George A. Davis

Genetic association between sensitivity to warfarin and expression of CYP2C9*3.

Cytochrome P4502C9 (CYP2C9) is largely responsible for terminating the anticoagulant effect of racemic warfarin via hydroxylation of the pharmacologically more potent S-enantiomer to inactive metabolites. Mutations in the CYP2C9 gene result in the expression of three allelic variants, CYP2C9*1, CYP2C9*2 and CYP2C9*3. Both CYP2C9*2 and CYP2C9*3 exhibit altered catalytic properties in vitro relative to the wild-type enzyme. In the present study, a patient was genotyped who had proven unusually sensitive to warfarin therapy and could tolerate no more than 0.5 mg of the racemic drug/day. PCR-amplification of exons 3 and 7 of the CYP2C9 gene, followed by restriction digest or sequence analysis, showed that this individual was homozygous for CYP2C9*3. In addition, patient plasma warfarin enantiomer ratios and urinary 7-hydroxywarfarin enantiomer ratios were determined by chiral-phase high performance liquid chromotography in order to investigate whether either parameter might be of diagnostic value in place of a genotypic test. Control patients receiving 4-8 mg warfarin/day exhibited plasma S:R ratios of 0.50 +/- 0.25:1, whereas the patient on very low-dose warfarin exhibited an S:R ratio of 3.9:1. In contrast, the urinary 7-hydroxywarfarin S:R ratio of 4:1 showed the same stereoselectivity as that reported for control patients. Therefore, expression of CYP2C9*3 is associated with diminished clearance of S-warfarin and a dangerously exacerbated therapeutic response to normal doses of the racemic drug. Analysis of the plasma S:R warfarin ratio may serve as a useful alternative test to genotyping for this genetic defect.

Clinical Pharmacokinetics in the 21st Century Does the Evidence Support Definitive Outcomes

Clinical pharmacokinetics emerged as a clinical discipline in the late 1960s and early 1970s. Clinical pharmacokinetic monitoring (CPM) helped many pharmacists to enter the clinical arena, but the focus was more on the pharmacists and tools. With the widespread acceptance of pharmaceutical care and patientfocused pharmacy, we now must take a sobering look at how clinical pharmacokinetics fits into the pharmaceutical care process.The existing literature is laden with articles that evaluate the effect of CPM on surrogate end-points. Many pharmacists have also had personal experiences that attest to the usefulness of CPM. Decreased mortality, decreased length of treatment, decreased length of hospital stay, decreased morbidity, and decreased adverse effects from drug therapy have been examined in an effort to measure and evaluate the impact of CPM on patient outcomes. While many of these studies demonstrated significant positive outcomes, several showed that CPM did not have a significant impact on specific patient outcomes. A few studies even found a negative impact on specific patient outcomes. Ultimately, there is good evidence in only a few specific patient groups to support the benefit of CPM.Despite the limitations of data supporting the routine use of CPM in managing drug therapy in diverse populations, many pharmacists continue to expend considerable time and effort in this activity. We need to define those patients who are most likely to benefit from CPM and incorporate this into our provision of pharmaceutical care, while minimising the time and money spent on CPM that provides no value.In redefining the patients who will benefit from CPM, we need to critically re-evaluate clinical studies on the relationship between drug concentration and response. Similarly, we need to pay special attention to recent studies evaluating the impact of CPM on outcomes in specific subpopulations. In the absence of specific studies demonstrating the value of CPM in particular patients, we propose that a more comprehensive decision-making process be undertaken that culminates in the quintessential question: ‘Will the results of the drug assay make a significant difference in the clinical decision-making process and provide more information than sound clinical judgement alone?’ We also need to consider opportunities to expand the use of CPM for new drugs and where new evidence suggests benefit.Even when there is strong evidence that CPM is useful in managing therapy in particular patient groups, clinicians need to remember that the therapeutic range is no more than a confidence interval and, therefore, we need to ‘treat the patient and not the level’. We need to incorporate the patient-specific and outcome-oriented principles of pharmaceutical care into our CPM, even as we utilise CPM as an essential tool in pharmaceutical care.

