Integration of genetic, clinical, and INR data to refine warfarin dosing

Well-characterized genes that affect warfarin metabolism (cytochrome P450 (CYP) 2C9) and sensitivity (vitamin K epoxide reductase complex 1 (VKORC1)) explain one-third of the variability in therapeutic dose before the international normalized ratio (INR) is measured. To determine genotypic relevance after INR becomes available, we derived clinical and pharmacogenetic refinement algorithms on the basis of INR values (on day 4 or 5 of therapy), clinical factors, and genotype. After adjusting for INR, CYP2C9 and VKORC1 genotypes remained significant predictors (P < 0.001) of warfarin dose. The clinical algorithm had an R(2) of 48% (median absolute error (MAE): 7.0 mg/week) and the pharmacogenetic algorithm had an R(2) of 63% (MAE: 5.5 mg/week) in the derivation set (N = 969). In independent validation sets, the R(2) was 26-43% with the clinical algorithm and 42-58% when genotype was added (P = 0.002). After several days of therapy, a pharmacogenetic algorithm estimates the therapeutic warfarin dose more accurately than one using clinical factors and INR response alone.

The Effects of Tadalafil on Cold-induced Vasoconstriction in Patients with Raynaud's Phenomenon

Raynaud's phenomenon (RP) is a disorder characterized by episodic periods of vasoconstriction typically provoked by exposure to cold. Phosphodiesterase 5 (PDE5) inhibitors may improve digital blood flow and clinical symptoms in patients with RP, but the mechanisms are unknown. We examined the hypothesis that a PDE5 inhibitor, tadalafil, attenuates cold-induced vasoconstriction. Additionally, we examined whether tadalafil reduced vascular dysfunction following ischemia, thus altering the response to repeated cooling. We conducted a double-blind, placebo-controlled crossover study in 20 subjects with RP on two separate study days, when subjects received either placebo or tadalafil (10 mg). Digital blood flow (flux) was measured by laser Doppler flowmetry at rest and during two graduated local heat and cold exposure cycles. Temperature-response curves were evaluated by E(max) (maximal flux during heating), E(min) (minimal flux during cooling), and ET(50) and ET(90) (the local temperature at which flux decreased by 50% and 90% of E(max)-E(min), respectively). Tadalafil did not increase baseline flux (81.0+/-73.0 vs 91.3+/-114.0 arbitrary unit (AU), P=0.57), E(max) (280.0+/-107.6 vs 279.5+/-119.8 AU, P=0.94), ET(50) (25.4+/-4.4 vs 26.6+/-5.7 degrees C, P=0.62), or ET(90) (21.2+/-3.9 vs 21.8+/-5.0 degrees C, P=0.78), (cycle 1 values presented). There were no differences between cycles on either study day. In conclusion, in patients with RP, single-dose tadalafil does not increase digital blood flow at baseline or in response to heating, nor does it attenuate cold-induced vasoconstriction. Furthermore, it does not precondition the endothelium to resist a second cooling challenge. The clinical benefit in patients with RP treated with PDE5 inhibitors probably involves mechanisms other than acute inhibition of cold-induced vasoconstriction.

Bioavailability of oral vs. subcutaneous low-dose methotrexate in patients with Crohn's disease

BACKGROUND

Oral methotrexate and folic acid are partly absorbed by a common intestinal transporter.

AIM

: To determine the relative bioavailability of oral low-dose methotrexate administered with and without concomitant folic acid vs. subcutaneous administration in patients with stable Crohn's disease.

METHODS

Ten patients were randomized to receive their regular maintenance dose of methotrexate (15-25 mg) for three consecutive weeks: orally, orally with 5 mg folic acid or subcutaneously. Blood samples were drawn at specified intervals during 24 h, and methotrexate levels were determined by fluorescence immunoassay. Areas under the curve extrapolated to infinity (AUC infinity ) were compared between the three routes.

RESULTS

The geometric mean AUC infinity values (95% confidence intervals) were 360 nmol x h/L (301-430 nmol x h/L), 261 nmol x h/L (214-318 nmol x h/L) and 281 nmol x h/L (209-377 nmol x h/L) per milligram of methotrexate administered for subcutaneous, oral and oral with folic acid administration, respectively (P < 0.05 and P < 0.01 for oral with folic acid and oral vs. subcutaneous administration, respectively). The geometric mean relative bioavailabilities (95% confidence intervals) were 0.73 (0.62-0.86) and 0.77 (0.60-0.99) for oral and oral with folic acid administration, respectively (difference not significant).

