Interaction of triazolam and ketoconazole in P-glycoprotein-deficient mice.

The role of P-glycoprotein (P-gp) on the distribution of the benzodiazepine triazolam (TRZ) and the azole antifungal agent ketoconazole (KET), and on the TRZ-KET interaction, was studied using mdr1a(-) or mdr1a/b(-/-) mice (P-gp-deficient mice) and matched controls. TRZ and KET also were studied in Caco-2 cells in Transwell culture. After single i.p. injections of TRZ or KET in separate groups of control mice, brain concentrations of TRZ exceeded those in serum [brain/serum area under the concentration curve (AUC) ratio, 5.0], whereas brain/serum AUC ratios for KET were approximately 0.5. On the basis of single time points, brain concentrations of TRZ, or brain/serum ratios, were similar in P-gp-deficient animals compared with controls, whereas P-gp-deficient animals had significantly higher KET brain concentrations and brain/serum ratios. Coadministration of KET with TRZ increased TRZ concentrations in serum, liver, and brain, both in controls and in P-gp-deficient animals, probably attributable to impairment by KET of CYP3A-mediated clearance of TRZ. However, KET did not increase brain/serum ratios of TRZ in either group. In Caco-2 cells, basal-to-apical flux of TRZ was higher than apical-to-basal flux. However, verapamil (100 microM) did not alter flux in either direction. KET inhibited basal-to-apical transport of rho-damine-123, with a 50% inhibitory concentration of 2.7 microM. Thus, TRZ does not appear to undergo measurable blood-brain barrier efflux transport by P-gp in this animal model. KET impairs clearance of TRZ but does not increase tissue uptake. However, KET itself may be a substrate for efflux transport at the blood-brain barrier.     

Pharmacokinetics of acute and sub-chronic aripiprazole in P-glycoprotein deficient mice

Background

P-glycoprotein (P-gp), an efflux transporter localized in the blood-brain barrier, limits the access of multiple xenobiotics to the central nervous system (CNS). For the new antipsychotic aripiprazole and its active metabolite dehydroaripiprazole differences in disposition in blood and brain were investigated after acute and sub-chronic administration in a P-gp knockout mouse model.

Methods

Serum and brain concentrations of both drugs were measured at several time points 1-24 h after i.p. injection of 10 mg/kg aripiprazole and after 11 days of sub-chronic administration in several tissues. Moreover, the expression of P-gp was determined by Western blot analysis after sub-chronic administration of the drug.

Results

In both wild type and abcb1ab (−/−) mice concentration of aripiprazole in brain were up to 9 fold higher than in serum. For dehydroaripiprazole the mean brain to serum ratios were below two. Brain to serum concentrations of both substances were significantly higher after acute and sub-chronic administration in connection to the expression of P-gp indicated by higher levels in abcb1ab (−/−) mice especially for dehydroaripiprazole.Sub-chronic aripiprazole treatment in WT animals had no effect on P-gp expression in the blood-brain barrier.

Conclusions

Aripiprazole and, even more pronounced its active metabolite dehydroaripiprazole could be identified as substrates of P-gp. The efflux transporter P-gp must therefore be considered as a relevant factor that contributes to wanted or unwanted clinical effects in patients treated with aripiprazole.     

P-glycoprotein ATPase activating effect of opioid analgesics and their P-glycoprotein-dependent antinociception in mice

It is well known that opioid analgesics exert central antinociceptive actions. However, in vivo and in vitro studies have shown that some opioid analgesics given systemically have limited access to the central nervous system because of the blood-brain barrier (BBB). P-glycoprotein (P-gp), an ATP-dependent drug efflux transporter, is one component of the BBB. In this report, we assessed the antinociceptive effect of morphine, fentanyl, and meperidine in P-gp deficient (mdr1a KO) mice, and compared these effects with those in wild type (WT) mice. The antinociceptive effects of morphine and fentanyl in mdr1a KO mice were significantly greater than those in WT mice. However, there was no clear difference in the antinociceptive effects of meperidine in the two genotypes. In addition, we determined the effect of opioid analgesics on P-gp ATPase activity, which is requisite for drug transport, using mouse brain capillary endothelial cells. In our observations, morphine and fentanyl, but not meperidine, significantly increased P-gp ATPase activity, and the drugs' concentration-response curves were bell-shaped, reaching a peak at a concentration of 1 muM. These results suggest that P-gp ATPase activity may be, at least in part, involved in the antinociceptive potencies of those opioid analgesics that are substrates for P-gp.     

