A double-blind, placebo-controlled study of the short term effects of a spring water supplemented with magnesium bicarbonate on acid/base balance, bone metabolism and cardiovascular risk factors in postmenopausal women

Background

A number of health benefits including improvements in acid/base balance, bone metabolism, and cardiovascular risk factors have been attributed to the intake of magnesium rich alkaline mineral water. This study was designed to investigate the effects of the regular consumption of magnesium bicarbonate supplemented spring water on pH, biochemical parameters of bone metabolism, lipid profile and blood pressure in postmenopausal women.

Findings

In this double-blind, placebo-controlled, parallel-group, study, 67 postmenopausal women were randomised to receive between 1500 mL and 1800 mL daily of magnesium bicarbonate supplemented spring water (650 mg/L bicarbonate, 120 mg/L magnesium, pH 8.3-8.5) (supplemented water group) or spring water without supplements (control water group) over 84 days. Over this period biomarkers of bone turnover (serum parathyroid hormone (PTH), 1,25-dihydroxyvitamin D, osteocalcin, urinary telopeptides and hydroxyproline), serum lipids (total cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides), venous and urinary pH were measured together with measurements of standard biochemistry, haematology and urine examinations.

Serum magnesium concentrations and urinary pH in subjects consuming the magnesium bicarbonate supplemented water increased significantly at Day 84 compared to subjects consuming the spring water control (magnesium - p = 0.03; pH - p = 0.018). The consumption of spring water led to a trend for an increase in parathyroid hormone (PTH) concentrations while the PTH concentrations remained stable with the intake of the supplemented spring water. However there were no significant effects of magnesium bicarbonate supplementation in changes to biomarkers of bone mineral metabolism (n-telopeptides, hydroxyproline, osteocalcin and 1,25-dihydroxyvitamin D) or serum lipids or blood pressure in postmenopausal women from Day 0 to Day 84.

Conclusions

Short term regular ingestion of magnesium bicarbonate supplemented water provides a source of orally available magnesium. Long term clinical studies are required to investigate any health benefits.

Trial registration

ACTRN12609000863235

A phase I study to explore the activity and safety of SCH532706, a small molecule chemokine receptor-5 antagonist in HIV type-1-infected patients

BACKGROUND

SCH532706 is a novel small molecule chemokine receptor-5 (CCRS) antagonist with high in vitro potency (mean 90% inhibitory concentration [IC90] 0.15-7.0 nM) against diverse HIV type-1 (HIV-1) isolates.

METHODS

A single arm study was undertaken to examine the safety, antiviral activity and pharmacokinetics (PK) of 10 days of SCH532706 coadministered with ritonavir (RTV). The trial enrolled formerly treated (off therapy >3 months) or untreated HIV-1-infected patients.

RESULTS

The study enrolled 12 males with CD4+ T-cell count >100 cells/microl. Median (range) CD4+ T-cell count was 327 cells/microl (117-1008), HIV-1-RNA was 4.6 log10 copies/ml (3.8-5.5) and patients had phenotypically confirmed R5-tropic HIV-1 only. Mean (95% confidence interval) changes from baseline plasma HIV-1-RNA at days 10 and 15 (4 days off SCH532706) were -1.31 log10 copies/ml (-1.6 - -1.0) and -1.62 log10 copies/ml (-2.0 - -1.3), respectively. Day 10 median (range) time to maximum plasma concentration, mean (+/-SD) effective half-life and mean (+/-SD) trough concentration were 1.4 h (1.0-4.0), 39.4 h (+/-14.5) and 178 ng/ml (+/-34), respectively. All virus isolates remained R5-tropic pre-study, on study and at study end. There were no laboratory or QTc interval changes reportable as adverse events. In total, 11 patients reported > or =1 treatment emergent adverse event, most commonly gastrointestinal upset. One serious adverse event, pericarditis (grade 2), occurred 13 days after drug administration. It was considered to be possibly related to study drug.

CONCLUSIONS

Overall, SCH532706 with RTV was safe, generally well tolerated and active against HIV-1 over 10 days of dosing. In this setting, SCH532706 trough concentrations exceed the mean in vitro IC90 (1.1 ng/ml) by >30-fold (after correction for 80% plasma protein binding) and provide a PK rationale for the observed efficacy.

A Phase I study to explore the activity and safety of SCH532706, a small molecule chemokine receptor-5 antagonist in HIV type-1-infected patients

Background

SCH532706 is a novel small molecule chemokine receptor-5 (CCR5) antagonist with high in vitro potency (mean 90% inhibitory concentration [IC90] 0.15– 7.0 nM) against diverse HIV type-1 (HIV-1) isolates.

Methods

A single arm study was undertaken to examine the safety, antiviral activity and pharmacokinetics (PK) of 10 days of SCH532706 coadministered with ritonavir (RTV). The trial enrolled formerly treated (off therapy >3 months) or untreated HIV-1-infected patients.

Results

The study enrolled 12 males with CD4+ T-cell count >100 cells/μl. Median (range) CD4+ T-cell count was 327 cells/μl (117–1,008), HIV-1–RNA was 4.6 log10 copies/ml (3.8–5.5) and patients had phenotypically con-firmed R5-tropic HIV-1 only. Mean (95% confidence interval) changes from baseline plasma HIV-1–RNA at days 10 and 15 (4 days off SCH532706) were -1.31 log10 copies/ ml (-1.6– -1.0) and -1.62 log10 copies/ml (-2.0– -1.3), respectively. Day 10 median (range) time to maximum plasma concentration, mean (±sd) effective half-life and mean (±sd) trough concentration were 1.4 h (1.0-4.0), 39.4 h (±14.5) and 178 ng/ml (±34), respectively. All virus isolates remained R5-tropic pre-study, on study and at study end. There were no laboratory or QTc interval changes reportable as adverse events. In total, 11 patients reported ≥1 treatment emergent adverse event, most commonly gastrointestinal upset. One serious adverse event, pericarditis (grade 2), occurred 13 days after drug administration. It was considered to be possibly related to study drug.

