What is the typical sig (prescription instruction) for a medication?

Typical Sig (Prescription Instructions) for Medications

The term "sig" refers to the prescriber's directions to the patient on how to take a medication, derived from the Latin "signa" meaning "write" or "label." The typical sig format includes the dose, route, frequency, and duration of therapy, though the specific instructions vary dramatically by medication class, indication, and patient factors. 1

Standard Sig Components and Format

A complete sig should contain:

• Dose: The amount of medication to take (e.g., "Take 1 tablet," "Take 10 mg") 1
• Route: How to administer (e.g., "by mouth," "IV," "subcutaneous") 2
• Frequency: How often to take (e.g., "once daily," "every 12 hours," "twice daily") 2
• Duration: How long to continue (e.g., "for 10 days," "until finished") 2, 3
• Special instructions: Timing relative to meals, swallowing instructions, etc. 3

Common Sig Examples by Medication Class

Oral Medications - Simple Dosing

For acetaminophen (over-the-counter): "Take 2 caplets every 8 hours with water; swallow whole; do not crush, chew, split or dissolve; do not take more than 6 caplets in 24 hours; do not use for more than 10 days unless directed by a doctor" 3

Antibiotics - Tuberculosis Treatment

For rifampin in adults: "Take 10 mg/kg (600 mg maximum) by mouth once daily" or "Take 10 mg/kg (600 mg maximum) by mouth twice weekly" 2

For ethambutol in adults: "Take 15 mg/kg by mouth once daily" for daily dosing or "Take 25 mg/kg by mouth three times per week" for intermittent dosing 2

Antibiotics - Nontuberculous Mycobacterial Disease

For azithromycin: "Take 250-500 mg by mouth once daily" 2

For clarithromycin: "Take 500 mg by mouth twice daily" for both daily and thrice-weekly regimens 2

For linezolid in adults: "Take 600 mg by mouth (or IV) every 12 hours" 2, 4

For linezolid in children under 12 years: "Give 10 mg/kg IV every 8 hours" 4

Inhaled Medications - Asthma Control

For salmeterol DPI: "Inhale contents of 1 blister (50 mcg) every 12 hours" 2

For fluticasone/salmeterol combination: "Inhale twice daily; dose depends on level of severity or control" 2

For cromolyn nebulizer solution: "Inhale 1 ampule (20 mg) four times daily" 2

Antiemetics - Chemotherapy-Induced Nausea

For aprepitant (high emetic risk): "Take 125 mg by mouth on day 1, then 80 mg by mouth on days 2-3" 2

For ondansetron: "Take 24 mg by mouth as a single dose before chemotherapy" or "Take 8 mg by mouth twice daily" 2

For granisetron transdermal: "Apply 1 patch to clean, dry skin" (delivers therapy over multiple days) 2

Parenteral Medications - Serious Infections

For amikacin (daily dosing): "Give 10-15 mg/kg IV once daily, adjusted according to drug level monitoring" 2

For amikacin (intermittent dosing): "Give 15-25 mg/kg IV 2-3 times per week, adjusted according to drug level monitoring" 2

For streptomycin: "Give 10-15 mg/kg IV or IM once daily, adjusted according to drug level monitoring" 2

Critical Variability and Quality Concerns

Research demonstrates substantial variability even for simple instructions: The concept "Take 1 tablet by mouth once daily" had 832 different permutations in a national sample of 25,000 e-prescriptions 1

Approximately 10% of prescription sigs contain quality-related events that could pose patient safety risks or require pharmacist callbacks for clarification 1

Common pitfalls include:

• Incomplete instructions missing dose, frequency, or duration 1
• Ambiguous timing (e.g., "as needed" without maximum daily dose) 1
• Missing special instructions (e.g., "take with food," "swallow whole") 3, 1
• Handwritten modifications that create confusion 5

Monitoring and Adjustment Requirements

For medications requiring therapeutic drug monitoring: The sig should specify monitoring intervals, particularly for aminoglycosides (weekly CBC for linezolid, drug levels for amikacin/streptomycin) 2, 4

For extended therapy: Duration should be clearly specified, as many medications have different dosing for initial vs. continuation phases (e.g., tuberculosis treatment requires 6-12 months total) 2

For renal impairment: Dose adjustments and interval changes must be incorporated into the sig based on creatinine clearance 2, 6