signature,

date.

Generic prescribing

In most situations the generic name (the officially accepted chemical name) of the drug is preferred to the proprietary trade name (a ‘brand’ name approved for use by a specific pharmaceutical company). One advantage of the generic name is that it is likely to indicate the nature of the drug. For example, all β-adrenoceptor antagonist drugs (β-blockers) end with -olol, such as atenolol, bisoprolol and metoprolol, but the trade names for these drugs, for example Tenormin^®, Monocor^® and Lopressor^®, give little idea of the active ingredient. Another problem with trade names is that they rarely give any indication when there is more than one active ingredient; for example, Tenoret^® contains both atenolol and chlortalidone. The generic names for many compound preparations have this indicated by the term ‘co-’; for example, co-tenidone is the generic equivalent of Tenoret.

Another advantage of generic prescribing is that pharmacists can dispense any product that meets the necessary specifications, rather than having to buy in a specific brand. This helps to simplify stock holding and avoids unnecessary delays when dispensing. However, different generic preparations of the same drug may differ in the tablet size, colour or scoring as well as brand name. Therefore it is important to inform the person taking the drug if a different brand is dispensed.

Generic prescribing is sometimes cheaper than prescribing by trade name, although the difference depends on pack size and other commercial factors and is sometimes marginal. In recent years there has been an increasing tendency for doctors to prescribe by generic name. It is likely that economic arguments and the increasing use of electronic prescribing systems have been the chief factors leading to this change.

One potential hazard of generic prescribing involves drugs with a narrow therapeutic index. Stringent controls have eliminated the problem of variations in bioavailability from different brands, except for some modified-release formulations of drugs such as those for lithium or theophylline. Different release characteristics from the formulation can influence the plasma concentration profile of the drug and affect efficacy and toxicity, and in these situations prescribing by brand is recommended.

Dosage

The total exposure to a medicine during a course of treatment is related to the individual dose size, its frequency and the duration of therapy. The route of administration may also be important.

Dose

This is an essential item on all prescriptions and should be written in grams (g), milligrams (mg) or micrograms (which should not be abbreviated).

The route of administration

The route should be identified if there is any possibility of confusion. Confusion can arise with intravenous administration of drugs since there are numerous methods for delivery: drugs can be given by direct injection (either as a bolus or by slow injection) into a vein or can be infused, for example through the side-arm of a continuously running intravenous drip, via a motor-driven pump or added to the intravenous infusion fluid reservoir. It is particularly important when prescribing drugs for intravenous administration to make clear the precise intentions.

Frequency and times of administration

Sometimes, drugs are taken once only, while others must be given on a regular basis, in which case the frequency or times of administration should be specified, for example twice daily or at 12 h intervals.

The quantity to be supplied or the duration of therapy

Most general practice and outpatient prescriptions specify the amount to be dispensed, for example the total number of tablets or capsules. The duration of therapy will then be determined by the amount dispensed and the frequency of dosing. Duration can be specified in a number of ways. When the medicine is to be administered by a health professional or by a carer in a sheltered environment, the duration can be specified on the prescription sheet. Alternatively, it can be written on the prescription to be dispensed by a pharmacist. Medicines are now dispensed in original packs with tablets individually packed by the pharmaceutical company. Specifying the duration of therapy is essential in the case of controlled drugs (preparations that are subject to the prescription requirements of the UK Misuse of Drugs Regulations 2001 and subsequent amendments), such as opioids, for which there is a legal requirement that the total amount to be dispensed must be written in both figures and words.

Other items on a prescription

Other essential items on prescriptions include the prescriber's signature and the address of his or her place of work. The latter is effectively waived for hospital prescriptions since it is assumed that the prescriber is based at the hospital in question. The prescription must be dated. Computer-issued prescriptions are now almost universal in primary care. The specific requirements for these are essentially similar to those outlined above. Use of computer-issued prescriptions avoids handwriting problems and assists in record keeping and in data collection and analysis.

Abbreviations

Directions for prescribing should preferably be in English (rather than Latin) without abbreviation. However, there are a number of abbreviations that are widely accepted. They include the following for route of administration: o or p.o., oral; i.v., intravenous; i.m., intramuscular; s.c., subcutaneous; and p.r., per rectum. Others, such as intrathecal, must not be abbreviated, because of the potential seriousness of inappropriate administration. Inappropriate intrathecal administration of vincristine, for example, has caused the death of several people. Besides the abbreviations already listed for quantities, ml or mL is acceptable. Quantities of less than 1 g should be written in milligrams (e.g. 400 mg, rather than 0.4 g), whereas quantities of less than 1 mg should be written in micrograms [e.g. 500 micrograms (in full), rather than 0.5 mg; when handwritten, µg is easily mistaken for mg]. Decimal points should be avoided wherever possible, but, if unavoidable, a zero should precede the decimal point when there is no figure (e.g. 0.5 mL, not .5 mL).

When indicating the timing of doses, od (omni die) is acceptable, but there is nothing wrong with saying once daily! The abbreviation om (omni mane) stands for in the morning and on (omni nocte) for at night; ac is short for ante cibum (before food) and pc for post cibum (after food). Twice daily can be abbreviated to bd (bis die), thrice daily to tds (ter die sumendus) and four times daily to qds (quater die sumendus).