Conclusions

Overall, SCH532706 with RTV was safe, generally well tolerated and active against HIV-1 over 10 days of dosing. In this setting, SCH532706 trough concentrations exceed the mean in vitro IC (1.1 ng/ml) by >30-fold (after correction for 80% plasma protein binding) and provide a PK rationale for the observed efficacy.

A benefit-risk assessment of benzbromarone in the treatment of gout. Was its withdrawal from the market in the best interest of patients?

Benzbromarone, a potent uricosuric drug, was introduced in the 1970s and was viewed as having few associated serious adverse reactions. It was registered in about 20 countries throughout Asia, South America and Europe. In 2003, the drug was withdrawn by Sanofi-Synthélabo, after reports of serious hepatotoxicity, although it is still marketed in several countries by other drug companies. The withdrawal has greatly limited its availability around the world, and increased difficulty in accessing it in other countries where it has never been available.The overall aim of this paper is to determine if the withdrawal of benzbromarone was in the best interests of gouty patients and to present a benefit-risk assessment of benzbromarone. To determine this, we examined (i) the clinical benefits associated with benzbromarone treatment and compared them with the success of alternative therapies such as allopurinol and probenecid, particularly in patients with renal impairment; (ii) the attribution of the reported cases of hepatotoxicity to treatment with benzbromarone; (iii) the incidence of hepatotoxicity possibly due to benzbromarone; (iv) adverse reactions to allopurinol and probenecid. From these analyses, we present recommendations on the use of benzbromarone.Large reductions in plasma urate concentrations in patients with hyperuricaemia are achieved with benzbromarone and most patients normalize their plasma urate. The half-life of benzbromarone is generally short (about 3 hours); however, a uricosuric metabolite, 6-hydroxybenzbromarone, has a much longer half-life (up to 30 hours) and is the major species responsible for the uricosuric activity of benzbromarone, although its metabolism by cytochrome P450 (CYP) 2C9 in the liver may vary between patients as a result of polymorphisms in this enzyme. It is effective in patients with moderate renal impairment. Standard dosages of benzbromarone (100 mg/day) tend to produce greater hypouricaemic effects than standard doses of allopourinol (300 mg/day) or probenecid (1000 mg/day).Adverse effects associated with benzbromarone are relatively infrequent, but potentially severe. Four cases of benzbromarone-induced hepatotoxicity were identified from the literature. Eleven cases have been reported by Sanofi-Synthélabo, but details are not available in the public domain. Only one of the four published cases demonstrated a clear relationship between the drug and liver injury as demonstrated by rechallenge. The other three cases lacked incontrovertible evidence to support a diagnosis of benzbromarone-induced hepatotoxicity. If all the reported cases are assumed to be due to benzbromarone, the estimated risk of hepatotoxicity in Europe was approximately 1 in 17 000 patients but may be higher in Japan.Benzbromarone is also an inhibitor of CYP2C9 and so may be involved in drug interactions with drugs dependent on this enzyme for clearance, such as warfarin. Alternative drugs to benzbromarone have significant adverse reactions. Allopurinol is associated with rare life-threatening hypersensitivity syndromes; the risk of these reactions is approximately 1 in 56 000. Rash occurs in approximately 2% of patients taking allopurinol and usually leads to cessation of prescription of the drug. Probenecid has also been associated with life-threatening reactions in a very small number of case reports, but it frequently interacts with many renally excreted drugs. Febuxostat is a new xanthine oxidoreductase inhibitor, which is still in clinical trials, but abnormal liver function is the most commonly reported adverse reaction.Even assuming a causal relationship between benzbromarone and hepatotoxicity in the identified cases, benefit-risk assessment based on total exposure to the drug does not support the decision by the drug company to withdraw benzbromarone from the market given the paucity of alternative options. It is likely that the risks of hepatotoxicity could be ameliorated by employing a graded dosage increase, together with regular monitoring of liver function. Determination of CYP2C9 status and consideration of potential interactions through inhibition of this enzyme should be considered. The case for wider and easier availability of benzbromarone for treating selected cases of gout is compelling, particularly for patients in whom allopurinol produces insufficient response or toxicity.We conclude that the withdrawal of benzbromarone was not in the best interest of patients with gout.

How much might cardiovascular disease risk be reduced by intensive therapy in people with screen-detected diabetes?

AIMS

To assess the cardiovascular disease (CVD) risk of people with screen-detected Type 2 diabetes and to estimate the risk reduction achievable through early intensive pharmacological intervention.

METHODS

In ADDITION-Cambridge, diabetic patients were identified among people aged 40-69 years through a stepwise screening procedure including a risk score, random and fasting capillary blood glucose, HbA(1c) and oral glucose tolerance test. In those without prior macrovascular disease, 10-year CVD risk was computed using UK Prospective Diabetes Study (UKPDS) and Framingham engines. The absolute risk reduction achievable and its plausible range were predicted using relative risk reductions for individual therapies from published trials and sensitivity analysis.

RESULTS

Of the 867 individuals with undiagnosed diabetes, 19% had pre-existing CVD, 97% were overweight or obese, 86% had hypertension, 75% had dyslipidaemia, 20% had microalbuminuria and 18% were smokers. Of those with hypertension, 35% were not prescribed drugs and 42% were suboptimally treated. Of participants with dyslipidaemia, 68% were not prescribed medications and 22% were poorly controlled. Median 10-year CVD risk was 34.0%[interquartile range (IQR) 26.2-44.6] in men and 21.5% (IQR 15.7-28.7) in women using the UKPDS engine; 38.6% (IQR 27.8-53.0) in men and 24.6% (IQR 17.2-32.9) in women using Framingham equations. In the most conservative scenario (no additive effect of therapies), the absolute risk reduction achievable through multifactorial therapy ranged from 4.9 to 9.5% (UKPDS) and from 5.4 to 10.5% (Framingham). The corresponding ranges of numbers needed to treat were 11-20 and 10-19.

