Erythrocytapheresis in Children and Young Adults with Hemoglobinopathies and Iron Overload in Need of Iron Chelation Therapy.

Limited data regarding erythrocytapheresis in children, adolescents, and young adults have been published. The aim of this study was to evaluate erythrocytapheresis, either as a standalone therapy or in combination with iron chelation therapy, in children and young adults with hemoglobinopathies in whom current iron chelation therapy is not sufficient in decreasing the iron overload during management. We retrospectively analysed erythrocytapheresis in 19 patients with hemoglobinopathies in need of iron chelation therapy diagnosed with sickle cell disease (SCD) or ß-thalassemia major. Patients were divided into (1) a case cohort who received erythrocytapheresis alone or in combination with iron chelation therapy and (2) a control cohort who received oral iron chelation therapy alone. Serum ferritin and haemoglobin levels were compared at five different time points over a one-year period. In the erythrocytapheresis cohort, there was a significant decrease in serum ferritin (p < 0.001). In the iron chelation therapy alone cohort, there was no significant decrease in serum ferritin over time (p = 0.156). Comparing the evolution of median serum ferritin between therapy with erythrocytapheresis and iron chelation therapy showed a statistically significant difference (p = 0.008). Patients with ß-thalassemia major receiving erythrocytapheresis showed a greater reduction in serum ferritin compared to patients without (p = 0.036). A difference could not be shown between the erythrocytapheresis and iron chelation single therapies (p = 0.100). This study showed an overall significant reduction in serum ferritin in patients with hemoglobinopathies treated with erythrocytapheresis in addition to iron chelation. A clinical, although not statistical, trend of higher haemoglobin levels was maintained. Erythrocytapheresis in paediatric patients with ß-thalassemia major was as effective in decreasing ferritin levels as in previously reported studies with SCD. Erythrocytapheresis is a promising therapy for treating and preventing transfusion-related iron overload.

Joint status, pain and quality of life in elderly people with haemophilia: A case-control study.

INTRODUCTION: Elderly people with haemophilia (PwH) develop haemophilic arthropathy, pain, and reduced health-related quality of life (HR-QoL). The condition of elderly mild haemophilia patients have rarely been evaluated. This study aimed to compare joint status, pain, and HR-QoL between elderly with mild, moderate/severe haemophilia and healthy elderlies. METHODS: Knee/ankle abnormalities were assessed by ultrasound (HEAD-US) and physical examination (HJHS 2.1). Pain severity and pain interference were investigated using the Brief Pain Inventory. Pressure pain thresholds (PPTs) were obtained at knees/ankles and forehead. Functional limitations were evaluated using the 2-Minute-Walking-Test, Timed-Up-and-Go and HAL. The EQ-5D-5L questionnaire evaluated HR-QoL. Healthy controls (HCs) and elderly individuals with moderate/severe and mild haemophilia were compared using Kruskal-Wallis and Mann-Whitney U tests. RESULTS: From the 46 elderly PwH approached, 40 individuals (≥60 years) with haemophilia A/B (17 moderate/severe; 23 mild) and 20 age-matched HCs were recruited. Moderate/severe PwH displayed worse joint status, lower PPTs, and poorer HR-QoL than mild PwH and HCs (p-value = .010-<.001). HEAD-US abnormalities were observed in 100% of knees and 94% of ankles in moderate/severe PwH, versus 50% of knees and 61% of ankles in mild PwH. Pain was reported by 80% and 57% of moderate/severe and mild PwH, respectively. Low PPTs, functional limitations, and poor HR-QoL scores were likewise observed in some mild PwH, yet without significantly differing from HCs. CONCLUSION: This study highlights poor joint/functional status, pain, and HR-QoL outcomes in elderly with moderate/severe haemophilia. A few mild haemophilia subjects presented joint abnormalities, pain, functional limitations, and poor HR-QoL, without significantly differing from HCs. HIGHLIGHTS: Elderly individuals with mild haemophilia have not yet been extensively studied, whereas moderate/severe haemophilia individuals have proven to suffer from haemophilic arthropathy, pain, and poor health-related quality of life (HR-QoL). Using a case-control design, joint status, pain, and HR-QoL outcomes were examined in elderly haemophilia individuals and compared with those of healthy controls (HCs). Elderly moderate/severe haemophilia individuals exhibited worse joint status, increased joint pain sensitivity, and reduced HR-QoL compared with both mild haemophilia subjects and HCs. A subset of mild haemophilia subjects exhibited poor joint status, pain, and HR-QoL outcomes, without any differences noted when compared with HCs.

