Thrombopoietin receptor agonists (TPO-RAs) offer different clinical opportunities based on their pharmacokinetic, pharmacodynamic, and mechanistic characteristics. |
In addition to the safety and efficacy of each agent, pharmacists counseling patients on TPO-RA use should consider patient preference for route of administration, the need for stable platelet control and impact of dietary restrictions. |
An in-depth knowledge of the TPO-RA class will empower pharmacists and other healthcare professionals to participate in appropriate decision making with individual patients. |
1 Introduction
2 Thrombopoietin Receptor Agonists (TPO-RAs) in Immune Thrombocytopenia (ITP)
2.1 Thrombopoietin and Platelet Life Cycle
Avatrombopag | Eltrombopag | Lusutrombopag | Romiplostim | |
---|---|---|---|---|
Molecular structure | Small molecule | Small molecule | Small molecule | Peptibody |
Site of action | Transmembrane domain | Transmembrane domain | Transmembrane domain | Extracellular domain |
Onset of action in ITP | In ITP, platelet response was observed in 65.6% of patients receiving avatrombopag by day 8 on therapy | Median time to platelet response in ITP estimated at 12 days (95% CI 8–13) | NA | The platelet counts were > 50 × 109/L in 25% of patients within 1 week of treatment initiation |
PK | Avatrombopag displayed dose-proportional pharmacokinetics after single doses of 10–80 mg. Healthy subjects on avatrombopag (40 mg) had a Cmax of 166 ng/mL and AUC0–inf of 4198 ng-h/mL Tmax occurred at 5–8 h post-dose Terminal elimination half-life is estimated at 19 h Avatrombopag is excreted in the feces (88%) and urine (6%). Approximately 34% of the dose administered is recovered unchanged in feces | Following oral administration, Cmax was achieved at a Tmax of 2–6 h A high-fat breakfast significantly delayed plasma AUC0–inf by 59%, Cmax by 65%, and Tmax by 1 h Administration of a single 25-mg dose of eltrombopag to adults with a high calcium, moderate-fat, moderate-calorie meal reduced AUC0-inf by 75% and Cmax by 79% Administration of a single 25-mg dose of eltrombopag for oral suspension 2 hours after the high-calcium meal reduced AUC0–inf by 47% and Cmax by 48% Administration of a single 25-mg dose of eltrombopag for oral suspension 2 hours before the high-calcium meal reduced AUC0–inf by 20% and Cmax by 14% Eltrombopag oral suspension delivers 22% higher plasma AUC0–inf than the tablet formulation Eltrombopag is excreted in the feces (59%) and urine (31%). Approximately 20% of the dose administered is recovered unchanged in feces | The geometric mean maximal concentration of lusutrombopag is 111 ng/mL, with an AUC0–inf of 2931 ng-h/mL. Excretion is primarily fecal (83%), with 16% of the dose excreted as the unchanged compound. Urinary excretion accounts for 1% of excretion. The terminal elimination half-life in healthy adults is estimated at 27 h. Peak concentrations of lusutrombopag are achieved 6–8 hours after oral administration | After weekly injections with romiplostim (3–15 μg/kg), the time to peak serum concentration (Tmax) was about 7–50 h (median: 14 hours) with half-life (t½) values of 1–34 days (median: 3.5 days) The serum concentrations varied among patients and did not correlate with the dose administered. The elimination of serum romiplostim is in part dependent on the TPO receptor on platelets. As a result, for a given dose, patients with high platelet counts are associated with low serum concentrations and vice versa. In another ITP clinical study, no accumulation in serum concentrations was observed (n = 4) after 6 weekly doses of romiplostim (3 μg/kg) |
Absorption | Absorption is not reduced by dietary fat or divalent cations (such as calcium) | Absorption is reduced in the presence of medications or products containing polyvalent cations such as antacids, calcium-rich foods, and mineral supplements (iron, calcium, aluminum, magnesium, selenium, zinc) | Absorption, including area under the concentration-time curve and Cmax, were not affected by food or coadministration with a multivalent cation | NA |
