Efavirenz (EFV) is associated with hyperlipidemia when used in combination with other antiretroviral drugs. EFV is a mixed inducer/inhibitor of cytochrome P450 (CYP) 3A4 isozyme and may interact with hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors that are primarily metabolized via CYP3A4. To assess the drug-drug interaction of EFV used in combination with simvastatin (SIM), atorvastatin (ATR), or pravastatin (PRA), an open-label trial was conducted in 52 healthy adult HIV-seronegative subjects across AIDS Clinical Trials Group sites in the United States. Subjects received 40 mg of SIM, 10 mg of ATR, or 40 mg of PRA daily on days 0 through 3 and days 15 through 18. EFV was administered daily at a dose of 600 mg on days 4 through 18. SIM, ATR, and PRA concentrations were determined before and after EFV, and EFV concentrations were determined before and after statins. EFV reduced SIM acid exposure (area under the curve at 0 to 24 hours [AUC0-24 h]) by 58% (Wilcoxon signed rank test, P=0.003) and active HMG-CoA reductase inhibitory activity by 60% (P<0.001). EFV reduced ATR exposure by 43% (P<0.001) and the total active ATR exposure by 34% (P=0.005). EFV administration resulted in a 40% decrease in PRA exposure (P=0.005). SIM, ATR, and PRA had no effect on non-steady-state EFV concentrations. In conclusion, EFV, when administered with SIM, ATR, or PRA, can result in significant induction of statin metabolism. The reduced inhibition of HMG-CoA reductase activity during coadministration of EFV may result in diminished antilipid efficacy at usual doses of SIM, ATR, and PRA.

A sensitive and reliable procedure for the simultaneous determination of simvastatin (SV) and its active beta-hydroxy acid metabolite (SVA) in human plasma was developed and validated. The analytes were extracted simultaneously from 0.5 ml aliquots of human plasma samples by methyl tert-butyl ether (MTBE) via Chem Elut cartridge extraction [also called liquid-solid extraction (LSE) or liquid-liquid cartridge extraction (LLCE)], separated through a Kromasil C(18) column (50 x 2 mm i.d. 5 microm) and detected by tandem mass spectrometry with a turbo ionspray interface. Stable isotope-labeled SV and SVA, (13)CD(3)-SV and (13)CD(3)-SVA, were used as internal standards. SV and SVA were detected in positive and negative ion modes, respectively, via within-run polarity switching. The use of Chem Elut cartridges not only provided a simple and efficient means of plasma sample extraction but also successfully reduced the interconversion between SV and SVA to an undetectable (for lactonization of SVA) or negligible (<0.07%, for hydrolysis of SV) level. The method showed excellent reproducibility, with intra- and inter-assay precisions <4.5% (RSD), and intra- and inter-assay accuracy between 94% and 107% of nominal values, for both analytes. The extraction recoveries were 78% and 87% on average for SV and SVA, respectively. The analyte was found to be stable in plasma through three freeze (-70 degrees C)-thaw (4 degrees C) cycles and for at least 3 h under bench-top storage condition in an ice-bath (4 degrees C), and also in the reconstitution solution at 4 degrees C for at least 24 h. The method has a lower limit of quantitation (LOQ) of 50 pg ml(-1) with a linear calibration range of 0.05-50 ng ml(-1) for both analytes, and has proved to be very reliable for the analysis of clinical samples.

The effects of liquid chromatography mobile phase buffer contents on the ionization and fragmentation of drug molecules in liquid chromatographic/ionspray tandem mass spectrometric (LC/MS/MS) determination were evaluated for simvastatin (SV) and its hydroxy acid (SVA). The objective was to improve further the sensitivity for SV by overcoming the unfavorable condition caused by the formation of multiple major adduct ions and multiple major fragment ions when using ammonium as LC mobile phase buffer. Mobile phases (70:30 acetonitrile-buffer, 2 mM, pH 4.5) with buffers made from ammonium, hydrazine or alkyl (methyl, ethyl, dimethyl or trimethyl)-substituted ammonium acetate were evaluated. Q1 scan and product ion scan spectra were obtained for SV in each of the mobile phases under optimized conditions. The results showed that, with the alkylammonium buffers, the alkylammonium-adducted SV was observed as the only major molecular ion, while the formation of other adduct ions ([M + H](+), [M + Na](+) and [M + K](+)) was successfully suppressed. On the other hand, product ion spectra with a single major fragment ion were not observed for any of the alkylammonium-adducted SVs. The affinity of the alkylammoniums to SV and the basicity of the alkylamines are believed to be factors influencing the formation and abundance of molecular and fragment ions, respectively. Methylammonium acetate provided the most favorable condition among all the buffers evaluated and improved the sensitivity several-fold for SV in LC/MS/MS quantitation compared with that obtained using ammonium acetate buffer. Better precision for SV in both Q1 and SRM scans was observed when using methylammonium buffer compared with those using ammonium buffer. The mobile phase buffer contents did not seem to affect the ionization, fragmentation and chromatography of SVA. The results of this evaluation can be applied to similar situations with other organic molecules in ionspray LC/MS/MS determination.

