Injectable Drug Dosages

Parenteral medications are those that are administered as injection to the patient. Due to the route and the presentation of these medications the effects are faster.

Drugs for parenteral use are dispensed as either liquid or powder form. The drugs may also be supplied in glass or plastic ampoules or in a vial with a rubber stopper. Management of these different ampoules will be the focus of lessons throughout the drug administration course. You may also access some medications in pre-filled syringes where they are distributed by the manufacturer already drawn up into a syringe ready for administration. At times the dose supplied by the manufacturer may exceed the dose that has been ordered and it will be necessary for you to discard a portion of the medication from the syringe prior to administration.

When calculating drug dosages for injection it is important to take into account the type of syringe in which they will be measured. It is important that you use the smallest syringe available that will accommodate the volume of fluid to be administered. When considering which syringe to use ensure that there is ample room for the volume. It is not safe practice to use a syringe that is filled to capacity and the plunger is threatening to fall out the end.

When completing drug calculations for injectable medications it may be necessary to round off the answer in order for the dosage to be determined.

The following rules apply.

  • Round injectable medications less than 1 mL to hundredths - use a Tuberculin (1mL) syringe which is calibrated in hundredths
  • Round injectable medications more than 1 mL to tenths - use a 3mL or larger syringe which is calibrated in tenths

Note: When giving injectable medications that are 1 mL or less, and the calculation works out to even tenths, accurate measurement is possible with either a TB or 3mL syringe.

Injectable medications that may be unstable in solution, are packaged in powder form. All package or label directions must be followed exactly. These directions will specify the amount and type of diluent to use, and the strength of the prepared solution. Other information, like proper storage after reconstitution and the length of time the preparation can be safely used is also included. In a multi-dose vial, it is essential that the nurse mark on the container the date and time of preparation, the strength of the resulting solution, the expiration of potency, storage directions and his/ her initials.

Some packaging for drugs to be reconstituted will have several options that yield different strengths of medication. When in this position, the nurse should select the strength closest to the ordered dose and consider the number of injections required for administration. The goal, where possible is to provide the medication as one injection and not multiple. Factors such as weight, age and site for administration should be considered when reconstituting powdered medications.