Preventing Off-weight Tablets

Weight is a crucial parameter of any finished drug tablet, whether prescription, over-the-counter, or nutritional supplement. Overweight tablets can result in too much of an ingredient, which may lead to a harmful effect. But tablets that are too light are also problematic because they may not offer enough of a particular ingredient to bring about an intended therapeutic benefit.  A manufacturer’s goal should be two-fold: do not produce off-weight tablets in the first place, and catch and reject them, accurately and reliably, if they are produced. The best ways to prevent the manufacturing of off-weight tablets begin before product is loaded into the hopper—through comprehensive operator training, diligent and rigorous preventive maintenance, and regularly scheduled calibration of the press and its subassemblies.

Operator training
The best and first line of defense is training on both press and process. Operators should be tested regularly to ascertain and reconfirm their proficiency with making a tablet in the absence of automation (i.e., “Tableting 101”) and with making tablets using the specific equipment their company employs as part of the manufacturing process. Training should cover the prevention of virtually all the potential causes of off-weight tablets, including how to avoid the following common causes:

• Incorrect or suboptimal weight-related machine settings, such as filling depth

• Poor or inconsistent filling of dies

• Improperly set (or missing) recirculation components

• Tablet back-up at the take-off, where rogue tablets may jump the bar and potentially re-enter a feeder

• No rejection of start-up material or improper settings related to start-up

• Suboptimal punch penetration settings

• Improper manipulation of a feeder by the operator or a poor understanding of how a feeder configuration can be modified to better suit a particular product’s flow characteristics.

The importance of training cannot be overstated.  Companies should have standard operating procedures (SOPs) and ensure that operators follow the SOPs. A tablet-press vendor should be able to demonstrate and confer comprehensive knowledge of their technology and of how it can be used to manufacture tablets of optimal quality.

A press vendor can provide training specific to understanding the feeder and optimizing its use, because the feeder has a direct correlation to maintaining acceptable tablet weights. Users should also understand and use the relationship between feeder speeds and consistent die filling.

Maintenance and calibration
Thorough preventive maintenance and regular inspection and calibration should be conducted on the entire tablet press.  In particular, users should maintain calibration of devices controlling filling depth regulation on a press.  Tooling and cams should be consistently and carefully inspected. Cam-wear indicators should be used whenever possible. A guideline for what constitutes a worn tool should be established, and it should serve as a prompt for timely replacement.

A force-based relative standard deviation should be used as an indicator of consistent tablet weights. Given the correlation between force and final tablet weight, this statistic allows an operator, with a quick glance, to determine how consistently they are compressing tablets. Many modern presses calculate this figure for the user, further streamlining the ability to quickly analyze results in real time.

Seek outside help
Companies should solicit the help of third-party experts such as tablet-press vendors, reputable consultants, or specialists in overall equipment effectiveness. Such assessments can immediately uncover multiple inadequacies in the process, machine, and/or user. The engagement of these individuals or organizations is especially valuable because they generally view the situation through a different lens, rather than being focused on getting product out the door. Off-weight tablets warrant serious attention, but through collaborative efforts this problem should be reversible and avoidable.

Matt Bundenthal is direct sales and communications manager at Fette Compacting America.

For further information on this topic, read the January 2014 issue of Pharmaceutical Technology for the full article, “Battling Off-Weight Tablets.”