Formulation in Pharmacy Practice - eMixt


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Trimethoprim is practically insoluble in water (0.004mg per mL, at room temperature).

Compounding alternatives
Tablets or tablet fractions may disperse in water. Manufactured products such as "specials" are also available.

Compounded formulations
The current recommendation using a base of methylcellulose and syrup is based on the only published stability study.1
At present there are no data to support the use of Ora-Blend or Ora-Plus/Ora-Sweet to prepare trimethoprim suspension. However, available data suggest that trimethorom should be stable for at least 30 days in these bases.

Formula 1

Trimethoprim 10mg per mL
*Trimethoprim Tablets 100mg 10 
Methylcellulose 1% 50  mL
**Syrup BP or NF 50  mL

Prepare 100mL of a mixture of equal parts methylcellulose 1% and syrup.  Crush the trimethoprim tablets and then slowly add the base whilst mixing.  Make up to volume.
* If 100 mg tablets not available use 300 mg tablets; e.g. 4 x 300 mg tablets in a final volume of 120 mL
** A suspending base of methylcellulose 1 - 2% without syrup can be used if preferred.
Expiry:  30 days from preparation.
Stability:  6 weeks at 25°C; 3 months at 4°C.1
Storage:  Amber, plastic bottles.

1.Nahata M.C.  Stability of trimethoprim in an extemporaneous liquid dosage form.  J Ped Pharm Pract 1997; 2 (2): 82-4.

2.Stabilis database Trimethoprim