Objectives Our pharmacy works in accordance with the Good Manufacturing Practice in the area of multidose individual blister repackaging. This required validating the cleaning procedure of the blister machines accounting for the characteristics of our setting and investigating worst possible production scenarios.

Methods Visual clean: After machine cleaning we inspected surfaces for visible residues. Cross-contamination: A tablet vulnerable to contamination was analysed after blister packaging for residues of a medication with high contamination risk using. Critical medications in the machine were identified by their dust formation potential. Placebo tablets were blister-packaged and analysed for residues of these critical medications using mass spectrometry. We assessed pharmacological relevance of contamination from these two analyses by the dose criterion. Validity of results: Comparing production conditions and technical construction of the blister machines, validity of the validation results for the whole setting was investigated.

Results After cleaning no residues were visible on the machine. No contamination was detected on the vulnerable tablet. In 80% of 280 analysed placebo tablets contamination was not measurable or below 1% of the cut-off limits according to the dose criterion, the highest value being 8.5%. Production volume and cleanability were comparable in the other machines.

Conclusions Blister machine cleaning was successfully validated: visual cleanliness was achieved; contamination values were clearly below the cut-off limits, ruling out relevant cross-contamination of copackaged drugs. The results proved valid for the whole site. The study contributes evidence to safety and quality of blister repackaging and may serve as reference for similar settings.