Food/high-fat meals | No impact. Take with any food | Food (high in fat and calcium) can interfere with absorption, and eltrombopag is to be taken on an empty stomach or at least 2 hours after a meal | No impact. Take with any food | NA |
Chelating ability | No chelating ability | Chelates polyvalent cations Chelates extracellular and intracellular calcium and iron and may affect the disposition of metal ions in relation to cells; can cause a TPO-independent effect on stimulating stem cells and MKs | No chelating ability | No chelating ability |
2.2 Potency Comparisons of TPO-RAs in ITP
2.3 Efficacy of TPO-RAs in ITP in Adults
2.3.1 Methods
2.3.2 Avatrombopag
2.3.3 Eltrombopag
2.3.4 Romiplostim
2.4 Switching Between TPO-RAs
3 Treatment and Dispensing Considerations
3.1 ITP Treatment Considerations for Pharmacists
3.2 Administration Considerations
3.3 Dispensing Considerations
Avatrombopag | Eltrombopag | Lusutrombopag | Romiplostim | |
---|---|---|---|---|
Current indicationsa | Thrombocytopenia in adult patients with chronic liver disease who are scheduled to undergo a procedure Thrombocytopenia in adult patients with chronic immune thrombocytopenia who have had an insufficient response to a previous treatment | Treatment of thrombocytopenia in adult and pediatric patients 1 year and older with chronic ITP who have had an insufficient response to corticosteroids, immunoglobulins, or splenectomy. Eltrombopag should be used only in patients with ITP whose degree of thrombocytopenia and clinical condition increase the risk for bleeding Treatment of thrombocytopenia in patients with chronic hepatitis C to allow the initiation and maintenance of interferon-based therapy (only in patients with chronic hepatitis C whose degree of thrombocytopenia prevents the initiation of interferon-based therapy or limits the ability to maintain interferon-based therapy) Use in combination with standard immunosuppressive therapy for the first-line treatment of adult and pediatric patients 2 years and older with severe aplastic anemia (US only) Treatment of patients with severe aplastic anemia who have had an insufficient response to immunosuppressive therapy | Treatment of thrombocytopenia in adult patients with chronic liver disease who are scheduled to undergo a procedure | Adult patients with ITP who have had an insufficient response to corticosteroids, immunoglobulins, or splenectomy Pediatric patients 1 year of age and older with ITP for at least 6 months who have had an insufficient response to corticosteroids, immunoglobulins, or splenectomy |
Route of administration | Oral | Oral | Oral | Subcutaneous |
Administration | Avatrombopag should be taken with food Tablets may be crushed into a fine powder and mixed with whole milk yogurt or chocolate pudding up to 30 min prior to administration | Administer the oral suspension immediately after preparation, discarding any unused suspension within 30 min of preparation Prepare suspension only with water (and not hot water) Take eltrombopag without a meal or with a meal low in calcium (≤ 50 mg) Take at least 2 h before or 4 h after any medications or products containing polyvalent cations such as antacids, calcium-rich foods, and mineral supplements (iron, calcium, aluminum, magnesium, selenium, zinc) Do not crush tablets and mix with food or liquids | Lusutrombopag should be taken once daily with or without food | Prepared in a health care setting and injected subcutaneously by a health care professional once weekly |
