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Chapter: Basic & Clinical Pharmacology : Rational Prescribing & Prescription Writing

The Prescription

Although a prescription can be written on any piece of paper (as long as all of the legal elements are present), it usually takes a specific form.


Although a prescription can be written on any piece of paper (as long as all of the legal elements are present), it usually takes a specific form. A typical printed prescription form for outpatients is shown in Figure 65–1.


In the hospital setting, drugs are prescribed on a particular page of the patient’s hospital chart called the physician’s order sheet(POS) or chart order. The contents of that prescription arespecified in the medical staff rules by the hospital’s Pharmacy and Therapeutics Committee. The patient’s name is typed or written on the form; therefore, the orders consist of the name and strength of the medication, the dose, the route and frequency of adminis-tration, the date, other pertinent information, and the signature of the prescriber. If the duration of therapy or the number of doses is not specified (which is often the case), the medication is contin-ued until the prescriber discontinues the order or until it is termi-nated as a matter of policy routine, eg, a stop-order policy.

A typical chart order might be as follows:




10:30 a.m.


(1)       Ampicillin 500 mg IV q6h × 5 days


(2) Aspirin 0.6 g per rectum q6h prn temp over 101 [Signed] Janet B. Doe, MD

Thus, the elements of the hospital chart order are equivalent to the central elements (5, 8–11, 15) of the outpatient prescription.

Elements of the Prescription

The first four elements (see circled numerals in Figure 65–1) of the outpatient prescription establish the identity of the prescriber: name, license classification (ie, professional degree), address, and office telephone number. Before dispensing a prescription, the pharmacist must establish the prescriber’s bona fides and should be able to contact the prescriber by telephone if any questions arise. Element [5] is the date on which the prescription was writ-ten. It should be near the top of the prescription form or at the beginning (left margin) of the chart order. Since the order has legal significance and usually has some temporal relationship to the date of the patient-prescriber interview, a pharmacist should refuse to fill a prescription without verification by telephone if too much time has elapsed since its writing.Elements [6] and [7] identify the patient by name and address.The patient’s name and full address should be clearly spelled out.


The body of the prescription contains the elements [8] to [11] that specify the medication, the strength and quantity to be dispensed, the dosage, and complete directions for use. When writing the drug name (element [8]), either the brand name (proprietary name) or the generic name (nonproprietary name) may be used. Reasons for using one or the other are discussed below. The strength of the medication [9] should be written in metric units. However, the prescriber should be familiar with bothsystems now in use: metric and apothecary. For practical purposes, the following approximate conversions are useful:


1  grain  (gr)  =  0.065  grams  (g),  often  rounded  to 60 milligrams (mg)


15 gr = 1 g


1 ounce (oz) by volume = 30 milliliters (mL)


1 teaspoonful (tsp) = 5 mL


1 tablespoonful (tbsp) = 15 mL


1 quart (qt) = 1000 mL


1 minim = 1 drop (gtt)


20 drops = 1 mL


2.2 pounds (lb) = 1 kilogram (kg)


The strength of a solution is usually expressed as the quantity of solute in sufficient solvent to make 100 mL; for instance, 20% potassium chloride solution is 20 grams of KCl per deciliter (g/dL) of final solution. Both the concentration and the volume should be explicitly written out.


The quantity of medication prescribed should reflect the anticipated duration of therapy, the cost, the need for continued contact with the clinic or physician, the potential for abuse, and the potential for toxicity or overdose. Consideration should be given also to the standard sizes in which the product is available and whether this is the initial prescription of the drug or a repeat prescription or refill. If 10 days of therapy are required to effec-tively cure a streptococcal infection, an appropriate quantity for the full course should be prescribed. Birth control pills are often prescribed for 1 year or until the next examination is due; how-ever, some patients may not be able to afford a year’s supply at one time; therefore, a 3-month supply might be ordered, with refill instructions to renew three times or for 1 year (element [12]). Some third-party (insurance) plans limit the amount of medicine that can be dispensed—often to only a month’s supply. Finally, when first prescribing medications that are to be used for the treat-ment of a chronic disease, the initial quantity should be small, with refills for larger quantities. The purpose of beginning treat-ment with a small quantity of drug is to reduce the cost if the patient cannot tolerate it. Once it is determined that intolerance is not a problem, a larger quantity purchased less frequently is sometimes less expensive.


The directions for use (element [11]) must be both drug-specific and patient-specific. The simpler the directions, the better; and the fewer the number of doses (and drugs) per day, the better. Patient noncompliance (also known as nonadherence, failure to adhere to the drug regimen) is a major cause of treatment failure. To help patients remember to take their medications, prescribers often give an instruction that medications be taken at or around mealtimes and at bedtime. However, it is important to inquire about the patient’s eating habits and other lifestyle patterns, because many patients do not eat three regularly spaced meals a day.


The instructions on how and when to take medications, the duration of therapy, and the purpose of the medication must be explained to each patient both by the prescriber and by the phar-macist. (Neither should assume that the other will do it.)

Furthermore, the drug name, the purpose for which it is given, and the duration of therapy should be written on each label so that the drug may be identified easily in case of overdose. An instruction to “take as directed” may save the time it takes to write the orders out but often leads to noncompliance, patient confusion, and medica-tion error. The directions for use must be clear and concise to prevent toxicity and to obtain the greatest benefits from therapy.


Although directions for use are no longer written in Latin, many Latin apothecary abbreviations (and some others included below) are still in use. Knowledge of these abbreviations is essential for the dispensing pharmacist and often useful for the prescriber. Some of the abbreviations still used are listed in Table 65–1.


Note: It is always safer to write out the direction without abbreviating.


Elements [12] to [14] of the prescription include refill infor-mation, waiver of the requirement for childproof containers, and additional labeling instructions (eg, warnings such as “may cause drowsiness,” “do not drink alcohol”). Pharmacists put the name of the medication on the label unless directed otherwise by the pre-scriber, and some medications have the name of the drug stamped or imprinted on the tablet or capsule. Pharmacists must place the expiration date for the drug on the label. If the patient or pre-scriber does not request waiver of childproof containers, the phar-macist or dispenser must place the medication in such a container. Pharmacists may not refill a prescription medication without authorization from the prescriber. Prescribers may grant authori-zation to renew prescriptions at the time of writing the prescrip-tion or over the telephone. Elements [15] to [17] are the prescriber’s signature and other identification data.


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