Characterizing the pharmacokinetics and biodistribution of therapeutic proteins: an industry white paper

Characterization of the pharmacokinetics (PK) and biodistribution of therapeutic proteins (TPs) is a hot topic within the pharmaceutical industry, particularly with an ever-increasing catalog of novel modality TPs. Here, we review the current practices, and provide a summary of extensive cross-company discussions as well as a survey completed by International Consortium for Innovation and Quality (IQ consortium) members on this theme. A wide variety of in vitro, in vivo and in silico techniques are currently used to assess PK and biodistribution of TPs, and we discuss the relevance of these from an industry perspective, focusing on PK/PD understanding at the preclinical stage of development, and translation to human. We consider that the 'traditional in vivo biodistribution study' is becoming insufficient as a standalone tool, and thorough characterization of the interaction of the TP with its target(s), target biology, and off-target interactions at a microscopic scale are key to understand the overall biodistribution at a full-body scale. Our summary of the current challenges and our recommendations to address these issues could provide insight into the implementation of best practices in this area of drug development, and continued cross-company collaboration will be of tremendous value. Significance Statement The Innovation & Quality Consortium (IQ) Translational and ADME Sciences Leadership Group (TALG) working group for the ADME of therapeutic proteins evaluates the current practices, recent advances, and challenges in characterizing the PK and biodistribution of therapeutic proteins during drug development, and proposes recommendations to address these issues. Incorporating the in vitro, in vivo and in silico approaches discussed herein may provide a pragmatic framework to increase early understanding of PK/PD relationships, and aid translational modelling for first-in-human dose predictions.

Secukinumab dosing every two weeks demonstrated superior efficacy compared with dosing every four weeks in patients with psoriasis weighing 90 kg or more: Results of a randomised controlled trial

BACKGROUND

Obesity is a common comorbidity of psoriasis and can attenuate response to biologic treatment.

OBJECTIVES

To investigate the efficacy, safety and tolerability of secukinumab 300 mg every 2 weeks (Q2W) vs. secukinumab 300 mg every 4 weeks (Q4W) in patients with a higher body weight.

METHODS

In this multicentre, double-blind, parallel-group trial, 331 patients with moderate-to-severe chronic plaque psoriasis weighing ≥90 kg were randomised to receive secukinumab 300 mg Q2W or secukinumab 300 mg Q4W. Patients who did not achieve PASI90 at Week 16 on the Q4W regimen were reallocated to remain on the Q4W regimen or up-titrate to Q2W.

RESULTS

At Week 16, Q2W dosing (N=165) led to significantly higher PASI90 responses vs. Q4W [N=166; 73.2% vs. 55.5%, one-sided p-value=0.0003, odds ratio estimate (95% confidence intervals): 2.3 (1.4, 3.8). At Week 52, higher efficacy responses were maintained in the Q2W arm (N=165) vs. Q4W (N=83); PASI75: 88.9% vs. 74.8%; PASI90: 76.4% vs. 52.4%, PASI100: 46.7% vs. 27.3%; IGA 0/1: 75.9% vs. 55.6% and DLQI 0/1: 66.1% vs. 48.8%. PASI90 non-responders at Week 16 who up-titrated to Q2W (N=31) showed higher efficacy responses at Week 32 (16 weeks post-up-titration, PASI90: 38.7% vs. 16.5%) vs. those who remained on Q4W (N=40). Safety results were comparable across treatment arms and consistent with the established secukinumab safety profile.

CONCLUSIONS

Secukinumab 300 mg Q2W demonstrated superior and sustained efficacy compared with Q4W in moderate-to-severe plaque psoriasis patients weighing ≥90 kg. PASI90 non-responders derived additional benefits from up-titration to a Q2W regimen. (NCT03504852).

Secukinumab demonstrates efficacy, safety and tolerability upon administration by 2 mL autoinjector in adult patients with plaque psoriasis: 52-week results from MATURE, a randomized, placebo-controlled trial

Convenient administration is an important factor for treatment adherence in patients with psoriasis. MATURE study reports the efficacy, safety, tolerability, and pharmacokinetics of secukinumab 300 mg 2 mL autoinjector (AI) from MATURE trial (NCT03589885). Eligible patients were randomized to secukinumab 300 mg 2 mL AI or 2x 1 mL pre-filled syringe (PFS) or placebo. The co-primary endpoints were Psoriasis Area and Severity Index (PASI) 75 and Investigator's Global Assessment (IGA) 0/1 response rates at Week 12 versus placebo. Other endpoints included PASI90/100 response, Dermatology Life Quality Index (DLQI) 0/1, pharmacokinetics, 2 mL AI usability rated using Self-Injection Assessment Questionnaire (SIAQ), and safety. The study met both co-primary and secondary endpoints (p < 0.0001). Secukinumab 300 mg 2 mL AI and 2x 1 mL PFS treatments led to superior PASI75/90/100 (2 mL AI: 95.1%/75.6%/43.9%; 2x 1 mL PFS: 83.2%/62.6%/37.5% and placebo: 10%/5.0%/0.0%, respectively), IGA, and DLQI 0/1 responses compared with placebo, and efficacy was sustained through 52 weeks. SIAQ results showed high usability of self-injection with 2 mL AI device. No new safety signals were observed. Study design may bias the interpretation of safety profile after Week 12, due to different exposure of secukinumab versus placebo. Secukinumab 300 mg administered with the 2 mL AI demonstrated superior efficacy over placebo, good tolerability and convenient administration. This article is protected by copyright. All rights reserved.