Pharmacokinetics and pharmacodynamics of amitriptyline in depression.

1. The therapeutic effect and pharmacokinetics of amitriptyline were assessed in thirty-five patients suffering from primary depressive illness during inpatient treatment. 2. Contrary to our previous study, no significant correlation was obtained between the plasma concentrations of amitriptyline, nortriptyline or total tricyclics with Hamilton rating score at 6 weeks or percentage improvement after 6 weeks treatment. 3. There was also no correlation with the plasma concentrations of tricyclics with the corrected subjective side-effects score. 4. A linear correlation (rs = 0.80; p less than 0.001) was observed between the plasma concentration of nortriptyline and decreased tyramine sensitivity, an index of noradrenaline reuptake blocking effect. 5. The corrected side-effect score during the trial correlated (r = 0.64; p less than 0.001) with Hamilton rating score at week 6, i.e. the patients who complained of more side-effects had less clinical benefit during amitriptyline therapy.     

Pharmacokinetics and pharmacodynamics in toxicology

1. Pharmacokinetics aids interpretation of the dose-response relationship in individual toxicology studies. 2. When used to compare across studies, even in a single species other factors, including variation in pharmacodynamic response, must be taken into account. Variation in pharmacodynamic response becomes more profound when one compares across species. 3. Examples do occur where plasma concentration-response relationships are constant across species, particularly when corrected for unbound drug. These examples should not be taken as support, however, of a general universal principle. 4. Owing to multiple factors such as species differences in receptors, enzymes and ion channels,dose or plasma concentration-response relationships can vary enormously across species. In the light of this, the results of toxicology studies should be viewed as qualitative rather than quantitative. Once sufficient clinical experience is gained the human database is the overriding measure of drug safety.     

The disposition of saquinavir in normal and P-glycoprotein deficient mice, rats, and in cultured cells.

Protease inhibitors are very effective in treating patients infected with HIV. However, many drugs in this class penetrate poorly into the central nervous system (CNS) and may permit this site to be a sanctuary from which resistant virus can emerge. Previous studies have shown that the protease inhibitor saquinavir (SQV) interacts with the multidrug transport system, P-glycoprotein (P-gp), expressed in epithelial cells in the gut mucosa and at the blood-brain barrier, and thus might affect both the oral absorption and the penetration of SQV into the CNS. To determine whether SQV is a substrate for P-gp, its uptake was determined in cancer cells, which do (Dx5) and do not (MES-SA) express P-gp. The distribution of SQV between brain tissue and plasma was also investigated in rats and in normal and P-gp-deficient mdr1a(-/-) mice. The distribution ratio of SQV in plasma:brain:cerebrospinal fluid was approximately 100:10:0.2 in rats. The accumulation of SQV was enhanced in MES-SA cells (P-gp-negative) versus Dx5 cells (P-gp-positive). Bolus i.v. injection of [(14)C]SQV (2 and 5 mg/kg) into mdr1a(-/-) and normal mice (n = 3 or 4) resulted in 3-fold higher radioactivity in brains from mdr1a(-/-) mice. Similarly, oral administration of [(14)C]SQV (500 mg/kg) resulted in a 5-fold increase in systemic exposure and a 10-fold increase in brain levels in mdr1a(-/-) mice. These data demonstrate that saquinavir is a substrate for P-gp and that this transport system may play a role in limiting oral absorption and CNS exposure to this protease inhibitor.     