CONCLUSIONS

People with screen-detected diabetes have an adverse cardiovascular risk profile, which is potentially modifiable through application of existing treatment recommendations.

Pharmacodynamic interaction of warfarin with cranberry but not with garlic in healthy subjects

BACKGROUND AND PURPOSE

Patients commonly take complementary medicines in conjunction with warfarin yet evidence supporting the safety or the risk of a herb-drug interaction is lacking. The aim of this study was to investigate the possible impact of two commonly used herbal medicines, garlic and cranberry, on the pharmacokinetics and pharmacodynamics of warfarin in healthy male subjects.

EXPERIMENTAL APPROACH

An open-label, three-treatment, randomized crossover clinical trial was undertaken and involved 12 healthy male subjects of known CYP2C9 and VKORC1 genotype. A single dose of 25 mg warfarin was administered alone or after 2 weeks of pretreatment with either garlic or cranberry. Warfarin enantiomer concentrations, INR, platelet aggregation and clotting factor activity were measured to assess pharmacokinetic and pharmacodynamic interactions between warfarin and herbal medicines.

KEY RESULTS

Cranberry significantly increased the area under the INR-time curve by 30% when administered with warfarin compared with treatment with warfarin alone. Cranberry did not alter S- or R-warfarin pharmacokinetics or plasma protein binding. Co-administration of garlic did not significantly alter warfarin pharmacokinetics or pharmacodynamics. Both herbal medicines showed some evidence of VKORC1 (not CYP2C9) genotype-dependent interactions with warfarin, which is worthy of further investigation.

CONCLUSIONS AND IMPLICATIONS

Cranberry alters the pharmacodynamics of warfarin with the potential to increase its effects significantly. Co-administration of warfarin and cranberry requires careful monitoring.

Pharmacokinetic and pharmacodynamic interaction between allopurinol and probenecid in healthy subjects

BACKGROUND AND OBJECTIVE

Combination therapy with allopurinol and probenecid is used to treat tophaceous gout in patients who do not respond sufficiently to allopurinol alone. However, the potential interaction between these drugs has not been systematically investigated. The objective of this study was to investigate the pharmacokinetics and hypouricaemic effect of oxypurinol (the active metabolite of allopurinol) and probenecid when administered alone and in combination in healthy subjects.

METHODS

An open-label, randomized, three-way crossover clinical trial was conducted in 12 healthy adults. Subjects were randomized to receive treatment for 7 days with allopurinol (150 mg twice daily), probenecid (500 mg twice daily) or combination therapy with both drugs, with a 7-day washout period between treatments. Venous blood samples were collected predose (at 0 hours) and 1, 2, 3, 4, 6, 8, 10 and 12 hours after dosage for determination of oxypurinol and/or probenecid concentrations. Plasma and urinary urate concentrations were determined on each study day and at the end of each washout period. Pharmacokinetic and pharmacodynamic parameters were analysed using two-way ANOVA.

RESULTS

Coadministration of allopurinol and probenecid significantly reduced average steady-state plasma oxypurinol concentrations (mean+/-SD: allopurinol alone 9.7+/-2.1 mg/L vs combination 5.1+/-1.0 mg/L, p<0.001). Probenecid concentrations were unaffected. Plasma urate concentrations decreased (p<0.01) during allopurinol therapy (0.16+/-0.05 mmol/L), probenecid therapy (0.13+/-0.02 mmol/L) and combination therapy (0.09+/-0.02 mmol/L) compared with baseline (0.30+/-0.05 mmol/L).

CONCLUSION

Coadministration of allopurinol and probenecid to healthy subjects had a greater hypouricaemic effect than either allopurinol or probenecid alone, despite a reduction in plasma oxypurinol concentrations when the drugs were taken concomitantly.

Effects of St John's wort and CYP2C9 genotype on the pharmacokinetics and pharmacodynamics of gliclazide

BACKGROUND AND PURPOSE

Patients commonly take complementary medicines in conjunction with conventional drugs without clear evidence of safety or the risk of herb-drug interactions. The aim of this study was to assess potential pharmacokinetic (PK) and pharmacodynamic (PD) interactions between St John's wort and gliclazide in healthy subjects with different cytochrome P450 2C9 (CYP2C9) genotypes.

EXPERIMENTAL APPROACH

A crossover controlled study was conducted in 21 healthy subjects. Each received gliclazide (80 mg) either alone or during 15 days treatment with St John's wort. The area under the plasma concentration-time curve (AUC(0-infinity)), apparent clearance (CL/F) and elimination half-life (t 1/2) of gliclazide and incremental changes in glucose and insulin AUC(0-4) were compared. CYP2C9*2 and CYP2C9*3 alleles were identified using PCR followed by restriction enzyme digestion analysis.

KEY RESULTS

St John's wort significantly altered gliclazide pharmacokinetics in all except for four healthy subjects. The mean ratio and 90% confidence interval (CI) of gliclazide AUC(0-infinity) and CL/F were 0.67 (0.55-0.81) and 1.50 (1.24-1.81), respectively, after St John's wort treatment. St John's wort decreased gliclazide t (1/2), with mean ratio and 90% CI of 0.85 (0.74-0.93). There were no significant changes in glucose or insulin AUC(0-4) after St John's wort treatment and no significant differences according to CYP2C9 genotype.