Phase I pharmacokinetic studies evaluating single and multiple doses of oral GW572016, a dual EGFR-ErbB2 inhibitor, in healthy subjects

GW572016 is a dual EGFR-ErbB2 inhibitor that has promise as an anticancer agent. Two phase I studies were conducted to determine the safety, tolerability and pharmacokinetics of single and multiple doses given to healthy subjects. The single dose study evaluated two groups of eight subjects in an ascending dose, 4-way cross-over, while the multiple dose study evaluated twenty-seven healthy volunteers in an ascending dose, double-blind, randomized, placebo-controlled, staggered parallel design. No serious adverse events were seen in either study. The most common adverse events for subjects receiving GW572016 were headache, diarrhea, rash, cold symptoms, gastrointestinal symptoms, and elevated LFTs, which were similar between treatment and placebo groups. Absorption of single doses of GW572016 was slightly delayed, with median tlag of 15 minutes (range 0–90 minutes) and achieved peak serum concentrations at a median of three hours (range 1.5–6 hours) post-dose. Serum concentrations after multiple doses of GW572016 demonstrated no significant accumulation at the 25 mg dose, and approximately 50% accumulation at the 100 mg and 175 mg doses, achieving steady state in six to seven days. A modest time-dependent increase in serum concentrations also was detected with multiple doses of GW572016. Single and multiple oral doses of GW572016 were well tolerated in healthy subjects, and resulted in dose-related systemic exposure of GW572016.

Dose-escalation study of ICA-17043 in patients with sickle cell disease.

Study Objective. To determine the dose tolerance, safety, and pharmacokinetics of a single oral dose of ICA‐17043 in patients with sickle cell disease.

A clinical-laboratory algorithm incorporating optical density value to predict heparin-induced thrombocytopenia

The diagnosis of heparin-induced thrombocytopenia (HIT) is complex and involves integrating both clinical and laboratory findings. Readily available diagnostic tests such as the heparin-dependant antibody assay (HDAA) lack desired specificity when utilised alone. A diagnostic algorithm incorporating the 4T pretest probability score, HDAA, and optical density (OD) value was implemented as a tool to assist in the diagnosis of HIT and with the decision to treat patients. Patients with a 4T score >3 and/or positive HDAA result with an OD ≥1 were considered positive. Utilisation of this algorithm was hypothesised to improve the identification of patients without SRA confirmed HIT and improve overall specificity compared to other diagnostic strategies. Retrospective chart review was conducted and included patients with a positive or equivocal HDAA result and a serotonin release assay result during a two-year period. Each patient was evaluated for the diagnosis of HIT using the algorithm. The specificity and sensitivity of the diagnostic algorithm to identify subjects with SRA confirmed HIT was evaluated. A total of 83 patients were identified for inclusion in the study. The diagnostic algorithm identified 22 patients for direct thrombin inhibitor (DTI) therapy. Nine of these patients were SRA positive. The sensitivity of the algorithm was 0.9 with a specificity of 0.822. The diagnostic algorithm was found to be both more specific and sensitive than other diagnostic strategies including the 4T score alone, HDAA alone, and the combination of the 4T score and HDAA results. This preliminary data suggest a diagnostic algorithm combining 4T score, HDAA, and OD value may be a tool to aid in the identification SRA positive patients for DTI therapy.

Risk Factors for Venous Thromboembolism in Patients with Chronic Liver Disease

BACKGROUND Pharmacologic prophylaxis for venous thromboembolism (VTE) in patients with chronic liver disease (CLD) presents a unique challenge because of coagulopathies associated with the disease. When evaluating whether these patients require VTE prophylaxis upon hospitalization, it would be advantageous if risk factors for the development of VTE in this population were known. OBJECTIVE To evaluate risk factors associated with the development of VTE in patients with CLD. METHODS A retrospective case-control study was conducted. Patients admitted to the University of Kentucky Chandler Hospital from October 2006 to July 2010 with a diagnosis of CLD and VTE were matched in a 1:3 fashion with CLD patients without VTE. The primary objective was to determine whether there were significant differences in laboratory values between the 2 groups. RESULTS During this time, 27 patients with CLD (1.0%) were diagnosed with VTE. These patients had significantly lower median aspartate aminotransferase (AST) (47 vs 70 U/L, p = 0.04), alanine transaminase (ALT) (24.5 vs 36 U/L, p = 0.02), albumin (2.1 vs 2.4 g/dL, p = 0.02) and hematocrit (Hct) (28.3% vs 32%, p = 0.03) values compared to the control patients. Patients with albumin lower than 1.9 g/dL had a 5.1 times greater risk of VTE compared to patients with albumin of 2.8 g/dL and higher (OR 5.14, 95% CI 1.05–25.2). CONCLUSIONS Patients with CLD who developed VTE had significantly lower AST, ALT, albumin, and Hct compared to those of control patients. Studies are necessary to further examine the significance of this finding.

