Using Parameter Constraints to Choose State Structures in Cost-Effectiveness Modelling

BACKGROUND

This article addresses the choice of state structure in a cost-effectiveness multi-state model. Key model outputs, such as treatment recommendations and prioritisation of future research, may be sensitive to state structure choice. For example, it may be uncertain whether to consider similar disease severities or similar clinical events as the same state or as separate states. Standard statistical methods for comparing models require a common reference dataset but merging states in a model aggregates the data, rendering these methods invalid.

METHODS

We propose a method that involves re-expressing a model with merged states as a model on the larger state space in which particular transition probabilities, costs and utilities are constrained to be equal between states. This produces a model that gives identical estimates of cost effectiveness to the model with merged states, while leaving the data unchanged. The comparison of state structures can be achieved by comparing maximised likelihoods or information criteria between constrained and unconstrained models. We can thus test whether the costs and/or health consequences for a patient in two states are the same, and hence if the states can be merged. We note that different structures can be used for rates, costs and utilities, as appropriate.

APPLICATION

We illustrate our method with applications to two recent models evaluating the cost effectiveness of prescribing anti-depressant medications by depression severity and the cost effectiveness of diagnostic tests for coronary artery disease.

CONCLUSIONS

State structures in cost-effectiveness models can be compared using standard methods to compare constrained and unconstrained models.

The choice between hip prosthetic bearing surfaces in total hip replacement: a protocol for a systematic review and network meta-analysis

BACKGROUND

Prosthetic hip implants have many combinations of bearing surface materials, sizes, and fixation techniques, which can determine the quality of life of patients after primary total hip replacement (THR) and the likelihood of needing revision surgery. When an implant fails, patients require revision THR, which is distressing to the patient and expensive for the health care payer. Primary THR is one of the most common elective procedures performed worldwide, with over 300,000 performed annually in the USA and over 80,000 in England and Wales. It is important to review all available randomised controlled trial (RCT) evidence to determine which implant bearing surface materials, size, and fixation technique are most effective for patients.

METHODS/DESIGN

This is a protocol for a systematic review and meta-analysis of RCTs comparing outcomes of hip implant bearing surfaces, size, and fixation techniques used in THR. Implant combinations compared in the literature include four bearing surface combinations (metal-on-polyethylene, metal-on-metal, ceramic-on-polyethylene, and ceramic-on-ceramic); two femoral head sizes (large vs small heads); and four fixation techniques (uncemented, cemented, hybrid, and reverse hybrids). The primary outcome will be revision surgery. We will also collect data on patient characteristics, mortality, quality of life, and other outcomes. In network meta-analysis, we will estimate the relative effectiveness of every implant bearing surface, head size (large vs small), and fixation permutation, using evidence where implants have been compared directly in an RCT and indirectly through common comparators in different RCTs.

DISCUSSION

There has been much debate about materials used for prosthetic implants in THR. Different combinations of prosthetic materials, sizes, and fixation, can vary widely in cost and fail at different rates for different patient groups. Given the number of THRs performed yearly, and the increasing use of expensive implants, it is important to review evidence to inform surgeons, patients, and health care providers of optimal implant bearing combinations for given patient characteristics. This review will inform a cost-effectiveness model that will include evidence from other sources, to determine the most effective and cost-effective implant bearing combination for patients.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42015019435.

Comparative efficacy of antibiotics for the treatment of acute bacterial skin and skin structure infections (ABSSSI): a systematic review and network meta-analysis

OBJECTIVE

The objective was to conduct a systematic review and network meta-analysis (NMA) of existing treatments for ABSSSI focusing on the novel lipoglycopeptide oritavancin.

METHODS

EMBASE, MEDLINE, MEDLINE in Process, CENTRAL (Cochrane), and select conferences were searched for randomized controlled trials investigating antimicrobial agents for the treatment of ABSSSI. NMA was used to estimate the odds ratios of the Test-Of-Cure (TOC) and Early Clinical Response (ECR) outcomes for treatments relative to vancomycin in the ITT populations. Sub-group analyses in MRSA and MSSA populations were conducted for TOC; sensitivity analyses investigated the use of the clinically evaluable (CE) populations and the restriction to trials following the recent FDA guidelines for clinical trials.