CONCLUSIONS AND IMPLICATIONS

Treatment with St John's wort significantly increases the apparent clearance of gliclazide which is independent of CYP2C9 genotype. People with diabetes receiving this combination should be closely monitored to evaluate possible signs of reduced efficacy.

Clinical pharmacokinetics and pharmacodynamics of allopurinol and oxypurinol

Allopurinol is the drug most widely used to lower the blood concentrations of urate and, therefore, to decrease the number of repeated attacks of gout. Allopurinol is rapidly and extensively metabolised to oxypurinol (oxipurinol), and the hypouricaemic efficacy of allopurinol is due very largely to this metabolite. The pharmacokinetic parameters of allopurinol after oral dosage include oral bioavailability of 79 +/- 20% (mean +/- SD), an elimination half-life (t((1/2))) of 1.2 +/- 0.3 hours, apparent oral clearance (CL/F) of 15.8 +/- 5.2 mL/min/kg and an apparent volume of distribution after oral administration (V(d)/F) of 1.31 +/- 0.41 L/kg. Assuming that 90 mg of oxypurinol is formed from every 100mg of allopurinol, the pharmacokinetic parameters of oxypurinol in subjects with normal renal function are a t((1/2)) of 23.3 +/- 6.0 hours, CL/F of 0.31 +/- 0.07 mL/min/kg, V(d)/F of 0.59 +/- 0.16 L/kg, and renal clearance (CL(R)) relative to creatinine clearance of 0.19 +/- 0.06. Oxypurinol is cleared almost entirely by urinary excretion and, for many years, it has been recommended that the dosage of allopurinol should be reduced in renal impairment. A reduced initial target dosage in renal impairment is still reasonable, but recent data on the toxicity of allopurinol indicate that the dosage may be increased above the present guidelines if the reduction in plasma urate concentrations is inadequate. Measurement of plasma concentrations of oxypurinol in selected patients, particularly those with renal impairment, may help to decrease the risk of toxicity and improve the hypouricaemic response. Monitoring of plasma concentrations of oxypurinol should also help to identify patients with poor adherence. Uricosuric drugs, such as probenecid, have potentially opposing effects on the hypouricaemic efficacy of allopurinol. Their uricosuric effect lowers the plasma concentrations of urate; however, they increase the CL(R) of oxypurinol, thus potentially decreasing the influence of allopurinol. The net effect is an increased degree of hypouricaemia, but the interaction is probably limited to patients with normal renal function or only moderate impairment.

Has the use of disease-modifying anti-rheumatic drugs changed as a consequence of controlled access to high-cost biological agents through the Pharmaceutical Benefits Scheme?

BACKGROUND

A prerequisite for access to biological agents for the treatment of rheumatoid arthritis under Australia's Pharmaceutical Benefits Scheme (PBS) is evidence of an adequate trial of conventional disease-modifying anti-rheumatic drugs (DMARDs). The aim of this study was to examine whether there were changes in prescribing DMARDs since the introduction of the PBS criteria for access to biologicals in August 2003.

METHODS

A retrospective study was undertaken of the national use of DMARDs in the period before and after the introduction of biologicals under the PBS. Dispensing data were analysed for changes in patterns of DMARD prescription rates (2000-2005).

RESULTS

There were 2 887 746 prescriptions for DMARDs between August 2000 and June 2005. PBS prescriptions accounted for 95% of these. Government expenditure for the DMARDs was $A156m. Trends in the use of DMARDs remained relatively steady over the study period without a significant change around the time the PBS criteria for biologicals were introduced. Use of hydroxychloroquine and leflunomide increased steadily, use of methotrexate and sulfasalazine was stable and use of gold preparations and penicillamine was considerably lower during this 5-year period.

CONCLUSION

Introduction of PBS criteria for access to biologicals did not alter the trends in use of DMARDs based on national dispensing data. This study emphasized the value that would accrue from availability of more comprehensive, de-identified, individual patient data that would enable more detailed examination of the use of medicines. These data are available, but cannot be easily accessed. It is time to make the data available for approved, ethical research in the interests of better outcomes from medicines supplied under PBS.

The Safety, Efficacy, and Pharmacokinetic Profile of a Switch in Antiretroviral Therapy to Saquinavir, Ritonavir, and Atazanavir Alone for 48 Weeks and a Switch in the Saquinavir Formulation

BACKGROUND

Toxicities observed with current combination antiretroviral therapy (CART) warrant a search for novel options, such as class-sparing regimens. Ritonavir-boosted double-protease inhibitor (PI)-only regimens are such an option but are prone to pharmacokinetic interactions.

METHODS

This 48-week randomized study examined the safety and efficacy of a switch in CART to a once-daily regimen of saquinavir (SQV), ritonavir (RTV), and atazanavir (ATV) that did not include nucleoside reverse-transcriptase inhibitors (NRTIs). The study also assessed the pharmacokinetic profile of a change in the SQV formulation, from 200 mg to 500 mg, in 2 regimens (SQV-RTV twice per day plus NRTIs [arm 1] and SQV-RTV-ATV once per day without NRTIs [arm 2]) in human immunodeficiency virus type 1-infected subjects (plasma human immunodeficiency virus RNA level, <50 copies/mL). Patients underwent an initial SQV formulation change or a CART change to SQV-RTV-ATV with intense pharmacokinetic sampling. All patients were subsequently assigned to receive SQV-RTV-ATV (1500, 100, and 300 mg once per day, respectively) without NRTIs for 48 weeks. The primary end point was the percentage of patients who experienced virologic failure.