The Classification of Suspected Predominant Nociplastic Pain in People with Moderate and Severe Haemophilia: A Secondary Exploratory Study.

In people with haemophilia (PwH), joint pain is a major comorbidity that is often overlooked and under-treated. It is believed that, to ensure the most successful outcome, pain management should be tailored to the predominant pain phenotype (i.e., nociceptive, neuropathic and nociplastic). The 2021 clinical criteria and grading system for nociplastic pain, established by the International Association for the Study of Pain (IASP), emphasize the necessity of early-stage identification and predominant pain type classification. Consistent with findings in other chronic musculoskeletal pain conditions, studies suggest that a subgroup of PwH suffers from nociplastic pain, i.e., pain arising from altered nociception rather than structural damage, but this has not yet been explored in PwH. This study aimed to identify PwH with "unlikely", "possible" and "probable" nociplastic pain and investigate differences in anthropometric, demographic and clinical characteristics and psychological factors between subgroups of PwH and healthy individuals.: The IASP clinical criteria and grading system were used to classify pain types in adult men with moderate or severe haemophilia recruited from two Belgian haemophilia treatment centres. Statistical analyses were applied to study between-subgroup differences. Of 94 PwH, 80 PwH (85%) were classified with "unlikely" and 14 (15%) with "at least possible" nociplastic pain (including 5 PwH (5%) with "possible" and 9 PwH (10%) with "probable" nociplastic pain). PwH in both the "unlikely" and "at least possible" nociplastic pain groups showed significantly higher levels of unhelpful psychological factors compared to healthy individuals. Additionally, age may partially account for the observed differences in body height and psychological factors. Larger sample sizes may be needed to detect more subtle between-group differences. study confirmed the presence of nociplastic pain in haemophilia, categorising a notable subgroup as individuals who experience at least possible nociplastic pain. These exploratory insights may provide a starting point for future studies and the development of more effective and tailored pain management.

Psychophysical assessment of pain in adults with moderate and severe haemophilia: A cross-sectional study.

BACKGROUND: Joint pain is the hallmark of haemophilia; therefore it seems clinically rather a musculoskeletal than a bleeding disorder. Although joint pain in people with haemophilia (PwH) is a complex and multidimensional problem, pain assessment remains primarily focused on the structural evaluation of their joints. Whereas, only few data are available on the potential implication of psychophysical and psychological factors. OBJECTIVE: This study aimed to perform a psychophysical pain assessment including quantitative sensory testing (QST) and an evaluation of psychological factors in a large sample of PwH, to get insight into the individuals' pain system. METHODS: Ninety-nine adults (36.9 ± 13.5 years) with moderate/severe haemophilia A/B and 46 healthy controls filled in self-reported pain and psychological questionnaires and underwent a QST evaluation including static and dynamic tests. Static tests focused on the determination of thermal detection and pain thresholds and mechanical pressure pain thresholds. Dynamic tests evaluated pain facilitation and the efficacy of endogenous pain inhibition. Besides comparing PwH and healthy controls, between-subgroup differences were studied in PwH based on their pain distribution. RESULTS: The study revealed increased thermal and mechanical pain sensitivity and the presence of unhelpful psychological factors such as anxiety/depression in PwH. Among the subgroups, especially PwH with widespread pain showed altered somatosensory functioning. Enhanced pain facilitation and impaired efficacy of endogenous pain inhibition in PwH could not be observed. CONCLUSION: Altered somatosensory functioning and unhelpful psychological factors, appear to play an important role in the pathophysiology of pain in PwH, especially in PwH with widespread pain.

ACTIVLIM-Hemo: A new self-reported, unidimensional and linear measure of activity limitations in persons with haemophilia.