Role of P-glycoprotein in drug disposition

P-glycoprotein (Pgp), which is coded by human MDR1 (multidrug resistance) gene, is an energy-dependent efflux pump that exports its substrates out of the cell. Human Pgp is present not only in tumor cells but also in normal tissues including the kidney, liver, small and large intestine, brain, testis, and adrenal gland, and the pregnant uterus. This tissue distribution indicates that Pgp plays a significant role in excreting xenobiotics and metabolites into urine and bile and into the intestinal lumen, and in preventing their accumulation in the brain. The roles of Pgp in drug disposition include a urinary excretion mechanism in the kidney, a biliary excretion mechanism in the liver, an absorption barrier and determinant of oral bioavailability, and the blood-brain barrier that limits the accumulation of drugs in the brain. The inhibition of the transporting function of Pgp can cause clinically significant drug interactions and can also increase the penetration of drugs into the brain and the accumulation of drugs in the brain. Digoxin is a typical substrate for Pgp, which regulates the renal tubular secretion and brain distribution of digoxin. At present, potent Pgp inhibitors are being investigated in clinical trials aimed at overcoming the intrinsic or acquired multidrug resistance of human cancers. The clinical application of these Pgp inhibitors should take into consideration the physiologic function of pgp.     

Pharmacokinetics and pharmacodynamics of nifedipine in pregnant sheep.

The calcium channel blocker nifedipine was administered to pregnant sheep by a four-level iv infusion at rates of 1-10 micrograms/kg/min. The maternal and fetal plasma nifedipine concentrations were measured along with maternal and fetal heart rate, blood pressure, pH, and blood gases. The two-compartment maternal pharmacokinetics demonstrated a rapid phase t1/2 of 11 min and a slower phase t 1/2 of 137 min. The drug reached the fetus via a first-order process with a t 1/2 of 22 min. At the highest dose, the maternal systemic vascular resistance dropped 49% in association with a 59% increase in heart rate. The uterine blood flow decreased 29%. Tachycardia was the only significant effect in the fetus. In a subgroup of sheep, chronic dosing with phenobarbital increased maternal nifedipine clearance 3-fold.     

Role of brain dynorphin in nitrous oxide antinociception in mice

Earlier studies indicate that nitrous oxide antinociception is mediated by opioid receptors, and we have hypothesized that nitrous oxide stimulates a neuronal release of an endogenous opioid peptide (EOP) that stimulates opioid receptors. To further test this hypothesis, male NIH Swiss mice were pretreated intracerebroventricularly with rabbit antisera to opioid peptides or with various inhibitors of peptidases involved in the degradation of EOPs. Mice were subsequently exposed to three different concentrations of nitrous oxide in oxygen, and their antinociceptive responsiveness was measured using the acetic acid abdominal constriction test. Nitrous oxide antinociception was significantly attenuated by 24-h pretreatment with antisera to various fragments of dynorphin (DYN) but not by antisera against methionine-enkephalin (ME) or beta-endorphin (beta-EP). In other experiments, nitrous oxide antinociception was significantly enhanced by 30-min pretreatment with phosphoramidon, an inhibitor of endopeptidase 24.11, which has been implicated in DYN degradation, but not bestatin or captopril, which inhibit aminopeptidase and angiotensin-converting enzyme, respectively. The latter enzymes have been implicated in degradation of certain EOPs albeit not DYN. These findings support the hypothesis that nitrous oxide antinociception in the mouse abdominal constriction test is mediated by endogenous DYN acting in the central nervous system.     

Pharmacokinetics and pharmacodynamics of the nitroimidazole antimicrobials.

