Lost in Translation: Interprofessional Variability in Understanding Pro Re Nata (PRN) Prescribing in Geriatric Practice—A Prospective Observational Study

Background/Objectives: Medication safety is a critical concern in older adults due to age-related vulnerability, multimorbidity, and polypharmacy. Pro Re Nata (PRN, “as needed”) prescribing is common in geriatric care but may be interpreted inconsistently across healthcare professionals, potentially increasing the risk of medication errors. This study aimed to evaluate PRN prescribing patterns in hospitalized older adults and assess interprofessional perceptions of the clarity and appropriateness of PRN prescribing for conditions. Methods: We conducted a prospective, single-day observational study in a French geriatric university hospital, including all patients aged ≥65 years with at least one medication prescription. PRN prescriptions were extracted from electronic medical records and independently assessed by a pharmacist, nurse, and physician for clarity and appropriateness. Descriptive statistics summarized PRN use, chi-square tests assessed interprofessional differences, and multivariate logistic regression identified predictors of appropriate PRN wording. Results: Among 316 patients, 1035 PRN prescriptions were analyzed, representing 24.5% of all medication entries. Only 51.3% (n = 531) were deemed appropriate by all evaluators. Significant differences in interpretation were observed across professional groups (p < 0.001 for most pairwise comparisons). PRN prescriptions were most frequent in long-term care units and primarily involved gastrointestinal agents, analgesics, and psychotropic medications. Multivariate analysis showed that hospitalization in long-term care (OR = 4.17; 95% CI 2.48–7.03) or rehabilitation units (OR = 2.07; 95% CI 1.22–3.53) with a higher number of prescriptions administered under a therapeutic protocol PRN (OR = 2.27; 95% CI 1.39–3.63) were independently associated with appropriate wording, while a higher total number of PRN prescriptions reduced appropriateness (OR = 0.87; 95% CI 0.82–0.94). Conclusions: PRN prescribing is frequent in hospitalized older adults and often involves high-risk or potentially inappropriate medications. Substantial interprofessional variability in the interpretation of PRN medication wording requires appropriate, standardized, and clinical PRN guidelines to improve medication safety and reduce potential adverse events in geriatric practice.