Efficacy, tolerability, patient usability, and satisfaction with a 2 mL pre-filled syringe containing secukinumab 300 mg in patients with moderate to severe plaque psoriasis: results from the phase 3 randomized, double-blind, placebo-controlled ALLURE study

BACKGROUND

Evidence shows good tolerability in patients for subcutaneous injection volumes up to 3 mL.

OBJECTIVES

We investigated efficacy, pharmacokinetics, and tolerability of secukinumab 300 mg/2 mL pre-filled syringe (PFS) in patients with moderate to severe plaque psoriasis.

METHODS

ALLURE was a 52-week, multicenter, randomized (1:1:1), double-blind, placebo-controlled, parallel-group study. Co-primary endpoints were secukinumab Psoriasis Area Severity Index (PASI) 75 and Investigator's Global Assessment modified 2011 0/1 (IGA mod 2011 0 or 1) responses at week 12 versus placebo. Other endpoints included the Self-Injection Assessment Questionnaire (SIAQ), and the ability to follow the instructions for use (IFU).

RESULTS

Overall, 214 patients were randomized. The secukinumab 300 mg/2 mL PFS showed superiority over placebo for both PASI 75 (88.9% versus 1.7%; p<.0001) and IGA mod 2011 0 or 1 (76.4% versus 1.4%; p<.0001) responses at week 12. All secondary efficacy endpoints were met. The SIAQ scores were similar across groups and improved similarly over 12 weeks. All patients completed critical steps in the IFU at week 1.

CONCLUSIONS

The secukinumab 300 mg/2 mL PFS groups showed superiority versus placebo, and it was a safe, effective, and convenient option for patients with psoriasis. NCT02748863.

Comparison of pharmacokinetics, safety and tolerability of secukinumab administered subcutaneously using different delivery systems in healthy volunteers and in psoriasis patients

AIMS

The aim of the study was to compare the pharmacokinetics (PK), safety and tolerability of secukinumab with different devices for subcutaneous (s.c.) administration of 2 mL.

METHODS

A phase 1 study in healthy subjects with 6 devices to administer 2 mL injection volumes was conducted to evaluate the serum PK, safety and tolerability of secukinumab following single s.c. injection of 300 mg in the abdomen (either side) or in the thigh (either leg). Primary PK endpoints were maximum observed serum concentration and area under the serum concentration-time curve. The impact of device, site and side of injection on serum exposure was evaluated. In a phase 3 study in psoriasis patients, PK of secukinumab was evaluated following multiple s.c. injections of 300 mg by either 2 × 1-mL prefilled syringe or 1 × 2-mL prefilled syringe.

RESULTS

Mean serum concentration-time profiles for administration as 2 × 1 mL injections or as 1 × 2 mL injections were similar. With an injection volume of 2 mL, perceived injection pain was not different from 2 × 1 mL injections. A nonclinically significant difference in PK endpoints was observed between thigh and abdomen. Results with a 2 mL prefilled syringe in a 1-year phase 3 study in patients confirmed PK results observed in the phase 1 study.

CONCLUSION

Collective evidence from both studies demonstrated that 2-mL injections of secukinumab into the abdomen or thigh using different devices resulted in comparable PK characteristics and were all well tolerated without noticeable local reactions.

Secukinumab Treatment Does Not Alter the Pharmacokinetics of the Cytochrome P450 3A4 Substrate Midazolam in Patients With Moderate to Severe Psoriasis

This open‐label disease‐drug–drug interaction study assessed whether blockade of the interleukin (IL)‐17A pathway by secukinumab and subsequent downregulation of inflammatory cytokines like IL‐6 or high‐sensitivity C‐reactive protein affects the pharmacokinetics (PKs) of a sensitive probe substrate of the cytochrome P450 3A4 isoform (CYP3A4). The PKs of midazolam, metabolized by CYP3A4, was evaluated before and after 7 and 35 days of treatment initiation of subcutaneous secukinumab at a dose of 300 mg weekly in 24 patients with moderate‐to‐severe psoriasis. Although demonstrating the expected decrease in downstream inflammatory cytokines, secukinumab had no clinically relevant effects on the PKs of midazolam, provided substantial clinical benefit, and was generally well tolerated. In summary, blockade of IL‐17A signaling in patients with moderate‐to‐severe psoriasis does not significantly affect CYP3A4 enzyme activities and, therefore, the use of secukinumab is unlikely to influence the PKs of CYP3A4 substrates.

Secukinumab Immunogenicity over 52 Weeks in Patients with Psoriatic Arthritis and Ankylosing Spondylitis

Objective.

Secukinumab, a fully human antiinterleukin 17A monoclonal antibody, is efficacious for the treatment of psoriatic arthritis (PsA) and ankylosing spondylitis (AS). This study examined the immunogenicity of secukinumab in patients with PsA and AS exposed to secukinumab for up to 52 weeks.

Methods.

