Dilantin Shortage: What Providers and Prescribers Need to Know in 2026

Phenytoin (Dilantin, Phenytek) has had a complex supply history over the past several years. As a prescriber or pharmacist, staying current on shortage status and understanding the clinical implications of supply disruptions is essential to protect patients on this narrow therapeutic index (NTI) antiepileptic drug. This guide provides a clinical summary of the 2026 shortage situation, with actionable guidance for managing affected patients.

Current Shortage Status by Formulation (2026)

The following is a summary of phenytoin availability as of early 2026, based on ASHP Drug Shortage Database data and manufacturer communications:

Oral extended-release capsules (100 mg, 30 mg): Multiple manufacturers have stock. Intermittent spot shortages with individual suppliers (e.g., Accord phenytoin capsules have had extended periods of unavailability). Generic ER capsules from other manufacturers can support increased demand.

Oral suspension (Dilantin-125, 125 mg/5 mL): ASHP listed this formulation as in shortage effective May 2025. Both Viatris (237 mL bottles) and Sun Pharma (8 oz bottles) have been on back-order. This formulation is critical for pediatric patients and those unable to swallow capsules.

Injectable phenytoin (50 mg/mL): Shortage initiated December 2022 by Hikma. Resolved by August 2025. Both Acella (2 mL and 5 mL vials) and Hikma (2 mL and 5 mL vials) now report available supply. Monitor for renewed disruptions.

Chewable tablets (Infatabs, 50 mg): Historically subject to periodic supply disruptions. Check ASHP database for current status.

NTI Classification: Clinical Implications for Substitution

Phenytoin's NTI status has significant implications during shortage situations:

The therapeutic range is 10–20 mcg/mL. Saturable (Michaelis-Menten) pharmacokinetics mean that small dose changes produce disproportionately large changes in serum concentration.

Switching between the sodium salt form (capsules) and the free acid form (suspension, Infatabs) requires dose adjustment: the free acid has approximately 8% higher drug content by weight. A patient on 300 mg phenytoin sodium would need approximately 276 mg phenytoin acid for equivalent dosing.

Switching between extended-release and immediate-release formulations changes dosing frequency and absorption kinetics. Chewable tablets and suspension use immediate-release phenytoin and require 2–3 times daily dosing; extended-release capsules can be dosed once daily in stable patients.

State pharmacy laws vary on generic substitution for NTI drugs. If you prefer a specific manufacturer for your patient, write 'DAW' and specify the manufacturer on the prescription. Without this notation, pharmacists in most states may substitute freely between generic manufacturers.

Monitoring Recommendations When Manufacturer Substitution Is Unavoidable

If a patient must switch to a different manufacturer's phenytoin product due to supply constraints, consider the following monitoring approach:

Document the prior manufacturer and serum level at baseline.

Check a trough phenytoin level 1–2 weeks after initiating the new manufacturer's product.

Confirm again at 4 weeks, particularly in patients with hepatic impairment, hypoalbuminemia, or renal disease (where protein binding is altered).

For patients with renal failure or hypoalbuminemia, use the Sheiner-Tozer equation to interpret total phenytoin levels — or order a free phenytoin level directly.

Counsel patients on signs of toxicity: nystagmus, ataxia, slurred speech, confusion — and instruct them to contact the office if these emerge.

HLA-B*1502 Testing: A Reminder for New Starts and Switches

If a patient of Southeast Asian descent (Filipino, Han Chinese, Thai, Malaysian, and other Southeast Asian ethnicities) is being newly started on phenytoin, or switched to phenytoin as an alternative, HLA-B*1502 testing is recommended before initiation. This allele is strongly associated with Stevens-Johnson syndrome and toxic epidermal necrolysis in this population. The same applies to carbamazepine. Most commercial labs can run HLA-B*1502 in 3–5 business days.

When to Consider Transitioning Patients Off Phenytoin

For patients experiencing frequent supply disruptions, a planned transition to a modern AED may reduce long-term risk. Consider transition when:

The patient has missed doses multiple times due to supply issues

The patient's seizure type would be equally well-served by a newer agent with a more favorable safety and interaction profile (e.g., levetiracetam for focal seizures)

The patient has a polypharmacy burden where phenytoin's CYP3A4 induction is complicating management of other conditions

The patient is a woman of childbearing potential who may benefit from a less teratogenic option

Alternative AEDs to Consider When Transitioning

Levetiracetam (Keppra): Fewest drug interactions; no TDM required; IV and oral forms available; watch for behavioral side effects

Lamotrigine: Broad-spectrum; weight-neutral; phenytoin reduces lamotrigine levels (adjust dosing); requires slow titration

Carbamazepine: Similar sodium channel mechanism; also NTI; significant drug interactions via CYP3A4 induction

Valproate: Broadest spectrum; avoid in women of childbearing potential; significant teratogenicity (Category X in pregnancy for migraine, Category D for epilepsy)

How medfinder Can Help Your Patients

Rather than directing patients to call pharmacies themselves, you can recommend medfinder for providers. medfinder calls pharmacies near the patient and texts them results showing which pharmacies can fill their specific prescription. This reduces the burden on your office staff and helps patients locate their medication faster, reducing the risk of missed doses.