Effects of Food on Bioavailability of Analgesics; Resulting Dosage and Administration Recommendations.

OBJECTIVES: To evaluate currently approved analgesics, that is, opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), anticonvulsants, and serotonin and norepinephrine reuptake inhibitors (SNRIs) used as analgesics, for 1) differences in pharmacokinetic parameters under fed vs fasting conditions and 2) factors involved in dosage recommendations in relation to food. DESIGN: Systematic review. RESULTS: Food effect on the rate, extent of absorption, or shape of concentration-time profile can alter the onset of action, duration of action, or tolerability of a medication. Based on 79 analgesic products reviewed, food effect dosage recommendations depend on whether an analgesic will be dosed on a regular interval around-the-clock vs on an as-needed basis, the shape of concentration-time profile, steady-state concentrations, the type of meals used in the pharmacokinetic study, and drug administration with regard to food in clinical trials. Overall, most opioids do not have food restriction and are taken without regard to food, with the exception of OPANA products and XTAMPZA ER. For many NSAIDs, food does not affect absorption characteristics, with the exception of ZORVOLEX and CELEBREX. Although NSAIDs are commonly to be taken without regard to food, prescribers recommend administering them with food to reduce their propensity for gastrointestinal adverse events. A larger percentage of anticonvulsants and SNRIs used as analgesics are taken with food to improve their tolerability. Of all analgesic products, seven NSAIDs and six opioids lack food effect information, maybe due to their approval before Food and Drug Administration food effect guidance. CONCLUSIONS: Overall, because food effects could alter the onset and/or duration of pain relief, analgesic medication should be used as per labeled recommendations for proper pain management.

Effect of Formulation Variables on the Nasal Permeability and Stability of Naloxone Intranasal Formulations.

Naloxone is an opioid antagonist with high affinity for µ-opioid receptor, and for this reason it is used for the emergency treatment of opioid overdose. Originally, it was available only as an injectable product. However, for the ease of administration, intranasal (IN) formulations have also become available. These IN formulations contain preservatives and stabilizers such as benzalkonium chloride (BKC), benzyl alcohol (BA), and ethylenediaminetetraacetic acid (EDTA). Some of these ingredients are known to affect permeability of drugs. This study focuses on investigating the effect of formulation variables including choice of preservatives, stabilizer, and pH on the permeability and stability of naloxone IN formulations. The in vitro permeability of naloxone was evaluated employing EpiAirway™ tissue-mounted Ussing chambers. BKC was found to enhance the apparent permeability (Papp) of naloxone significantly (p < 0.05) at very low concentration, while BA caused similar enhancement at a much higher concentration. EDTA was found to decrease Papp of naloxone by lowering the pH, and the Papp of naloxone was found to decrease approximately 51-fold with the decrease in formulation pH from 6.0 to 4.0. The product stability was, however, found optimal only below pH 5.0. Thus, selection of formulation ingredients, buffering agent, and pH of IN formulation is a balancing act for achieving desired permeability and optimal stability to achieve reasonable shelf life of naloxone IN formulation.

Human liver expression of CYP2C8: gender, age, and genotype effects.

Research investigating CYP2C8 as a drug-metabolizing enzyme has gained momentum over the past few years. CYP2C8 is estimated to oxidatively metabolize approximately 5% of therapeutically prescribed drugs. It is polymorphically expressed, and several single nucleotide polymorphisms have been identified with varying effects on the clearance of CYP2C8 substrates. However, the human liver expression of CYP2C8 and effects of genetic variation, age, and gender on mRNA and protein levels have not been fully explored. In this report, interindividual variation in CYP2C8 mRNA and protein expression in 60 livers from white individuals was examined. The livers were genotyped for CYP2C8*3 and CYP2C8*4 polymorphisms. The effects of genotype, age, and gender on hepatic CYP2C8 expression and the correlation of CYP2C8 mRNA expression with CYP3A4 and other CYP2C members were evaluated. The mean +/- S.D. protein levels in CYP2C8*1/*1 livers was 30.8 +/- 17.5 pmol/mg protein, and a trend for decreased protein levels was observed for CYP2C8*1/*4 livers (15.8 +/- 9.7 pmol/mg, p = 0.07). The mean expression levels of CYP2C8 was comparable in males and females (p = 0.18). The mRNA expression of CYP2C8, CYP2C9, CYP2C19, and CYP3A4, but not CYP2C18, was highly correlated (p < 0.0001). Moreover, the hepatic CYP2C8 and CYP3A4 protein levels were strongly correlated (r = 0.76, p < 0.0001). This correlation is most likely due to common regulation factors for both genes. CYP2C8 mRNA or protein expression levels were not significantly affected by CYP2C8*3 or *4 genotype, gender, or age, and variation observed clinically in CYP2C8 activity warrants further investigation.