Antibody bridging assays were used to assess the immunogenicity of secukinumab in patients with PsA [FUTURE 1–3 studies, and AS (MEASURE 1–4 studies)]. Evaluations were at baseline and at weeks 16 (AS only), 24, and 52. Treatment-emergent antidrug antibodies (TE-ADA) were defined as a positive ADA signal in ≥ 1 posttreatment sample in patients negative at baseline. Positive samples were analyzed for drug-neutralizing potential, and effect of TE-ADA on secukinumab pharmacokinetics, immunogenicity-related adverse events (AE), and efficacy through Week 52 were assessed.

Results.

Of 1414 treated PsA and 1164 treated AS patients with samples available for immunogenicity evaluation, 5 (0.35%) and 8 (0.69%), respectively, developed TE-ADA. All but 1 PsA patient were biologic-naive; two of the 5 PsA and one of the 8 AS patients received concomitant methotrexate, and two of the 8 AS patients received concomitant sulfasalazine. Associations between TE-ADA and secukinumab dose, frequency, or administration mode were not observed. Other than one PsA patient, all TE-ADA were non-neutralizing. No TE-ADA were associated with any AE. All TE-ADA were associated with normal secukinumab pharmacokinetics and none were associated with loss of secukinumab efficacy.

Conclusion.

Secukinumab treatment was associated with a low (< 1%) incidence of immunogenicity in patients with PsA or AS. (clinicaltrials.gov: NCT01392326; NCT01752634; NCT01989468; NCT01358175; NCT01649375; NCT02008916; NCT02159053)

Population Pharmacokinetic Modeling of Secukinumab in Patients With Moderate to Severe Psoriasis

Secukinumab is a human monoclonal antibody with demonstrated efficacy for moderate to severe psoriasis; it binds to and neutralizes interleukin (IL)-17A. The pharmacokinetic (PK) parameters of secukinumab were best described by a 2-compartment model. Only weight was included in the final model, as other covariates did not affect clinical relevance. The estimated serum clearance of secukinumab was 0.19 L/day, with interindividual variability (IIV) of 32% coefficient of variation (CV), and low total volume of distribution (central compartment volume, 3.61 L with IIV of 30% CV; peripheral compartment volume, 2.87 L with IIV of 18% CV). The bioavailability of secukinumab after subcutaneous dosing was approximately 73%, with an absorption rate of 0.18/day with IIV of 35% CV. The PK profile of secukinumab was linear, with no evidence of a dose dependence of clearance. Clearance and volume of secukinumab varied with body weight in an allometric relationship. The time to maximum serum concentration at steady state occurred approximately 6 days after dosing for both secukinumab 300 mg and secukinumab 150 mg. Overall, the PK properties of secukinumab were typical of a 150-kDa human IgG1 antibody interacting with a soluble target.

Secukinumab, a fully human anti-interleukin-17A monoclonal antibody, exhibits minimal immunogenicity in patients with moderate-to-severe plaque psoriasis

BACKGROUND

The proinflammatory cytokine interleukin (IL)-17A plays a pivotal role in psoriasis pathogenesis. Secukinumab, a fully human monoclonal antibody (mAb) that selectively targets IL-17A, has been demonstrated to be highly efficacious for the treatment of moderate-to-severe psoriasis, starting at early time points, with a sustained effect and a favourable safety profile. mAb therapies may be associated with production of antidrug antibodies (ADAs) that can affect drug pharmacokinetics, diminish response or cause hypersensitivity reactions.

OBJECTIVES

To investigate the immunogenicity of secukinumab across six phase III clinical trials in which patients with plaque psoriasis were treated with secukinumab for up to 52 weeks and additionally followed up at week 60.

METHODS

Immunogenicity in patients with plaque psoriasis exposed to secukinumab was evaluated at baseline and at weeks 12, 24, 52 and 60. Treatment-emergent (TE)-ADAs were defined as a positive ADA signal detected in post-treatment samples from patients with a negative baseline signal. Confirmed positive samples were further analysed for their drug-neutralizing potential.

RESULTS

Among 2842 patients receiving secukinumab and evaluated for ADAs, 11 (0·4%) developed TE-ADAs. Associations between TE-ADAs and secukinumab dose, frequency or mode of administration were not observed. Neutralizing antibodies were detected in three of nine evaluable patients with TE-ADAs.

CONCLUSIONS

Secukinumab immunogenicity was low, as shown by TE-ADA detection in only 11 of 2842 (0·4%) patients with moderate-to-severe plaque psoriasis treated with secukinumab. All but one of the patients with TE-ADAs were biologic naive. Neither TE-ADAs nor neutralizing antibodies were associated with loss of secukinumab efficacy or issues of clinical concern.