RESULTS

Of 25 subjects enrolled, scleral icterus was the most common adverse event (3 patients [12.5%]). Three subjects (12.5%) experienced virologic failure; and mean (+/- standard error of the mean) increase in the CD4(+) lymphocyte count was 63 +/- 36 cells/ mu L over 48 weeks (P=.012). The SQV geometric mean area under the time curve parameters were not significantly altered for the 2 SQV formulations (arm 1, 23.32 vs. 18.76 ngxh/mL [geometric mean ratio, 0.80] for the 200-mg vs. 500-mg formulations, respectively; arm 2, 50.31 vs. 44.79 ngxh/mL [geometric mean ratio, 0.88], for the 200-mg vs. 500-mg formulations, respectively).

CONCLUSIONS

A CART regimen of SQV-RTV-ATV alone demonstrated sustained virologic efficacy and was associated with significant increases in the CD4(+) lymphocyte count.

The funding and use of high-cost medicines in Australia: the example of anti-rheumatic biological medicines

Background

Subsidised access to high-cost medicines in Australia is restricted under national programs (the Pharmaceutical Benefits Scheme, PBS, and the Repatriation Pharmaceutical Benefits Scheme, RPBS) with a view to achieving cost-effective use. The aim of this study was to examine the use and associated government cost of biological agents for treating rheumatoid arthritis over the first two years of subsidy, and to compare these data to the predicted outcomes.

Methods

National prescription and expenditure data for the biologicals, etanercept, infliximab, adalimumab, and anakinra were collected and analysed for the period August 2003 to July 2005. Dispensing data on biologicals sorted by the metropolitan, rural and remote zones and by prescriber major specialty were also examined.

Results

A total of 27,970 prescriptions for biologicals was reimbursed. The government expenditure was A$53.1 million, representing only 19% of that expected. Almost all prescriptions were reimbursed by the PBS (98%, A$52 million) and the remainder by the RPBS. Approximately 62% of the prescriptions were for concessional patients (A$32.9 million). There was considerable variability in the use of biologicals across Australian states and territories, usage roughly correlating with the per capita adjusted number of rheumatologists. The total number of prescriptions continued to increase over the study period. Etanercept was the most highly prescribed agent (74% by number of prescriptions), although its use was beginning to plateau. Use of adalimumab increased steadily. Use of infliximab and anakinra was considerably lower. The resultant health outcomes for individual patients are unknown. Prescribers from capital cities and other metropolitan centres provided a majority of prescriptions of biologicals (89%).

Conclusion

The overall uptake of biologicals for treating rheumatoid arthritis over the first two years of PBS subsidy was considerably lower than expected. Long-term safety concerns and the expanded clinical uses of these drugs emphasise the need for evaluation. It is essential that there is comprehensive, ongoing analysis of utilisation data, associated expenditure and, importantly, patient outcomes in order to enhance accountability, efficiency and equity of policies that allocate substantial resources to subsidising national access to high-cost medicines.

Open-Label Extension Studies

The number of open-label extension studies being performed has increased enormously in recent years. Often it is difficult to differentiate between these extension studies and the double-blind, controlled studies that preceded them. If undertaken primarily to gather more patient-years of exposure to the new drug in order to understand and gain confidence in its safety profile, open-label extension studies can play a useful and legitimate role in drug development and therapeutics. However, this can only occur if the open-label extension study is designed, executed, analysed and reported competently. Most of the value accrued in open-label extension studies is gained from a refinement in the perception of the expected incidence of adverse effects that have most likely already been identified as part of the preclinical and clinical trial programme. We still have to rely heavily on post-marketing safety surveillance systems to alert us to type B (unpredictable) adverse reactions because open-label extension studies are unlikely to provide useful information about these types of often serious and relatively rare adverse reactions. Random allocation into test and control groups is needed to produce precise incidence data on pharmacologically expected, or type A, adverse effects. Some increased confidence about incidence rates might result from the open-label extension study; however, as these studies are essentially uncontrolled and biased, the data are not of great value. Other benefits have been proposed to be gained from open-label extension studies. These include ongoing access to an effective but otherwise unobtainable medicine by the volunteers who participated in the phase III pivotal trials. However, there are unappreciated ethical issues about the appropriateness of enrolling patients whose response to previous treatment is uncertain, largely because treatment allocation in the preceding randomised, double-blind, controlled trial has not been revealed at the time of entry into the open-label extension study. Negative aspects of open-label extension studies revolve around their use as a marketing tool, as they build a market for the drug and generate pressure for subsidised access to the drug from consumers and their physicians. Consumers, institutions where these studies are conducted and research ethics committees need to be convinced of the motives, as well as the quality, of the open-label extension study and its execution before supporting such studies. Open-label extension studies do have a legitimate but limited place in the clinical development of new medicines. The negative perceptions about these studies have arisen because of perversion of acceptable rationales for this type of study and a failure to recognise (or disclose) the limitations resulting from the inherent weaknesses in their design. Increased human exposure to a new medicine under reasonably controlled circumstances to increase confidence in the safety of the medicine is an acceptable rationale for an open-label extension study, and a useful activity to increase the knowledge of the safety profile of a new medicine. However, this goal is increasingly being achieved by means other than open-label extension studies.

Cytochrome P450 2B6 activity as measured by bupropion hydroxylation: effect of induction by rifampin and ethnicity

AIM

The aim of this study was to investigate the activity of the drug-metabolizing enzyme cytochrome P450 (CYP) 2B6 before and after in vivo induction by rifampin (INN, rifampicin) in white subjects and Chinese subjects by use of the probe drug bupropion (INN, amfebutamone).

METHODS

Healthy male white subjects (n = 9) and Chinese subjects (n = 9) (age range, 19-34 years) of known CYP2B6 genotype received orally administered bupropion (Zyban SR, 150 mg) alone and during daily treatment with rifampin (600 mg). Blood samples were taken for up to 72 hours after each bupropion dose, and plasma concentrations of bupropion and its active metabolites, hydroxybupropion, threohydrobupropion, and erythrohydrobupropion, were measured by HPLC. The subjects' CYP2B6 genotype was determined by use of a matrix-assisted laser desorption /ionization-time of flight (MALDI-TOF) mass spectrometry assay.

