Formulation in Pharmacy Practice   2nd Edition

FOLIC ACID
 
Folic Acid is practically insoluble in water but the addition of sodium hydroxide forms soluble sodium folate.  Folic Acid injection has a pH of 8 - 11.
Oral solutions and a range of tablet strengths (most brands disperse rapidly) are available in some countries.
The stability of a 1mg per mL folic acid solution for oral use has been briefly reported.1
The following recommendations are made on the basis of this study and from the formulation of the injection.

Formula A

Folic Acid 1mg per mL
 
Folic Acid injection, 15mg per mL mL
Parabens 0.1  %
*Sodium hydroxide solution 1M qs to  pH 8
Water to   60  mL
 
*Addition usually unnecessary; only necessary if final pH < 8
 
Expiry:  30 days
 
Storage:  Refrigerate.  Protect from light.
 

Formula B

Folic Acid 1mg per mL
 
Folic acid tablets 5mg 10   
Sodium hydroxide solution 1M qs to  pH 8
Parabens 0.1 
Water to   50  mL
 
Expiry:  30 days
 
Storage:  Refrigerate.  Protect from light.
 

 
NOTES
  1. Parabens are suggested on the basis that sodium propyl hydroxybenzoate was used in the
    study cited.
  2. For a preservative free preparation omit the parabens and assign an expiry date of 7 days.
  3. If sodium hydroxide is not used, folic acid may be in suspension and mixtures should be shaken prior to administration.

REFERENCE
  1. Smith S.G.  A folic acid solution for oral use.  Pharm J 1976; February 7: 108
Formulation in Pharmacy Practice
2nd Edition