Interleukin-17A blockade with secukinumab results in decreased neutrophil infiltration in psoriasis: minimally-invasive measurement by tape stripping

Psoriasis is a well characterized interleukin (IL)-17A-driven skin disease with neutrophil infiltration and epidermal hyperkeratosis. Several biomarkers, most prominently β-defensin-2 (BD-2), have been identified using local and systemic invasive measurements as responsive markers of IL-17A-driven skin pathology. We sought to determine whether measurements of epidermal proteins by tape stripping could offer a minimally-invasive method to assess treatment responses. We compared the expression of 170 proteins in the epidermis (tape stripping) and dermis (open flow microperfusion) of 8 psoriatic subjects before and after administration of a single dose of subcutaneous (s.c.) antiIL-17A mAb secukinumab. Proteomic analyses of tape strips revealed a >3-fold decrease in 32 epidermal and inflammatory cell proteins in response to secukinumab. The epidermal proteins with the largest (>10-fold) decreases were: matrix metalloproteinase-8 (MMP-8, 15.68-fold, p<0.05); myeloperoxidase (MPO, 14.72-fold, p<0.005); IL-8 (11.93-fold, p<0.05); MMP-9 (10.81-fold, p<0.005); and IL-1β (10.35-fold, p<0.05). For these proteins, greater-fold protein changes were detected in the epidermis compared to dermis. Immunohistochemical analysis confirmed that neutrophils are the predominant cell type in psoriatic skin lesions that express MPO, MMP-8 and MMP-9, and that secukinumab treatment dramatically decreases neutrophil accumulation. Thus, tape stripping may be used to assess epidermal neutrophils, and protein biomarker responses to anti-IL-17A therapy in psoriasis.

Population PK-PD Model for Tolerance Evaluation to the p38 MAP Kinase Inhibitor BCT197

The p38 mitogen‐activated protein kinase (p38) is a key signaling pathway involved in regulation of inflammatory cytokines. Unexpectedly, several clinical studies using p38 inhibitors found no convincing clinical efficacy in the treatment of chronic inflammation. It was the objective of this study to characterize the population pharmacokinetics (PK) of BCT197 in healthy volunteers and to examine the relationship between BCT197 exposure and pharmacodynamics (PD) measured as inhibition of ex vivo lipopolysaccharide (LPS)‐induced tumor necrosis factor alpha (TNFα), a downstream marker of p38 activity. PK was characterized using a two‐compartment model with mixed‐order absorption and limited‐capacity tissue binding. The PK‐PD relationship revealed that suppression of TNFα was partly offset over time, despite continuous drug exposure. This may indicate a mechanism by which the inflammatory response acquires the ability to bypass p38. Simulations of posology dependence in drug effect suggest that an intermittent regimen may offer clinical benefit over continuous dosing and limit the impact of tolerance development.

Nanoparticle flotation collectors--the influence of particle softness

The ability of polymeric nanoparticles to promote glass bead and pentlandite (Pn, nickel sulfide mineral) attachment to air bubbles in flotation was measured as a function of the nanoparticle glass transition temperature using six types of nanoparticles based on styrene/N-butylacrylate copolymers. Nanoparticle size, surface charge density, and hydrophobicity were approximately constant over the series. The ability of the nanoparticles to promote air bubble attachment and perform as flotation collectors was significantly greater for softer nanoparticles. We propose that softer nanoparticles were more firmly attached to the glass beads or mineral surface because the softer particles had a greater glass/polymer contact areas and thus stronger overall adhesion. The diameters of the contact areas between polymeric nanoparticles and glass surfaces were estimated with the Young-Laplace equation for soft, liquidlike particles, whereas JKR adhesion theory was applied to the harder polystyrene particles. The diameters of the contact areas were estimated to be more than an order of magnitude greater for the soft particles compared to harder polystyrene particles.

Secukinumab, a human anti-IL-17A monoclonal antibody, for moderate to severe Crohn's disease: unexpected results of a randomised, double-blind placebo-controlled trial

OBJECTIVE

The authors tested whether the anti-interleukin (IL)-17A monoclonal antibody secukinumab was safe and effective for the treatment of active Crohn's disease.

DESIGN

In a double-blind, randomised, placebo-controlled proof-of-concept study, 59 patients with moderate to severe Crohn's disease (Crohn's Disease Activity Index (CDAI) ≥220 to ≤450) were assigned in a 2:1 ratio to 2×10 mg/kg intravenous secukinumab or placebo. The primary end point, addressed by bayesian statistics augmented with historical placebo information, was the probability that secukinumab reduces the CDAI by ≥50 points more than placebo at week 6. Ancillary analyses explored associations of 35 candidate genetic polymorphisms and faecal calprotectin response.

RESULTS

59 patients (39 secukinumab, 20 placebo, mean baseline CDAI 307 and 301, respectively) were recruited. 18/59 (31%) patients discontinued prematurely (12/39 (31%) secukinumab, 6/20 (30%) placebo), 10/59 (17%) due to insufficient therapeutic effect (8/39 (21%) secukinumab, 2/20 (10%) placebo). Fourteen serious adverse events occurred in 10 patients (seven secukinumab, three placebo); 20 infections, including four local fungal infections, were seen on secukinumab versus none on placebo. Primary end point analysis estimated <0.1% probability (CDAI (SD) =33.9 (19.7), 95% credible interval -4.9 to 72.9) that secukinumab reduces CDAI by ≥50 points more than placebo. Secondary area under the curve analysis (weeks 4-10) showed a significant difference (mean ΔCDAI=49; 95% CI (2 to 96), p=0.043) in favour of placebo. Post hoc subgroup analysis showed that unfavourable responses on secukinumab were driven by patients with elevated inflammatory markers (CRP≥10 mg/l and/or faecal calprotectin≥200 ng/ml; mean ΔCDAI=62; 95% CI (-1 to 125), p=0.054 in favour of placebo). Absence of the minor allele of tumour necrosis factor-like ligand 1A was strongly associated with lack of response measured by baseline-adjusted changes in calprotectin at week 6 (p=0.00035 Bonferroni-corrected).

