Preparation of Ascorbic Acid Injection

Aim: Preparation of Ascorbic Acid Injection

Objective

The aim of this experiment is to prepare a sterile aqueous solution of ascorbic acid suitable for parenteral administration, ensuring the correct concentration, pH, and sterility, and adhering to pharmaceutical quality standards.

Introduction

Ascorbic acid (Vitamin C) is a water-soluble vitamin with potent antioxidant properties. It plays a critical role in collagen synthesis, wound healing, immune function, and as a cofactor in enzymatic reactions. Deficiency of ascorbic acid results in scurvy, characterized by weakness, gum bleeding, and poor wound healing.

Therapeutic Uses:

• Treatment of Vitamin C deficiency
• Adjunct therapy in wound healing
• Antioxidant in critical illnesses or sepsis
• Supportive therapy in certain cancer or viral infections

Chemical Profile:

• Chemical Name: L-Ascorbic Acid
• Molecular Formula: C₆H₈O₆
• Molecular Weight: 176.12 g/mol
• Appearance: White to slightly yellow crystalline powder
• Solubility: Freely soluble in water, insoluble in ethanol and ether
• Stability: Sensitive to light, heat, and alkaline conditions; hence, preparation must be done under controlled conditions.

Parenteral administration is preferred when rapid vitamin C supplementation is needed, as oral absorption is limited at high doses.

Materials and Equipment

Materials

• Ascorbic acid (USP grade)
• Sterile distilled water for injection
• pH adjusting agents: Sodium bicarbonate or Sodium hydroxide (to adjust pH if needed)
• Preservatives (optional, e.g., benzyl alcohol 0.9% w/v for multi-dose vials)

Equipment

• Analytical balance
• Glass beakers, graduated cylinders, and volumetric flasks
• Magnetic stirrer
• pH meter or pH indicator strips
• Sterilizing-grade filter (0.22 μm) for filtration
• Autoclave (121°C, 15 psi) if heat-stable
• Laminar airflow chamber for aseptic filling
• Sterile ampoules or vials for injection
• Hot air oven (optional for drying ampoules)

Formulation Example (100 mL Injection)

Remarks:

• Typical parenteral concentrations: 1–2% w/v
• pH adjustment is critical; ascorbic acid is acidic (pH 2–3 in water), and too low a pH can cause vein irritation.

Theoretical Calculations

Step 1: Determine weight of ascorbic acid required

For 1% w/v in 100 mL:

Amount required = 1% × 100 mL = 1g

For 2% w/v in 100 mL:

Amount required = 2% × 100 mL = 2g

Step 2: pH Adjustment

• Ascorbic acid solutions are naturally acidic (pH 2–3).
• Slowly add sodium bicarbonate or NaOH to adjust pH to 3–4 for parenteral safety.
• Avoid excessive alkalinity, as it degrades ascorbic acid.

Procedure

Preparation of Solution

1. Accurately weigh the required amount of ascorbic acid.
2. Dissolve in 80% of the total volume of sterile distilled water using a magnetic stirrer.
3. Check pH using a pH meter. Adjust to 3–4 with dilute sodium bicarbonate or NaOH.
4. Make up to the final volume with sterile distilled water.
5. Mix gently to avoid oxidation.

Sterilization

• Filtration (preferred for heat-sensitive solutions): Pass the solution through a 0.22 μm sterilizing filter into a sterile container under laminar airflow.
• Autoclaving: Only if using heat-stable formulations and properly sealed containers (rarely used due to thermal degradation).

Filling and Sealing

• Fill sterile solution into ampoules or vials under aseptic conditions.
• Seal ampoules by flame or cap vials with sterile rubber stoppers.
• Label with drug name, concentration, batch number, and expiry date.

Quality Control Tests

1. Appearance: Clear, colorless to slightly yellow solution, free of particulates
2. pH: 3–4
3. Sterility Test: As per USP <71>
4. Assay of Ascorbic Acid: Titrimetric (using 2,6-dichlorophenolindophenol) or HPLC
5. Pyrogen Test: LAL assay or rabbit pyrogen test
6. Particulate Matter: According to USP <788>

Storage Conditions

• Store in tight, light-resistant containers to prevent degradation.
• Temperature: 2–8°C (refrigeration) is preferred for prolonged stability.
• Avoid exposure to air, light, and heat.
• Use freshly prepared solutions if possible.

Precautions

• Perform all steps under aseptic conditions to avoid microbial contamination.
• Avoid prolonged exposure to air, as ascorbic acid oxidizes rapidly.
• Adjust pH carefully; avoid over-alkalinization to prevent degradation.
• Use amber-colored vials to protect from light-induced decomposition.
• Label vials clearly, including concentration, preparation date, and expiry.

References

1. United States Pharmacopeia (USP 43-NF 38), Ascorbic Acid Injection Monograph.
2. Indian Pharmacopoeia (IP), 2020, Volume II.