Pregnancy does not increase CYP3A or P-glycoprotein activity in the non-human primate, Macaca nemestrina.

Plasma concentrations of protease inhibitors are lower in pregnant women than in nonpregnant women or men. Using nelfinavir as a model protease inhibitor, we have shown that this phenomenon can be reproduced in a representative non-human primate model, Macaca nemestrina (J Pharmacol Exp Ther 329:1016-1022, 2009). Nelfinavir is cleared from the body predominantly by CYP3A metabolism and P-glycoprotein (P-gp) efflux. Therefore, using midazolam (MDZ) as a CYP3A probe and digoxin (DIG) as a P-gp probe, we determined the antepartum (73-118 days) and postpartum (61-130 days) in vivo intestinal and hepatic CYP3A or P-gp activity in the macaque. Although the systemic clearance of MDZ was significantly increased ( approximately 70%) during pregnancy after intra-arterial (IA) administration of the drug ((15)N-labeled MDZ; 40 microg/kg), pregnancy did not affect the oral clearance of the drug administered simultaneously (1 mg/kg p.o.) with the IA dose. In vitro studies in hepatic and intestinal S-9 fractions indicated no effect of pregnancy on CYP3A activity or protein expression in the small intestine or liver. In contrast, neither the oral (100 microg/kg) nor the IA (10 microg/kg) clearance of DIG was significantly altered by pregnancy, indicating no effect of pregnancy on P-gp activity. Assuming that MDZ and DIG are selective substrates of the macaque CYP3A enzymes and P-gp, respectively, these results suggest that factors other than increased CYP3A or P-gp activity contribute to the increased clearance of protease inhibitors during M. nemestrina pregnancy.

As in humans, pregnancy increases the clearance of the protease inhibitor nelfinavir in the nonhuman primate Macaca nemestrina.

The apparent oral clearance of protease inhibitors (PIs) is increased in pregnant women. Although this phenomenon is reproduced in the mouse, because of the multiplicity of mouse cytochrome P450 isoforms, lack of information on their substrate and inhibitor selectivity, and lack of reagents (e.g., antibodies, purified protein), it is difficult to study the mechanistic basis of this phenomenon in this animal model. To investigate the mechanistic basis of this phenomenon in a more representative model, the nonhuman primate, we first determined whether this phenomenon could be reproduced in Macaca nemestrina, using nelfinavir as a model PI. Consistent with the human and mouse studies, we found that the apparent oral clearance of nelfinavir (NFV) in the macaques was significantly increased (3.14-fold) antepartum (n = 3) versus postpartum (n = 4). This increased apparent oral clearance was a result of an increased systemic clearance (1.9-fold) and a decreased bioavailability (approximately 45%) during pregnancy. In vitro, pregnancy significantly enhanced the rate of NFV depletion in hepatic, but not intestinal S-9 fractions. Human CYP3A inhibitors erythromycin (0.5 mM), ketoconazole (0.5 microM), and troleandomycin (0.01-1 mM), but not the CYP2C inhibitor, sulfaphenazole (3 microM), significantly inhibited the depletion of NFV in hepatic S-9 fractions and expressed rhesus CYP3A64 enzyme. Based on these data, we conclude that increased hepatic activity of NFV-metabolizing enzymes (perhaps CYP3A enzymes) results in increased clearance of PIs during pregnancy in the macaques. The M. nemestrina should be further investigated as a model to study the mechanisms by which the clearance of PIs is increased during pregnancy.