CONCLUSIONS

Blockade of IL-17A was ineffective and higher rates of adverse events were noted compared with placebo.

CLINICAL TRIAL REGISTRATION

This trial was registered at ClinicalTrial.gov with the number NCT01009281.

Effects of AIN457, a fully human antibody to interleukin-17A, on psoriasis, rheumatoid arthritis, and uveitis

Interleukin-17A (IL-17A) is elaborated by the T helper 17 (T(H)17) subset of T(H) cells and exhibits potent proinflammatory properties in animal models of autoimmunity, including collagen-induced arthritis, experimental autoimmune encephalomyelitis, and experimental autoimmune uveitis. To determine whether IL-17A mediates human inflammatory diseases, we investigated the efficacy and safety of AIN457, a human antibody to IL-17A, in patients with psoriasis, rheumatoid arthritis, and chronic noninfectious uveitis. Patients with chronic plaque-type psoriasis (n = 36), rheumatoid arthritis (n = 52), or chronic noninfectious uveitis (n = 16) were enrolled in clinical trials to evaluate the effects of neutralizing IL-17A by AIN457 at doses of 3 to 10 mg/kg, given intravenously. We evaluated efficacy by measuring the psoriasis area and severity index (PASI), the American College of Rheumatology 20% response (ACR20) for rheumatoid arthritis, or the number of responders for uveitis, as defined by either vision improvement or reduction in ocular inflammation or corticosteroid dose. AIN457 treatment induced clinically relevant responses of variable magnitude in patients suffering from each of these diverse immune-mediated diseases. Variable response rates may be due to heterogeneity in small patient populations, differential pathogenic roles of IL-17A in these diseases, and the different involvement or activation of IL-17A-producing cells. The rates of adverse events, including infections, were similar in the AIN457 and placebo groups. These results support a role for IL-17A in the pathophysiology of diverse inflammatory diseases including psoriasis, rheumatoid arthritis, and noninfectious uveitis.

Thoracoabdominal aortic aneurysm repair: a prospective cohort study of 121 cases

Between October 1990 and June 2001, 121 patients underwent surgery for thoracoabdominal aortic aneurysm (TAAA)-99 procedures were elective and 22 were for ruptured aneurysms. Between October 1990 and September 1997, the clamp-and-go technique was used for all aneurysms (43 patients), and from October 1997, clamp-and-go was reserved for type IV TAAAs, and atriofemoral bypass (AFB) was used for types I, II, and III (78 patients). Overall hospital mortality was 21.4% (26/121)-12% for the elective group and 64% for the ruptured group. Hospital mortality was associated with age (67 years in survivors vs. 73 years in nonsurvivors, p = 0.03), FEV1<2 L (RR 4.1, p = 0.01), CSF drainage (RR 5.0, p = 0.03), type II aneurysms vs. other aneurysms (RR 3.7, p = 0.02), and relative inexperience (mean rank in the series was 52 in survivors vs. 30 in nonsurvivors, p = 0.01). The overall incidence of neurologic deficits due to spinal cord ischemia was 6.2% (paraplegia in 4.4%). Temporary dialysis was necessary in 13% of patients, and chronic dialysis in 2%. In long-term follow-up of patients undergoing elective repair, 5-year survival was 80% and median survival was 7.9 years. Mortality and neurologic deficits have improved over time as a consequence of either increased surgical experience, the adoption of a protocolized strategy for repair, or secular improvements in ICU care. Long-term survival after elective TAAA repair is excellent.

Perfusion of the subarachnoid space in cadavers: a technique applicable for prevention of paraplegia in surgery of the thoracic aorta

BACKGROUND

No safe technique of subarachnoid perfusion during thoracoabdominal aneurysm surgery has been described. We tested the hypothesis that in cold cadavers, perfusion of the subarachnoid space at the lumbar level with warm solution is feasible and increases the temperature at the thoracic level without an increase in cerebrospinal fluid (CSF) pressure.

METHODS

Six cadavers were used. A 5 Fr silastic catheter in the subarachnoid space between the second and third lumbar vertebra (L2-3) was used as an inflow and a 16-gauge catheter at L4-5 as an outflow. Normal saline at 38 degrees C was infused at 999 mL/h. Temperatures of inflow and outflow, of the thoracic subarachnoid space (T8), and of the cisterna magna, were recorded. CSF pressures were measured from the outflow catheter.

RESULTS

Outflow temperature was 9+/-1 degrees C at 10 minutes. At 15 minutes it was 27+/-4 degrees C, and thoracic subarachnoid temperatures was 22+/-5 degrees C. There was no statistical difference between the temperatures recorded at 10 and 15 minutes. The temperature of the cisterna magna was 8.5+/-1.2 degrees C at 15 minutes, significantly higher than the baseline (p=0.01), but lower than that at the T8 level (p=0.0001). CSF pressures during the experiment did not changed significantly from baseline and remained below 10 cm H20.

CONCLUSIONS

The technique described is simple to implement, and effective in changing the temperature of the subarachnoid space at the thoracic level. Whether spinal cord cooling by this technique safely reduces the risk of paraplegia remains to be established in an animal model.

