The error occurred when the worker put blister packs of Nevirapine into nine boxes marked as containing Zidovudine (AZT). Both drugs are commonly prescribed as part of first-line ARV treatment regimens.
Adcock became aware of the problem in June, but only notified the Medicines Control Council (MCC), South Africa's drug regulatory authority, in July and announced the recall of the two batches of drugs on 8 August.