Formulation in Pharmacy Practice   eMixt

Mercaptopurine
 
 
Overview: Mercaptopurine is practically insoluble in water.  The drug is susceptible to oxidative degradation which is increased by contact with water, exposure to light and alkaline pH.1
Mercaptopurine 10mg (Purinethol®) tablets are available in some countries and they disperse readily in water.
A 50mg per mL suspension prepared from tablets is reported to be stable for 14 days at room temperature2 but conclusons are limited due to small sample numbers.  Tablets were suspended in a base of 1/3 methylcellulose 9% solution and 2/3 syrup and stored in amber glass bottles.  The suspension was also stable at 5°C for 14 days but had an increased tendency to cake.
Alternative bases, such as simple syrup, have been suggested but no documented stability information has been located.  Preparation of mercaptopurine suspensions should be avoided if possible. A maximum expiry date of 7 days is advised.  Special attention should be paid to the possibility of caking and poor dose uniformity.

Alternatives: Commercially prepared product such as a special recommended (see below). An alternative to preparing a suspension is to supply the required dose as tablets in unit-dose oral syringes.3  The plunger of an oral liquid syringe is removed and the required dose (usually in multiples of 10mg) is placed in the barrel.  The plunger is replaced and depressed sufficiently to hold the tablets in place and prevent agitation.  The syringes are then capped and labelled with instructions for the caregiver.  To give the dose the cap is removed and about 2mL of water drawn up into the syringe which is then re-capped and allowed to stand for 1 - 3 minutes to allow the tablets to disperse.
The dispersion can then be administered, mixing with flavoured juice if required.
Used syringes can be rinsed and disposed of, or returned to the Pharmacy for disposal.



References
  1. Van Scoik.  6-Mercaptopurine.  In: Connors KA, Amidon GL, Stella VJ.  Chemical Stability of Pharmaceuticals, 2nd Ed. New York, John Wiley, 1986: 544-7.
  2. Dressman JB, Poust RI.  Stability of allopurinol and of five antineoplastics in suspension.
    Am J Hosp Pharm 1983;40: 616-18.
  3. Woods DJ, Simonsen K.   Administration of liquid dose forms of 6-mercaptopurine to paediatric patients.  Journal of Paediatrics and Child Health 1995; 31 (1): 62.
 
     
Formulation in Pharmacy Practice
Page updated October 2013