A cohort study of coagulation parameters and the use of blood products in surgery of the thoracic and thoracoabdominal aorta

OBJECTIVES

We sought to study the hemostatic profile and the use of blood products in patients undergoing thoracic and thoracoabdominal aortic aneurysm repair.

METHODS

This is a cohort study comparing three groups of patients: 7 undergoing elective acute normovolemic hemodilution (ANH); 15 undergoing elective procedures without ANH (non-ANH); and 8 undergoing repair of ruptured thoracoabdominal aneurysms. A control group of 10 patients was used for comparison of preoperative hemostasis. The parameters studied were platelet concentration, partial thromboplastin time (PTT), and international normalized ratio (before and after surgery), packed red blood cells, fresh frozen plasma, platelets, cryoprecipitates, donor exposure, and use of desmopressin and epsilon-aminocaproic acid. Analysis of variance and multiple stepwise regression analysis were used.

RESULTS

Before operation the patients with aneurysms had PTTs prolonged compared with control subjects (P <.05). After operation the ANH group had higher platelet counts than the ruptured group (P =.001) and higher platelet counts (P =.05) and lower PTTs (P =.001) than the non-ANH group. The ANH group was transfused fewer platelets than the non-ANH group (P =.001) and less of every blood product than the ruptured group (P =.05); statistically significant differences were not observed for packed red blood cells, fresh frozen plasma, or platelets. The ANH group was exposed to an average of 65 donors fewer than the ruptured group (P <.001) and 34 fewer than the non-ANH group (P <.05). These differences could not be explained by baseline coagulation status or by the intraoperative use of desmopressin or epsilon-aminocaproic acid.

CONCLUSIONS

The coagulation abnormality identified before surgery is that of higher PTT values, suggesting a disturbance of the extrinsic coagulation pathway. Blood losses, donor exposure, and platelet use were highest in the ruptured group and lowest in the ANH group. After surgery the ruptured group exhibited the worst coagulation parameters, and the ANH group exhibited the best with higher platelet count and lower PTT values than the other groups. The ANH technique appears to be an useful adjunct in the anesthetic management of these patients.

Kommerell's diverticulum and aneurysmal right-sided aortic arch: a case report and review of the literature

Right-sided aortic arch is a rare variant of the thoracic vascular anatomy that may be accompanied by an aberrant origin of the left subclavian artery. We report a true aneurysm of the distal arch and descending thoracic aorta in a patient with right-sided arch and review previous descriptions of aneurysms of anomalous right-sided aortas. In our patient, the left subclavian artery originated at the junction between the distal arch and the descending thoracic aorta located in the right chest and was aneurysmal (Kommerell's diverticulum); the thoracic aorta was also aneurysmal. Extra-anatomic left subclavian-to-carotid transposition was performed before the intrathoracic procedure. Subsequently, a right thoracotomy provided adequate exposure for repairing the aortic aneurysm and oversewing the aneurysmal origin of the subclavian artery. Because the distal aortic arch was involved, deep hypothermia and circulatory arrest were used. Only five previous instances of true aneurysms of a right-sided aortic arch have been reported; four of these patients underwent operative repair (via bilateral thoracotomy, median sternotomy, or right thoracotomy). We believe that a right thoracotomy provides good exposure and avoids the morbidity associated with bilateral thoracotomy. The reconstruction of the subclavian artery has not previously been reported in this setting. Performing subclavian reconstruction as an extrathoracic procedure before the intrathoracic repair would be expected to reduce the subsequent risk of distal ischemia or subclavian steal without increasing the overall morbidity associated with the procedure.

Effects of acute normovolaemic haemodilution and partial exchange transfusion on blood product utilization, haemostasis and haemodynamics in surgery of the thoracoabdominal aorta. A cohort study in consecutive patients

BACKGROUND

This paper outlines the technique of acute normovolaemic haemodilution with partial exchange transfusion (ANHPET) in surgery of the thoracic and thoracoabdominal aorta. Perioperative coagulation parameters and patterns of blood product utilization observed with this technique are described and compared with results for historical controls treated without ANHPET.

METHODS

During thoracoabdominal aneurysm repair, acute normovolaemic haemodilution with partial exchange transfusion (ANHPET) was used to withdraw of up to 3 L of blood. This was returned to the patient at the end of the reconstruction. Albumin 5% and stored packed red cells (PRC) were used for replacement. Seven patients underwent surgery with ANHPET, and fifteen without. Univariate and multivariate analysis of variance was used to examine differences between these groups.

RESULTS

No differences were observed between the two groups for estimated blood loss, PRC transfused, and postoperative haemoglobin concentration. The ANHPET group received fewer platelets (8 vs 22 units, p = 0.0004), cryoprecipitate (0 vs 13 units, p = 0.02), and desmopressin or epsilon-aminocaproic acid (0 of 7 vs 4 of 15 patients, p = 0.04). FFP use was not significantly different (11 vs 17 units). Postoperatively, PTT values were less prolonged (26 vs 34 sec, p = 0.05) and platelet concentration higher (218 vs 169 x 109/L, p = 0.01) in the ANHPET group. A significant reduction in the total of blood products transfused was observed in the ANHPET group (30 vs 68 units, p = 0.003). Control of hypertension was facilitated by phlebotomy so that nitroglycerine was necessary in low doses only (0.25-1.0 microgram/kg/min).

