PEDIATRIC DOSAGE FORMS & COMPLIANCE
The form in which a drug is manufactured and the way in which the parent dispenses the drug to the child determine the actual dose administered. Many drugs prepared for children are in the form of elixirs or suspensions. Elixirs are alcoholic solutions in which the drug molecules are dissolved and evenly distributed. No shaking is required, and unless some of the vehicle has evaporated, the first dose from the bottle and the last dose should contain equivalent amounts of drug. Suspensions contain undissolved particles of drug that must be distributed throughout the vehicle by shaking. If shaking is not thorough each time a dose is given, the first doses from the bottle may contain less drug than the last doses, with the result that less than the expected plasma concen-tration or effect of the drug may be achieved early in the course of therapy. Conversely, toxicity may occur late in the course of ther-apy, when it is not expected. This uneven distribution is a poten-tial cause of inefficacy or toxicity in children taking phenytoin suspensions. It is thus essential that the prescriber know the form in which the drug will be dispensed and provide proper instruc-tions to the pharmacist and patient or parent.
Compliance may be more difficult to achieve in pediatric practice than otherwise, since it involves not only the parent’s conscientiouseffort to follow directions but also such practical matters as mea-suring errors, spilling, and spitting out. For example, the measured volume of “teaspoons” ranges from 2.5 to 7.8 mL. The parents should obtain a calibrated medicine spoon or syringe from the pharmacy. These devices improve the accuracy of dose measure-ments and simplify administration of drugs to children.
When evaluating compliance, it is often helpful to ask if an attempt has been made to give a further dose after the child has spilled half of what was offered. The parents may not always be able to say with confidence how much of a dose the child actually received. The parents must be told whether or not to wake the infant for its every-6-hour dose day or night. These matters should be discussed and made clear, and no assumptions should be made about what the parents may or may not do. Noncompliance fre-quently occurs when antibiotics are prescribed to treat otitis media or urinary tract infections and the child feels well after 4 or 5 days of therapy. The parents may not feel there is any reason to con-tinue giving the medicine even though it was prescribed for 10 or 14 days. This common situation should be anticipated so the parents can be told why it is important to continue giving the medicine for the prescribed period even if the child seems to be “cured.”
Practical and convenient dosage forms and dosing schedules should be chosen to the extent possible. The easier it is to admin-ister and take the medicine and the easier the dosing schedule is to follow, the more likely it is that compliance will be achieved.
Consistent with their ability to comprehend and cooperate, children should also be given some responsibility for their own health care and for taking medications. This should be discussed in appropriate terms both with the child and with the parents. Possible adverse effects and drug interactions with over-the-counter medicines or foods should also be discussed. Whenever a drug does not achieve its therapeutic effect, the possibility of noncom-pliance should be considered. There is ample evidence that in such cases parents’ or children’s reports may be grossly inaccurate. Random pill counts and measurement of serum concentrations may help disclose noncompliance. The use of computerized pill containers, which record each lid opening, has been shown to be very effective in measuring compliance.
Because many pediatric doses are calculated—eg, using body weight—rather than simply read from a list, major dosing errors may result from incorrect calculations. Typically, tenfold errors due to incorrect placement of the decimal point have been described. In the case of digoxin, for example, an intended dose of 0.1 mL containing 5 mcg of drug, when replaced by 1.0 mL— which is still a small volume—can result in fatal overdosage. A good rule for avoiding such “decimal point” errors is to use a lead-ing “0” plus decimal point when dealing with doses less than “1” and to avoid using a zero after a decimal point .