RESULTS

Rifampin treatment increased the apparent clearance of bupropion in Chinese subjects and white subjects combined (n = 16) from 2.6 L x h(-1) x kg(-1) (95% confidence interval [CI], 2.3-3.0 L x h(-1) x kg(-1)) after bupropion alone to 7.9 L x h(-1) x kg(-1) (95% CI, 6.8-10.1 L x h(-1) x kg(-1)) during rifampin treatment. Rifampin treatment decreased the half-life of bupropion from 15.9 hours (95% CI, 13.5-20.4 hours) to 8.2 hours (95% CI, 6.7-12.4 hours). Rifampin treatment increased the hydroxybupropion maximum concentration from 395 ng/mL (95% CI, 341-497 ng/mL) to 548 ng/mL (95% CI, 490-638 ng/mL), decreased the area under the concentration-time curve extrapolated to infinity of hydroxybupropion from 14.7 microg x h/mL (95% CI, 12.7-18.4 microg x h/mL) to 8.4 microg x h/mL (95% CI, 7.4-10.2 microg x h/mL), and reduced the elimination half-life of hydroxybupropion from 21.9 hours (95% CI, 20.3-24.0 hours) to 10.7 hours (95% CI, 8.6-14.5 hours). There was no significant difference in the pharmacokinetics of bupropion or hydroxybupropion between white subjects and Chinese subjects before and after treatment with rifampin, once corrected for body weight.

CONCLUSIONS

Rifampin significantly induces CYP2B6 activity in vivo, and the clinical consequences of potential interactions between rifampin and CYP2B6 substrates deserve further investigation. Rifampin appears to induce the elimination of hydroxybupropion. Differences in bupropion pharmacokinetics that were observed between white subjects and Chinese subjects can be attributed to differences in body weight, suggesting that, for a given subject weight, CYP2B6 activity is similar in white subjects and Chinese subjects.

Accessing health outcome data on high-cost medicines in Australia

Data on health outcomes resulting from the use of medicines provide important evidence of cost-effectiveness. Currently, clinical information on individual patients, collected by Medicare Australia to assess eligibility for subsidised treatment with high-cost medicines, is inaccessible for research. Comprehensive data on drug use and health outcomes should be made accessible, with appropriate regulation, so that the effectiveness, utility and appropriateness of our systems of access to medicines can be independently analysed. In the interests of continuous improvement in medical care and optimal use of limited resources, we strongly advocate the enhancement of Medicare Australia databases and liberalisation of arrangements for access to administrative and clinical data.

Access to tumour necrosis factor inhibitors for rheumatoid arthritis treatment under the Australian Pharmaceutical Benefits Scheme: are we on target?

BACKGROUND

Access to tumour necrosis factor inhibitors (TNFI) for the treatment of rheumatoid arthritis under the Australian Pharmaceutical Benefits Scheme (PBS) is governed by a set of arrangements, operational from August 2003. Patients must meet strict criteria for both starting and continuing TNFI. Examination of utilization data is important for assessing the broader implications of arrangements for access to expensive pharmaceuticals under schemes such as the PBS.

AIM

To examine the uptake of TNFI over the first year of subsidized availability of etanercept under the PBS, and to compare these data to the predicted utilization and expenditure.

METHODS

Collection and analysis of prescription and expenditure data for the three listed TNFI: etanercept, infliximab and adalimumab processed under the PBS for the period August 2003 to July 2004.

RESULTS

A total of 8,053 prescriptions for TNFI was reimbursed at a total cost of 15.2 m Australian dollars. The total PBS expenditure on etanercept was just over 14 m Australian dollars, 14% of the predicted annual expenditure. The relative per capita uptake of etanercept was highest in the Australian Capital Territory and lowest in the Northern Territory. More than 50% of prescriptions for etanercept were for concessional patients (7.3 m Australian dollars).

CONCLUSION

Prescription rates and expenditure on etanercept were substantially below those forecast over the first year. There are opportunities to adjust the PBS restrictions for subsidized access to TNFI to benefit more patients.

Recent developments in targeting access to high cost medicines in Australia

Background

In Australia, the Pharmaceutical Benefits Scheme (PBS) has developed a set of arrangements to control access to high-cost medicines to ensure their use is cost-effective. These medicines include the tumour necrosis factor-alpha inhibitors (TNFIs) for the treatment of rheumatoid arthritis. The aim of this first phase of a qualitative study was to explore basic views on the restricted access to TNFIs in order to confirm where further investigation should take place in the next phase.

Methods

Semi-structured interviews were conducted in 2004 with a member of the four relevant stakeholder groups. Participants were asked their opinions about features of the establishment, process and effects of the system of restricted access to TNFIs. Views on the collaboration between stakeholder groups in the decision-making process were also collected.

Results

The principle of 'controlled access' to TNFIs was supported in general. There were concerns regarding some of the specific eligibility criteria. Wider and more transparent stakeholder consultation was judged desirable. Some flexibility around prescribing of TNFIs by physicians, and regular review of the arrangements were proposed. These themes will inform the next phase of the study.

Conclusion

This first phase highlighted a range of issues associated with the PBS arrangements restricting access to TNFIs. Timely review and report of issues and concerns associated with such policy developments that arose in practice are essential. There is a need for a more comprehensive exploration across a wide range of stakeholders with different perspectives that will in turn be helpful in guiding policy and practice around national arrangements to manage access to high-cost medicines.