CONCLUSIONS

ANHPET reduced blood product transfusion, improved postoperative haemostatic parameters and simplified the management of cross-clamping hypertension.

Acute normovolemic hemodilution (ANH) in surgery of the thoraco-abdominal aorta. A cohort study to evaluate coagulation parameters and blood products utilization

OBJECTIVE

To assess whether a modified technique of acute normovolemic hemodilution (ANH) reduces the utilization of blood products and donor exposures, and/or improves hemostasis in surgery of the thoracoabdominal aorta.

METHODS

EXPERIMENTAL DESIGN

cohort study comparing fifteen control patients and seven treated with the adjunct of ANH. Mean follow-up 23 (SD=15.4) months.

SETTING

community hospital acting as a referral centre for vascular diseases. Patients' selection: Thirty patients between 1990 and 1995 were entered into the study, eight were excluded because of rupture.

INTERVENTIONS

the ANH technique used the withdrawal of up to 3000 ml blood during the time between induction of anesthesia and clamping of the thoracic aorta. Colloids were preferentially used for replacement together with up to three units of packed red blood cells (PRC). The autologous blood was retransfused during the final phases of the procedure.

MEASURES

Parameters measured included pre- and postoperative PTT, INR, and platelets; the quantity of stored blood products and total donor exposures.

RESULTS

Blood losses, PRC transfused, and postoperative hemoglobin concentration were not statistically different in the two groups. Repeated measures Analysis of variance on coagulation parameters showed lower PTT values (F1,20=4.2, p=0.05) and higher platelet concentration (F1,20=8.2, p=0.01) after surgery in the ANH group. In the latter, the reduction in fresh frozen plasma (FFP) utilization did not reach statistical significance (T19.5=1.79, p=0.08). This group, however, required fewer transfusions of platelets (T20=4.27, p=0.0004), and cryoprecipitate (T20=2.52, p=0.02), and no coagulation adjuncts (dDAVP, epsilon-aminocaproic acid), (Fisher's test=0.04). Total donor exposures was also significantly lower in the ANH group (T20=3.28, p=0.003).

CONCLUSIONS

The ANH technique reduces homologous transfusions and donor exposures, and has a beneficial effect on hemostasis. Moreover, the technique may be useful in the management of cross clamping hypertension.

Analgesic effect of interscalene block using low-dose bupivacaine for outpatient arthroscopic shoulder surgery

BACKGROUND AND OBJECTIVES

Although interscalene brachial plexus block (ISBPB) is often used to provide anesthesia for arthroscopic shoulder surgery, its selective analgesic effect, provided by low-dose local anesthetic, has not been studied. We hypothesized that ISBPB using a low volume and low concentration of bupivacaine can provide effective postoperative analgesia for shoulder surgery without producing significant sensory or motor block elsewhere.

METHODS

In this double-blind study, 30 outpatients scheduled to undergo shoulder arthroscopy were randomly assigned to receive either an ISBPB with 10 mL 0.125% bupivacaine with epinephrine 1:400,000 (n = 15) or 10 mL of normal saline (n = 15). The block was performed preoperative, prior to a standardized general anesthetic. Postoperative pain scores, imorphine and oral analgesic consumption, recovery profile, and patient satisfaction were recorded.

RESULTS

In the ISBPB group, verbal analog pain scores within 120 minutes after surgery were lower, morphine consumption in the postanesthesia care unit was significantly lower (2.7+/-2.6 mg vs 9.5+/-5.2 mg), the time to postoperative administration of the first systemic or oral analgesic was significantly longer (141+/-182 minutes vs 13+/-10 minutes), the degree of motor and sensory block 120 minutes after surgery was minimal, time to reach hospital discharge criteria was earlier, and patient satisfaction with postoperative analgesia at 24-hour follow-up was greater. Thirty-three percent of the patients receiving ISBPB did not require any analgesic prior to hospital discharge.

CONCLUSIONS

Interscalene brachial plexus block with low-dose bupivacaine is a useful and selective analgesic technique for outpatient shoulder arthroscopic surgery.

Predictive value of foal kinematics for the locomotor performance of adult horses

The gait of 24 horses was recorded on a treadmill when they were trotting at 4 m sec-1, first when they were four months old and again when they were 26 months. The data recorded at four months were used to predict the locomotion of the adult horses, and the predictions were assessed against the data recorded at 26 months. The locomotion of the foals and the adults appeared to be closely related, when the differences in segment length and joint angles due to growth were taken into account. The duration of swing, the total range of protraction and retraction, and the maximum tarsal flexion could be used to predict adult locomotion, because they correlated very well between the foals and adults. The durations of stance and stride in the foals had to be linearly and dynamically scaled to the height at the withers to become predictive for the adult values. The duration of swing, and the total range of protraction and retraction and the maximum tarsal flexion are also indicators of the quality of gait and as a result studies of foal kinematics can be used objectively to predict the locomotor performance of adult horses.