Storage | Store tablets at 20–25 °C (68–77 °F), excursions permitted to 15–30 °C (59–86°F). Store tablets in original package | Tablets: Store at room temperature between 20 °C and 25 °C (68–77 °F); excursions permitted to 15–30 °C (59–86 °F) Dispense in original bottle Oral suspension: Store at room temperature between 20 °C and 25 °C (68–77°F); excursions permitted to 15–30 °C (59–86 °F). Following reconstitution, the product should be administered immediately but may be stored for a maximum period of 30 minutes between 20 °C and 25 °C (68–77 °F); excursions permitted to 15–30 °C (59–86 °F). Throw away (discard) the mixture if not used within 30 minutes | Store at room temperature, 20–25 °C (68–77 °F); excursions permitted between 15 °C to 30 °C (59–86 °F). Do not remove desiccants | Store vials in the refrigerator at 2–8 °C (36–46 °F) in the original carton to protect from light. Do not freeze If needed, unopened vials may be stored in the original carton at room temperature up to a maximum of 25 °C (77 °F) for a single period of up to 30 days. The new expiration date must be written in the space provided on the carton. Once stored at room temperature, do not place back in the refrigerator. If not used within the 30 days, discard |
Dosing | Chronic ITP: Initiate avatrombopag at 20 mg (1 tablet) once daily. Adjust the dose or frequency of dosing to maintain platelet count ≥ 50 × 109/L. Do not exceed 40 mg per day Chronic liver disease: Dose avatrombopag based on platelet count prior to procedure, orally for 5 days beginning 10–13 days before procedure. For platelet count < 40 × 109/L, the dose is 60 mg (3 tablets) once daily; for platelet count 40 to < 50 × 109/L, the dose is 40 mg (2 tablets) once daily | Chronic ITP: Initiate eltrombopag at 50 mg once daily for most adult and pediatric patients 6 years and older and at 25 mg once daily for pediatric patients aged 1–5 years. Dose reductions are needed for patients with hepatic impairment and some patients of Asian ancestry. Adjust to maintain platelet count ≥ 50 × 109/L. Do not exceed 75 mg per day Chronic hepatitis C-associated thrombocytopenia: Initiate eltrombopag at 25 mg once daily for all patients. Adjust to achieve target platelet count required to initiate antiviral therapy. Do not exceed a daily dose of 100 mg First-line severe aplastic anemia: Initiate eltrombopag once daily at 2.5 mg/kg (in pediatric patients aged 2–5 years), 75 mg (pediatric patients aged 6–11 years), or 150 mg for patients 12 years and older concurrently with standard immunosuppressive therapy. Reduce initial dose in patients of Asian ancestry. Modify dosage for toxicity or elevated platelet counts Refractory severe aplastic anemia: Initiate eltrombopag at 50 mg once daily. Reduce initial dose in patients with hepatic impairment or patients of Asian ancestry. Adjust to maintain platelet count > 50 × 109/L. Do not exceed 150 mg per day | Chronic liver disease: Lusutrombopag 3 mg daily for 7 days starting 8–14 days prior to a scheduled procedure, with the last dose administered 2–8 days before the procedure | The initial dose of romiplostim is 1 μg/kg. Actual body weight at initiation of treatment should always be used when calculating the initial dose. In adults, future dose adjustments are based on changes in platelet counts only Adjust the weekly dose of romiplostim by increments of 1 μg/kg until the patient achieves a platelet count ≥ 50 × 109/L as necessary to reduce the risk for bleeding; do not exceed a maximum weekly dose of 10 μg/kg. In clinical studies, most adult patients who responded to romiplostim achieved and maintained platelet counts ≥ 50 × 109/L with a median dose of 2 μg/kg Adjust the dose as follows for adult patients: If the platelet count is < 50 × 109/L, increase the dose by 1 μg/kg If platelet count is >200 × 109/L and ≤ 400 × 109/L for 2 consecutive weeks, reduce the dose by 1 μg/kg If platelet count is > 400 × 109/L, do not dose. Continue to assess the platelet count weekly. After the platelet count has fallen to < 200 × 109/L, resume romiplostim at a dose reduced by 1 μg/kg (Note: In some cases, discontinuing romiplostim in patients with high platelet counts may lead to wide variations in platelet counts)b |