INTRODUCTION: To assess activity limitations in people with haemophilia (PwH), the self-reported Haemophilia Activity List (HAL) is widely employed, despite several methodological limitations impacting the interpretation of categorical scores. Modern psychometric approaches avoid these limitations by using a probabilistic model, such as the Rasch model. The ACTIVLIM is a Rasch-built measurement of activity limitations previously validated in several clinical conditions like neuromuscular disorders. AIMS: This study sought to develop the ACTIVLIM-Hemo, meaning an ACTIVLIM scale version specifically adapted to assess daily activity limitations in adult PwH. METHODS: Daily activities were assessed as "impossible," "difficult" or "easy" by 114 PwH (median age of 44 years) with 63 of them reassessed after 12 days. The Rasch Rating Scale model was used to identify activities delineating a unidimensional and linear scale unbiased by demographic and clinical status. Concurrent validity was determined through correlation with the HAL sub-scores and sum score. RESULTS: The ACTIVLIM-Hemo included 22 pertinent activities, with difficulties independent of demographic and clinical conditions, allowing a reliable measure of activity limitations (PSI = .92) expressed on a linear and unidimensional scale in PwH (7%-100 % range, ceiling effect of 1/114) with excellent test-retest reliability (ICC = .978). Spearman rank correlations between ACTIVLIM-Hemo and HAL sub-scores ranged between .623 and .869. CONCLUSIONS: The ACTIVLIM-Hemo is an easy-to-administer, valid and reliable alternative to HAL in assessing activity limitations in PwH. Its invariant scale can be used across conditions and time to compare the functional status of PwH over a wide measurement range.

Efficacy and safety in patients with haemophilia A switching to octocog alfa (BAY 81-8973): Final results of the global real-world study, TAURUS.

OBJECTIVES: To report the final results of the 2-year TAURUS study, assessing weekly prophylaxis dosing regimens of octocog alfa (Kovaltry®/BAY 81-8973) used in standard clinical practice in patients with moderate-to-severe haemophilia A. METHODS: TAURUS (NCT02830477) is a phase 4, multinational, prospective, non-interventional, single-arm study in patients of any age with moderate or severe haemophilia A (≤5% factor [F]VIII activity). TAURUS was designed to primarily investigate weekly prophylaxis dosing regimens used in standard clinical practice. Annualised bleeding rates (ABRs), treatment satisfaction and adherence, and safety were also assessed. RESULTS: Of 302 patients included in the full analysis set, 84.4% (n = 255) maintained their octocog alfa prophylaxis baseline regimen throughout the study, with a majority of patients (76.5%, n = 231) on two times or three times weekly regimens at the end of the observation period (≥1-≤2 years). ABRs, treatment satisfaction, and adherence remained stable during the observation period. Octocog alfa was well tolerated and there were no new or unexpected adverse events. CONCLUSIONS: These data show that a smooth transition is observed when switching to octocog alfa from a previous FVIII treatment, with no safety issues and stable bleeding rates in a real-world setting of patients with moderate-to-severe haemophilia A.

Efficacy and safety of von Willebrand factor concentrate almost devoid of factor VIII (Wilfactin®) in paediatric patients under 6 years of age with severe von Willebrand disease.

BACKGROUND: Plasma-derived von Willebrand factor (VWF) (Wilfactin®, LFB, France) was developed for prophylaxis and treatment of haemorrhages in both adults and adolescents with von Willebrand disease (VWD). Replacement therapy in paediatric patients is a key element of the clinical trial programme. MATERIAL AND METHODS: Patients aged <6 years with severe VWD were enrolled in a multinational, open-label study to evaluate the in vivo recovery for Wilfactin®, and its efficacy in preventing and treating bleeding episodes and during surgery. Overall haemostatic efficacy based on a 4-point scale was assessed by investigators. The treatment period ≥18 months investigated the long-term safety. RESULTS: Nine patients, including 7 with type 3 VWD were exposed to treatment with Wilfactin® for up to 4.2 years. Recovery of VWF in 7 patients (n=5 type 3, n=1 type 2, n=1 type 1) was 1.8±0.4 IU/dL per IU/kg. Of the 62 bleeds, 89% were controlled with one (73%) or two (16%) infusions of Wilfactin®. The median dose per infusion was 54 IU/kg. A factor VIII dose was co-administered in 1.6% of bleeds. "Excellent"/"Good" haemostatic efficacy was achieved in 90.3% of episodes. Six patients underwent 11 minor surgical interventions. Treatment duration was 1 day (range: 1-6 days) with a dose administered 30-60 minutes before procedure of 56 IU/kg (range: 41-106 IU/kg). Haemostasis was rated as "Excellent" in all surgeries. During 4-year prophylactic treatment in one patient, breakthrough bleeds were reported in 2.2% of infusions. No VWF inhibitors, thromboembolic events or allergic/anaphylactic-type reactions were observed following a total exposure of 770 days. DISCUSSION: The results show that Wilfactin® provides a safe and effective treatment in patients <6 years of age with severe VWD.

Effect of Poloxamer 188 vs Placebo on Painful Vaso-Occlusive Episodes in Children and Adults With Sickle Cell Disease: A Randomized Clinical Trial.