How the horse moves: 2. Significance of graphical representations of equine hind limb kinematics

Kinematic data of the equine hind limb are presented graphically and related to functional aspects of the hind limb in locomotion. The trot of 24 two-year-old Dutch Warmblood horses was recorded at 4 m/s on a high-speed treadmill using kinematic analysis equipment. Joint angle-time, angle-angle, stick and marker diagrams were used to present graphically the data following standardised procedures. As the kinematic data were expressed with reference to the joint angles of the horse standing squarely and were time-standardised to the duration of the stride cycle, mean joint curves for the total group could be calculated and therefore describe the function of the different segments of the equine hind limb. The motion of the hind limb in the sagittal plane appeared to be pendular around a rotation point in the acetabulum. During the stance phase the extension of the fetlock joint and stance flexion of the stifle, tarsal and coffin joints illustrate the shock absorption of the hind limb. In the swing phase the reciprocal apparatus, which forms the coupling mechanism between stifle and tarsal joint, also influences the fetlock joint because synchronous flexion and extension between these 3 joints were demonstrated. By graphically presenting hind limb motion we were able to illustrate the relation between kinematics and function. This graphic analysis can be used in clinical studies involving quantification of equine hind limb coordination in the sagittal plane.

How the horse moves: 1. Significance of graphical representations of equine forelimb kinematics

The kinematics of 24 two-year-old Dutch Warmblood horses were recorded at the trot (4 m/s) on a high-speed treadmill to study the coordination of joints within the equine forelimb. Joint angle-time, angle-angle, stick, and marker diagrams were used to show forelimb motion graphically. Because the kinematic data referred to the joint angles of the horse standing squarely and were time-standardised to the duration of the stride cycle, mean joint curves could be calculated for the total group. The motion of each segment in the equine forelimb during a complete stride is described and its function in intralimb coordination evaluated. It appeared that the rotation of the scapula and the cranio-caudal movement of the distal forelimb are synchronous and pendular. The carpal joint rapidly snaps into overextension at the beginning of the stance phase to enable the forelimb to work as a propulsive strut. The fetlock joint acts as an elastic spring, thereby conserving energy and, at the same time, absorbs oscillations generated by initial ground contact. Furthermore, the coordination between carpal and fetlock joints in the swing phase appears to be strongly influenced by inertia. Using the graphic tools evaluated in this paper, we were able to visualise the kinematics of the equine forelimb and relate these to specific functions of the forelimb in locomotion. This information can be used to select kinematic variables for clinical studies in which equine forelimb function has to be described and quantified.

Kinematic detection of superior gait quality in young trotting warmbloods

This study was conducted to identify objective criteria to select young horses with a good gait, which is a prerequisite for good performance in adult horses. The trot of 24 26-month-old Dutch Warmbloods, led on a loose shank, was subjectively scored by a judge and objectively assessed on a treadmill by using kinematic analysis equipment. It appeared that forelimb and hind limb stride and swing duration, scapula rotation, forelimb maximal fetlock extension, forelimb maximal retraction, hind limb maximal protraction, maximal stifle flexion, and maximal tarsal flexion significantly correlated with a generally accepted gait score in which length, suppleness, and strength are judged. Moreover, the ranking of the individual horses on the basis of gait quality according to their objectively measured kinematic variables was similar to the subjective ranking given by the judge. Thus, a complete picture was obtained of the variables in equine locomotion that determine the quality of the trot in warmbloods.

The effect of toe weights on linear and temporal stride characteristics of standardbred trotters

Toe weights are applied to influence the stride characteristics of trotters. The quantitative effect of 88-g toe weights on the stride characteristics of Standardbred trotters was evaluated in a kinematic study using a CODA-3 analysis system. Six trotters were studied at a speed of 11 m/s on a treadmill. Temporal gait variables, joint angles, and the trajectories of the forelimb hoof were calculated. The stride patterns of the individual trotters were assessed by a judge and compared to the CODA-output. Those trotters with poor flexion of the carpal joint during the swing phase or with insufficient knee action responded with better carpal flexion and more knee action when toe weights were attached. No effect of toe weights on the protraction of the forelimb could be demonstrated. Stride length, stride duration, and the relative duration of the stance and swing phase as a percentage of the stride did not respond to toe weights. It is concluded that toe weights can be useful in Standardbred trotters, but their effect depends on the individual gait pattern.

Adaptation and overtraining in horses subjected to increasing training loads

To evaluate markers for overtraining, seven male race horses were subjected to 272 days of training consisting of daily exercise bouts of either endurance running (heart rate 140/min) or interval training (maximal heart rate), both increasing in duration and intensity. An incremental exercise test was held every 4 wk, and from day 187 it was held every 2 wk. Muscle glycogen, muscle lactate, energy-rich phosphates, adrenal response to adrenocorticotropic hormone, plasma and red blood cell volumes, and a number of blood chemical variables were measured. The horses showed symptoms of weight loss, irritability, and an inability to complete the training after the intensity of the endurance exercise was increased. Test performance was not decreased. The adrenal response to adrenocorticotropic hormone was not changed during overtraining. The decline in muscle ATP concentration during maximal exercise was less during the period of staleness, whereas plasma volume, red blood cell volume, and blood chemical variables were unchanged. It was concluded that as long as exhaustive training is alternated by light exercise, overtraining is unlikely to occur. Furthermore, no single parameter can be used to detect early overtraining.