Effect of ginkgo and ginger on the pharmacokinetics and pharmacodynamics of warfarin in healthy subjects

AIM

The aim of this study was to investigate the effect of two common herbal medicines, ginkgo and ginger, on the pharmacokinetics and pharmacodynamics of warfarin and the independent effect of these herbs on clotting status.

METHODS

This was an open label, three-way crossover randomized study in 12 healthy male subjects, who received a single 25 mg dose of warfarin alone or after 7 days pretreatment with recommended doses of ginkgo or ginger from herbal medicine products of known quality. Dosing with ginkgo or ginger was continued for 7 days after administration of the warfarin dose. Platelet aggregation, international normalized ratio (INR) of prothrombin time, warfarin enantiomer protein binding, warfarin enantiomer concentrations in plasma and S-7-hydroxywarfarin concentration in urine were measured. Statistical comparisons were made using anova and the 90% confidence intervals (CIs) of the ratio of log transformed parameters are reported.

RESULTS

INR and platelet aggregation were not affected by administration of ginkgo or ginger alone. The mean (95% CI) apparent clearances of S-warfarin after warfarin alone, with ginkgo or ginger were 189 (167-210) ml h(-1), 200 (173-227) ml h(-1) and 201 (171-231) ml h(-1), respectively. The respective apparent clearances of R-warfarin were 127 (106-149) ml h(-1), 126 (111-141) ml h(-1) and 131 (106-156) ml h(-1). The mean ratio (90% CI) of apparent clearance for S-warfarin was 1.05 (0.98-1.21) and for R-warfarin was 1.00 (0.93-1.08) when coadministered with ginkgo. The mean ratio (90% CI) of AUC(0-168) of INR was 0.93 (0.81-1.05) when coadministered with ginkgo. The mean ratio (90% CI) of apparent clearance for S-warfarin was 1.05 (0.97-1.13) and for R-warfarin was 1.02 (0.95-1.10) when coadministered with ginger. The mean ratio (90% CI) of AUC(0-168) of INR was 1.01 (0.93-1.15) when coadministered with ginger. The mean ratio (90% CI) for S-7-hydroxywarfarin urinary excretion rate was 1.07 (0.85-1.32) for ginkgo treatment, and 1.00 (0.81-1.23) for ginger coadministration suggesting these herbs did not affect CYP2C9 activity. Ginkgo and ginger did not affect the apparent volumes of distribution or protein binding of either S-warfarin or R-warfarin.

CONCLUSIONS

Ginkgo and ginger at recommended doses do not significantly affect clotting status, the pharmacokinetics or pharmacodynamics of warfarin in healthy subjects.

Effect of St John's wort and ginseng on the pharmacokinetics and pharmacodynamics of warfarin in healthy subjects

M: The aim of this study was to investigate the effect of St John's wort and ginseng on the pharmacokinetics and pharmacodynamics of warfarin.

METHODS

This was an open-label, three-way crossover randomized study in 12 healthy male subjects, who received a single 25-mg dose of warfarin alone or after 14 days' pretreatment with St John's wort, or 7 days' pretreatment with ginseng. Dosing with St John's wort or ginseng was continued for 7 days after administration of the warfarin dose. Platelet aggregation, international normalized ratio (INR) of prothrombin time, warfarin enantiomer protein binding, warfarin enantiomer concentrations in plasma and S-7-hydroxywarfarin concentration in urine were measured. Statistical comparisons were made using anova and 90% confidence intervals are reported.

RESULTS

INR and platelet aggregation were not affected by treatment with St John's wort or ginseng. The apparent clearances of S-warfarin after warfarin alone or with St John's wort or ginseng were, respectively, 198 +/- 38 ml h(-1), 270 +/- 44 ml h(-1) and 220 +/- 29 ml h(-1). The respective apparent clearances of R-warfarin were 110 +/- 25 ml h(-1), 142 +/- 29 ml h(-1) and 119 +/- 20 ml h(-1) [corrected]. The mean ratio and 90% confidence interval (CI) of apparent clearance for S-warfarin was 1.29 (1.16, 1.46) and for R-warfarin it was 1.23 (1.11, 1.37) when St John's wort was coadministered. The mean ratio and 90% CI of AUC(0-168) of INR was 0.79 (0.70, 0.95) when St John's wort was coadministered. St John's wort and ginseng did not affect the apparent volumes of distribution or protein binding of warfarin enantiomers.

CONCLUSIONS

St John's wort significantly induced the apparent clearance of both S-warfarin and R-warfarin, which in turn resulted in a significant reduction in the pharmacological effect of rac-warfarin. Coadministration of warfarin with ginseng did not affect the pharmacokinetics or pharmacodynamics of either S-warfarin or R-warfarin.

Human subcutaneous tissue distribution of fluconazole: comparison of microdialysis and suction blister techniques

AIMS

To investigate uptake of fluconazole into the interstitial fluid of human subcutaneous tissue using the microdialysis and suction blister techniques.

METHODS

A sterile microdialysis probe (CMA/60) was inserted subcutaneously into the upper arm of five healthy volunteers following an overnight fast. Blisters were induced on the lower arm using gentle suction prior to ingestion of a single oral dose of fluconazole (200 mg). Microdialysate, blister fluid and blood were sampled over 8 h. Fluconazole concentrations were determined in each sample using a validated HPLC assay. In vivo recovery of fluconazole from the microdialysis probe was determined in each subject by perfusing the probe with fluconazole solution at the end of the 8 h sampling period. Individual in vivo recovery was used to calculate fluconazole concentrations in subcutaneous interstitial fluid. A physiologically based pharmacokinetic (PBPK) model was used to predict fluconazole concentrations in human subcutaneous interstitial fluid.

