Purpose

The present study details characterisation of the electrostatic properties of a range of active pharmaceutical ingredients (APIs) and blends and investigates the role of electrostatics as a potential root cause of punch sticking during tabletting.

Methods

Microcrystalline cellulose (AVICEL® PH-102) and magnesium stearate were used to prepare blends of constant drug loading (10% w/w) with a range of APIs. The electrostatic properties of the APIs and blends were then determined using a JCI Chilworth 155v6 Charge Decay Time Analyser (CDTA) under controlled environmental conditions. The measurements recorded were then correlated to a punch sticking assessment of each blend, which was obtained utilising a Material Adhesion Screen for Sticking (MASS) Punch.

Results

The APIs became electrostatically charged to a higher extent than the blends. The linear relationship between particle punch sticking and the maximum surface voltage (Vs) attained post charging was poor (R2 = 0.58). However, a reduction in the susceptibility of the blend to retain electrostatic charge, as determined by the measurement of charge decay times (Time 1/e and Time 10%), was found to be linearly proportional (R2 = 0.89 and 0.88 respectively) to the sticking propensity.

Conclusion

Despite the excipients significantly damping the charging propensity of the API in a formulation, the electrostatic behaviour and punch sticking propensity of the majority of the formulated blends were shown to be dominated by the API (even at only 10% w/w). It is anticipated that the use of formulations with fast charge decay rates may reduce sticking problems during tablet production.

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