Effects of subchronic coexposure to arsenic and endosulfan on the erythrocytes of broiler chickens: a biochemical study.

Arsenic is a known global groundwater contaminant. The organochlorine insecticide endosulfan has gained significance as an environmental pollutant due to its widespread use in the control of many food- and non-food-crop-damaging insects. The adverse effects produced by arsenic or endosulfan alone in humans and animals are well documented, but very little is known about the consequences of their coexposure. We evaluated whether their simultaneous exposure can induce oxidative stress and affect antioxidative systems and certain membrane-bound enzymes in erythrocytes of broiler chickens. Day-old chicks were exposed to 3.7 ppm of arsenic via drinking water or 30 ppm of endosulfan-mixed feed or similarly coexposed to these in the same dose levels for 60 days. At term, the impact of their coexposure was assessed by evaluating lipid peroxidation (LPO), activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione-S-transferase (GST), different ATPases and acetylcholinesterase (AChE) in erythrocytes, serum glucose, and levels of glutathione (GSH) and glycosylated hemoglobin (GHb) in blood. LPO was increased with all of the treatments. Catalase was decreased with endosulfan and the coexposure, but not with arsenic, whereas GSH was decreased with arsenic and endosulfan, but not with the coexposure. All of the treatments increased SOD and GPx activities. GST activity was increased only in the coexposed birds. None of the treatments affected the activities of total ATPase and Mg2+-ATPase. Na+-K+-ATPase activity was decreased in the endosulfan-treated and the coexposed birds. All three exposures increased erythrocyte AChE activity. Endosulfan increased the serum glucose level and arsenic and endosulfan increased GHb levels, but these were not altered in the coexposed birds. Erythrocyte protein content was insignificantly decreased with these treatments. Overall, the effects of coexposure were not appreciably different from either of the agents, except on AChE, GSH, and glucose. The results do not reflect any specific type of interaction between these agents in chicken erythrocytes, but they do indicate that the coexposure induces a low level of oxidative stress, which is comparable to that induced by arsenic or endosulfan.

Effects of simultaneous repeated exposure at high levels of arsenic and malathion on hepatic drug-biotransforming enzymes in broiler chickens.

Groundwater contamination with arsenic is a major global health concern. The organophosphorus insecticide malathion has gained significance as an environmental pollutant due to its widespread use in agriculture, grain storage, ectoparasite control and public health management. The deleterious effects produced by arsenic or malathion alone are documented, but very little is known about the consequences of their coexposure. The aim of the current study was to examine the effects of repeated simultaneous exposure to arsenic and malathion on drug-biotransforming enzymes in the liver of broiler chickens. One-month-old broiler chickens were exposed daily to arsenic (50 ppm)-supplemented drinking water, malathion (500 ppm)-mixed diet or in a similar fashion coexposed to these agents for 28 days. At the term, changes in body weight, organ weights, and levels of hepatic cytochrome P450 (CYP), cytochrome b(5), microsomal and cytosolic proteins; aminopyrine N-demethylase (ANDM), aniline P-hydroxylase (APH), glutathione S-transferase (GST) and uridine diphosphate glucuronosyltransferase (UGT) were assessed. Arsenic, malathion or their coexposure decreased the body weight gain and liver weight. Brain weight (relative) was increased with arsenic or malathion, but not with the coexposure. Treatment with arsenic decreased the CYP and cytochrome b(5) contents by 39 and 36%, than with malathion by 54 and 22% and the coexposure by 45 and 28%, respectively. The ANDM activity was decreased with arsenic (44%), malathion (23%) and the coexposure (32%). Arsenic (23%) and the coexposure (37%), but not malathion (14%), reduced the APH activity. The activities of hepatic microsomal and cytosolic GST were increased with all the three treatments [Arsenic (microsomal: 88% cytosolic: 113%), malathion (microsomal: 137%, cytosolic: 94%) and coexposure (microsomal: 140%, cytosolic: 148%)]. These treatments did not significantly affect the hepatic UGT activity, but reduced the hepatic microsomal (arsenic: 28%, malathion: 34% and coexposure: 43%) and cytosolic (17-19%) protein contents. The effects of coexposure on the activities of various phase I and phase II drug-biotransforming enzymes were almost similar to that of arsenic or malathion. This study provides evidence that repeated coexposure to arsenic and malathion may influence the extent of drug metabolism in chickens.