RESULTS

The systematic review identified 52 trials. The most commonly investigated treatments were vancomycin and linezolid; most trials reported TOC, but not ECR. The posterior mean and 95% credible intervals for odds ratios of TOC for antimicrobial agents relative to vancomycin were: linezolid (1.55; 0.91-2.57), daptomycin (2.18; 0.90-5.42), and oritavancin 1200 mg (1.06; 0.80-1.43). The odds ratio of ECR for oritavancin 1200 mg was 1.02 (0.23-4.33). In the MRSA sub-group the odds ratios relative to vancomycin for TOC were: linezolid (1.55; 0.96-2.46), daptomycin (0.74; 0.13-3.66), and oritavancin 1200 mg (0.94; 0.44-2.02). In the MSSA sub-group they were linezolid (1.36; 0.15-13.34) and oritavancin 1200 mg (0.82; 0.08-7.83). These results were robust to the sensitivity analyses.

CONCLUSIONS

This NMA provides a unified framework for the comparison of all available antimicrobial agents used in the treatment of ABSSSI and is the first to assess the ECR end-point. The results suggest equivalence of clinical efficacy between vancomycin, daptomycin, linezolid, and novel antimicrobial agents including oritavancin for the treatment of ABSSSI at TOC. The wide uncertainty margins indicate the heterogeneity of the available evidence and the need for further research.

Cost-effectiveness of initial stress cardiovascular MR, stress SPECT or stress echocardiography as a gate-keeper test, compared with upfront invasive coronary angiography in the investigation and management of patients with stable chest pain: mid-term outcomes from the CECaT randomised controlled trial

OBJECTIVES

To compare outcomes and cost-effectiveness of various initial imaging strategies in the management of stable chest pain in a long-term prospective randomised trial.

SETTING

Regional cardiothoracic referral centre in the east of England.

PARTICIPANTS

898 patients (69% man) entered the study with 869 alive at 2 years of follow-up. Patients were included if they presented for assessment of stable chest pain with a positive exercise test and no prior history of ischaemic heart disease. Exclusion criteria were recent infarction, unstable symptoms or any contraindication to stress MRI.

PRIMARY OUTCOME MEASURES

The primary outcomes of this follow-up study were survival up to a minimum of 2 years post-treatment, quality-adjusted survival and cost-utility of each strategy.

RESULTS

898 patients were randomised. Compared with angiography, mortality was marginally higher in the groups randomised to cardiac MR (HR 2.6, 95% CI 1.1 to 6.2), but similar in the single photon emission CT-methoxyisobutylisonitrile (SPECT-MIBI; HR 1.0, 95% CI 0.4 to 2.9) and ECHO groups (HR 1.6, 95% CI 0.6 to 4.0). Although SPECT-MIBI was marginally superior to other non-invasive tests there were no other significant differences between the groups in mortality, quality-adjusted survival or costs.

CONCLUSIONS

Non-invasive cardiac imaging can be used safely as the initial diagnostic test to diagnose coronary artery disease without adverse effects on patient outcomes or increased costs, relative to angiography. These results should be interpreted in the context of recent advances in imaging technology.

TRIAL REGISTRATION

ISRCTN 47108462, UKCRN 3696.

3 alpha, 7 alpha, 12 alpha-trihydroxy-24-nor-5 beta-cholan-23-sulfonate: synthesis and suitability for the study of cholate transport

In order to facilitate the study of transport processes of unconjugated C-24 bile salts, simple syntheses of 3 alpha, 7 alpha, 12 alpha-trihydroxy-24-nor-5 beta-cholan-23-sulfonate (norcholansulfonate) and 3 alpha, 7 alpha, 12 alpha-trihydroxy-24-nor-5 beta-[7 beta 5H] cholan-23-sulfonate were devised. The hydrophilic-hydrophobic properties of norcholansulfonate, as determined by its chromatographic behavior as well as by its partition between l-octanol and water, are more similar to those of cholyltaurine than to those of cholate. Self-association of norcholansulfonate in phosphate buffer, pH 7.4, with an ionic strength of 150 mM begins at a concentration of about 1 mM, comparable to that of cholyltaurine and cholate, as determined by spectral changes in fluorescence emissions of {N-[7-(4-nitrobenzo-2-oxa-1, 3-diazol)]-7b-amino-3a, 12a-dihydroxy-5b-cholan-24 - oyl}-2'-aminoethanesulfonate (7 beta-NBD-NCT). The apparent CMC value obtained from solubilization of the dye Orange OT, 8.5 mM, is comparable to that of cholytaurine. 7.5 mM, and lower than that of cholate, 9.5 mM. Norcholansulfonate is readily taken up by rat liver and completely excreted unmetabolized into bile with about the same secretion maximum (Tm) as cholyltaurine. Biliary excretion of norcholansulfonate is inhibited by cholyltaurine, and, vice versa, norcholansulfonate inhibits cholyltaurine secretion. Concerning metabolism and excretion, norcholansulfonate with the sulfonate group in the position where cholate has the carboxylate group should behave as an appropriate cholate analogue in mediated transport processes.