Metronidazole, the prototype nitroimidazole antimicrobial, was originally introduced to treat Trichomonas vaginalis, but is now used for the treatment of anaerobic and protozoal infections. The nitroimidazoles are bactericidal through toxic metabolites which cause DNA strand breakage. Resistance, both clinical and microbiological, has been described only rarely. Metronidazole given orally is absorbed almost completely, with bioavailability > 90% for tablets; absorption is unaffected by infection. Rectal and intravaginal absorption are 67 to 82%, and 20 to 56%, of the dose, respectively. Metronidazole is distributed widely and has low protein binding (< 20%). The volume of distribution at steady state in adults is 0.51 to 1.1 L/kg. Metronidazole reaches 60 to 100% of plasma concentrations in most tissues studied, including the central nervous system, but does not reach high concentrations in placental tissue. Metronidazole is extensively metabolised by the liver to 5 metabolites. The hydroxy metabolite has biological activity of 30 to 65% and a longer elimination half-life than the parent compound. The majority of metronidazole and its metabolites are excreted in urine and faeces, with less than 12% excreted unchanged in urine. The pharmacokinetics of metronidazole are unaffected by acute or chronic renal failure, haemodialysis, continuous ambulatory peritoneal dialysis, age, pregnancy or enteric disease. Renal dysfunction reduces the elimination of metronidazole metabolites; however, no toxicity has been documented and dosage alterations are unnecessary. Liver disease leads to a decreased clearance of metronidazole and dosage reduction is recommended. Recent pharmacodynamic studies of metronidazole have demonstrated activity for 12 to 24 hours after administration of metronidazole 1 g. The post-antibiotic effect of metronidazole extends beyond 3 hours after the concentration falls below the minimum inhibitory concentration (MIC). The concentration-dependent bactericidal activity, prolonged half-life and sustained activity in plasma support the clinical evaluation of higher doses of metronidazole given less frequently. Metronidazole-containing regimens for Helicobacter pylori in combination with proton pump inhibitors demonstrate higher success rates than antimicrobial regimens alone. The pharmacokinetics of metronidazole in gastric fluid appear contradictory to these results, since omeprazole reduces peak drug concentration and area under the concentration-time curve for metronidazole and its hydroxy metabolite; however, concentrations remain above the MIC. Other members of this class include tinidazole, ornidazole and secnidazole. They are also well absorbed and distributed after oral administration. Their only distinguishing features are prolonged half-lives compared with metronidazole. The choice of nitroimidazole may be influenced by the longer administration intervals possible with other members of this class; however, metronidazole remains the predominant antimicrobial for anaerobic and protozoal infections.     

Pharmacokinetics and pharmacodynamics of diprophylline

Diprophylline is used in many countries as a bronchodilator. It is an N-substituted theophylline derivative which does not release theophyllinein vitro orin vivo. It therefore has its own pharmacokinetic and pharmacodynamic properties. In a cross-over study in ten healthy volunteers serum concentrations and urinary excretion were studied after administration of diprophylline.Its serum decay after intravenous administration shows two-compartment kinetics with a rapid distribution. The-phase lasted on average 0.75 h and was 0.427±0.118 h^–1, corresponding with a-phase half-life of 1.7±0.4 h. The mean volume of distribution was 0.70±0.20 l/kg, total body clearance 0.29±0.09 l.kg^–1.h^–1. About 84% of the drug is excreted unchanged in the urine. A comparison of the area under the curve suggests that the drug was almost completely absorbed from the gastro-intestinal tract. Its bioavailability is about 90%. Mean renal clearance values are higher than paired creatinine clearance values, which is an indication for active renal transport.Peak levels of diprophylline were 7.4±2.2 mg/l at about 30 min after oral administration. The normal dose advocated is 200–400 mg three times a day. Inin vitro studies and in pharmacological animal studies diprophylline appears to be much less active than theophylline. Consequently estimated effective dosages are irrationally high.In honour of ProfessorHuizinga on the occasion of his retirement.     

Pharmacokinetics and pharmacodynamics of isothiocyanates

Isothiocyanates from Brassica vegetables are of great interest for use in the cure of bacterial infections, as is their potential application in the prevention and treatment of cancer. Although much information is available on their mode of action within the cell, when it comes to the question of whether the necessary pharmacologic concentration has been reached at the target organ, detailed knowledge is still lacking. However, a basic prerequisite for clinical application to humans is knowledge of isothiocyanate pharmacokinetic and dynamic behavior in the human body (e.g., to define intake intervals or to ascertain constant levels of the active compound). In this context, we, therefore, reviewed the available literature on in vitro studies, as well as animal and human intervention trials conducted with isothiocyanate and isothiocyanate-containing food preparations.     

