Comparative clinical pharmacology of short-acting mu opioids in drug abusers

The clinical pharmacology of fentanyl and alfentanil was examined in opioid-experienced volunteers with agonist and antagonist sensitivity measures. Two studies used within-subject, placebo-controlled, crossover designs. In study 1, fentanyl (0.125, 0.25 mg/70 kg i.v.) was followed at 0, 20, 60 and 180 min by naloxone (10 mg/70 kg i.m.). Agonist effects during 180-min and 0-min (control; simultaneous fentanyl-naloxone i.v. infusion) challenge sessions were compared. Fentanyl rapidly constricted pupils, depressed respiration and produced subjective "high" and opiate symptoms lasting 60 to 120 min, depending on the measure. Naloxone precipitated withdrawal symptoms of comparable intensity at each challenge point. In study 2, fentanyl (0.125, 0.25 mg/70 kg i.v.), alfentanil (1, 2 mg/70 kg i.v.) and saline were followed at 1 and 6 hr by naloxone (10 mg/70 kg i.m.). Agonist effects were examined during 6-hr challenge sessions. The two drugs produced a comparable range of effects with similar peak magnitude for 0.125 mg/70 kg fentanyl and 1 mg/70 kg alfentanil and for 0.25 mg/70 kg fentanyl and 2 mg/70 kg alfentanil. Alfentanil's duration of action was brief ( < 60 min). Withdrawal was precipitated at 6 hr only after 0.25 mg/70 kg fentanyl. These findings support typical mu opioid characteristics (pleasurable subjective effects, physical dependence) for both drugs, differential duration of action (fentanyl > alfentanil) and peak effects consistent with a 1:8 (fentanyl/alfentanil) potency ratio.     

Clinical pharmacology and therapeutic drug monitoring in neonates and children

From a pharmacotherapy perspective, the process of development and growth represents an unstable and dynamic condition. Age-related changes in drug absorption, distribution, and metabolism among neonates, infants, and prepubescent children create a unique situation that may increase drug toxicity of some agents and protect from toxicity of other agents. Understanding the age-related changes in drug disposition that are relevant for therapeutic response and toxicity is essential for optimizing pharmacotherapy at different stages of childhood.     

Newer anticonvulsant drugs: role of pharmacology, drug interactions and adverse reactions in drug choice

In the last few years a number of new anticonvulsants have been introduced into clinical practice mainly as add-on therapy in patients who do not become seizure-free while receiving established anticonvulsants. Up to now, no single drug has been shown to be more effective at controlling seizures of a particular type than another, so other factors such as mechanism of action, pharmacokinetics, dosage regimens or the spectrum of adverse drug reactions and interactions are used when making a choice between one agent and another. The mechanism of action of tiagabine and vigabatrin is very specific; both agents increase gamma-aminobutyric acid (GABA) levels through inhibition of reuptake and catabolism respectively. However, the mechanism of action of gabapentin is unknown and those of felbamate, lamotrigine and topiramate are not sufficiently clarified as yet, and may be multiple. Great advances have been made in improving the pharmacokinetic characteristics of these newer anticonvulsants. Gabapentin and vigabatrin exhibit relatively ideal pharmacokinetic properties as they are not bound to proteins, are excreted mostly unchanged in the urine and show linear pharmacokinetics. Lamotrigine possesses a highly variable elimination half-life depending on the co-medication. Tiagabine is highly protein bound and zonisamide shows nonlinear pharmacokinetics; both these drugs are extensively metabolised. Problematic drug interactions between newer anticonvulsants and other drugs in general occur rarely when these agents are given concomitantly. However, in common with most new drugs, there are very few data on the use of the newer anticonvulsants in women of childbearing age. Studies done so far on interactions with oral contraceptives used low anticonvulsant dosages for a very short time. The newer anticonvulsants elicit adverse reactions that, while not being unique, are particularly associated with that drug. For example, felbamate may cause aplastic anaemia and fulminant liver failure, lamotrigine is prone to cause skin rash, and oxcarbazepine may cause symptomatic hyponatraemia. Topiramate and zonisamide cause kidney stones, and vigabatrin may induce psychiatric syndromes. Although highly diverse in structure and activity, these newer drugs offer new possibilities for treating refractory epilepsy. However, since no single factor can dictate the choice of drug nor predict the success of treatment, prescribing of these rather expensive drugs has to depend upon careful consideration of the aims of treatment, the characteristics of the drug and the needs of the individual patient.     

