Abatacept

Introduction Overview

Generic Name

abatacept

Brand Name

Orencia; Orencia ClickJect

Dosage Form

Lyophilized powder for intravenous infusion and ready-to-use solution for subcutaneous injection in prefilled syringes or a ClickJect autoinjector.

Drug Class

Selective T-cell costimulation modulator; biologic disease-modifying antirheumatic drug (DMARD); CTLA-4 immunoglobulin fusion protein.

Pharmacokinetics

Absorption:
Intravenous abatacept is infused directly into the bloodstream, so systemic availability is immediate. Subcutaneous abatacept is absorbed more slowly from the injection site; in adults with rheumatoid arthritis, subcutaneous bioavailability is about 79%.

Distribution:
Abatacept is a large fusion protein composed of the extracellular domain of CTLA-4 linked to a modified human IgG1 Fc region. Because it is a biologic protein, it distributes mainly in vascular and extracellular spaces rather than freely crossing cell membranes.

Metabolism:
Abatacept is expected to be degraded by normal protein catabolism into peptides and amino acids. It is not metabolized by cytochrome P450 enzymes, so classic CYP-mediated drug interactions are not expected.

Elimination:
The terminal half-life is about 13 to 16 days in adult rheumatoid arthritis studies. Clearance is influenced by body weight, which is why intravenous dosing for adult RA and adult PsA is weight-tiered. Renal and hepatic impairment have not been formally studied as dose-adjustment categories, but abatacept is not primarily cleared unchanged by the kidney or through hepatic CYP metabolism.

Dosage Forms

Available dosage forms:
- Intravenous vial: 250 mg abatacept lyophilized powder for reconstitution and dilution.
- Subcutaneous prefilled syringes: 50 mg/0.4 mL, 87.5 mg/0.7 mL, and 125 mg/mL.
- ClickJect autoinjector: 125 mg/mL for subcutaneous use.

Adult rheumatoid arthritis:
- Intravenous: 500 mg if less than 60 kg, 750 mg if 60 to 100 kg, and 1000 mg if more than 100 kg. Give at weeks 0, 2, and 4, then every 4 weeks as a 30-minute infusion.
- Subcutaneous: 125 mg once weekly. An optional intravenous loading dose may be used; if used, give the first subcutaneous dose within 1 day of the infusion.

Polyarticular juvenile idiopathic arthritis:
- Intravenous is for patients 6 years and older: 10 mg/kg if less than 75 kg; if 75 kg or more, use the adult IV weight-tiered regimen, not exceeding 1000 mg. Give at weeks 0, 2, and 4, then every 4 weeks.
- Subcutaneous is for patients 2 years and older: 50 mg weekly for 10 to less than 25 kg, 87.5 mg weekly for 25 to less than 50 kg, and 125 mg weekly for 50 kg or more.

Psoriatic arthritis:
- Adults may receive intravenous weight-tiered dosing or 125 mg subcutaneously once weekly.
- Pediatric patients 2 years and older use the same subcutaneous weight bands as pJIA.

Acute graft-versus-host disease prophylaxis:
For adults and pediatric patients 2 years and older undergoing HSCT from a matched or 1 allele-mismatched unrelated donor, abatacept is used with a calcineurin inhibitor and methotrexate. The label dosing is intravenous, weight based, and scheduled around transplant; follow the transplant protocol and current prescribing information.

Mechanism Of Action

T cells need two signals to become fully activated. Signal 1 comes from the T-cell receptor recognizing antigen. Signal 2, the costimulation signal, commonly occurs when CD28 on T cells binds CD80 or CD86 on antigen-presenting cells.

Abatacept acts like a soluble CTLA-4 signal blocker. It binds CD80 and CD86, preventing them from binding CD28. Without this costimulation, T-cell activation, proliferation, and cytokine production are reduced.

In autoimmune arthritis, this lowers pathologic immune activation that drives synovial inflammation, pain, swelling, and joint damage. In acute graft-versus-host disease prophylaxis, reducing donor T-cell costimulation helps lower the immune attack against host tissues after allogeneic stem cell transplantation.

Pharmacological Actions

Blocks CD80/CD86-mediated costimulation of T cells.
Reduces T-cell activation, proliferation, and downstream cytokine signaling.
Decreases inflammatory activity in rheumatoid arthritis, psoriatic arthritis, and polyarticular juvenile idiopathic arthritis.
May slow progression of structural joint damage in rheumatoid arthritis when disease activity is controlled.
Provides an alternative biologic mechanism for patients who do not respond adequately to conventional DMARDs or other biologic options.
Helps prevent acute graft-versus-host disease when used with calcineurin inhibitor and methotrexate prophylaxis in indicated transplant settings.

Therapeutic Or Clinical Uses

Moderately to severely active rheumatoid arthritis in adults.
Moderately to severely active polyarticular juvenile idiopathic arthritis in patients 2 years of age and older.
Active psoriatic arthritis in patients 2 years of age and older.
Prophylaxis of acute graft-versus-host disease, in combination with a calcineurin inhibitor and methotrexate, in adults and pediatric patients 2 years and older undergoing hematopoietic stem cell transplantation from a matched or 1 allele-mismatched unrelated donor.
May be used alone or with selected non-biologic DMARDs, depending on the condition and route.