Herein, we describe two cases and review 14 cases of equestrian chilblain or 'equestrian cold panniculitis' in the literature. The first, a 23-year-old healthy female horse trainer, presented with burning nodular swelling on her lateral thighs. The second was a 34-year-old healthy woman with recurrent nodular eruption on the lateral thighs after horseback riding in the winter. Physical examination of both patients revealed erythematous to violaceous nodules with eczema craquelé-like changes. Laboratory workup for systemic and autoimmune connective tissue disease was negative. Punch biopsies from both patients showed a superficial and deep perivascular and periadnexal lymphocytic infiltrate with focal extension into the subcutaneous fat. Parakeratosis, subtle spongiosis and increased pandermal interstitial mucin were also present. Previously reported cases generally showed a similar clinical course and similar histopathologic findings. In contrast, our cases revealed increased pandermal interstitial mucin, resembling tumid lupus erythematosus. We aim to better characterize the histopathologic findings of equestrian chilblain and discuss its relationship to other cold-induced skin injuries and autoimmune connective tissue disease, namely lupus erythematosus.

AIMSTo characterize pharmacokinetic parameters of MK-0916 and its safety and tolerability in lean, healthy male subjects following single and multiple oral doses. To assess (by stable-isotope labelling) the in vivo inhibition of cortisone-to-cortisol conversion following oral MK-0916. METHODSData are presented from two randomized, controlled, double-blind, rising-dose phase I studies. In the first study, subjects received single oral doses of 0.4-100 mg MK-0916 (n = 16). In the second study, subjects received 0.2-225 mg MK-0916 followed by daily doses of 0.2-100 mg for 13 days beginning on day 2 or day 15 (n = 80). Plasma and urine drug concentrations were measured for pharmacokinetic analysis. For pharmacodynamic analysis, concentrations of plasma [13 C4]cortisol were measured by high-pressure liquid chromatography and tandem mass spectrometry following a single oral dose of 5 mg [ 13 C4]cortisone. RESULTSDoses Ն3 mg were rapidly absorbed (time at which maximal concentration was achieved in plasma, 1.1-1.8 h). Exposure (measured as the area under the concentration-time curve from 0 to 168 h) increased approximately in proportion to dose. Values for the maximal plasma concentration and the plasma concentration at 24 h increased in excess of dose proportionality at doses <6 mg and roughly in proportion to dose at doses >6 mg. In subjects dosed with 6 mg MK-0916 once daily for 14 days, the mean trough plasma concentration was 240 nM and in vivo cortisone-to-cortisol conversion was inhibited by 84%. The relationship between plasma MK-0916 and hepatic 11b-hydroxysteroid dehydrogenase type 1 inhibition was well represented by a simple Emax model with an IC50 of 70.4 nM. Exposure to MK-0916 was generally well tolerated. CONCLUSIONSThese findings indicate that 11b-hydroxysteroid dehydrogenase type 1 is effectively inhibited in human subjects by doses of MK-0916 that are well tolerated. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• The intracellular enzyme 11b-hydroxysteroid dehydrogenase type 1 converts the inactive glucocorticoid cortisone into the active hormone cortisol in many tissues, including the liver and adipocytes. It is thought that increased conversion of cortisone to cortisol contributes to pathophysiology associated with the metabolic syndrome.• MK-0916 is an inhibitor of 11b-hydroxysteroid dehydrogenase type 1 that has been evaluated clinically as a potential therapy for type 2 diabetes, obesity or hypertension. WHAT THIS STUDY ADDS• In lean, healthy male subjects, MK-0916 was well tolerated when given in oral doses that were sufficient to provide profound inhibition of hepatic conversion of cortisone to cortisol.• Multiple-dose administration of 6 mg day -1 MK-0916 provided mean plasma concentrations >200 nM at all times, a plasma drug concentration that inhibited systemic 11b-hydroxysteroid dehydrogenase type 1 by 84%.