Importance: Although effective agents are available to prevent painful vaso-occlusive episodes of sickle cell disease (SCD), there are no disease-modifying therapies for ongoing painful vaso-occlusive episodes; treatment remains supportive. A previous phase 3 trial of poloxamer 188 reported shortened duration of painful vaso-occlusive episodes in SCD, particularly in children and participants treated with hydroxyurea. Objective: To reassess the efficacy of poloxamer 188 for vaso-occlusive episodes. Design, Setting, and Participants: Phase 3, randomized, double-blind, placebo-controlled, multicenter, international trial conducted from May 2013 to February 2016 that included 66 hospitals in 12 countries and 60 cities; 388 individuals with SCD (hemoglobin SS, SC, S-ß0 thalassemia, or S-ß+ thalassemia disease) aged 4 to 65 years with acute moderate to severe pain typical of painful vaso-occlusive episodes requiring hospitalization were included. Interventions: A 1-hour 100-mg/kg loading dose of poloxamer 188 intravenously followed by a 12-hour to 48-hour 30-mg/kg/h continuous infusion (n = 194) or placebo (n = 194). Main Outcomes and Measures: Time in hours from randomization to the last dose of parenteral opioids among all participants and among those younger than 16 years as a separate subgroup. Results: Of 437 participants assessed for eligibility, 388 were randomized (mean age, 15.2 years; 176 [45.4%] female), the primary outcome was available for 384 (99.0%), 15-day follow-up contacts were available for 357 (92.0%), and 30-day follow-up contacts were available for 368 (94.8%). There was no significant difference between the groups for the mean time to last dose of parenteral opioids (81.8 h for the poloxamer 188 group vs 77.8 h for the placebo group; difference, 4.0 h [95% CI, -7.8 to 15.7]; geometric mean ratio, 1.2 [95% CI, 1.0-1.5]; P = .09). Based on a significant interaction of age and treatment (P = .01), there was a treatment difference in time from randomization to last administration of parenteral opioids for participants younger than 16 years (88.7 h in the poloxamer 188 group vs 71.9 h in the placebo group; difference, 16.8 h [95% CI, 1.7-32.0]; geometric mean ratio, 1.4 [95% CI, 1.1-1.8]; P = .008). Adverse events that were more common in the poloxamer 188 group than the placebo group included hyperbilirubinemia (12.7% vs 5.2%); those more common in the placebo group included hypoxia (12.0% vs 5.3%). Conclusions and Relevance: Among children and adults with SCD, poloxamer 188 did not significantly shorten time to last dose of parenteral opioids during vaso-occlusive episodes. These findings do not support the use of poloxamer 188 for vaso-occlusive episodes. Trial Registration: ClinicalTrials.gov Identifier: NCT01737814.

Pharmacokinetics and safety of ticagrelor in infants and toddlers with sickle cell disease aged <24 months.

Inhibition of platelet activation may reduce vaso-occlusion rates in patients with sickle cell disease (SCD). In the HESTIA4 (NCT03492931) study, 21 children with SCD received a single oral dose of the antiplatelet agent ticagrelor (0.1 mg/kg <6 months; 0.2 mg/kg ≥6 to <24 months). All patients had measurable ticagrelor plasma concentrations. Ticagrelor and active metabolite (AR-C124910XX) exposure were comparable across all groups (<6 months, ≥6 to <12 months and ≥12 to <24 months). Ticagrelor was well tolerated. Palatability was generally acceptable. These data will be used to enable dose selection for further investigations of ticagrelor efficacy and safety in children with SCD.

BAY 81-8973 prophylaxis and pharmacokinetics in haemophilia A: Interim results from the TAURUS study.

OBJECTIVES: To report interim data from TAURUS, a study assessing real-world prophylactic treatment with unmodified, full-length recombinant FVIII BAY 81-8973 (Kovaltry® ; Bayer) indicated for haemophilia A. METHODS: TAURUS (NCT02830477) is an international, open-label, prospective, non-interventional, single-arm study with a one-year observation period (target N = 350). Patients have moderate or severe haemophilia A (FVIII ≤5% or ≤1%) and ≥50 exposure days to any FVIII product. Clinician- and patient-reported outcomes are captured on previous product use, changes in prophylaxis dose and dosing frequency, FVIII consumption, reported bleeding rates, treatment satisfaction and adherence, pharmacokinetic (PK) data (if available) and safety data. RESULTS: At cut-off, baseline data were available from 160 patients (89 had ≥6 months of follow-up data). Most patients had severe haemophilia A (85%), infused BAY 81-8973 ≥ 3×/wk (59%) and experienced a median number of total bleeds of 2.0 (non-annualised; 246 days median documentation period). Good levels of treatment satisfaction (Hemo-SATA,P ) and adherence (VERITAS-Pro) were maintained. TAURUS demonstrated a favourable PK profile of BAY 81-8973 in comparison with other standard half-life rFVIIIs and supported the WAPPS PopPK model. No patients developed inhibitors. CONCLUSIONS: TAURUS data demonstrate effective prophylaxis with BAY 81-8973 in the real world without compromising patient satisfaction or adherence.