The role of stereochemistry and chiral pharmacology in psychotropic drug development.

The drug development process often involves the investigation of novel chemical compounds, some of which demonstrate alternative mechanisms of action that are distinct from the presently available agents. Another line of development focuses on exploring how established therapeutic agents can be enhanced or improved to produce a more robust therapeutic effect, a more rapid onset of action, or a more desirable side-effect profile. One strategy is based on advances in synthetic and analytical chemistry that have provided the tools to better characterize the stereochemical molecular arrangements of established drugs. Medicinal chemists and psychopharmacologsts are using these techniques to "purify" currently available drugs by isolating their constituent stereochemical forms and determining whether one of these forms may be predominantly responsible for favorable clinical effects. In this article, the authors review basic principles underlying this technology and discuss several psychotropic drugs that have been developed and recently brought to market using this approach. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparative pharmacology of site directed antithrombin agents. Implication in drug development

Beside the direct inhibition of thrombin and its regulatory functions, many of the newer antithrombin agents produce several additional effects, unrelated to their anticoagulant actions. Synthetic peptide inhibitors are capable of producing fibrinolytic compromise by virtue of their actions on fibrinolytic enzymes such as t-PA, plasmin, urokinase and protein Ca. In addition, the low molecular weight arginine-containing peptides are also known to produce hemodynamic and hemostatic deficits. The designs of the ongoing clinical trials are largely empirical because of the non-availability of valid pharmacologic and toxicologic data on thrombin inhibitors. In contrast to heparin, none of the thrombin inhibitors produce endogenous release of tissue factor pathway inhibitor (TFPI) in the experimental and clinical settings. These observations suggest that beside the direct inhibition of thrombin, these agents also produce multiple additional effects that can significantly contribute to their pharmacologic and toxicologic profile.     

Solute distribution during steady-state cellular growth

A theoretical model is developed to compute solute distribution in the liquid region and interface position in unidirectional solidification of cylindrical cells using Galerkin's method.^{[13, 14, 15]} The model is based on satisfaction of mass conservation and the Gibbs-Thomson shift of the melting point at the interface. Cell shapes and solute composition profiles measured on directionally solidified Sn-0.9 wt pct Pb are in good agreement with the predictions of this analysis. The model confirms that the cellular mode of solidification in an alloy is feasible or preferred only over a limited range of growth conditions. It appears that with decreasing temperature gradient, regular cylindrical cell growth may not commence immediately after the breakdown of planar front. P.S. BASAK, formerly Research-Scholar, Department of Metallurgical Engineering, Indian Institute of Technology-Kharagpur     

Follicular tissues reduce drug effects on ion channels in oocytes of Xenopus laevis

The influence of follicular tissues on drug effects on ion channels in Xenopus oocytes was tested by investigating the pharmacological properties of a cloned potassium channel in oocytes with and without follicular tissues. The data show that the efficacy of blocking agents (ranging from metal ions to peptides) is drastically reduced by the follicular tissues (reductions by as much as 90% and increases of the IC50 values up to 30-fold). Furthermore, the time course of the blocking effect was slowed down by the tissues (increases of the t50 values up to 40-fold). The described impairment could be mitigated, but not abolished by partial removal of the follicular tissues (so-called defolliculation, leaving only the vitelline envelope and part of the follicle cells on the oocyte surface). The results indicate that the follicular tissues can induce significant errors in pharmacological measurements on membrane proteins in Xenopus oocytes.     

Effects of cellular interactions on calcium dynamics in prolactin-secreting cells

