Omeprazole showed an inter-individual variability and therefore a significant number of patients with acid-related disorders required higher or multiple doses to achieve symptom relief and healing. Astra started a new research program in 1987 to identify a new analogue to omeprazole with less interpatient variability. Only one compound proved superior to omeprazole and that was the (S)-(−)-isomer, esomeprazole, which was developed as the magnesium salt. Esomeprazole magnesium (brand name Nexium) received its first approval in 2000 and provided more pronounced inhibition of acid secretion and less inter-patient variation compared to omeprazole. In 2004, Nexium had already been used to treat over 200 million patients.