Failure to meet process capability Index

I have a product with three active pharmaceutical ingredients. During data analysis of the assay (% content of the API) from 10 batches, two APIs out of three donot comply the process capability Index. The content of the API were 500 mg, 60 mg and 4 mg. The Cpk was more than 1.33 only in the API of 500 mg. However, all three were within the specification. The USL and LSL were respectively 110% and 90%. The maximum assay obtained was 107% which was responsible to cause high standard deviation, otherwise other were in the range of 100%.

Now my question is although the process capability index is less than 1.33, could we conclude that the process is suitable as all the parameter meets their specification?

I think You need to calculate Cp also alongwith Cpk to confirm that your process is suitable

For which tablet parameters we need to calculate CpK?

It depends on the acceptance criteria, but just because your product was good means nothing. The point of the validation is to predict future lots and what your results are telling you is that your process is not very capable. CpK of 1.33 means there will be about 64 ppm failing. a CpK of 1-1.33 is 64-2700ppm failing… less than 1 is really bad and you probably need to fix your process and is more than 2700ppm will not be meeting your specifications.