PRN vs SOS: Correct Use in Prescriptions
PRN (Pro Re Nata) is the correct and standard terminology for "as needed" medication administration in prescriptions, while SOS (Si Opus Sit) is less commonly used and not recommended in modern prescribing practice. 1
Understanding PRN Prescriptions
PRN is derived from the Latin phrase "pro re nata," meaning "as the situation arises" or "as needed." It is the standard terminology used in medical prescribing when medications should be administered based on patient needs rather than at fixed times.
- PRN medications should be prescribed with clear indications for use (e.g., "for pain," "for nausea," "for anxiety") 1, 2
- The prescription should specify the dose, route, frequency limitations, and maximum daily dose 2, 3
- PRN orders require documentation of administration and effectiveness 1, 4
Examples of Correct PRN Prescriptions
Pain Management
- "Acetaminophen 500mg PO PRN for mild pain every 6 hours, maximum 4g/day" 1
- "Morphine 2-4mg IV PRN for severe pain every 4 hours" 1
Nausea Management
- "Ondansetron 8mg PO PRN for nausea every 8 hours" 1
- "Prochlorperazine 10mg PO PRN for nausea every 6 hours" 1
Gastrointestinal Symptoms
- "Alma gel 10-15mL PO PRN for heartburn every 6 hours" 5
PRN vs SOS: Key Differences
While both terms conceptually mean "as needed," PRN is the preferred terminology in modern medical practice:
- PRN is recognized universally in medical practice across different healthcare settings 2, 4
- SOS (Si Opus Sit - "if there is a need") is an older Latin term that has fallen out of common usage in formal prescribing 6, 7
- Using PRN ensures clarity and standardization in medication orders, reducing potential for medication errors 4, 3
Best Practices for PRN Prescriptions
For Prescribers
- Always specify the indication for use (e.g., "for pain," "for nausea") 1, 2
- Include clear dosing parameters including minimum time between doses 2, 3
- Set maximum daily limits to prevent overuse 4, 7
- Review PRN medications regularly and discontinue those not used for >1 month 3
For Medication Administration
- Document each administration with time, dose, and indication 4
- Evaluate and document effectiveness after administration 2, 7
- Consider non-pharmacological alternatives before administering PRN medications when appropriate 7
Important Clinical Considerations
- For chronic pain management, scheduled (regular) medication is preferred over PRN to prevent pain recurrence 1
- For breakthrough pain, rescue doses should be prescribed as PRN in addition to regular analgesia 1
- PRN medications should be monitored for overuse, which may indicate a need to adjust regular medication regimens 6, 7
- In psychiatric settings, PRN psychotropic medications require particular attention to prevent inappropriate use or polypharmacy 6, 7
Common Pitfalls to Avoid
- Prescribing PRN medications without clear indications leads to inconsistent administration 2, 3
- Failing to specify maximum doses or frequency can result in overuse 4, 7
- Not reviewing PRN medication use patterns may miss opportunities to optimize regular medication regimens 7, 3
- Using non-standard terminology like SOS may cause confusion among healthcare providers 6, 4