氟卡胺的药代动力学与药效动力学

氟卡胺是抑制心脏传导间期AH,HV,QRS,QT的抗心律不齐新药。犬iv 2,4 mg/kg氟卡胺后呈二室型代谢动力学特点,其t_(1/2)为60～70min。健康人po 200 mg/kg与小鼠sc 10 mg/kg氟卡胺后呈一级吸收一室型,t_(1/2)为60～76 min。 以抑制传导间期为药效指标,犬iv 4 mg/kg氟卡胺后测各传导间期变化,计算药效动力学,公式为:△％=(△_(max)％)c~(-kt)。以血药浓度对数对相应时间传导间期变化(△％)作图呈线性相关,计算公式为:C=ae~b(△％)。     

Pharmacokinetics and pharmacodynamics of azosemide

Azosemide is used in the treatment of oedematous states and hypertension. The exact mechanism of action is not fully understood, but it mainly acts on both the medullary and cortical segments of the thick ascending limb of the loop of Henle. Delayed tolerance was demonstrated in humans by homeostatic mechanisms (principally an increase in aldosterone secretion and perhaps also an increase in the reabsorption of solute in the proximal tubule). After oral administration to healthy humans in the fasting state, the plasma concentration of azosemide reached its peak at 3-4 h with an absorption lag time of approximately 1 h and a terminal half-life of 2-3 h. The estimated extent of absolute oral bioavailability in humans was approximately 20.4%. After oral administration of the same dose of azosemide and furosemide, the diuretic effect was similar between the two drugs, but after intravenous administration, the effect of azosemide was 5.5-8 times greater than that in furosemide. This could be due to the considerable first-pass effect of azosemide. The protein binding to 4% human serum albumin was greater than 95% at azosemide concentrations ranging from 10 to 100 microg/ml using an equilibrium dialysis technique. The poor affinity of human tissues to azosemide was supported by the relatively small value of the apparent post-pseudodistribution volume of distribution (Vdbeta), 0.262 l/kg. Eleven metabolites (including degraded products) of azosemide including M1, glucuronide conjugates of both M1 and azosemide, thiophenemethanol, thiophencarboxylic acid and its glycine conjugate were obtained in rats. Only azosemide and its glucuronide were detected in humans. In humans, total body clearance, renal clearance and terminal half-life of azosemide were 112 ml/min, 41.6 ml/min and 2.03 h, respectively. Azosemide is actively secreted in the renal proximal tubule possibly via nonspecific organic acid secretory pathway in humans. Thus, the amount of azosemide that reaches its site of action could be significantly modified by changes in the capacity of this transport system. This capacity, in turn, could be predictably changed in disease states, resulting in decreased delivery of the diuretic to the transport site, as well as in the presence of other organic acids such as nonsteroidal anti-inflammatory drugs which could compete for active transport of azosemide. The urinary excretion rate of azosemide could be correlated well to its diuretic effects since the receptors are located in the loop of Henle. The diuretic effects of azosemide were dependent on the rate and composition of fluid replacement in rabbits; therefore, this factor should be considered in the evaluation of bioequivalence assessment.     