Signals derived from other pituitary cells can have a dramatic effect on PRL gene expression and secretion by mammotropes. However, the intracellular mechanisms by which these effects are manifested on the target cell remain unexplored. Inasmuch as calcium is a key modulator of both gene expression and hormone export in mammotropes, we evaluated the effects of cell to cell contact vs. specific cellular interactions on calcium dynamics within these cells. This was accomplished by digital-imaging fluorescence microscopy of fura-2 in pituitary cells that were isolated in culture (singles) or adjoining one other cell (doublets). After calcium imaging, we then subjected cells to immunocytochemistry for PRL. Doublets were further categorized into mammotropes attached to another mammotrope (M-M) or to a nonmammotrope (M-nonM). We then calculated and compared Mean [Ca2+]i values as well as Oscillation Indices (which reflect the oscillatory behavior of cells) in singles and doublets and found that they were not different (P > 0.05). However, the phenotype of the adjoining cell had a profound influence on both of these calcium parameters, such that the presence of one mammotrope could consistently decrease (P < 0.05) the Mean [Ca2+]i value (39.17 +/- 3.83 vs. 56.24 +/- 5.56 in M-nonM) and Oscillation Index (10.19 +/- 1.76 vs. 21.21 +/- 3.73 in M-nonM) of its neighboring counterpart. A more detailed analysis of oscillatory patterns in these cells revealed that nonoscillators were more abundant in M-M (23%) than in M-nonM (12%) doublets. Taken together, our results indicate that PRL-secreting cells convey a signal that dampens the oscillatory behavior of neighboring mammotropes. Thus, it appears that it is the phenotype rather than the physical presence of a neighbor that controls intercellular regulation of calcium dynamics among mammotropes.     

Multidrug resistance-reversing agents increase vinblastine distribution in normal tissues expressing the P-glycoprotein but do not enhance drug penetration in brain and testis

The aim of this study was to assess whether P-glycoprotein (Pgp) inhibitors altered the blood-brain barrier and enhanced vinblastine (VBL) distribution in brain, testis and other Pgp-expressing tissues. Trifluoperazine, cyclosporin A, amiodarone, quinidine, the nifedipine analog Bay K8644 and verapamil were selected among Pgp inhibitors and were administered intraperitoneally 1 hr before an intravenous dose of 10 mg/kg VBL. Trifluoperazine and cyclosporin A were also administered intraperitoneally for 7 days before VBL. VBL and its metabolite O4-deacetylvinblastine were measured in tissues by high-performance liquid chromatography assay. None of the reversing agents (RA) appreciably raised VBL concentrations in brain and testis, whereas all except quinidine significantly enhanced VBL distribution in liver and kidney; the most effective were trifluoroperazine and cyclosporin A. In mice treated with RA and VBL combined, O4-deacetylvinblastine levels in liver and kidney reached either the same or higher levels than in mice treated with VBL alone, indicating that the increase in VBL levels is not due to inhibition of its metabolism. The main conclusions are that (1) inhibitors of Pgp, even at high doses, do not increase the permeability of the blood-brain barrier in mice, suggesting caution in the clinical use of RA combined with antitumor agents for brain tumors; and (2) several RA achieve high enough concentrations to enhance the distribution of VBL in other normal tissues expressing Pgp, thus potentially increasing VBL toxicity.     

Delivery of therapeutic drug monitoring services: survey of Australasian clinical pharmacology laboratories

Therapeutic drug monitoring (TDM) services, like many diagnostic services in public hospitals, have been under scrutiny over recent years as funding has decreased. The Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists (ASCEPT) sought to review clinical pharmacology departments to consider how the changes that have been implemented have affected the delivery of TDM in recent years. A questionnaire was sent to such departments and all those known to be delivering TDM services responded. The survey demonstrated that of the 11 departments contributing TDM assays, 10 had lost tests and staffing to general biochemistry departments; eight departments had been delivering research and development in TDM. The TDM tests retained in clinical pharmacology were typically the more complex chromatographic or labor-intensive toxicology tests or the more expensive immunoassays. If this direction in Australasia is typical of the situation internationally, it should be a matter of great concern to all those with a particular interest in TDM. Is the future of TDM to be one in which only rapid immunoassays will be provided, and by a staff not fully able to provide pharmacokinetic support and interpretation of such tests (i.e., to become simply number-generating services) despite all the pharmacoeconomic data that is increasingly available?     

Tissue distribution of ketamine in a mixed drug fatality

While reports of ketamine abuse are increasing, reports of ketamine deaths and tissue concentrations associated with fatalities are rare. We report here a case of a mixed drug fatality involving ketamine and ethanol. Ketamine analysis was carried out by gas chromatography with a nitrogen-phosphorus detector (NPD). We found the following tissue concentrations: blood 1.8 mg/L; urine 2.0 mg/L; brain 4.3 mg/kg; spleen 6.1 mg/kg; liver 4.9 mg/kg, and kidney 3.6 mg/kg. The blood ethanol concentration was 170 mg/dL. Because an empty nalbuphine ampule was found in the possession of the deceased, the blood was assayed for this opioid compound using a gas chromatography/mass spectrometry (GC/MS) method. None was detected at a limit of detection of 0.02 mg/L.