Effect of fluticasone propionate nasal spray on bioavailability of intranasal hydromorphone hydrochloride in patients with allergic rhinitis.

Study Objective. To investigate the effect of the nasal corticosteroid fluticasone propionate on the bioavailability and pharmacokinetics of single‐dose intranasal hydromorphone hydrochloride in patients with allergic rhinitis.

Bioavailability and Pharmacokinetics of Intranasal Hydromorphone in Patients Experiencing Vasomotor Rhinitis

Background and objectiveNarcotic analgesics such as hydromorphone undergo an extensive first-pass effect resulting in a low systemic bioavailability following oral administration. Alternative dosing routes, such as rectal and intranasal (IN) routes, have been suggested as options for oral or intravenous administration. Rhinitis and pharmacological agents used for treatment are considered factors that could alter the rate and extent of absorption of drugs administered by the nasal route. The purpose of this study was to evaluate the pharmacokinetics of intranasal hydromorphone hydrochloride (HCl) in patients with vasomotor rhinitis.MethodsTen patients completed the randomised, three-way crossover study. During the three treatment periods, a single dose of hydromorphone HCl 2.0mg was administered via intravenous infusion (treatment A) and the intranasal route without (treatment B) or with (treatment C) vasoconstrictor pretreatment for rhinitis. Blood samples were collected serially from 0 to 16 hours. Noncompartmental methods were used to determine pharmacokinetic parameters.ResultsMaximum plasma concentrations were 3.69 and 3.38 μg/L for treatments B and C, respectively. Mean (% coefficient of variation) bioavailability of intranasal hydromorphone was 54.4% (34.8) and 59.8% (22.1) with and without pretreatment, respectively. Pretreatment of rhinitis did not significantly affect the rate or extent of absorption of hydromorphone in this study. There was not a significant difference in bioavailability between treated and untreated rhinitis.ConclusionsThis study found intranasal administration of hydromorphone in patients experiencing vasomotor rhinitis had acceptable bioavailability and a pharmacokinetic profile comparable to previous studies. These data support further investigation of this single-dose delivery system for clinical use.

A Retrospective Evaluation of Vitamin K1 Therapy to Reverse the Anticoagulant Effect of Warfarin

Study Objective. To assess compliance with the 2001 consensus guidelines of the American College of Chest Physicians (ACCP) regarding administration of vitamin K1 to reverse the anticoagulant effect of warfarin.

Vancomycin Clearance in High-Volume Venovenous Hemofiltration

OBJECTIVE To report the pharmacokinetic and pharmacodynamic properties of vancomycin in 4 patients undergoing high-volume continuous venovenous hemofiltration (CVVH). CASE SUMMARY Data from 4 patients prescribed high-volume CVVH for acute renal failure treated with vancomycin were analyzed. Vancomycin plasma concentrations were measured 4 and 24 hours after the end of a 1-hour vancomycin infusion. The mean therapy fluid rate on initiation of vancomycin was 56.2 mL/kg/h (range 48.0–65.5). The mean loading dose of vancomycin was 18.3 mg/kg (range 14.7–19.7). Median vancomycin concentration 4 hours after the dose was 18.1 mg/L (range 13.1–30.0). At 24 hours after the dose, only 1 patient had a detectable vancomycin concentration (5.2 mg/L). DISCUSSION There was a large variability in the clearance of vancomycin in this patient population. Current strategies for dosing vancomycin may lead to subtherapeutic trough concentrations. Vancomycin dosing in this patient population should be based on a detailed assessment of the CVVH prescription, vancomycin concentrations, and clinical needs and response. CONCLUSIONS An initial vancomycin dose of 20–25 mg/kg with frequent monitoring and adjustment is recommended for patients receiving high-volume CVVH.