Kygevvi

Kygevvi is used to treat thymidine kinase 2 deficiency (TK2d) in adults and children whose symptoms started at age 12 or younger. It contains two active ingredients, doxecitine and doxribtimine, which are pyrimidine nucleosides that help restore mitochondrial DNA in skeletal muscle. Kygevvi is a prescription medicine taken orally with food 3 times a day.

Your doctor will determine if this medication is right for you based on genetic testing and your medical history.

Kygevvi gained FDA approval on November 3, 2025. There is no generic.

Kygevvi works by providing pyrimidine nucleosides (deoxycytidine and deoxythymidine) that get incorporated into your skeletal muscle's mitochondrial DNA. In studies with mice that have TK2 deficiency, this helped restore mitochondrial DNA to healthier levels.

Important: Only use Kygevvi with the ZX2000 administration kit provided by your pharmacy. This kit helps you to mix the dose of Kygevvi.

Dosing schedule

Your doctor will start you at a lower dose and gradually increase it based on how well you tolerate the medication:

• Starting dose: 260 mg/kg/day (130 mg doxecitine + 130 mg doxribtimine)
• Intermediate dose: 520 mg/kg/day (260 mg doxecitine + 260 mg doxribtimine)
• Maintenance dose: 800 mg/kg/day (400 mg doxecitine + 400 mg doxribtimine)

You'll stay on each dose level for at least 2 weeks before moving to the next level, if appropriate.

How to prepare and take Kygevvi

• Prepare a fresh one-day supply each morning using the ZX2000 kit
• Take the medication in 3 equal doses throughout the day about 6 hours apart with food
• Discard any unused solution after 16 hours or after taking all 3 doses, whichever comes first
• Store unopened packets at room temperature (68°F to 77°F)
• The prepared solution can be stored at room temperature or in the refrigerator.

Your doctor will check your liver function (ALT and AST levels) before you start treatment. Tell your doctor about all your medical conditions and medications you're taking, including if you are pregnant, plan to become pregnant, are breastfeeding, or plan to breastfeed. It is not known if Kygevvi will harm your unborn baby or if it passes into breast milk.

There are no absolute contraindications for Kygevvi.

Common side effects

The most common side effects (occurring in 5% or more of patients) include:

• Diarrhea
• Abdominal pain or upper abdominal pain
• Vomiting
• Increased liver enzymes (ALT and AST).

Serious side effects

Elevated liver enzymes: Kygevvi can cause your liver enzymes to increase. Contact your doctor right away if you experience:

• Loss of appetite
• Pain on the right side of your stomach area
• Dark urine
• Yellowing of your skin or eyes (jaundice).
• Nausea and vomiting
• Itching

Your doctor will monitor your liver function yearly and as needed throughout treatment.

Severe gastrointestinal problems: If you experience severe or persistent diarrhea or vomiting that lasts more than a few days, contact your healthcare provider. Your doctor may need to reduce your dose, temporarily stop treatment, or discontinue Kygevvi permanently, depending on the severity.

These are not all the possible side effects of Kygevvi. Call your doctor for medical advice about side effects. You may report side effects to UCB, Inc. at 1-844-599-2273 or to the FDA at 1-800-FDA-1088.

Kygevvi's effectiveness was studied in patients with TK2d who developed symptoms at age 12 or younger. The research included one Phase 2 clinical trial (NCT03845712) with 47 patients (38 with early symptom onset), two retrospective studies (NCT03701568, NCT05017818) reviewing patient charts, and an expanded access program. Patients received doses ranging from 260 to 800 mg/kg/day.

The studies showed improved survival rates in treated patients compared to untreated patients from historical records. Most patients in the prospective trial continued treatment, while some patients in the retrospective studies discontinued due to side effects.

Based on laboratory studies, doxecitine and doxribtimine do not interact with common drug-processing enzymes (CYP enzymes) or most drug transporters at therapeutic levels. However, you should still tell your doctor about all medications, vitamins, and supplements you take.

Kygevvi comes as a powder for oral solution. Each packet contains 2 grams of doxecitine and 2 grams of doxribtimine, along with inactive ingredients (colloidal silicon dioxide and magnesium stearate).

• Store unopened packets at room temperature between 68°F to 77°F (20°C to 25°C)
• Brief temperature variations between 59°F to 86°F (15°C to 30°C) are acceptable
• Once prepared, store the solution at room temperature or refrigerated
• Throw away any solution after 16 hours or after taking all 3 daily doses.

For more information about Kygevvi or to report side effects, contact UCB, Inc. at 1-844-599-2273.

Manufactured for:UCB, Inc., Smyrna, GA 30080.