Clinical Pharmacology and Therapeutics. Группа авторов
due to the rapid, predictable delivery of treatment. Alternative routes may also be preferred in those patients unable to swallow (e.g. rectal administration of aspirin to dysphagic stroke patients).
What dose and how often?
Recommended doses and dosing intervals are given in the British National Formulary (BNF), which should be consulted when prescribing any drug with which you are not intimately familiar. Particular care should be taken when the patient's ability to metabolise or excrete a drug may be compromised, for example patients with hepatic or renal impairment.
Writing the prescription: practical aspects
There are two principle ways in which drugs are prescribed. Drug prescriptions may be recorded on prescription forms to be dispensed by a pharmacist to the patient. Alternatively, a drug may be prescribed on a hospital in‐patient prescription to be administered by a member of staff other than a dispensing pharmacist (Figures 4.1 and 4.2).
Figure 4.1 Example community prescription conforming to the principles outlined in this chapter.
Source: NHS Scotland.
Figure 4.2 Examples of hospital prescription chart prescribing, including some important examples of poor prescribing practice with the potential to lead to error.
Both types of prescription require similar information and you should adhere carefully to the following principles to ensure that your prescription is clear and safe. Drug administration errors often arise because an insufficient amount of attention has been given to making a prescription clear.
1 Ensure that the prescription contains sufficient patient‐identifiable information. The legal requirement is for the name and address of the patient (and the age if under 12) but in practice you should include the date of birth and appropriate identifying numbers, such as the Community Health Index (CHI) number in Scotland.
2 The prescription should be completed in an indelible manner – for example printed or written in ink. All prescriptions should be signed in a manner that allows the prescriber to be identified later.
3 The prescription should include the drug name, dose, route of administration and frequency. Dispensing prescriptions should always include the number of days treatment or the total quantity of drug to be administered.
4 Use the approved generic name of the drug wherever possible. Only prescribe a branded product if it is important that the patient receives that product.
5 Avoid abbreviations unless approved and universally accepted. Abbreviating grams (g), milligrams (mg), millilitres (ml or mL) is acceptable but micrograms, nanograms and units must be written out in full to avoid confusion. Similarly, decimal points should be avoided wherever possible and leading decimal points should never be used (i.e. 0.5 mg rather than 0.5 mg although 500 micrograms would be better).
6 Make sure that the entire prescription is legible and avoid crossing out and correcting mistakes – it is better to rewrite the prescription if a mistake is made.
7 Note that there are specific requirements for writing controlled drug prescriptions:The form of the medicine (i.e. tablets, capsules, etc.) must be stated even if only one form is available.The total quantity of medicine to be dispensed must be stated in both words and figures (i.e. 20 (twenty) 10 mg tablets). It is not necessary to state the dose in words and figures.The prescription can be printed but must have a handwritten signature.While it is not a legal requirement, the supply of a controlled drug should not exceed 30 days except in exceptional circumstances, which should be recorded.
General pointers on good prescribing
The ability to prescribe drugs in a safe, effective and thoughtful manner is one of the defining characteristics of a good clinician. It can be a deceptively difficult skill to acquire and requires constant maintenance as the range of drugs available expands. The following advice is distilled from many years of experience of prescribing and is offered to provide some general principles applicable to most situations.
1 Wherever possible, minimise the number of drugs and total number of doses to be given. Always satisfy yourself that a prescription is necessary before considering a pharmacological solution to the problem.
2 Make an effort to ensure that the patient understands the reason for the prescription, and is aware of how it should be taken. Patients are much more likely to take a drug if they feel they understand why it is felt to be necessary.
3 Familiarise yourself with a limited number of well‐established drugs with known effects and side effects. Do not chop and change amongst equivalent preparations on whim or fancy. Avoid trying out new preparations simply because of novelty or extensive commercial promotion.
4 Check the dose carefully each time you prescribe. Do not trust to memory and be particularly careful when doses are in the microgram range or when prescribing for children and the elderly.
5 Finally, always review drug prescriptions regularly: every day in hospital patients, or weekly or monthly as appropriate in outpatients or general practice. When reviewing prescriptions ask the following questions:Is it clear why the drug has been prescribed and is it still necessary?Is the drug achieving its desired effect?Are there any symptoms or adverse effects that could be secondary to drug treatment?In general practice, has a maximum of 1 month's supply been prescribed?In patients receiving more than one treatment, is there any clinically significant drug–drug interaction that should be addressed?
Do not continue treatment by repeating prescriptions over long periods of time without assessing the response in the patient, or worse still, without seeing the patient.
Adverse drug reactions
Drug treatment is inherently dangerous. While no prescriber intends to cause harm with the drugs they prescribe, some patients will inevitably experience adverse effects from treatment. Such adverse effects can range from the mild, for example transient nausea after taking the tablets, through to life‐threatening complications. Admission to hospital due to harm related to prescription drugs is common and this is an important reason to prescribe medication only when justified.
Adverse drug reactions can be broadly classified into two groups. Type A reactions are those that are predictable, based on the known pharmacological action of the drug in question. They are common, usually dose related and typically happen relatively soon after the drug is first prescribed. In contrast, Type B reactions are those that cannot be easily predicted from the known effects of the drug. Such adverse effects are typically uncommon, not dose dependent and may occur a long time after the drug was first given. Examples of each are shown in Table 4.1.
Table 4.1 Examples of different types of drug reaction.
| Type A (predictable) adverse effects | Type B (unpredictable) adverse effects |
|---|---|
|
Dizziness or other symptoms of low |