Liquid Paraffin

What Liquid Paraffin Is

Liquid paraffin (also called liquid petrolatum or mineral oil) is a purified mixture of liquid saturated hydrocarbons obtained from petroleum. It is chemically inert, colourless, tasteless and odourless.

In pharmacology it is grouped with the lubricant (emollient) laxatives. It is given orally for constipation and applied on the skin and eyes as a lubricant/emollient.

• Nature: a mineral oil — a mix of liquid hydrocarbons, not a single chemical.
• Class: lubricant / emollient laxative.
• Key property: taken by mouth, it is essentially not absorbed and passes through the gut largely unchanged.

Mechanism of Action

Liquid paraffin works physically rather than chemically. It coats the faecal mass and the lining of the intestine with a water-repellent film.

• Lubricates the stool and bowel wall, reducing friction so faeces slide through more easily.
• Reduces reabsorption of water from the stool in the colon, keeping it soft and moist.
• Softens hard, dry stool, easing painful defecation.
• Because it is not absorbed, it acts locally within the gut lumen.

Therapeutic Uses

• Constipation — to soften stool and make it easier to pass.
• Conditions where straining must be avoided — piles (haemorrhoids), anal fissure, and after anorectal surgery.
• As an emollient in dry skin conditions and in some ointments.
• As a lubricant in eye preparations for dry eyes.

Adverse Effects and Cautions

Liquid paraffin is best used short-term. Long-term or careless use causes the problems most exam questions focus on.

• Anal leakage (seepage) of oil and perianal irritation, especially with larger doses.
• Impaired absorption of the fat-soluble vitamins A, D, E and K on prolonged use.
• Lipoid (aspiration) pneumonia if it is inhaled — a real risk in the very young, the elderly, and those with swallowing difficulty. Do not take lying down or at bedtime.
• Contraindicated in intestinal obstruction and in children under about 3 years and other patients at risk of aspiration.

Key Terms

Lubricant laxative

A laxative that eases stool passage by coating and lubricating the stool and bowel wall rather than by chemical stimulation. Liquid paraffin is the classic example.

Emollient

A substance that softens and soothes the skin or a surface. Liquid paraffin is used as an emollient in skin and eye preparations.

Lipoid pneumonia

Lung inflammation caused by inhaling (aspirating) oil such as liquid paraffin — the main serious hazard of the drug.

Practice Quiz — 8 Questions

1. Liquid paraffin is chemically best described as:

   • A.A single organic acid
   • B.A mixture of liquid hydrocarbons (mineral oil)
   • C.A polysaccharide
   • D.A magnesium salt
   B. A mixture of liquid hydrocarbons (mineral oil) — It is a purified mixture of liquid hydrocarbons obtained from petroleum.

2. To which class of laxatives does liquid paraffin belong?

   • A.Osmotic
   • B.Stimulant
   • C.Bulk-forming
   • D.Lubricant / emollient
   D. Lubricant / emollient — It lubricates rather than stimulating or osmotically drawing water.

3. How does liquid paraffin help relieve constipation?

   • A.Stimulates colonic nerves
   • B.Coats and lubricates stool and reduces water reabsorption
   • C.Increases stool bulk by absorbing water
   • D.Kills gut bacteria
   B. Coats and lubricates stool and reduces water reabsorption — It forms a water-repellent film that lubricates and keeps stool soft.

4. A well-known hazard of liquid paraffin if it is inhaled is:

   • A.Kidney stones
   • B.Lipoid (aspiration) pneumonia
   • C.Liver failure
   • D.Hearing loss
   B. Lipoid (aspiration) pneumonia — Aspirated oil causes lipoid pneumonia; avoid giving it to those at risk of aspiration.

5. Prolonged use of liquid paraffin can reduce absorption of:

   • A.Vitamin C
   • B.Iron
   • C.Fat-soluble vitamins A, D, E and K
   • D.Calcium
   C. Fat-soluble vitamins A, D, E and K — Being an oil, it impairs absorption of the fat-soluble vitamins.

6. Liquid paraffin is CONTRAINDICATED in:

   • A.Mild seasonal allergy
   • B.Intestinal obstruction
   • C.Common cold
   • D.Mild headache
   B. Intestinal obstruction — It must not be used when the bowel is obstructed.

7. After oral administration, liquid paraffin is:

   • A.Completely absorbed and metabolised in the liver
   • B.Largely not absorbed and passes through the gut
   • C.Converted to glucose
   • D.Excreted mainly by the kidneys
   B. Largely not absorbed and passes through the gut — It is essentially non-absorbable and acts locally in the gut lumen.

8. Besides constipation, liquid paraffin is also used as a(n):

   • A.Antibiotic
   • B.Emollient/lubricant for skin and eyes
   • C.Painkiller
   • D.Antacid
   B. Emollient/lubricant for skin and eyes — It is used as an emollient in skin preparations and a lubricant in eye drops.

References

• Liquid Paraffin — ScienceDirect Topics (Pharmacology): https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/liquid-paraffin
• Liquid paraffin: a reappraisal of its role in the treatment of constipation (review)