Comparison of IgG subclasses in foetal serum, maternal serum at delivery and milk in IgA-deficient and control women

Immunoglobulin G subclass concentrations were measured in paired foetal (cord) and maternal serum specimens at delivery from 27 IgA-deficient (serum IgA < 0.01 g/l) and 15 control women. IgA-deficient women had significantly higher serum IgG1 and IgG3 concentrations than control women but 2 of the group had concomitant IgG2/IgG4 deficiency and a further 12 had low IgG4 concentrations (serum IgG4 < 0.025 g/l). Foetal serum also had significantly higher IgG1 concentrations than control foetal serum but lower IgG2 and IgG4 levels. Concentrations of IgG subclasses and IgM were measured in breast milk collected on the fifth day postpartum from 19 of these IgA-deficient and 18 control women. Between-group differences in IgG subclass levels resembled those in serum. Compared with serum, proportionally less IgG3 was present in milk in both groups although the contribution of IgG3 to total IgG was not less than that of IgG4. Slightly higher IgM was found in milk from the IgA-deficient mothers.

Ammonia and carnitine concentrations in children treated with sodium valproate compared with other anticonvulsant drugs

Plasma ammonia was measured in 59 children requiring anticonvulsant drugs: 37 children (group 1) on sodium valproate alone or in combination with other drugs and 22 children (group 2) on drugs other than sodium valproate. Plasma ammonia was higher in group 1 children. Total and free carnitine was measured in plasma and erythrocytes of all children and in the urine of 16 children from group 1 and eight from group 2. Plasma and erythrocyte free carnitine was significantly lower in the children on sodium valproate, along with a significant increase in the ratio of acyl (bound) carnitine to free carnitine. No significant correlation was found between plasma ammonia and carnitine concentrations for either group of children. Plasma and erythrocyte concentrations were not related. Urinary free carnitine was reduced in children treated with valproate, with a significant increase in the ratio of bound to free carnitine. Carnitine supplementation is discussed.

[Prevention of hip dislocation in children with spastic paralysis by using a specific therapeutic wheelchair]

The hip joints of children with spastic cerebral palsy, notably in those with more severe forms of paresis as well as those with bilateral or tetraparetic involvement, are in any case exposed to extraordinarily great risks. Totally inconspicuous at birth, constant dominance of the spastically contracting hip adductor and flexor muscles leads to gradually advancing malpositioning of the femoral heads, along with flattening of the hip socket and its eventual total destruction. Complete dislocation of the hip joints results, in very severely affected cases already at age 2-3, but in the majority of children only several years later. In this equally tragic as, on the other hand, almost invariably preventable maldevelopment, the wheelchair takes on a doubly crucial role. This, for one, has to do with the many hours the child has to spend in it every day. On account of the fact that the regular wheelchair, above all when "sportively styled", is forcing both legs, i.e. the thighs and lower legs as well as the feet, to adopt a strictly parallel position, it enhances, and accelerates, the highly undesirable development of spastic hip dislocation. If, however, the wheelchair is redesigned in an appropriate manner, i.e. provided with an abduction seating orthosis, along with laterally repositioned foot rests, it will in the majority of cases be possible to prevent the development of hip dislocation. Detailed guidelines to achieve this end are included, and instructions are given for adapting commercially available wheelchairs.

