Functions and Uses of National Drug Standard Pharmacopoeia-Grade Castor Oil as Raw Material for Pharmaceutical-Grade Castor Oil Preparations

I. Pharmacopoeia Quality Standards for Pharmaceutical-Grade Castor Oil

1. Characteristics

- Appearance: An almost colorless or slightly yellow clear viscous liquid; faint odor, mild taste followed by slight pungency.

- Physicochemical Properties:

- Relative Density: Should be 0.956–0.969 at 25°C.

- Refractive Index: Should be 1.478–1.480 at 20°C.

- Viscosity: Kinetic viscosity not less than 100 mm2/s (25°C, capillary viscometer method).

- Acid Value: Not more than 2.0 (indicating free fatty acid content).

- Saponification Value: Should be 176–186 (reflecting fatty acid glyceride content).

- Iodine Value: Should be 82–90 (indicating degree of unsaturation).

2. Identification

- Chemical Identification:

- Take 1 ml of the sample, add 3 ml of ethanol, shake, filter, and heat 1 ml of the filtrate on a water bath; a black precipitate forms.

- Infrared Spectroscopy Identification: The infrared absorption spectrum should match the reference spectrum (Spectrum Collection Figure 152).

3. Tests

- Color: Compare with an equal volume of reference solution; the sample should not be darker.

- Impurities: Heat 50 g of the sample to 105°C, cool, and weigh; weight loss should not exceed 0.5%; residue on ignition should not exceed 0.1%.

- Free Fatty Acids: Calculated as oleic acid, not more than 1.0% (determined by titration).

- Heavy Metals: Heavy metal content should not exceed 10 ppm.

- Arsenic Salts: Should not exceed 2 ppm.

- Microbial Limits: Must comply with pharmacopoeial standards, such as bacterial count not exceeding 100 cfu per gram, mold and yeast count not exceeding 100 cfu per gram, and absence of Escherichia coli.

4. Assay

- The pharmacopoeia does not specify assays for the main components of castor oil but ensures quality by controlling physicochemical properties (e.g., acid value, saponification value, iodine value).

Functions and Uses of National Drug Standard Pharmacopoeia-Grade Castor Oil as Raw Material for Pharmaceutical-Grade Castor Oil Preparations

Efficacy and Uses of Pharmaceutical-Grade Castor Oil

1. Laxative (Oral)

- Mechanism of Action: Castor oil is hydrolyzed by esterases in the intestine to form ricinoleic acid, which stimulates the intestinal mucosa, promotes peristalsis, and increases intestinal fluid secretion, thereby producing a laxative effect.

- Indications: Used to treat habitual constipation, pre-surgery or pre-examination bowel cleansing, particularly suitable for populations such as pregnant women (under medical guidance) and children who should avoid stimulant laxatives. However, caution is needed due to its strong effect to prevent dehydration from overdose.

2. Ointment Base and Emulsifier

- Use as Pharmaceutical Excipient:

- As an ointment base, castor oil provides good viscosity and moisturizing properties, commonly used in topical ointments (e.g., antifungal ointments, dermatological medications) to enhance drug adhesion and permeability.

- As an emulsifier, it can be combined with other excipients (e.g., stearic acid, polysorbates) to prepare oil-in-water (O/W) or water-in-oil (W/O) emulsions for ointments, creams, or liniments.

3. Lubricant (Topical)

- For local application, castor oil serves as a lubricant for the skin and mucous membranes, alleviating dryness and cracking (e.g., hand and foot crack creams) or for instrument lubrication (e.g., lubricant during anal examinations) to reduce friction and irritation.

4. Drug Carrier (Solvent)

- Due to its ability to dissolve various fat-soluble drugs (e.g., certain hormones, vitamins, antibiotics), castor oil is often used as a solvent in injectables (e.g., some intramuscular formulations) or oral preparations to improve drug solubility and stability. For example, dexamethasone palmitate injection uses castor oil as the solvent.

5. Other Medical Uses (Extended)

- Labor Induction Aid: In obstetrics, it was historically used orally for labor induction (by stimulating intestinal reflexes to induce uterine contractions), though it is now less commonly used alone in clinical practice and requires strict medical supervision.

- Cosmetic and Daily Chemical Excipient: Owing to its moisturizing and nourishing properties, castor oil is also commonly used in medicinal cosmetics (e.g., conditioners, skincare creams) as an auxiliary ingredient to improve product performance.