The relationship between income and performance indicators in general practice: a cross-sectional study

OBJECTIVE

To explore the relationship between the income of general practitioners (GPs) and the performance characteristics of their practices.

DESIGN

Cross-sectional survey.

SETTING

All practices (n = 166) in an inner city health authority, two years before the introduction of the new GP contract in April 2004 were studied.

MAIN OUTCOME MEASURES

True income per GP was unavailable to us. Instead, the proxy measure - superannuable pay - was calculated (gross eligible income per GP minus the national average sum for GP expenses). Practice staff funding figures were also obtained. These two financial indicators were compared with practice characteristics and performance indicators.

RESULTS

Data were available from 151 out of 166 practices. Based on regression analysis, larger list sizes and higher practice staff budgets predicted 31% of the variation in GP income (standardized beta = 0.66, P < 0.001; beta = 0.19, P = 0.02; respectively). Higher staff budgets were independently associated with better cervical smear and two-year-old vaccination rates (standardized beta = 0.24, P < 0.01; beta = 0.18, P = 0.03; respectively). No association was demonstrated between performance indicators and income.

CONCLUSION

Under the previous contract, GPs were able to maximize their income by taking on more patients, whereas achievement of performance targets had very little impact on overall income. The opportunity costs of pursuing higher-quality care might have outweighed the modest financial rewards attached to performance targets. Provided rewards for good-quality care are sufficiently high, the new GP contract is likely to tip the balance in favour of generating earnings by improving the quality of clinical care. To deliver this care, as measured by available performance indicators, our findings imply that a greater investment in practice staff will be needed.

Specific peptide inhibitors of trypanothione reductase with backbone structures unrelated to that of substrate: potential rational drug design lead frameworks

By introducing cationic charge sites novel peptide lead inhibitor structures for trypanothione reductase have been designed using molecular modelling methods. The inhibitors showed reversible, linear competitive inhibition and the strongest peptide inhibitor to date was found to be N-benzyloxycarbonyl-Ala-Arg-Arg-4-methoxy-beta-naphthylamide with a Ki value of 2.4 microM and a selectivity for parasitic enzyme (trypanothione reductase) over the host enzyme (human glutathione reductase) of over 3 orders of magnitude.

Synthesis and enzymology of modified N-benzyloxycarbonyl-L-cysteinylglycyl-3,3-dimethylaminopropylamide++ + disulphides as alternative substrates for trypanothione reductase from Trypanosoma cruzi: Part 3

Kinetic data for alternative substrates of recombinant trypanothione reductase from Trypanosoma cruzi were measured for a series of N-substituted-L-cysteinylglycyl-3-dimethylaminopropylamides, in which the cysteine N-substituent was either a variant of the benzyloxycarbonyl group or was L-phenylalanine or L-tryptophan. Replacing the benzylic ether oxygen atom by CH2 or NH had relatively minor effects on kcat, but raised the value of K(m) 4.5- and 10-fold, respectively. Similarly, relative to the carbobenzoxy group, an N-L-phenylalanyl or N-L-tryptophanyl replacement on the cysteine hardly altered kcat, but increased K(m) values by 16.6 and 7.4 fold, respectively. These observations were consistent with the K(m) values referring primarily to binding for this series of nonspecific substrates.

Phenothiazine inhibitors of trypanothione reductase as potential antitrypanosomal and antileishmanial drugs

Given the role of trypanothione in the redox defenses of pathogenic trypanosomal and leishmanial parasites, in contrast to glutathione for their mammalian hosts, selective inhibitors of trypanothione reductase are potential drug leads against trypanosomiasis and leishmaniasis. In the present study, the rational drug design approach was used to discover tricyclic neuroleptic molecular frameworks as lead structures for the development of inhibitors, selective for trypanothione reductase over host glutathione reductase. From a homology-modeled structure for trypanothione reductase, replaced in the later stages of the study by the X-ray coordinates for the enzyme from Crithidia fasciculata, a series of inhibitors based on phenothiazine was designed. These were shown to be reversible inhibitors of trypanothione reductase from Trypanosoma cruzi, linearly competitive with trypanothione as substrate and noncompetitive with NADPH, consistent with ping-pong bi bi kinetics. Analogues, synthesized to define structure-activity relationships for the active site, included N-acylpromazines, 2-substituted phenothiazines, and trisubstituted promazines. Analysis of Ki and I50 data, on the basis of calculated log P and molar refractivity values, provided evidence of a specially favored fit of small 2-substituents (especially 2-chloro and 2-trifluoromethyl), with a remote hydrophobic patch on the enzyme accessible for larger, hydrophobic 2-substituents. There was also evidence of an additional hydrophobic enzymic region available to suitable N-substituents of the promazine nucleus. Ki data also indicated that the phenothiazine nucleus can adopt more than one inhibitory orientation in its binding site. Selected compounds were tested for in vitro activity against Trypanosoma brucei, T. cruzi, and Leishmania donovani, with selective activities in the micromolar range being determined for a number of them.

Rational design of selective ligands for trypanothione reductase from Trypanosoma cruzi. Structural effects on the inhibition by dibenzazepines based on imipramine

Trypanothione reductase, the enzyme which in trypanosomal and leishmanial parasites catalyses the reduction of trypanothione disulphide to the redox-protective dithiol and has been identified as a potential target for rational antiparasite drug design, has been found to be strongly inhibited by tricyclic compounds containing the saturated dibenzazepine (imipramine) nucleus, with Ki values in the low micromolar range. This drug lead structure was designed by molecular graphics analysis of a three-dimensional homology model, focussing on the active-site. Inhibition studies were carried out to determine the effect of inhibitor structure on the inhibitory strength towards recombinant trypanothione reductase from Trypanosoma cruzi. Hansch analysis showed that inhibitory strength depended on terms in pi, pi 2 and sigma m indicating dependence on both lipophilicity and inductive effect for ring-substituted analogues of imipramine. The side-chain omega-aminoalkyl chain had to be longer than 2-carbon units for inhibition. The effect on inhibition strength of the substituent at the omega-amino position on the side-chain of the central ring nitrogen atom depended markedly on the detailed substitution pattern of the rest of the molecule. This provides kinetic evidence studies of multiple binding modes within a single, blanket binding site for the inhibitor with the tricyclic ring system in the general region of the hydrophobic pocket lined by Trp21, Tyr110, Met113 and Phe114. This aspect of the structural sensitivity of the precise active-site triangulation adopted by the inhibitor is probably a function of the use of hydrophobic interactions of low directional specificity in this pocket combined with an electrostatic anchoring by the omega-N+ HMe2 function of the inhibitor, presumably with a glutamate side-chain, such as Glu-18, Glu-466' and/or Glu-467'.

Rationally designed selective inhibitors of trypanothione reductase. Phenothiazines and related tricyclics as lead structures

Trypanothione reductase, an essential component of the anti-oxidant defences of parasitic trypanosomes and Leishmania, differs markedly from the equivalent host enzyme, glutathione reductase, in the binding site for the disulphide substrate. Molecular modelling of this region suggested that certain tricyclic compounds might bind selectively to trypanothione reductase without inhibiting host glutathione reductase. This was confirmed by testing 30 phenothiazine and tricyclic antidepressants, of which clomipramine was found to be the most potent, with a K(i) of 6 microM, competitive with respect to trypanothione. Many of these compounds have been noted previously to have anti-trypanosomal and anti-leishmanial activity and thus they can serve as lead structures for rational drug design.