Objective To clarify the effects of the suspension vehicle on the properties of an extemporaneously compounded nifedipine oral suspension (1 mg/ml) prepared from ground-up commercial nifedipine tablets.

Methods Oral suspensions of nifedipine were compounded with six different vehicles: commercial vehicles Suspension Diluent A, Ora-Plus/Ora-Sweet, Ora-Plus/Ora-Sweet SF and SyrSpend SF Cherry, and extemporaneously prepared Methylcellulose 1%/Syrup NF and Hypromellose 1%. The suspensions were stored at room temperature and analysed at 1, 2 and 4 weeks. The effect of mixing on the content uniformity was studied by evaluating two mixing protocols: inverting the bottle manually 10–15 times or inverting it three times. The concentration of nifedipine, the uniformity of mass and the sedimentation volume were determined.

Results The content uniformity of all the suspensions complied with the Pharmacopoeia test at all time points when they were mixed by inverting the bottle 10–15 times. Bottles inverted three times did not comply with the test at 1 week when Methylcellulose 1%/Syrup NF or Hypromellose 1% were used. The uniformity of mass was within acceptable limits in all suspensions. The sedimentation volume of the unmixed Methylcellulose 1%/Syrup NF and Hypromellose 1% was higher than that of the commercial vehicles.

Conclusions In order to comply with the Pharmacopeia test for content uniformity, suspensions compounded with Methylcellulose 1%/Syrup NF or Hypromellose 1% require mixing by inverting the bottle 10–15 times. In contrast, the commercial suspension vehicles passed the test if the bottle was inverted only three times.