Oliver Jones sets out a few markers

For many newly qualified doctors, being handed a drug chart on their first day at work can be bewildering. Although basic and clinical pharmacology are covered at medical school, students are often unfamiliar with the actual mechanics of prescribing.

Before you start

Always check that the patient in the bed corresponds to the name on the drug chart that you are holding. Always ask patients if they have any drug allergies and what form the allergic reaction takes. You should not rely on the (often inaccurate) information either in the notes or written on the chart itself.

Practical prescribing

Apart from the name of the drug itself, you will have to consider the dose, the route of administration, and the frequency and maximum dosage or both permitted. Write quantities in grams if over a gram; if less than a gram but more than a milligram, write as milligrams; if less than a milligram write as micrograms. Acceptable abbreviations are g and mg, but ug, mcg, or mg are not. The last three may be mistaken for mg, and so the full and unambiguous microgram should be used. Decimal points should generally be avoided as they may become "lost." If necessary always precede a decimal point with a zero-that is, 0.5 mls not .5 mls. Abbreviations are frequently and safely employed; the common ones are listed in the table.

Drug chart layout

There is a section on the front for the patient's details. The full name and hospital number should be written in as a minimum.

There are, broadly speaking, four ways to prescribe a drug and each has its own section on a drug chart:

• Drugs may be given as a single dose - for example, antibiotics as prophylaxis before an intervention. This section is usually on the front of the chart. In addition to dose and route of administration, the time and date on which you wish the drug to be given should be entered.
• Drugs may be prescribed on a regular basis, at the same times and doses each day. This section of the chart includes a column where the timing of doses should be included.
• Many medications are prescribed on an "as required" basis. The patient or the nursing staff will use their judgment on when these drugs are required. For this type of prescription, you must specify the dose itself and a minimum dose interval, such as "maximum frequency every four hours."
• The fourth part of the chart is for infusions. It can be used for fluid management, analgesia, and other drugs. The quantity of drug, its reconstitution or dilution, route, and rate of infusion should all be specified.

Brand name or generic name

Generally, it is best to prescribe using the generic (non-proprietary) name of a drug. This gives the pharmacist the option of prescribing whatever is available in the pharmacy; this saves time. Cheaper formulations may also be substituted, when available. Lithium and theophylline (and perhaps phenytoin) should be prescribed by brand (proprietary) name as bioavailability may vary between preparations.

The new patient

Much of the preregistration year is spent in clerking and admitting patients to hospital. Patients may be admitted electively for investigation or surgery. In these instances, almost invariably their usual medications should be written on to their drug charts unless these are likely to interfere with their reason for admission, such as warfarin and surgery. It is important to ask which medications are taken, their doses, frequencies, and routes. The safest and most accurate method of doing this is to ask to see the drugs themselves and for the patient to confirm which drugs are taken and by what means. Computer printouts, handwritten lists, and relatives (especially carers) may also be less reliable sources of information. A telephone call to a patient's general practitioner may resolve any residual uncertainties.

Patients who are admitted as an emergency should often receive their normal medications but several other considerations need to be borne in mind:

• The reason for admission might be attributable to some aspect of the drug regimen, such as digoxin toxicity.
• The institution of an acute or new therapeutic regimen, such as nebulised bronchodilators, may render aspects of the usual drug regimen temporarily or permanently redundant.
• The likely outcome of the admission modifies the drug regimen. For example, patients likely to undergo surgery may be kept "nil by mouth." Drugs could be given via another route, such as intravenously, but in practice anaesthetists will often be keen (but this may vary among individuals) on important drugs, such as antihypertensives, still being given with a sip of water.

Further considerations

If in doubt, ask your colleagues or the hospital pharmacist. Accurate prescribing and neat handwriting will minimise the confusion, error, and bleeps to you from pharmacists and nursing staff. You might also consider in all your patients prescribing several additional drugs on an "as required" basis. These additional drugs might include analgesics, night sedation, antiemetics, and nebulisers. This may prevent a phone call from a nurse able to manage a patient but powerless to give the drug required. However, the indiscriminate and careless prescribing of these drugs should be discouraged.