Retention of Reserved sample

Why Reserved sample are retained 1 year after expiration.

It is recommended by different regulatory agencies.

Ya. Its true but why it is needed. We can keep it till expiry date also. Why one year more than expiry date.

All documents of the batch has to be stored one year after expiration date of the batch. As like this, Retention sample also should store one year after expiration.It is need of regulatories.

As per schedule M control sample shall be stored upto 03 months after expiry. Then what is the need to store retention sample for one year.