Prolonged versus standard native E. coli asparaginase therapy in childhood acute lymphoblastic leukemia and non-Hodgkin lymphoma: final results of the EORTC-CLG randomized phase III trial 58951.

Asparaginase is an essential component of combination chemotherapy for childhood acute lymphoblastic leukemia and non-Hodgkin lymphoma. The value of asparaginase was further addressed in a group of non-very high-risk patients by comparing prolonged (long-asparaginase) versus standard (short-asparaginase) native E. coli asparaginase treatment in a randomized part of the phase III 58951 trial of the European Organization for Research and Treatment of Cancer Children's Leukemia Group. The main endpoint was disease-free survival. Overall, 1,552 patients were randomly assigned to long-asparaginase (775 patients) or short-asparaginase (777 patients). Patients with grade ≥2 allergy to native E. coli asparaginase were switched to equivalent doses of Erwinia or pegylated E. coli asparaginase. The 8-year disease-free survival rate (±standard error) was 87.0±1.3% in the long-asparaginase group and 84.4±1.4% in the short-asparaginase group (hazard ratio: 0.87; P=0.33) and the 8-year overall survival rate was 92.6±1.0% and 91.3±1.2% respectively (hazard ratio: 0.89; P=0.53). An exploratory analysis suggested that the impact of long-asparaginase was beneficial in the National Cancer Institute standard-risk group with regards to disease-free survival (hazard ratio: 0.70; P=0.057), but far less so with regards to overall survival (hazard ratio: 0.89). The incidences of grade 3-4 infection during consolidation (25.2% versus 14.4%) and late intensification (22.6% versus 15.9%) and the incidence of grade 2-4 allergy were higher in the long-asparaginase arm (30% versus 21%). Prolonged native E. coli asparaginase therapy in consolidation and late intensification for our non-very high-risk patients did not improve overall outcome but led to an increase in infections and allergy. This trial was registered at www.clinicaltrials.gov as #NCT00003728.

Renal papillary necrosis in patients with sickle cell disease: How to recognize this 'forgotten' diagnosis.

INTRODUCTION: Renal papillary necrosis is not commonly seen in daily practice, but can have severe consequences when it is not diagnosed in time. It is known to be associated with sickle cell hemoglobinopathies; however a wide range of etiologies are possible, and it is therefore not the first diagnosis clinicians consider in patients with sickle cell disease who present with hematuria. METHODS: A literature search was performed to summarize the current knowledge about renal papillary necrosis associated with sickle cell disease. These findings are illustrated with a case of a 9-year old girl with sickle cell disease who was referred with painless gross hematuria. RESULTS: Typical radiologic signs for renal papillary necrosis are necrotic cavities that fill with contrast, small collections of contrast peripheral to the calyces in the papillary region (ball-on-tee sign), calcification of the papillary defect, filling defects, hydronephrosis, blunted papillary tip, clefts in the renal medulla filled with contrast, hyperattenuated medullary calcifications, non-enhanced lesions surrounded by rings of excreted contrast, and clubbed calyces. DISCUSSION: This study focuses on the pathophysiology of renal papillary necrosis associated with sickle cell disease, the possible symptoms, as well as the diagnostic steps, with a special interest in particular presentation on old (retrograde pyelography) and new (computed tomography) gold standard in radiologic imaging, and the management for this pathology. CONCLUSION: This study aims to remind clinicians of this "forgotten" diagnosis and what signs to look for in pediatric patients with sickle cell disease who present with hematuria. In pediatric cases radiation protection is important, therefore knowing what radiologic signs can be found on retrograde pyelography can lead to early identification of this pathology without having to proceed to computed tomography.

Extremely elevated cerebrospinal fluid protein levels in a child with neurologic symptoms: beware of haemophagocytic lymphohistiocytosis.

