The Hidden Cost of “That’s How We’ve Always Done It”: Warfarin Edition

The inertia of 1960s workflow decisions

Warfarin entered clinical practice in 1948. Seventy-seven years later, most U.S. hospitals still require a standard administration time of 18:00....a timing convention built for healthcare system operations constraints that no longer exist. In earlier days, INR assays were batched overnight, results were slow, and evening dosing created a buffer between administration and next-day rounds. Modern labs return INRs in under 30 minutes, yet the 18:00 dose administration policy persists purely out of institutional habit. 

The legacy timing policies and practices however have created preventable inefficiency during the most critical phase of therapy - inpatient initiation. This is when patients require daily INR monitoring and rapid titration to reach therapeutic anticoagulation attempting to overcome a "warfarin hostage" situation where the patient stays inpatient only because of warfarin titration.

But, are we in a place where the workflow no longer matches the pharmacology and operationally we have options to choose a different path?

The mismatch is measurable

A quality improvement study from Bristol Royal Infirmary found that 64 percent of warfarin doses were administered after 17:00 during minimal-staffing periods, with only 24 percent given within an hour of the recommended 14:00 timing. Erratic dosing driven by inconsistent on-call prescribing and reactionary dosing that did not contemplate drug mechanics often produced supratherapeutic INRs in 23 percent of cases. Standardizing administration to a daytime window improved adherence from 24 percent to 49 percent and reduced high INRs from 23 percent to 9 percent.¹

The mechanism is straightforward. Warfarin’s anticoagulant effect does not materialize meaningfully for 24–36 hours, and full pharmacodynamic expression takes 72–96 hours. When INRs are drawn at 03:00–05:00 (only 9–11 hours after an evening dose) clinicians are interpreting the ascending limb of the curve rather than the true response to yesterday’s adjustment. The result is reactive overcorrection, oscillating INRs, delayed time-in-therapeutic-range, and longer length of stay.

AHRQ patient-safety analyses have repeatedly flagged mismatched dosing and monitoring windows as preventable contributors to anticoagulation errors. The Joint Commission evaluates hospitals on anticoagulant process variation using warfarin as a tracer. CMS surveyors do the same.

Systematic workflows deliver better outcomes

Pharmacist-managed inpatient anticoagulation services demonstrate substantial gains when workflows are coordinated rather than inherited. In one study, pharmacist consultation increased the proportion of patients reaching therapeutic INR within 5 days from 38 percent to 88 percent, cut mean time to therapeutic INR from 6.5 to 3.9 days, reduced INR overshoots (>4) from 27 percent to 2 percent, and shortened length of stay after warfarin initiation from 11 to 7.7 days.²

These outcomes are not driven by better drugs. They are driven by better processes including standardized protocols, daily INR review at predictable times, and dose adjustments grounded in pharmacokinetics, pharmacodynamics and physiologic timing rather than convenience.

Two operational changes fix most of the problem

The evidence points to two simple improvements:

• Shift warfarin standard administration time to 10:00–14:00.
  This aligns dosing with peak staffing and ensures pharmacists and physicians can interpret INR values and adjust therapy on the same day. It also eliminates isolated evening medication passes that add workload without improving safety.
  
• Align INR draws to 20–24 hours post-dose.
  This produces INRs that reflect true pharmacodynamic effect rather than early noise, enabling accurate titration and shorter time to therapeutic range.

Neither requires new technology, new capital, or new regulatory frameworks. Just a willingness to stop operating as if current workflows still serve the purpose they were designed for in 1968.

Warfarin isn’t going away

While DOACs have transformed anticoagulation management, warfarin remains essential for many clinical scenarios including mechanical valves, end-stage renal disease, LVADs, complex drug interactions, and patients who cannot afford newer agents. As long as the drug remains clinically necessary, its workflow should reflect current capabilities and not outdated constraints.

Healthcare’s inertia is well known, but warfarin timing is a case study in how small operational decisions accumulate real cost. Length of stay. Patient safety. Staff efficiency. All influenced by a schedule that no longer makes sense. Hospitals invest millions in throughput, digital command centers, and “patient-flow redesign.” Yet a small, evidence-backed shift in warfarin timing may deliver meaningful gains in INR stability, safety, and LOS.

"The 1960's have called and asked for their workflow back and it's past time for us to approach it with new eyes."

This is a high-ROI improvement addressed through a simple operational intervention: update a schedule that outlived its purpose half a century ago. The question is who will treat it as such? 

References

1. Dyar R, Hall S, McIntyre B. Warfarin prescription and administration: reducing the delay, improving the safety. BMJ Qual Improv Rep. 2015;4(1):u204509.w1983.
2. Wong YM, Quek YN, Tay JC, Chadachan V, Lee HK. Efficacy and safety of a pharmacist-managed inpatient anticoagulation service for warfarin initiation and titration. J Clin Pharm Ther. 2011;36(5):585-591.
3. Ageno W, Gallus AS, Wittkowsky A, et al. Oral Anticoagulant Therapy. Chest. 2012;141(2 Suppl):e44S-e88S.
4. Gage BF, Fihn SD, White RH. Management and dosing of warfarin therapy. Am J Med. 2000;109:481-488.
5. Schulman S. Care of patients receiving long-term anticoagulant therapy. N Engl J Med. 2003;349:675-683.
6. Yang W, Ma J, Hu W, et al. Associated factors and safety of rapidly achieving therapeutic warfarin targets in hospitalized patients. Int J Clin Pharm. 2022;44:939-946.
7. Holbrook A, Schulman S, Witt DM, et al. Evidence-based management of anticoagulant therapy. Chest. 2012;141(2 Suppl):e152S-e184S.
   FDA. Warfarin Sodium label. Updated 2025.