Perturbations in immune responses induced by concurrent subchronic exposure to arsenic and endosulfan.

The metalloid arsenic and the chlorinated insecticide endosulfan are common environmental contaminants. Humans, animals, and birds are exposed to these chemicals through water and food. Although health effects due to either arsenic or endosulfan exposure are documented, the toxicological impact of co-exposure to these environmental pollutants is unpredictable and unknown. The present study was undertaken to assess whether concurrent exposure to arsenic and endosulfan induces significant alterations in immunological functions. Day-old chicks were exposed to 3.7 ppm of arsenic via drinking water and to 30 ppm of endosulfan-mixed feed either individually or concurrently for up to 60 days. All the chicks were vaccinated with Ranikhet disease virus (F-strain; RD-F) on days 1 and 30. During the course of study and at term, parameters of cellular and humoral immunity were determined. None of the treatments altered the absolute body weight or body weight gain, except arsenic significantly reduced weight gain on day 60. Absolute, but not the relative, weights of spleen, thymus and bursa of Fabricius were significantly reduced in all the treatment groups. The metalloid and insecticide combination significantly depressed the ability of peripheral blood and splenic lymphocytes to proliferate in response to antigen RD-F and mitogen Con A. The delayed type hypersensitivity response to 2,4-dinitro-1-chlorobenzene or to PHA-P was also significantly decreased. Nitric oxide production by RD-F or lipopolysaccharide-stimulated peripheral blood and splenic mononuclear cells was significantly suppressed following concurrent exposure to arsenic and endosulfan. Furthermore, the combined exposure also decreased the antibody response to RD-F. The suppression of cellular and humoral immune responses was also evident following administration of individual compounds, and it was not exacerbated following concurrent exposure. To our knowledge, this is the first report describing the suppression of immune responses following exposure to arsenic alone or in combination with endosulfan at environmentally realistic concentrations in avian species. Therefore, immunotoxicological effects induced by concurrent exposure to arsenic and chlorinated pesticides should be considered when assessing the risk to human and animal health.

Concurrent subacute exposure to arsenic through drinking water and malathion via diet in male rats: effects on hepatic drug-metabolizing enzymes.

Arsenic is a known global groundwater contaminant, while malathion is one of the most widely used pesticides in agriculture and public health practices in the world. Here, we investigated whether repeated exposure to arsenic at the groundwater contamination levels and to malathion at sublethal levels exerts adverse effects on the hepatic drug-metabolizing system in rats, and whether concurrent exposure is more hazardous than the single agent. Male Wistar rats were exposed daily to 4 or 40 ppm of arsenic via drinking water, 50 or 500 ppm of malathion-mixed feed and in a similar fashion co-exposed to 4 ppm of arsenic and 50 ppm of malathion or 40 ppm of arsenic and 500 ppm of malathion for 28 days. At term, toxicity was assessed by evaluating changes in body weight, liver weight, levels of cytochrome P(450) (CYP), cytochrome b (5) and microsomal and cytosolic proteins, and activities of aminopyrine-N-demethylase (ANDM), aniline-P-hydroxylase (APH), glutathione-S-transferase (GST) and uridine diphosphate glucuronosyltransferase (UGT) in liver. Arsenic and malathion alone did not alter body weight and liver weight, but these were significantly decreased in both the co-exposed groups. These treatments decreased the activities of ANDM and APH and the levels of liver microsomal and cytosolic proteins, increased GST activity and had no effect on UGT activity. The effects of exposure to low-dose and high-dose combinations on the activities of either phase I or phase II drug-metabolizing enzymes and protein content were mostly similar to that produced by the respective low and high dose of either arsenic or malathion, except APH activity. The effect of arsenic (40 ppm) on APH activity was partially, but significantly, inhibited by malathion (500 ppm). Results indicate that the body or liver weights and the biochemical parameters were differentially affected in male rats following concurrent subacute exposure to arsenic and malathion, with the co-exposure appearing more hazardous to physical variables based on body or liver weights whilst producing biochemical changes comparable to those caused by the individual agents. From these findings, no specific toxicological interaction between arsenic and malathion can be conclusively generalized.

