Product Preparation, Compounding and Sterile Products
Compounding fundamentals
Non-sterile compounding requires a master formula or prescription, accurate weighing and measuring, and a complete compounding record. Key techniques include geometric dilution for a small amount of powder in a large volume, levigation to make an ointment smooth, trituration for potent drugs, and the aliquot method when the balance cannot weigh the required quantity accurately. Know percentage concentrations: percent w/v means grams per 100 mL; percent w/w means grams per 100 g. Ratio strengths such as 1:1000 must be converted before calculations.
Sterile products
Sterile compounding follows NAPRA standards: a segregated cleanroom, a HEPA-filtered primary engineering control, correct ISO classification, garbing and hand hygiene, aseptic technique, the first-air principle, and environmental monitoring. Hazardous drugs require a biological safety cabinet or containment isolator, closed-system transfer devices, and PPE. Beyond-use dates depend on the product, container, and storage conditions and must be assigned from validated data, not invented.
Worked example
Prepare 500 mL of a 1:5000 w/v solution from a 1:500 stock. Convert: 1:500 = 0.2 percent w/v; 1:5000 = 0.02 percent w/v. Use C1V1 = C2V2: 0.2 percent x V1 = 0.02 percent x 500 mL, so V1 = 50 mL, made up to 500 mL with diluent. Check: 50 mL of 2 mg/mL = 100 mg in 500 mL = 0.2 mg/mL = 1:5000.
Traps
- Confusing w/v and w/w, or mg/mL and percent.
- Forgetting displacement volume when adding powder to a liquid.
- Assigning a beyond-use date from memory rather than the standard.
- Touching critical surfaces or interrupting first air.
- Using a horizontal hood for hazardous drugs.
Rule of thumb: write the calculation, check units, and have a second person verify high-risk compounds.