## 1 Introduction  
It is the duty of pharmacists to dispense medicines that best fit a patient's medical needs [1, 2, 3]. Historically, pharmacists used to make medicines themselves, but, nowadays, the majority of the medicines are manufactured industrially [4]. While a one-size-fits-all approach with commercially available formulations works for many patients, it is definitely not suitable for all. Particularly for children, a tailor-made adjustment to the dose or dosage form may be desired to meet the specific needs in clinical practice [5, 6]. Furthermore, alternative solutions are sought if a patient is best treated with a medicine unavailable as a commercial formulation [2, 4, 7] or to cope with the worldwide recurring supply shortages [5, 8]. In all these cases, pharmacy preparations, which are also named extemporaneous preparations or compounded products, are in place. Pharmacy preparations are currently undergoing a revival after being considered less popular and declined for reasons of poor quality in the recent past [9]. The introduction of advanced therapy medicinal products (ATMPs) requiring on-site modifications also emphasizes the importance of having pharmacists available who possess the necessary knowledge, skills, and competences for these practices, combined with ample experience in quality assurance and quality control [2; 5]. The increased demand for tailor-made medicines has led to the development of large-scale compounding pharmacies with specialized facilities and equipment in many countries, where pharmacists prepare and distribute significant quantities of commercially unavailable medications to patients, hospitals, and other (non-compounding) pharmacies [4]. According to the [PERSON] and Strand definition of pharmaceutical care, medicines are administered for the purpose of achieving definite outcomes that improve the patient's quality of life [10]. This cannot be achieved without having access to qualitatively good and safe products. This applies to industrially manufactured medicinal products as well as to tailor-made medicines and on-site modifications that fall under the responsibility of pharmacists. Pharmacists play an increasingly important role in the on-site preparation of injections to make them ready for administration in order to reduce medication errors and improve patient safety [5]. Most hospital pharmacies maintain aseptic compounding facilities with cleanrooms to be able to provide their patients with the required individual dosing and with formulations that are not available from a commercial source [7]. There has been a clear shift from carrying out activities related to parenteral dosage forms at the ward of hospitals under limited product protection to cleanrooms where dedicated and appropriately trained staff prepare the required products under enhanced or maximal product protection using aseptic techniques [11; 12]. This approach has been shown to mitigate risks in aseptic preparations and reconstituted parenteral medicines in healthcare establishments, contributing to the improvement of patient safety and the production of optimal aseptic products [12; 13; 14]. This sterile compounding practice is recognized as essential for pharmaceutical care for the benefit of patients and health services [15]. As the responsibility of tailor-made medicine production lies with pharmacists, it is their task to optimize the practice of pharmacy preparations and monitor the environment, equipment, and procedures, ensuring that the highest quality is obtained and sterility maintained [7]. That a failure in this respect can be catastrophic is illustrated by a well-known case from 2012 in the Unites States. Poor microbiological quality of methylprednisolone acetate injections from a compounding pharmacy resulted in 137 cases of _Aspergillus fumigaticus_ and _Exserohlum rostratum_ fungal meningitis and 12 deaths [16; 17]. Over time, many more medication errors associated with injectable medicines, severe harm, and deaths have been reported [4; 18].