RESULTS

There was a lag-time (approximately 0.5 h) between detection of fluconazole in microdialysate compared with plasma in each subject. The in vivo recovery of fluconazole from the microdialysis probe ranged from 57.0 to 67.2%. The subcutaneous interstitial fluid concentrations obtained by microdialysis were very similar to the unbound concentrations of fluconazole in plasma with maximum concentration of 4.29 +/- 1.19 microg ml(-1) in subcutaneous interstitial fluid and 3.58 +/- 0.14 microg ml(-1) in plasma. Subcutaneous interstitial fluid-to-plasma partition coefficient (Kp) of fluconazole was 1.16 +/- 0.22 (95% CI 0.96, 1.35). By contrast, fluconazole concentrations in blister fluid were significantly lower (P < 0.05, paired t-test) than unbound plasma concentrations over the first 3 h and maximum concentrations in blister fluid had not been achieved at the end of the sampling period. There was good agreement between fluconazole concentrations derived from microdialysis sampling and those estimated using a blood flow-limited PBPK model.

CONCLUSIONS

Microdialysis and suction blister techniques did not yield comparable results. It appears that microdialysis is a more appropriate technique for studying the rate of uptake of fluconazole into subcutaneous tissue. PBPK model simulation suggested that the distribution of fluconazole into subcutaneous interstitial fluid is dependent on tissue blood flow.

Effects of Ca-ATPase inhibitors on the intracellular calcium activity and motility of human spermatozoa

Although evidence suggests that high intracellular calcium activity ([Ca2+]i) inhibits sperm motility, data concerning [Ca2+]i within, or slightly above, the physiological range are sparse, particularly in mammalian sperm. We investigated inhibitors of the sarcoplasmic/endoplasmic reticulum Ca-ATPase (SERCA) and the plasma membrane Ca-ATPase with the objective of increasing the intracellular calcium ion activity in human spermatozoa to study its effect on motility and other functions. Thapsigargin (20 micromol/L) increased [Ca2+]i from 140 +/- 7 nmol/L over an approximately 2-min period to reach a plateau of 530 +/- 84 nmol/L (mean +/- SEM, n = 3, p < 0.05). In sperm suspended in calcium-free medium thapsigargin increased [Ca2+]i from 13 +/- 3.3 to 35 +/- 7.5 nmol/L (p < 0.01), consistent with the release of calcium from intracellular stores. Cyclopiazonic acid (60 micromol/L) caused a transient decrease in [Ca2+]i. Quercetin, (200 micromol/L) caused a rapid increase in [Ca2+]i to 1280 +/- 90 nmol/L, after which [Ca2+]i fell quickly at first but then more slowly. Thapsigargin (20 micromol/L) caused approximately 70% of sperm to acrosome react in < or = 5 min, but once acrosome reacted, many sperm died over the next 30 min. Lower concentrations of thapsigargin caused fewer acrosome reactions but were less toxic. Both thapsigargin and quercetin caused rapid dose-dependent decreases in sperm motility. The results are consistent with high [Ca2+]i in the range observed in caput epididymal or cryopreserved spermatozoa inhibiting motility, but might be confounded by other events following the acrosome reaction.

Pharmacokinetics of estradiol, progesterone, testosterone and dehydroepiandrosterone after transbuccal administration to postmenopausal women

OBJECTIVE

To evaluate the pharmacokinetic profiles of estradiol, progesterone, testosterone and dehydroepiandrosterone in postmenopausal women following single and multiple dosing using a troche and the transbuccal route of administration.

METHODS

Each troche contained estradiol (0.5 mg), progesterone (200 mg), testosterone (2.0 mg) and dehydroepiandrosterone (10 mg). A half troche was administered to each of six women and the plasma concentration-time profiles determined over 24 h. Thereafter, a one-half troche was taken twice daily for 2 weeks and concentrations determined over a dosage interval (12 h). Blood and saliva samples were collected at specified time intervals on the first day and again after 2 weeks.

RESULTS

Each of the hormones was readily absorbed via the buccal mucous membrane. Peak plasma concentrations of estradiol and progesterone were comparable to those found normally in young menstruating women.

CONCLUSION

The transbuccal route is a novel approach to provide therapy for the management of menopause-related symptoms of postmenopausal women without the need to resort to conjugated or synthesized hormones, and may overcome the poor or erratic systemic availability associated with other routes of administration.

Muscle distribution of the neuromuscular blocker gallamine using microdialysis

Measurement of drug concentrations in target tissue has the potential to provide insight into the pharmacokinetics and pharmacodynamics of a drug. In this study, the distribution of the neuromuscular blocker, gallamine, into muscle tissue was investigated in urethane-anesthetized rats after an intravenous bolus dose (6 mg/kg). Microdialysis sampling was used to continuously determine gallamine concentrations in muscle interstitial fluid (MIF). In vivo microdialysis recovery of gallamine was determined as the relative loss of gallamine from the perfusate into muscle tissue after perfusion with gallamine (2 microg/mL). Recovery was determined in each rat before the pharmacokinetic studies. Terminal muscle sampling followed by homogenization was also performed to examine gallamine distribution within muscle tissue. All samples were assayed for gallamine using a validated high-performance liquid chromatography assay. Gallamine was rapidly distributed into MIF with a MIF-plasma partition coefficient of 0.9 +/- 0.1 (n = 6). By contrast, the estimated gallamine concentration in muscle tissue homogenate was only 23 +/- 5% (n = 5) of the concentration in MIF as estimated by microdialysis sampling at the terminal sampling time. These findings suggest that gallamine is not distributed uniformly within muscle but selectively distributes into MIF. Simulations using a hybrid physiologically based pharmacokinetic model which describes uptake of drug only into the interstitial space showed good agreement between predicted and observed concentration data obtained from microdialysis sampling, supporting the findings that gallamine selectively distributes into MIF. These studies demonstrate microdialysis combined with conventional terminal tissue sampling provides valuable information on intra-tissue drug distribution.