Serious medication administration errors are common in hospitals and nurse's interruptions during medication preparation and administration is associated with errors. Various interventions were developed to help prevention of errors such as visual intervention. Investigators aimed to study the effect of a medication safety vest to reduce medication errors. The vest serves as a visible signal to inform others that the nurse is preparing and administering medications and should not be disturbed. Patients and visitors are provided with an informational flyer to inform them about the use of medication safety vests.

The hypothesis is that the vest will reduce nurse's interruptions during medication preparation and administration, and ultimately reduce medication errors.

The study is a randomized controlled trial in 30 care units of four hospitals in France. Each unit will be randomized in either the control group or the experimental group using the medication safety vest. Nurses of the unit will be selected at random to determine who will be observed during the administration rounds.The observation method will be used to evaluate the error rates in the 2 groups. The number of interruptions and error rates will be evaluated.

Serious medication administration errors are common in hospitals. Significant association between medication administration errors rate and the frequency of nurse's interruptions was shown. The estimated risk of error without interruption during preparation and administration is 2.3% whereas it doubles with 4 or more interruptions.

Various interventions were developed to help prevention of errors such as visual interventions and technology interventions.

Investigators aimed to study the effect of a medication safety vest to reduce medication errors. The vest serves as a visible signal to inform others that the nurse is preparing and administering medications and should not be disturbed. On the back of the vest is written "Do not disturb me. I am preparing medications". Patients and visitors are provided with an informational flyer to inform them about the use of medication safety vests The hypothesis is that the vest will reduce nurse's interruptions during medication preparation and administration, and ultimately reduce medication errors.

The study is a randomized controlled trial in 30 care units of four hospitals in France. Each unit will be randomized in either the control group or the experimental group using the medication safety vest. Nurses of the unit will be randomized to determine who will be observed during the administration rounds.The observation method will be used to evaluate the error rates in the 2 groups. The number of interruptions and error rates will be evaluated.

Inclusion Criteria:

- Voluntary nurses of the 30 care units who have drugs to deliver during medication administration rounds will be included.

Exclusion Criteria:

• Nurses who refuse to be observed during medication administration rounds and nurses replacement that did not work usually in the studied units will not be included.
• Nurses in the European G. Pompidou hospital who work in the 4 units involved in an other research project.
• Medication administrations during emergencies (e.g., cardiopulmonary resuscitation) will also be excluded from this study.