Pharmacokinetics and pharmacodynamics of cannabinoids

Delta(9)-Tetrahydrocannabinol (THC) is the main source of the pharmacological effects caused by the consumption of cannabis, both the marijuana-like action and the medicinal benefits of the plant. However, its acid metabolite THC-COOH, the non-psychotropic cannabidiol (CBD), several cannabinoid analogues and newly discovered modulators of the endogenous cannabinoid system are also promising candidates for clinical research and therapeutic uses. Cannabinoids exert many effects through activation of G-protein-coupled cannabinoid receptors in the brain and peripheral tissues. Additionally, there is evidence for non-receptor-dependent mechanisms. Natural cannabis products and single cannabinoids are usually inhaled or taken orally; the rectal route, sublingual administration, transdermal delivery, eye drops and aerosols have only been used in a few studies and are of little relevance in practice today. The pharmacokinetics of THC vary as a function of its route of administration. Pulmonary assimilation of inhaled THC causes a maximum plasma concentration within minutes, psychotropic effects start within seconds to a few minutes, reach a maximum after 15-30 minutes, and taper off within 2-3 hours. Following oral ingestion, psychotropic effects set in with a delay of 30-90 minutes, reach their maximum after 2-3 hours and last for about 4-12 hours, depending on dose and specific effect. At doses exceeding the psychotropic threshold, ingestion of cannabis usually causes enhanced well-being and relaxation with an intensification of ordinary sensory experiences. The most important acute adverse effects caused by overdosing are anxiety and panic attacks, and with regard to somatic effects increased heart rate and changes in blood pressure. Regular use of cannabis may lead to dependency and to a mild withdrawal syndrome. The existence and the intensity of possible long-term adverse effects on psyche and cognition, immune system, fertility and pregnancy remain controversial. They are reported to be low in humans and do not preclude legitimate therapeutic use of cannabis-based drugs. Properties of cannabis that might be of therapeutic use include analgesia, muscle relaxation, immunosuppression, sedation, improvement of mood, stimulation of appetite, antiemesis, lowering of intraocular pressure, bronchodilation, neuroprotection and induction of apoptosis in cancer cells.     

Pharmacokinetics and pharmacodynamics of pegfilgrastim

Pegfilgrastim is a sustained-duration form of filgrastim, a recombinant methionyl form of human granulocyte colony-stimulating factor (G-CSF), to which a 20 kDa polyethylene glycol molecule is covalently bound to the N-terminal methionine residue. Similar to filgrastim, pegfilgrastim increases the proliferation and differentiation of neutrophils from committed progenitor cells, induces maturation, and enhances the survival and function of mature neutrophils, resulting in dose-dependent increases in neutrophils. After subcutaneous administration, pegfilgrastim exhibits nonlinear pharmacokinetics and exposure to pegfilgrastim increases in more than a dose-proportional manner, suggesting that the clearance of pegfilgrastim decreases with increased dosing. Filgrastim is primarily eliminated by the kidney and neutrophils/neutrophil precursors; the latter presumably involves binding of the growth factor to the G-CSF receptor on the cell surface, internalization of the growth factor-receptor complexes via endocytosis, and subsequent degradation inside the cells. Pegylation of filgrastim renders renal clearance insignificant, which was demonstrated in bilaterally nephrectomized rats and confirmed in subjects with renal impairment. As a result, the neutrophil-mediated clearance is the predominant elimination pathway for pegfilgrastim. During chemotherapy-induced neutropenia, the clearance of pegfilgrastim is significantly reduced and the concentration of pegfilgrastim is sustained until onset of neutrophil recovery. Pegfilgrastim concentrations are sustained longer in patients with profound neutropenia. Evidence supports the use of a postnadir absolute neutrophil count (ANC) of ≥ 1?×?109/L as a surrogate marker threshold for the clearance of pegfilgrastim to subtherapeutic levels. After repeated administration of pegfilgrastim, the peak concentrations of pegfilgrastim decrease, likely due to increased neutrophil and neutrophil precursor mass. A pharmacokinetic-pharmacodynamic model was developed to describe the pharmacokinetic and ANC profiles of pegfilgrastim; the analysis supported that 100 μg/kg was an adequate weight-based dose of pegfilgrastim and predicted that 6 mg would be an optimal fixed dose of pegfilgrastim to simplify treatment. Data from a pivotal study confirmed that a once-per-chemotherapy-cycle injection of pegfilgrastim at 6 mg was as safe and effective as 11 daily injections of filgrastim at 5 μg/kg in reducing neutropenia and its complications in patients with breast cancer receiving four cycles of doxorubicin/docetaxel chemotherapy. Because of the highly efficient regulation of pegfilgrastim clearance via neutrophils and neutrophil precursors, a single fixed dose of pegfilgrastim can be given once per chemotherapy cycle in conjunction with a variety of myelosuppressive chemotherapy regimens.