Coltellini was dismissed from the post in 1772 after one of his satires angered the Empress Maria Theresia, and he accepted the job of official librettist for the Imperial Theatre in Saint Petersburg, Russia. Here he provided texts for Giovanni Paisiello and Traetta (Antigona). He again fell into disgrace and his sudden death was rumoured to be the result of poisoning.
References
Sources
Booklet notes to Christophe Rousset's recording of Traetta's opera Antigona (Decca, 2000)