CONCLUSIONS

In patients with stable Crohn's disease, the oral bioavailability of methotrexate is highly variable and averages 73% of that of subcutaneous administration. Concomitant folic acid has no significant effect on the bioavailability. Dose adjustments based on individual pharmacokinetic assessment should be considered when switching patients from parenteral to oral therapy.

Short report: a consideration of primaquine dose adjustment for radical cure of Plasmodium vivax malaria

Relapse of Plasmodium vivax malaria following standard primaquine dosing has been reported from many areas, and more recently from sub-Saharan Africa. In this report we describe eight episodes (in five patients) of treatment failure in non-immune Israeli travelers returning from Ethiopia. Retrospective calculation of the primaquine dose per kilogram of body weight for 23 treatment courses showed a lower total dose per kilogram in heavier patients. The mean calculated dose (95% CI) in the eight failed treatments was 2.5 +/- 0.3 mg/kg compared with 4.4 +/- 0.5 mg/kg in the 15 successful treatment courses. Weight-adjusted dosing regimens may prevent inadvertent subtherapeutic drug failure, and thus apparent primaquine failure. In these cases, no relapses were observed in those who received > 3.5 mg/kg. Consideration should be given to adjusting the dose of primaquine according to body weight. For those infected by strains from Ethiopia a dose > 3.5 mg/kg is preferable.

A snake bite by the Burrowing Asp, Atractaspis engaddensis

During routine milking of a group of Burrowing Asps Atractaspis engaddensis, one of the authors was bitten in the index finger by one fang, as is characteristic of bites by snakes of the genus. Local effects, oedema, erythema and numbness appeared within minutes, followed by systemic effects, including general weakness, sweating, pallor, fluctuations in the level of consciousness, vomiting and watery non-bloody diarrhoea. Gross oedema of the hand developed and extended up to the forearm. Two hours after admission to the hospital, blood pressure rose to 180/110, the ECG showed normal sinus rhythm and no signs of atrioventricular conduction block. An ECG obtained 24 h after the bite showed new T-wave inversions in leads V5 + 6, which gradually returned to baseline within several days. The local effects healed during the following weeks, but some discoloration and tenderness remained even 10 months after the bite. A maximal exercise (SPECT) study carried out five months after the bite was normal and a multigated radionuclear ventriculogram (MUGA) showed normal left-ventricular function. It may be assumed that the rise in blood pressure observed in this case reflects a systemic vasoconstrictive effect of the sarafotoxins, while the ST changes may have been caused by the direct effect of the toxins on the heart or indirectly by vasoconstriction of the coronary arteries. However, ischaemia secondary to a rise in blood pressure or to excitement could also explain the observed ECG-changes.

Randomised blind controlled trial of a high fibre, low fat and low sodium dietary regimen in mild essential hypertension

Thirty-four patients with essential hypertension were allocated, in a controlled trial, to a treatment diet of high fibre, low fat and low sodium composition, or to a control diet by the hospital dietitian. Clinical observations were made by a separate 'blinded' nursing sister. After three months treatment, the modified diet-treated group showed a significant reduction in mean systolic (169.4 +/- 23.4 to 150.6 +/- 16.1 mmHg) and diastolic blood pressure (101.5 +/- 7.3 to 89.4 +/- 6.8 mmHg), accompanied by significant reductions in urinary sodium excretion (140.4 +/- 34.6 to 93.7 +/- 44 mmol/day) and weight (73.1 +/- 10 to 71.2 +/- 8.4 kg). The changes in control were; systolic 171.2 +/- 14.1 to 162.1 +/- 19.5 mmHg and diastolic pressure 97.2 +/- 10.8 to 91.7 +/- 9.7 mmHg. The mean differences in reductions between treated and control were 8.8 mmHg Systolic (95% confidence intervals: -2.6 to 21.2 mmHg) and 7.0 mmHg diastolic blood pressure (95% confidence intervals: 0.4 to 14.4 mmHg). The number of patients with normal blood pressure in the diet treated group at three months was double that in the control (eleven versus five). No relationships were shown between blood pressure changes and those of weight or urinary sodium excretion during the trial. The findings in this study are broadly in agreement with similar ones in essential hypertension and suggest that this form of dietary regimen has a clinically worthwhile hypotensive effect and this should be readily achievable in routine clinical practice.