Formulation in Pharmacy Practice - eMixt

Allopurinol
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A New Zealand standardised formulation is available Formula and Batch Sheet
This formula uses Ora-Blend/SF or Ora-Plus and Ora-Sweet/SF; 1:1, and has been approved by the Extemporaneous Compounding Pharmacists' Group.
Alternatives are given below.


Allopurinol is very slightly soluble in water and alcohol.  The aqueous solubility is increased at alkaline pH but all published investigations have been performed on suspensions at acidic pH.

A 20mg per mL suspension, prepared from allopurinol tablets and a base consisting of one third methylcellulose solution 9% and two thirds of cherry flavored syrup, is reportedly chemically stable for at least 14 days at room temperature and under refrigeration.1

Allopurinol 20mg per mL prepared from tablets in a vehicle of Ora-Sweet and Ora-plus 1:1 or Ora-Sweet SF and Ora-Plus 1:1 or cherry syrup is chemically stable for 60 days at 5 or 25°C protected from light.2  The final pH of these preparations was in the range 3.2 - 4.3.  Microbial testing was not performed.

If possible allopurinol suspension should be made in accordance with the directions of the published studies1,2 but if commercial suspending vehicles are not available the following is suggested based on evaluation of the literature.

Formula

Allopurinol Suspension
Allopurinol tablets qs 
* Methylcellulose 1% 50  mL
Citric acid 250  mg
Syrup 20  mL
Water to   100  mL
*Use either 50 mL of a 1% solution or 0.5g per 100mL.  If the final product is too viscous reduce the amount of methylcellulose.
Expiry:  30 days.
Storage:  Refrigerate.  Protect from light.
Shake well before use
 

 
REFERENCES
  1. Dressman J.B., Poust R.I.  Stability of allopurinol and five antineoplastics in suspension.  Am J Hosp Pharm 1983; 40: 616-8. [PubMed]
  2. Allen LV, Erickson MA.  Stability of acetazolamide, allopurinol, azathioprine, clonazepam, and flucytosine in extemporaneously compounded oral liquids. 
     Am J Health-Syst Pharm 1996; 53: 1944-9.[PubMed]

 
Formulation in Pharmacy Practice
Page Updated August 2011