The breast cancer resistance protein (Bcrp1/Abcg2) limits fetal distribution of glyburide in the pregnant mouse: an Obstetric-Fetal Pharmacology Research Unit Network and University of Washington Specialized Center of Research Study.

Breast cancer resistance protein (BCRP) is most abundantly expressed in the apical membrane of placental syncytiotrophoblasts, suggesting that it may protect the fetus by impeding drug penetration across the placental barrier. Glyburide (GLB) is an antidiabetic drug routinely used to treat gestational diabetes. In this study, we first determined whether GLB is a BCRP/Bcrp1 substrate. The intracellular [(3)H]GLB concentrations in Madin-Darby canine kidney (MDCK)/BCRP cells were significantly lower than those in MDCK/vector cells. The addition of 10 muM fumitremorgin C, a specific BCRP inhibitor, significantly increased the intracellular [(3)H]GLB concentrations approximately 2-fold in MDCK/BCRP cells, but it had no effect in MDCK/vector cells. Similar results were obtained using MDCKII parent and MDCKII/Bcrp1 cells. GLB was also shown to be a BCRP/Bcrp1 substrate in transwell transport experiments. We then examined whether Bcrp1 limits fetal distribution of GLB in the pregnant mouse. GLB was administered by retro-orbital injection to the wild-type and Bcrp1(-/-) pregnant mice. The maternal plasma samples and fetuses were collected at various times (0.5-240 min) after drug administration. The GLB concentrations in the maternal plasma samples and homogenates of fetal tissues were determined by high-performance liquid chromatography/mass spectrometry. Although the maternal plasma area under the concentration-time curves (AUCs) of GLB in the wild-type and Bcrp1(-/-) pregnant mice were comparable, the fetal AUC of GLB in the Bcrp1(-/-) pregnant mice was approximately 2 times greater than that in the wild-type pregnant mice. These results suggest that GLB is a BCRP/Bcrp1 substrate, and Bcrp1 significantly limits fetal distribution of GLB in the pregnant mouse, but it has only a minor effect on the systemic clearance of the drug.

Validation of a sensitive LC-MS assay for quantification of glyburide and its metabolite 4-transhydroxy glyburide in plasma and urine: an OPRU Network study.

Glyburide (glibenclamide, INN), a second generation sulfonylurea is widely used in the treatment of gestational diabetes mellitus (GDM). None of the previously reported analytical methods provide adequate sensitivity for the expected sub-nanogram/mL maternal and umbilical cord plasma concentrations of glyburide during pregnancy. We developed and validated a sensitive and low sample volume liquid chromatographic-mass spectrometric (LC-MS) method for simultaneous determination of glyburide (GLY) and its metabolite, 4-transhydroxy glyburide (M1) in human plasma (0.5 mL) or urine (0.1 mL). The limits of quantitation (LOQ) for GLY and M1 in plasma were 0.25 and 0.40 ng/mL, respectively whereas it was 1.06 ng/mL for M1 in urine. As measured by quality control samples, precision (% coefficient of variation) of the assay was <15% whereas the accuracy (% deviation from expected) ranged from -10.1 to 14.3%. We found that the GLY metabolite, M1 is excreted in the urine as the glucuronide-conjugate.