Monitoring | Platelet counts should be assessed weekly until reaching a stable platelet count of 50 × 109/L or higher, with monthly platelet counts thereafter. Platelet counts should be assessed weekly for at least 4 weeks after discontinuation | Liver function testing (including assessment of serum ALT, AST, and bilirubin) should be performed at baseline and every 2 weeks during dose adjustment and monthly after reaching a stable daily dose. Treatment may be discontinued if ALT levels rise to ≥ 3 times the upper limit of normal in patients with normal liver function at baseline or ≥ 3 to 5 times baseline levels in patients with elevated ALT prior to treatment Clinical hematology parameters, including platelet counts, should be monitored during treatment Patients should receive a baseline ocular examination and should be regularly monitored for signs and symptoms of cataracts during therapy | Platelet counts should be assessed prior to the start of lusutrombopag therapy and within the 2 days prior to the scheduled procedure | Complete blood count including platelets weekly while adjusting therapy, monthly after attaining a stable dose, and weekly for at least 2 weeks following discontinuation |
Average wholesale price (USD) | $391.68/20-mg tab | $225.61/tab (12.5 mg or 25 mg) $408.29/tab (50 mg) $612.43/tab (75 mg) | $1457.14/3-mg tab | $1238.82/125-μg vial $2477.62/250-μg vial $4955.23/500-μg vial |
Average wholesale price per month in ITP (USD) | $11,750.40c Range: $11,750.40–$23,500.80 (based on a dose range of 20–40 mg daily) | $12,248.70d Range: $6768.30–$18,372.90 (based on a dose range of 12.5–75 mg daily) | NA | $4955.28e Range: $4955.28–$29,731.40 (assuming dose range of 1–10 μg/kg/week for a 70-kg adult) |
3.4 History of Risk Evaluation and Management System (REMS) Program
3.5 Extemporaneous Compounding
3.6 Drug Interactions
Avatrombopag | Eltrombopag | Romiplostim | Lusutrombopag |
---|---|---|---|
Moderate or strong dual CYP2C9 and CYP3A4 inducers or inhibitors may reduce efficacy of avatrombopag | Polyvalent cations (take eltrombopag 2 hours before or at least 4 hours after foods, supplements, or medications containing polyvalent cations) OATP1B1 substrates (atorvastatin, bosentan, ezetimibe, fluvastatin, glyburide, olmesartan, pitavastatin, pravastatin, rosuvastatin, repaglinide, rifampin, simvastatin, SN-38 [an active metabolite of irinotecan], valsartan) BCRP substrates such as imatinib, irinotecan, lapatinib, methotrexate, mitoxantrone, rosuvastatin, sulfasalazine, topotecan | No drug interaction studies performed; romiplostim is compatible with other ITP therapies (e.g., corticosteroids, danazol, azathioprine, intravenous immunoglobulin, and anti-D) | No clinically significant changes were observed in clinical trials of lusutrombopag when coadministered with the multivalent cation calcium carbonate, the P‐gp and BCRP inhibitor cyclosporine, or the CYP3A substrate midazolam. In vitro studies found low potential for interactions with CYP enzymes |
3.7 Adverse Events with TPO-RAs in ITP
3.7.1 Avatrombopag—Common Adverse Events
3.7.2 Eltrombopag—Common Adverse Events
3.7.3 Romiplostim—Common Adverse Events
3.7.4 Thromboembolic Events
3.7.5 Reticulin Fibrosis
3.7.6 Transaminase Elevation
3.7.7 Ocular Abnormalities
Avatrombopag | Eltrombopag | Romiplostim | |
---|---|---|---|
Reticulin fibrosis | Not reported | 6% of patients in a 2-year follow-up | 6% (8/142) over a median of 69 weeks of follow-up |
Thrombosis/thromboembolic events (arterial or venous) | 7% (9/128) | 6% (46/763) | 5.9% (39/653) |
Hepatic transaminitis | ALT (3.1%), AST (2.3%), GGT (2.3%)a | ALT (5%), AST (4%), and bilirubin (4%) | Not reported |
Iron studies | No chelating ability | Chelates with calcium and iron | No chelating ability |
Cataracts | Not reported | 7% | Up to 9% in an 8-year follow-up; 2.2 cases per 100 patient-years in a pooled analysis |