Side Or Adverse Effects

Upper respiratory tract infection, nasopharyngitis, headache, and nausea.
Infusion-related reactions such as dizziness, headache, hypertension, flushing, rash, pruritus, cough, dyspnea, or wheezing.
Injection-site reactions with subcutaneous use, such as redness, itching, bruising, or swelling.
Serious infections, including pneumonia, sepsis, tuberculosis, and opportunistic infections.
Hypersensitivity reactions, including rare anaphylaxis.
Increased respiratory adverse events in patients with chronic obstructive pulmonary disease.
Possible malignancy signal has been observed, but the role of abatacept in human malignancy development is uncertain.
In aGVHD prophylaxis after HSCT, CMV and EBV reactivation are important monitored risks.
For aGVHD prophylaxis, common adverse reactions can include anemia, hypertension, CMV reactivation or infection, fever, pneumonia, nosebleed, reduced CD4 lymphocytes, increased magnesium, and acute kidney injury.

Precautions

Evaluate for active infection before starting abatacept; do not start during a clinically important active infection unless a specialist determines benefits outweigh risks.
Screen for latent tuberculosis and treat according to standard practice before starting therapy when indicated.
Screen for viral hepatitis risk and monitor patients at risk for hepatitis B reactivation.
Avoid combining abatacept with TNF antagonists, other biologic DMARDs, or JAK inhibitors because infection risk increases and benefit is not established.
Update needed vaccines before starting therapy when possible.
Avoid live vaccines during abatacept treatment and for 3 months after discontinuation.
Monitor patients with COPD carefully because respiratory adverse events and serious events were more frequent in COPD patients receiving abatacept in trials.
Have medical support available for hypersensitivity reactions during intravenous infusion.
For transplant use, monitor for CMV and EBV reactivation according to transplant protocols.
Patients with diabetes using the intravenous formulation should use glucose testing methods that do not react with maltose on infusion days, because some monitors may read falsely high.

Warnings

Concomitant use with TNF antagonists, other biologic RA/PsA therapies, or JAK inhibitors is not recommended because of increased infection risk.
Serious infections have been reported; interrupt treatment if a serious infection develops.
Hypersensitivity reactions can occur during or after administration; discontinue for serious allergic reactions.
Live vaccines should not be given during treatment or for 3 months after stopping abatacept.
Use caution in patients with COPD because respiratory adverse events may be more common.
Immunosuppression may affect host defenses against infections and malignancies.
CMV and EBV reactivation can occur in the HSCT prophylaxis population and require monitoring.

Contraindication

Current U.S. prescribing information lists no formal contraindications for Orencia. This does not mean the medicine is risk-free. Active serious infection, prior serious hypersensitivity, severe COPD risk, live vaccines, and combination with other potent immunosuppressants are handled as warnings, precautions, or not-recommended uses rather than label-listed absolute contraindications.

Drug Interactions

TNF antagonists, other biologic DMARDs, and JAK inhibitors: not recommended with abatacept because additive immunosuppression increases infection risk.
Live vaccines: avoid during abatacept treatment and for 3 months after stopping therapy.
Non-biologic DMARDs such as methotrexate may be used with abatacept in indicated settings.
Corticosteroids and other immunosuppressants may increase infection risk and should be reviewed during medication reconciliation.
CYP450-mediated interactions are not expected because abatacept is a biologic protein degraded by proteolysis.
Intravenous abatacept contains maltose, which can cause falsely elevated blood glucose readings with certain test-strip systems on infusion days.

Preparations Of The Drug

Orencia for intravenous infusion: single-dose vial with 250 mg abatacept lyophilized powder for reconstitution and dilution.
Orencia prefilled syringe: 50 mg/0.4 mL, 87.5 mg/0.7 mL, or 125 mg/mL abatacept solution for subcutaneous injection.
Orencia ClickJect autoinjector: 125 mg/mL abatacept solution for subcutaneous injection.
Intravenous vials and subcutaneous products should be refrigerated at 2 to 8 C (36 to 46 F), stored in the original package, protected from light, and not frozen.
Subcutaneous products are clear to slightly opalescent, colorless to pale yellow solutions.
All products are single-dose preparations; unused portions should be discarded according to product instructions.

Student Key Points

Abatacept is not a TNF inhibitor; it blocks T-cell costimulation through CD80/CD86.
Think "CTLA-4 fusion protein" and "blocks signal 2" for the mechanism.
It is used in RA, pJIA, PsA, and selected HSCT patients for aGVHD prophylaxis.
Do not combine it routinely with other biologic DMARDs or JAK inhibitors.
Live vaccines are avoided during therapy and for 3 months after stopping.
The IV product contains maltose, so some glucose meters may show false high readings on infusion days.