Calcium hydrogen phosphate is used in drug formulation as an excipient. Once tablet compressed calcium hydrogen phosphate generates dark spots. Why are these spots generated and what about it's safety?
You need first to isolate the root cause of the dark spots. Do the compression with and without API. If it is only the excipient ask yourself if it generated phosphoric acid during compression and thus reaction with metal ions. Do excipient compatibility with the API, etc.
You may want to check this somewhat related RG discussion: https://www.researchgate.net/post/Anybody_observed_Black_particles_in_the_tablets_while_in_compression_stage
Dibasic Calcium phosphate is in abrasive nature, so upon compression at high speed, abrasion of the punches may cause dark spots. Check properly the cleanliness of the equipment to draw a conclusion whether the problem with drug(low melting point of drug cause black spots upon compression at high speed), excipients or actually with the equipment. Another reason may be aging of tools which apparently gives spots after compression.
Dibasic Calcium Phosphate is a monoclinic crystal, Due to abrasion with turret of tablet press, the blend becomes dark over a period of time. The blackening of blend containing major portion of DCP is common in conventional tablet press turret with no special coating to prevent abrasion. In such cases, to over come the blackening first rinse / condition the turret by smearing with DCP and clean off. Then load the blend and perform compression and you will see substantial improvement.
The possible causes might be:
1.Dibasic Calcium phosphate is abrasive in nature. so it might have abrasion with punches or turret of tablet machine.
2. The most possible cause might be improper cleaning. Batch to batch cleaning if not properly done, it might cause interaction with new batch ingredients. There might be incompatibility.
3.Lubrication oil on tablet press dries and circulates freely in air and finally settles on blend leading to black particles.
4. Rectification in this case is proper cleaning and lubrication.
5.If the spots are metallic Grey in color those may be of alluminium scrapping away from feed frame. Rectification in this case is visually ensure proper assembly of feed frame and empty run is recommended to identify any sound of metal touch.
6.Scrapper blade may be scrapping away. Rectification of above case is done by proper assembly of scrapper blade.
7.Feeder wheel might be rubbing against housing of feed frame.
8. Another most possible reason is incompatibility with other excipients in a formulation.
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