Methylparaben|Role of excipient

 Methylparaben

Methylparaben is used as an antimicrobial preservative in food, cosmetics, and pharmaceutical formulations. In simple words, the role of methylparaben is to preserve food for a long duration and to protect pharmaceutical products from microbial growth.

Any pharmaceutical formulation where we use natural ingredients like sugar or gum acacia may promote microbial growth because natural ingredients are good sources to promote microbial growth to prevent this grown methyl parabenes are used alone or in combination with other parabenes like propylparaben.

Methylparaben is also used as an antimicrobial preservative in liquid dosage forms and multi-dose sterile preparations.

Other Names

Alternative names of Methyl Parabenes are as follows,

• Uniphen P-23
• Nipagin M
• E218

Function or Role

• It is used as an antimicrobial preservative.
• Parabenes are more effective against moulds and yeast but they also show a broad spectrum of antimicrobial activity.
• In the case of bacteria, parabenes are more effective against gram-positives as compared to gram-negative bacteria.
• The antimicrobial activity of methylparaben is increased with an increase in the chain length of the alkyl group.
• Aqueous solubility of methylparaben is decreased with an increase in the chain length of the alkyl group.
• Methyl parabenes show antimicrobial activity at pH 4-8.

Increased Activity

• The antimicrobial preservative effect of methylparaben is increased when we use propylene glycol 2-5% with it or by using other preservatives like imidurea.

Solubility

• Methylparaben is also available in salt form as methylparaben sodium.
• Methylparaben without salt form means simple methylparaben is not soluble in cold water rather it is soluble only in hot water.
• If methylparaben is added in cold water or water at room temperature then it is not dissolved and form very hard lumps which are very difficult to break and if  it is added in any liquid manufacturing vessel which has outflow valve at the bottom then this hard mass may block the opening of vessel valve and then it will be very difficult to open it.
• So care should always be required while selecting the form of methylparaben, meaning if we want to use methylparaben then use hot water and never use cold water and if we want to use methylparaben sodium then we can use normal water.

Concentration Used

Methylparaben is used in different concentration for the preservation of different dosage forms and some examples are given as,

Combination

• Methylparaben and propylparaben are used in combination for the preservation of parenteral preparations and the concentration used for methylparaben is 0.18% and propylparaben is 0.02%.

Incompatible

• Methylparaben is incompatible with non-ionic surfactants like Polysorbate 80 so in the presence of polysorbate 80, the antimicrobial activity of methylparaben is reduced.
• If we use propylene glycol the methyl parabene(also other parabenes)does not react with the polysorbate 80.

Methylparaben is also incompatible with the following,

• Bentonite
• Talc
• Tragacanth
• Sorbitol

Methylparaben is reported to be absorbed by plastic bottles however the low density and high-density polyethylene bottles do not absorb methylparaben.Discoloration of methylparaben takes place in the presence of iron.

Safety

Methylparaben is used in food, cosmetics and a large number of pharmaceutical products.

 It is also used in the preservation of injections and ophthalmic preparations but now their use in injections and ophthalmic formulations is not considered suitable due to the irritating effect.

References:

1. Handbook of pharmaceutical excipients.
2. Self Experience.
3. Practical Observations.

Also Read:

1. Role of mannitol in pharmaceutical products.
2. Uses of Starch and modified starch in tablet manufacturing.
3. Different Grades of Microcrystalline Cellulose or Avicel .
4. Role of Dibasic calcium phosphate in tablet manufacturing.