Adherence, concordance and compliance

The term ‘compliance’ is used to describe the extent to which a person takes his or her medicine. However, other terms such as ‘adherence’ or ‘concordance’ are now preferred, because they emphasise the partnership between the person and health professions in the process of taking medicines, rather than simply following instructions. It is frequently assumed that once a prescription has been given, the recipient will automatically follow the prescriber's instructions. However, there is abundant evidence that this is often not the case. Indeed, many prescriptions are not even taken to the pharmacist for dispensing. Prescriptions are sometimes not presented to a pharmacist because of cost or because the prescriber failed to discuss the ‘hidden agenda’ for which the presenting complaint was an excuse to see the doctor. In addition, a very substantial proportion of medicines collected are not taken in the manner intended.

The degree of adherence is affected by many factors, which include the duration of treatment. Fewer than 50% of people adhere fully during long-term therapy, such as that for high blood pressure or psychotic illness. There is increasing evidence that adherence to prescribed therapy can determine the outcome of treatment. For example, in treating hypertension the control of blood pressure is substantially less good when adherence falls below 80% of prescribed doses.

The frequency of dosing has a major influence on adherence. Few people like taking their medicines with them to work. Therefore, adherence with twice-daily regimens tends to be much better than that for more frequent administration. There is a further improvement in the extent of adherence with once- rather than twice-daily dosing.

Unwanted effects can reduce the likelihood of a person complying with therapy, but at times this can be turned to an advantage. For example, giving the entire dose of a tricyclic antidepressant at night means that the sedation it produces can be used to aid sleep. Giving the person advanced warning of likely unwanted effects such as dry mouth with this compound may earn the person's trust and encourage continuation of the therapy.

A proportion of non-adherence is caused by people forgetting whether or not they have taken their medicine on a particular day. The use of calendar packs or prepacked dispensing boxes can be helpful in this situation.

The individual's health beliefs are also particularly important. Adherence can be improved by involving the person in monitoring his or her disease and its control by therapy, for example home monitoring of blood pressure, blood sugar in diabetes mellitus or peak flow measurements in people with asthma. Supplying accurate information about medicines can improve the level of satisfaction, and satisfied people are more likely to take their medicines.

Informing people about their medicines

It is almost incredible to think that at one time doctors were reluctant to allow the name of a medicine to be shown on the container in which it was dispensed. However, paternalistic attitudes among the medical profession have been slow to disappear. Several surveys carried out in the early 1980s showed that most people felt that neither doctors nor pharmacists gave sufficient explanations about medicines. People are particularly keen to know:

the name of the medicine,

the purposes of treatment,

when and how to take their medicine,

how long to take it for and what to do if a dose is missed,

unwanted effects and what to do about these,

any necessary precautions to take, such as possible effects on driving,

any problems with alcohol or with other drugs.

Manufacturers of pharmaceuticals now produce printed leaflets about medicines, which are included in original packs. However, leaflets are complementary to, and not a substitute for, discussion with the medical practitioner, pharmacist, practice nurse, etc. The internet provides an increasingly rich source of information for people about their medicines and the variety of treatments available for their condition(s). However, advertising and the lack of peer review of websites means that, in many cases, information the individual may have acquired before they first see their doctor may be incorrect and/or misunderstood.

Rational prescribing

A definition of good prescribing has been proposed that encompasses four goals. These are to:

maximise effectiveness,

minimise harms,

avoid wasting healthcare resources,

respect the person's choice.

Irrational prescribing can take several forms, such as use of antibacterial drugs for viral infections, statin therapy for someone with late-stage malignancy, using expensive drugs when there are equally effective cheaper alternatives, using too high a drug dose in renal or hepatic impairment or under-dosage with an appropriate drug.

The standards against which rational prescribing can be judged will depend on locally or nationally agreed treatment protocols or an agreed list of therapeutic alternatives. Ideally, prescribing should follow evidence-based guidelines, but it is often necessary to extrapolate these guidelines to situations not covered by the evidence. In the absence of evidence from clinical trials it may be appropriate to use consensus guidelines produced by experts, and derived from a relevant evidence base.

There has been considerable debate about ‘class effects’ of drugs, and whether it is reasonable to extrapolate data from a clinical study with one drug to another in the same class. This is a complex area, and in part depends on the definition of a drug class (e.g. a group of drugs with similar chemical structure, similar mechanisms of action, or similar pharmacological effects). Class effect may be related to clinical outcome (such as death or risk of stroke), effects on surrogate end-points (such as reduction in blood pressure) or specific unwanted effects. Many consensus guidelines assume that drug efficacy is related to a class effect when there is a large body of information about several drugs in a class that suggests similar outcomes.

The sequence of events leading to a rational prescription involves initially making a diagnosis and determining prognosis. This may not always be possible, and it may be necessary to substitute differential diagnoses and rank these in order of probability and/or importance to treat. The goal of treatment must then be determined. This may be curative, symptom relief, prevention or occasionally an aid to the diagnostic process. The prescriber should then decide whether any treatment is necessary and, if so, then select an appropriate first choice. The process is completed by monitoring the outcome, and reaching a decision to stop, modify or continue treatment.

Assuming that the choice of drug is appropriate for the condition that the prescriber believes he or she is treating, there will be several further considerations involved in individualising drug treatment.

Is this drug licensed for use in this condition? If it is not, prescribing may still be appropriate but the prescriber should be familiar with the evidence to support the use of the drug.

How does the drug compare with available alternatives in relation to published evidence, efficacy, safety, convenience and cost?

Does the individual have any coexisting conditions that will compromise the efficacy of the drug?

Are there comorbidities that might benefit from the use of this or an alternative option?

Are any other drugs being taken that might adversely interact with your choice?

Are there any absolute contraindications to using the drug in this individual?

Are there relative contraindications to use in this individual, including comorbidities or common unwanted effects?

Has the individual suffered previous adverse drug events that should make you cautious about using this particular drug?