[Results of hand surgery operations in spastic-athetotic paresis]

Between 1974 and 1986 a total of 123 patients with a spastic or spastic athetotic paresis of the upper limb underwent surgery. The interval between surgery and follow-up examination was between one and 13 years. There were 73 cases of hemiparesis and 50 dipareses or tetrapareses due to perinatal cerebral paresis and 35 cases due to a variety of causes. The patients were aged between 6 and 58 years, the majority between 8 and 28 years. All contractures in the arm and hand region were treated at a single sitting. The sole exception to this was surgery for swan-neck deformity of the long fingers. In none of the cases was a wrist arthrodesis indicated. As regards the elimination of the previously existing malpositions, some of which were severe, and the cosmetic outcome, the results were good in all cases. The postoperative reduction was also preserved through the subsequent years, until completion of growth. Also, the difference in growth between flexors and extensors had no detectable negative influence on the long-term results of surgery. Only in a few isolated cases was limited revisional surgery necessary to improve the result as regards extension in the elbow joint and the posture of the wrist joint, which it had not been possible to treat satisfactorily at the first sitting. Two patients with a pronounced athetotic component manifested unsatisfactory results in several respects, or overcorrection of extension in the wrist joint: special caution is called for here. As far as necessary, corresponding corrective surgery was performed simultaneously on the lower limbs.

The influence of maternal glucose metabolism on fetal growth, development and morbidity in 917 singleton pregnancies in nondiabetic women

To study the effects on the fetus of variations in maternal glucose tolerance, a 25 g rapid intravenous glucose tolerance test was performed at or about 32 weeks gestation in 917 randomly selected nondiabetic women with singleton pregnancies. The results were withheld from the patients and their obstetricians and paediatricians, and no treatment or advice was offered. Fasting plasma glucose and indices of glucose disposal (including a new index which we have termed "summed glucose") were distributed unimodally, with no evidence of a separate pathological group towards the diabetic end of the distributions. Significant associations were found between maternal glucose metabolism and various measures of neonatal nutrition and morbidity, including the incidence of congenital malformations and morbidity related to asphyxia, suggesting that variations within the normal range in maternal glucose metabolism can influence growth and development in the fetus. These relationships were continuous throughout the range of maternal glucose tolerance and were not of predictive value in individual cases.

Abnormal endothelial factor VIII associated with pulmonary hypertension and congenital heart defects

In patients with pulmonary hypertension associated with congenital heart defects, ultrastructural abnormalities are observed in endothelial cells, which suggest heightened metabolic function. If endothelial production of the von Willebrand factor (vWF) is increased, this may be associated with abnormal interactions with platelets leading to worsening of the pulmonary hypertension. We therefore evaluated vWF in 30 patients with pulmonary hypertension (25 with congenital heart defects) and in 30 individuals with normal pulmonary arterial pressure (12 with congenital heart defects). We measured the antigenic (vWF: Ag) and biologic (VWF: rist) activity of vWF in plasma and assessed endothelial vWF: Ag directly by an immunoperoxidase stain applied to lung biopsy tissue. Because of considerable variance and small size, the group of five patients with pulmonary hypertension and without congenital heart defects were excluded from statistical analyses. Patients with pulmonary hypertension and congenital heart defects had significant higher vWF: Ag levels than individuals with normal pulmonary arterial pressure without congenital heart defects (p less than .05), whereas values in those with normal pressure and congenital heart defects were intermediate. In lung biopsy tissue available from 29 patients in this study and from 11 others we previously reported, immunostain of pulmonary arterial endothelium for vWF was intense (suggesting increased production) in 29 of 32 with pulmonary hypertension and congenital heart defects and in only one of eight with normal pulmonary arterial pressure and congenital heart defects (p less than .01). Only three patients with congenital heart defects and pulmonary hypertension and increased vWF: Ag, however, had increased vWF: rist. Compatible with this discrepancy was a loss of vWF high-molecular weight forms as determined by both crossed immunoelectrophoresis and multimeric analysis. Our results suggest that increased vWF in most patients with congenital heart defects and pulmonary hypertension is associated with increased production of a biologically deficient molecule lacking high-molecular weight forms.

Maternal immunoglobulin allotype (Gm and Km) and neonatal group B streptococcal infection

Gm and Km(1) allotypes in 37 mothers of neonates with severe Group B streptococcal (GBS) infection were compared with 115 mothers of non-infected infants, 36 of whom were known to be colonized with GBS. Deficits in G1m(1) and Km(1), and an increased incidence of G2m(23), were found in mothers of infected infants. Km(1) was associated mainly with the phenotype Gm(1, (2), 3, 17; 23; 5, 10, 11, 21) in mothers of infected infants while being uniformly distributed in mothers of non-infected infants. This study would seem, therefore, to support reports of Gm and Km(1) allotype involvement in maternal response to GBS infection and immunity in the new-born.