Provider Briefing: Phenytoin XR Availability in 2026

Phenytoin sodium extended-release capsules — marketed as Dilantin Kapseals, Phenytek, and multiple generic formulations — remain a staple in the management of generalized tonic-clonic and complex partial seizures. However, intermittent supply disruptions have created challenges for prescribers and their patients over the past several years.

This briefing provides an overview of the current shortage landscape, prescribing considerations, and tools to help your patients maintain access to their medication.

Timeline of Supply Disruptions

Phenytoin products have experienced a series of supply-related events:

• 2020: Pfizer transferred the Dilantin brand to Viatris Specialty LLC as part of the Upjohn spinoff, creating a transitional period in distribution
• 2022-2023: Phenytoin sodium injection (50 mg/mL) entered shortage status, tracked by ASHP. Hikma Pharmaceuticals was the primary supplier during this period
• 2023-2024: Phenytoin oral suspension (240 mL bottles) was discontinued by Viatris, shifting demand toward extended-release capsules and the remaining Dilantin-125 suspension
• 2025: Injection shortage resolved (Hikma 5 mL vials confirmed available as of August 2025)
• 2026 (current): Extended-release capsules are generally available but with intermittent spot shortages affecting specific manufacturers and regions

Prescribing Implications

The supply disruptions carry several important clinical considerations:

Narrow Therapeutic Index

Phenytoin's narrow therapeutic index (target: 10-20 mcg/mL) means that switching between manufacturers or formulations is not trivial. The FDA classifies phenytoin as a narrow therapeutic index drug, and state pharmacy laws vary on whether generic substitution is permitted without prescriber approval.

Clinical recommendation: If a patient must switch manufacturers or formulations due to availability, consider checking a trough level 1-2 weeks after the transition and again at 4 weeks to confirm therapeutic stability.

Formulation Considerations

It's important to distinguish between phenytoin formulations:

• Extended-release capsules (100 mg, 200 mg, 300 mg): Labeled as "extended phenytoin sodium" — only these capsules are appropriate for once-daily dosing
• Prompt-release capsules: Rarely used; require more frequent dosing
• Chewable tablets (Dilantin Infatabs, 50 mg): Immediate-release; require 2-3 times daily dosing
• Oral suspension (Dilantin-125, 125 mg/5 mL): Immediate-release; note that 100 mg of phenytoin sodium ≈ 92 mg of phenytoin acid (the suspension uses the acid form)

Dose conversions between formulations require careful attention to the sodium salt vs. free acid distinction and the change from extended to immediate release dosing schedules.

Pharmacogenomics

For patients being started on phenytoin or switched to it as an alternative, consider HLA-B*1502 testing for patients of Southeast Asian descent (Filipino, Han Chinese, Thai, Malaysian, and others) before initiation. This allele is associated with significantly increased risk of Stevens-Johnson syndrome and toxic epidermal necrolysis.

Current Availability Picture

As of February 2026:

• Generic Phenytoin ER capsules: Available from multiple manufacturers; spot shortages with individual suppliers may occur
• Dilantin Kapseals (brand): Available through Viatris but at higher cost; may be easier to source in some markets
• Phenytek (brand): Available; pricing starts around $43 with discount programs
• Phenytoin sodium injection: Available (Hikma)
• Dilantin-125 oral suspension: Available but some smaller-volume presentations have been discontinued

For real-time availability data that you can share with patients, Medfinder for Providers offers pharmacy stock information searchable by zip code.

Cost and Access Considerations

Cost should not be a significant barrier for most patients:

• Generic Phenytoin ER: $18-$45/month with discount coupons (GoodRx, SingleCare)
• Brand Dilantin Kapseals: $80-$120+/month cash price
• Insurance coverage: Generic phenytoin ER is Tier 1 on most formularies

For uninsured or underinsured patients:

• Viatris Patient Assistance Program: May cover Dilantin for qualifying patients
• NeedyMeds and RxAssist: Directories of patient assistance programs
• Discount cards: GoodRx, SingleCare, and others can reduce generic prices to under $20/month

For a patient-facing resource on cost savings, you can direct patients to: How to Save Money on Phenytoin XR.

Tools and Resources for Your Practice

For Patients Having Trouble Finding Phenytoin XR

• Medfinder for Providers: Real-time pharmacy availability search — share with patients or check in clinic
• ASHP Drug Shortage Database: Official shortage tracking with manufacturer updates
• FDA Drug Shortage Database: Federal shortage reporting

For Clinical Decision-Making

• If switching to an alternative, consider Levetiracetam (fewest drug interactions, no monitoring required), Lamotrigine (broad-spectrum, weight-neutral, slow titration required), Carbamazepine (similar mechanism, also NTI), or Valproic Acid (broadest spectrum, avoid in women of childbearing potential)
• For a patient-facing alternatives discussion, see: Alternatives to Phenytoin XR

For Your Workflow

• Consider adding a note in your EHR for phenytoin patients flagging the availability situation and documenting an approved alternative in advance
• Provide patients with a written backup plan they can share with their pharmacy if their primary medication is unavailable
• When prescribing, specify "may substitute manufacturer" if appropriate to give the pharmacy maximum flexibility

For a step-by-step guide on helping patients navigate availability, see: How to Help Your Patients Find Phenytoin XR.

Looking Ahead

The long-term outlook for phenytoin availability depends on several factors:

• Market dynamics: As prescribing continues to shift toward newer anticonvulsants, the manufacturing base for phenytoin may continue to contract. However, phenytoin remains important for patients who are well-controlled on it and for use in acute settings (status epilepticus)
• Regulatory actions: The FDA has tools to incentivize production of drugs in shortage, but these have been inconsistently applied
• Generic landscape: Multiple generic manufacturers remain active, which provides some redundancy

For now, the most effective strategy is proactive planning — both for your patients' current supply and for a clinical contingency plan if phenytoin becomes consistently unavailable.

Final Thoughts

Phenytoin remains clinically relevant for a significant patient population despite its declining first-line status. The intermittent supply disruptions require providers to be proactive in monitoring availability, counseling patients on early refills, and having documented alternative plans.

Medfinder for Providers can help streamline the process of connecting patients with available pharmacy stock. For the patient perspective on this shortage, see our patient-facing shortage update.