Pharmaceutical Calculations Lecture 5

Injections

• Injections are sterile pharmaceutical solutions or suspensions of a drug substance in an aqueous or nonaqueous vehicle.
• They are administered by needle into various parts of the body, including joints, spinal column, arteries, and heart.
• Most injections are administered into a vein (intravenous), muscle (intramuscular), skin (intradermal), or under the skin (subcutaneous).

Packaging of Injections

• Injections are packaged in small volumes using ampules, prefilled disposable syringes, vials, pen-injectors, and large-volume plastic bags or glass containers for administration by slow intravenous infusion.
• Some injections are available as prepared solutions or suspensions, while others contain dry powder for reconstitution.

Parenteral and Intravenous Infusions

• Parenteral refers to any medication route other than the alimentary canal and includes all routes of injection.
• Intravenous (IV) infusions are sterile, aqueous preparations administered intravenously in relatively large volumes to extend blood volume and/or provide electrolytes, nutrients, or medications.
• IV infusions are used for critical care, infirm, dehydrated, or malnourished patients, or patients prior to, during, and/or following surgery.

Characteristics of IV Infusions

• Most IV infusions are solutions, but some are very fine dispersions of nutrients or therapeutic agents, or blood and blood products.
• Isotonicity is not absolutely necessary because the volumes of fluid usually administered are rapidly diluted by the circulating blood.
• Commercially prepared infusions are available in glass or plastic bottles or collapsible plastic bags in various volumes (50 mL, 100 mL, 250 mL, 500 mL, and 1000 mL).

Example Calculations of IV Infusions

• Example calculation: determining the amount of dextrose and sodium chloride used to prepare a 250-mL bag of D5 1⁄2NS for intravenous infusion.

Intravenous Admixtures

• The preparation of intravenous admixtures involves adding one or more drugs to large-volume sterile fluids such as sodium chloride injection, dextrose injection, and lactated Ringer's injection.
• Additives are generally in the form of small-volume sterile solutions, vials, small-volume minibags, or sterile solids, some requiring constitution with a sterile solvent before transfer.

Rate of Flow of IV Fluids

• The rate of flow of IV fluids is specified by the physician in milliliters per minute, drops per minute, amount of drug (as milligrams per hour), or approximate duration of time of administration.
• Pharmacists may be called on to perform or check rate-of-flow calculations using the following equation.
• Examples of rate-of-flow calculations include determining the rate of flow in milliliters per hour or drops per minute for a given medication order.