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,
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’),
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).