Skin pigmentation changes | Not reported | Postmarketing reports of hyperpigmentation and skin yellowing | Not reported |
4 Other Uses of TPO-RAs
4.1 TPO-RAs in Chronic Liver Disease and Perioperative Use
4.2 Severe Aplastic Anemia
4.3 Myelodysplastic Syndrome
4.4 Post-Hematopoietic Stem-Cell Transplant
Source | Type of article | Dose and treatment | Efficacy | Safety |
---|---|---|---|---|
Peffault de Latour et al. 2020 [76] | Prospective clinical trial | A total of 24 patients were enrolled in a prospective trial of romiplostim administered weekly for up to 12 weeks with weekly doses ranging from 1 to 10 μg/kg following HSCT. Of 24 patients, 19 completed treatment with all injections | Within 100 days, 17 patients experienced acute GvHD and 12 patients experienced chronic GvHD. The cumulative incidence of acute GvHD was 67% (95% CI 47–87). Within 1 year, the cumulative incidence of chronic GvHD was 55% (95% CI 32–78). The median time to attainment of platelet counts > 50 × 109/L was 45 days. Relapse occurred in 13% (95% CI 0–27) of patients at 1 year. Nonrelapse mortality was 21% (95% CI 7–42) | A total of 21 AEs occurred in 6 patients, including 6 grade 3 or 4 AEs. Four patients experienced hematologic complications, and 2 patients showed evidence of liver dysfunction |
Yuan et al. 2019 [77] | Retrospective analysis | 13 patients were treated with ELT at initial dose of 25–50 mg/day and dose adjustments made thereafter as required | The overall response rate (cumulative incidence of platelet recovery to ≥ 50 × 109/L without need for transfusion for at least 7 days) was 62%. Time to response (median) was 33 days (range 11–68) | Well tolerated; no discontinuations due to AEs |
Bento et al. 2019 [75] | Retrospective analysis | 86 patients (16 with PIT and 71 with SFPR) with persistent thrombocytopenia after allo-HSCT were treated with either ELT or ROM at a median of 127 days after allo-SCT for a median duration of treatment of 62 days. The median initial and maximum doses were 50 mg/day (range 25–150 mg/day) and 75 mg/day (range 25–150 mg/day) respectively for ELT and 1 μg/kg (range 1–7 μg/kg) and 5 μg/kg (range 1–10 μg/kg) respectively for ROM | Platelet recovery to ≥ 50 × 109/L without transfusion support was achieved in 72% of patients at a median time of 66 days (range 2–247 days) | Grade 3–4 AEs (hepatic and asthenia) were observed in 2% of patients. At last follow-up, 81% TPO-RA was discontinued in 81% of patients, and response was maintained |
Hartranft et al. 2017 [78] | Retrospective analysis | 13 patients received ROM at a median initial dose of 1.5 μg/kg (range 1–5 μg/kg) weekly and titrated to a maximum dose of 10 μg/kg/dose as treatment for SFPR, a median of 91 days following HSCT (range 21–208 days) | Platelet recovery to ≥ 50 × 109/L without transfusion support was achieved in 54% of patients at a median time of 35 days (range 14–56 days) | No serious AEs or increases in the risk of GvHD were identified |
Dyba et al. 2016 [79] | Systematic review | 5 case studies (total of 7 patients with ITP or PIT after allogenic transplantation) and 3 prospective clinical trials (total of 177 patients with 95 patients receiving TPO-RAs) Prospective studies addressed use of TPO-RA to accelerate initial engraftment either by starting treatment immediately after transplant in all patients (2 studies) or in patients with PIT at specific time points after allogenic transplant (1 study) | Results from the case reports describe variable response to TPO-RA treatment, and 6 of the 7 patients had a favorable response and did not require platelet transfusion within 7–23 days of treatment with ROM (6 patients) and ELT (1 patient) The phase I study started 19 patients on ELT 1 day post-transplant (MRD or MUD). The median time to platelet engraftment was 16 days and patients had an average of 4 platelet transfusions | No dose-limiting toxicities were observed |