Neurologic symptoms can be the initial manifestation of haemophagocytic lymphohistiocytosis (HLH). In this case study, we present a 3-year old boy with a clinical picture of encephalitis, a cerebrospinal fluid (CSF) protein level up to 1165 mg/dl and diffuse cerebral MRI abnormalities. The diagnosis of HLH was established only 6 weeks after initial presentation. The boy recovered after HLH therapy with persisting mild cognitive defects. Genetic investigation demonstrated X-linked lymphoproliferative disease (XLP) as the underlying cause of HLH. The extremely elevated protein level in CSF in this case has not yet been reported in patients with HLH.

Effectiveness of early initiation of protease inhibitor-sparing antiretroviral regimen in human immunodeficiency virus-1 vertically infected infants.

Each of the 17 vertically infected infants born to HIV-1-infected mothers in Belgian HIV reference centers since 1996 was treated with a combination of 3 reverse transcription inhibitors as soon as the diagnosis was established. Treatment was initiated in all patients before 66 days of life. Twelve patients, including 11/13 infants treated with the combination of zidovudine, lamivudine and nevirapine, experienced a complete viral suppression (<50 copies/mL) with their first drug regimen. At last follow-up, 12 patients were asymptomatic, 2 were CDC stage A and 3 were stage B; 15 had HIV-1 RNA levels of <50 copies/mL and 14 had >or=25% CD4 lymphocytes. These results suggest that early initiation of treatment with 3 reverse transcription inhibitors is highly effective to inhibit viral replication and to prevent clinical and immunologic progression of HIV infection in vertically infected infants.

Hydroxyurea for sickle cell disease in children and for prevention of cerebrovascular events: the Belgian experience.

Hydroxyurea (HU) is considered to be the most successful drug therapy for severe sickle cell disease (SCD). Nevertheless, questions remain regarding its benefits in very young children and its role in the prevention of cerebrovascular events. There were 127 SCD patients treated with no attempt to reach maximal tolerated doses who entered the Belgian Registry: 109 for standard criteria and 18 who were at risk of stroke only. During 426 patient-years of follow-up for patients with standard criteria, 3.3 acute chest syndromes, 1.3 cerebrovascular events, and 1.1 osteonecrosis per 100 patient-years were observed. A subgroup of 32 patients followed for 6 years experienced significant benefit over this period. In each subgroup of children (younger than 2 years, 2-5, 6-9, and 10-19 years) followed for 2 years, clinical and biologic changes were similar, except for children younger than 2 years who had no total hemoglobin increase and remained at risk of severe anemia. In 72 patients evaluated by transcranial Doppler studies (TCD), 34 patients were at risk of primary stroke and only 1 had a cerebrovascular event after a follow-up of 96 patient-years. These results confirm the benefit of HU, even in very young children, and its possible role in primary stroke prevention.

Resistance testing in children changing human immunodeficiency virus type 1 protease inhibitor.

OBJECTIVE: To assess genotypic and phenotypic resistance testing in HIV-1-infected children failing a first protease inhibitor (PI) therapy. METHODS: In a multicenter observational study 21 children, ages 3 to 16 years, were given two reverse transcriptase inhibitors and one PI (mainly ritonavir, n = 18). They were subsequently treated with single or dual PI-based therapy (predominantly nelfinavir, n = 10, or ritonavir-saquinavir, n = 7). Resistance testing was performed at the time of therapy switch via direct sequencing and a recombinant virus susceptibility assay. RESULTS: A total of 21 genotypic and 15 phenotypic resistance profiles were obtained. Most viruses displayed several reverse transcriptase mutations; however, 7 isolates maintained a wild-type protease. Ritonavir targeted the well-known pathway containing 82, 54, 46 and other secondary (nonactive site) mutations including T74A. No in vitro cross-resistance, i.e. > or = 8-fold resistance to saquinavir or amprenavir, was encountered. Secondary mutations enhanced the prediction of ritonavir resistance (i.e. L10I) and in vitro nelfinavir cross-resistance (i.e. K20R/I) conferred by primary (active site) resistance mutations. Either the 82, 54, 46 mutational genotype or the phenotype showing > or = 8-fold nelfinavir cross-resistance predicted a poorer virologic response to nelfinavir salvage therapy. CONCLUSION: In a small cohort of heavily pretreated pediatric patients, resistance testing appears to predict the response to nelfinavir as salvage for a ritonavir-based therapy. This is further supported by the correlation between ritonavir-selected mutations and in vitro nelfinavir cross-resistance. Prospective studies should assess clinical outcome in children undergoing regimen changes based on resistance testing.