Pharmaceutical Manufacturing Handbook: Production and

950 ROLE OF PREFORMULATION IN DEVELOPMENT OF SOLID DOSAGE FORMS
FIGURE 9 Measurement techniques for powder fl ow. ( a ) Angle of repose is determined
by pouring a powder through a funnel and noting the angle that the powder heap makes with
the horizontal surface. ( b ) Carr ’ s index is measured by pouring a known weight of the powder
into a graduated cylinder and tapping it on a hard surface until the powder is consolidated.
( c ) Carr ’ s index is measured as percent, while angle of repose is measured in degrees,
and both methods show good correlation. Powder fl ow is classifi ed based on either of the
measurement methods.
available for preformulation testing, either method may be used to estimate the
powder fl ow property. Poor fl owing powders may require glidants to improve their
fl ow property. Compressibility is studied by compressing the drug in a hydraulic or
IR press, and such experiments give early warnings to the formulator about capping
and lamination issues in tablets. Altogether, these preformulation tests give valuable
information to the formulator in deciding excipients and processes.
6.2.3
(a) (b)
Carr’s index (%)
5–15
12–16
18–21
23–35
33–38
>40
Powder flow
Excellent
Good
Fair to
passable
Poor
Very poor
Extremely
poor
(c)
SOLUBILITY CHARACTERISTICS
Bulk volume
Volume after tapping
Angle of repose (deg)
Drug solubility is one of the physicochemical parameters that receives lots of attention
during preformulation testing. In the initial stages, solubility studies are usually
kinetically determined, where the drug is placed in contact with the solvents and
then the solubility is assessed using turbidometric methods almost instantaneously.
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