AIMS OF THE STUDY: Inappropriate use of antimicrobials is associated with the emergence of antimicrobial resistance and adverse events. Antimicrobial stewardship programmes may both optimise treatment of infections and reduce antimicrobial resistance but are implemented in only a minority of Swiss hospitals. In addition, data on prescribing patterns and quality are scarce. We conducted a repeated point prevalence survey to evaluate the quality of antimicrobial prescribing in a single tertiary care centre. METHODS: Antimicrobial use was audited twice (summer 2017 and winter 2018) among all patients admitted to the University Hospital Basel, Switzerland. Data were collected from the electronic health record. Appropriateness of antimicrobial use was evaluated according to previously published rules and local national guidelines. RESULTS: We evaluated 1112 patients of whom 378 (34%) received 548 prescriptions in total (30% for prophylaxis). Penicillins with β-lactamase inhibitors were most commonly used (30%), followed by cotrimoxazole (12%) and ceftriaxone (7%). Intravenous administration was chosen in 56% of patients. Prior to antimicrobial therapy, blood cultures were collected in 69% of patients. Overall, 182 (33%) prescriptions were not appropriate; reasons included lack of indication (11%), incorrect dosing (7%), delay in intravenous to oral switch (9%) or non-adherence to local guidelines (15%). A minority of patients received antimicrobials despite documented allergies (2%). Almost 38% of empirical prescriptions were inappropriate, compared with only 19% of prophylactic and 20% of targeted prescriptions. Penicillins with β-lactamase inhibitors and cephalosporins were most commonly involved in inappropriate prescribing (>50%) followed by carbapenems (30%), narrow-spectrum penicillins (17%) and cotrimoxazole (6%), with oral administration being involved less frequently than intravenous administration (15 vs 37%). Infectious diseases consultation and presence of immunosuppression were associated with reduced odds (odds ra-tio [OR] 0.38, 95% confidence interval [CI] 0.21-0.70 and OR 0.31, 95% CI 0.17-0.54, respectively) of inappropriate prescription in the per-patient multivariable analysis, whereas being admitted to a surgical or intensive care unit was associated with increased odds (OR 1.83 and 5.67) compared with a medical unit. CONCLUSION: Almost one third of prescriptions were inappropriate in our tertiary care centre despite local guidelines and an on-demand infectious diseases consultation service. Our results underscore the need for expanding current antimicrobial stewardship efforts, including national initiatives such as stewardship and prescribing guidelines, repeated surveys and identification of areas for improvement including timely intravenous to oral switches in order to reduce the consequences of inappropriate prescribing and of multidrug resistant organisms.

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Background Solid-organ transplantation due to end-stage organ disease is increasingly performed in people living with HIV. Despite improved transplant outcomes, management of these patients remains challenging due to higher risk for allograft rejection, infection and drug–drug interactions (DDIs). Complex regimens for multi-drug resistant HIV-viruses may cause DDIs particularly if the regimen contains drugs such as ritonavir or cobicistat. Case presentation Here we report on a case of an HIV-infected renal transplant recipient on long-term immunosuppressive therapy with mycophenolate mofetil and tacrolimus dosed at 0.5 mg every 11 days due to the co-administration of a darunavir/ritonavir containing antiretroviral regimen. In the presented case the pharmacokinetic booster was switched from ritonavir to cobicistat for treatment simplification. A close monitoring of tacrolimus drug levels was performed in order to prevent possible sub- or supratherapeutic tacrolimus trough levels. A progressive decrease in tacrolimus concentrations was observed after switch requiring shortening of tacrolimus dosing interval. This observation was unexpected considering that cobicistat is devoid of inducing properties. Conclusions This case highlights the fact that the pharmacokinetic boosters ritonavir and cobicistat are not fully interchangeable. Therapeutic drug monitoring of tacrolimus is warranted to maintain levels within the therapeutic range.