Drug Incompatibilities Consider all drugs incompatible unless compatibility is stated. Compatibility is affected by several factors, including pH, temperature, strength, and composition, to name a few. Compatibility data are listed in drug package inserts and current drug references. This information includes the choice of diluents, such as SW or sterile NS solution. One may be compatible with a drug and the other may not. With increasing numbers of drugs, the need to check for drug interactions and incompatibilities becomes more urgent. Hypodermic General term used for injections “under the skin.” The most common sites for subcutaneous injection are the subcutaneous fatty areas of the upper posterior arm, the abdomen, and the anterior thigh (Figure 8-2). Medications for subcutaneous and intramuscular injections are administered with a variety of equipment, including vials, ampules, prefilled syringes, and syringe cartridges, as illustrated below. Ampules are single-dose glass containers containing liquid medications and solutions. Vials are supplied as singledose or multidose glass containers and may contain liquid or dry medication forms (Figure 8-4). Prefilled syringes reduce the chance of contamination during preparation of the medication. There is no substitute for supervised and, later, independent experience, but learning can be greatly expedited. Assuming that you have learned to identify syringe capacities and calibration amounts (covered in Chapter 6), focus on a commonly used syringe size for each route and an approximate needle size and usual amount. Try to learn syringe and needle size selection in sequential order from the intradermal to intramuscular or vice versa (Table 8-1). Then, in the clinical setting, modifications and the selection of needles and the appropriate angle of injection for specific-sized patients can be added to the body of knowledge. TABLE 8-1 Usual Syringe Size, Needle Size, and Doses *The intradermal route is not used for medication administration. Skin test amounts are usually 0.1 mL. RAPID PRACTICE 8-2 Parenteral Dose Calculations Estimated completion time: 20-30 minutes Answers on page 527 1. Ordered: nafcillin 0.45 g IM q4h, an antibiotic, for a patient with infection. a. Drug concentration after reconstitution: _______________________________ b. Estimated dose: _________________________________________________ c. How many mL will you prepare for the syringe provided below? d. Evaluation: ______________________________________________________ Draw a vertical line through the nearest measurable amount on the syringe provided. 2. Ordered: diazepam 6 mg stat for a patient with anxiety. a. Drug concentration: ______________________________ b. Estimated dose: _________________________________________________ c. How many mL will you prepare? d. Evaluation: ______________________________________________________ Draw a vertical line through the nearest measurable amount on the syringe provided. 3. Ordered: morphine sulfate 9 mg IM stat, an opioid narcotic, for a patient in pain. a. Drug concentration: _______________________________ b. Estimated dose: __________________________________________________ c. How many mL will you prepare? d. Evaluation: ______________________________________________________ Draw a vertical line through the nearest measurable dose on the syringe provided. 4. Ordered: lorazepam 2 mg bid IM stat, a sedative and anti-anxiety agent, for an agitated elderly patient. a. Drug concentration: _______________________________ b. Estimated dose: __________________________________________________ c. How many mL will you prepare? d. Evaluation: ______________________________________________________ Draw a vertical line through the nearest measurable dose on the syringe provided. 5. Ordered: digoxin 0.125 mg IM daily, for a patient with heart failure. a. Drug concentration: _______________________________ b. Estimated dose: __________________________________________________ c. How many mL will you prepare? d. Evaluation: ______________________________________________________ Draw a vertical line through the nearest measurable dose on the syringe provided.
Injectable Medication Calculations
Introduction
When in doubt, check with the pharmacist and document the finding.
Subcutaneous Injections
Administering Injections
However, they do not entirely eliminate that risk because dose adjustments may be required with prefilled syringes. They may contain 0.1 to 0.2 mL of extra medication in case of loss during preparation.
Route
Usual Syringe Size
Needle Size
Average/Usual Amount
Maximum Amount per Site
Intradermal*
1-mL syringe
½ inch or less
0.1-mL injection
0.5 mL*
Subcutaneous
1- to 3-mL syringe
½ to 1 inch
0.5 mL
1 mL
Intramuscular
3-mL syringe
1 to 2 inches
2 mL
3 mL
There are many variations on the sizes and amounts shown in Table 8-1. These figures are just averages.
Note the C II on the morphine label. Recall that it means that the drug is a federally controlled substance, Schedule II, a category of drugs with strong potential for abuse as well as useful medical purposes. Morphine is an opium-derived narcotic. There are strict record-keeping requirements for controlled drugs as well as limitations on the number of doses that can be prescribed before a renewal is required.
Assess the patient for respiratory depression before giving an opioid and thereafter until the drug effect has diminished. There are several visual analog scales (VAS) available for assessing current pain levels. The patient identifies the current level on a “no pain” to “worst pain” or “severest pain” subjective rating. Find out which scale your agency prefers. This practice may reduce the risk of overmedication.
Focus intently on decimals when they appear in medication orders or drug labels. Review decimal calculations in Chapter 1 as needed to ensure that you are comfortable with decimal addition, division, and multiplication. Dose calculation errors are large if a decimal point is misplaced. Write neatly and make decimal points prominent.
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