Pharmacokinetic Analysis of Intravenous Push Cefepime in Burn Patients with Augmented Renal Clearance

Patients with augmented renal clearance (ARC) are a subset of critically ill patients including burn patients that exhibit increased renal elimination of medications beyond that of similarly injured patients. Currently approved maximum regimens of medications primarily eliminated by the kidney, such as cefepime (>90% unchanged in the urine), may be inadequate (eg, compromising the bactericidal activity of cefepime) in patients with ARC. Due to recent resource limitations, centers have changed infusion practices of commonly prescribed medications to intravenous push (IVP), potentially exacerbating the problem of maintaining bactericidal cefepime concentrations. The hypothesis of the study was patients with ARC are not currently achieving adequate target attainment, when receiving cefepime 2 g every 8 h IVP. Eight blood samples were collected from each patient, and concentrations measured via LC-MS/MS. WinNonlin (version 8.3) was used to estimate the pharmacokinetic parameters of cefepime and simulate plasma concentrations of cefepime in each of the ten subjects. Simulations of cefepime plasma concentrations produced by a 2 g dose given every 8 h and a 1 g dose given every 4 h were performed and the time above a MIC of 4 mg/L, 8 mg/L, and 16 mg/L compared. The 2 g every 8 h regimen remained above the breakpoints for 92%, 85%, and 71% of the dosing interval, respectively. The 1 g every 4 h regimen remained above the same breakpoints at a frequency of 100%, 99%, and 92% of the dosing interval. Giving cefepime 1 g every 4 h is a simple approach to increase the likelihood of maintaining the optimal bactericidal activity of cefepime in patients with ARC.

Alcohol inhibits the metabolism of dimethyl fumarate to the active metabolite responsible for decreasing relapse frequency in the treatment of multiple sclerosis

Dimethyl fumarate (DMF) is a first-line prodrug for the treatment of relapsing-remitting multiple sclerosis (RRMS) that is completely metabolized to monomethyl fumarate (MMF), the active metabolite, before reaching the systemic circulation. Its metabolism has been proposed to be due to ubiquitous esterases in the intestines and other tissues, but the specific enzymes involved are unknown. We hypothesized based on its structure and extensive presystemic metabolism that DMF would be a carboxylesterase substrate subject to interaction with alcohol. We sought to determine the enzymes(s) responsible for the extensive presystemic metabolism of DMF to MMF and the effect of alcohol on its disposition by conducting metabolic incubation studies in human recombinant carboxylesterase-1 (CES1), carboxylesterase-2 (CES2) and human intestinal microsomes (HIM), and by performing a follow-up study in an in vivo mouse model. The in vitro incubation studies demonstrated that DMF was only metabolized to MMF by CES1. Consistent with the incubation studies, the mouse pharmacokinetic study demonstrated that alcohol decreased the maximum concentration and area-under-the-curve of MMF in the plasma and the brain after dosing with DMF. We conclude that alcohol may markedly decrease exposure to the active MMF metabolite in the plasma and brain potentially decreasing the effectiveness of DMF in the treatment of RRMS.

Comparison of caffeine disposition following administration by oral solution (energy drink) and inspired powder (AeroShot) in human subjects

AIMS

To determine the disposition and effects of caffeine after administration using a new dosage form (AeroShot) that delivers caffeine by inspiration of a fine powder into the oral cavity and compare it to an equivalent dose of an oral solution (energy drink) as the reference standard.

METHODS

Healthy human subjects (n = 17) inspired a 100 mg caffeine dose using the AeroShot device or consumed an energy drink on separate study days. Heart rate, blood pressure and subject assessments of effects were measured over an 8-h period. Plasma concentrations of caffeine and its major metabolites were determined by liquid chromatography-mass spectrometry. Pharmacokinetic, cardiovascular and perceived stimulant effects were compared between AeroShot and energy drink phases using a paired t test and standard bioequivalency analysis.

RESULTS

Caffeine disposition was similar after caffeine administration by the AeroShot device and energy drink: peak plasma concentration 1790 and 1939 ng ml-1 , and area under the concentration-time curve (AUC) 15 579 and 17 569 ng ml-1 × h, respectively, but they were not bioequivalent: AeroShot AUC of 80.3% (confidence interval 71.2-104.7%) and peak plasma concentration of 86.3% (confidence interval 62.8-102.8%) compared to the energy drink. Female subjects did have a significantly larger AUC compared to males after consumption of the energy drink. The heart rate and blood pressure were not significantly affected by the 100 mg caffeine dose, and there were no consistently perceived stimulant effects by the subjects using visual analogue scales.

CONCLUSION

Inspiration of caffeine as a fine powder using the AeroShot device produces a similar caffeine profile and effects compared to administration of an oral solution (energy drink).

Measurement of caffeine and its three primary metabolites in human plasma by HPLC-ESI-MS/MS and clinical application

Caffeine is a mild stimulant with significant potential for abuse, being consumed in larger doses with the widespread availability of energy drinks and by novel routes of administration such as inspired powder, oral sprays and electronic cigarettes. How these recent changes in caffeine consumption affecting caffeine disposition and abuse potential is of growing concern. In the study of caffeine disposition in humans, it is common to only measure the caffeine concentration; however, caffeine's three major metabolites (paraxanthine, theobromine and theophylline) retain central nervous system stimulant activity that may contribute to the overall pharmacological activity and toxicity. Therefore, it would be scientifically more rigorous to measure caffeine and its major metabolites in the evaluation of caffeine disposition in human subjects. Herein, we report a method for the simultaneous quantification of caffeine and its three major metabolites in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). Human plasma samples were treated by simple protein precipitation and the analytes were separated using a 6 min gradient program. Precision and accuracy were well within in the 15% acceptance range. The simple sample preparation, short runtime, sensitivity and the inclusion of caffeine's major metabolites make this assay methodology optimal for the study of caffeine's pharmacokinetics and pharmacodynamics in human subjects.

Pharmacokinetics of Imipenem/Cilastatin Burn Intensive Care Unit Patients Undergoing High-Dose Continuous Venovenous Hemofiltration

STUDY OBJECTIVE

High-dose continuous venovenous hemofiltration (CVVH) is a continuous renal replacement therapy (CRRT) used frequently in patients with burns. However, antibiotic dosing is based on inference from studies assessing substantially different methods of CRRT. To address this knowledge gap for imipenem/cilastatin (I/C), we evaluated the systemic and extracorporeal clearances (CLs) of I/C in patients with burns undergoing high-dose CVVH.

DESIGN

Prospective clinical pharmacokinetic study.

PATIENTS

Ten adult patients with burns receiving I/C for a documented infection and requiring high-dose CVVH were studied.

METHODS

Blood and effluent samples for analysis of I/C concentrations were collected for up to 6 hours after the I/C infusion for calculation of I/C total CL (CL_Total ), CL by CVVH (CL_HF ), half-life during CVVH, volume of distribution at steady state (Vd_ss ), and the percentage of drug eliminated by CVVH.

RESULTS

In this patient sample, the mean age was 50 ± 17 years, total body surface area burns was 23 ± 27%, and 80% were male. Nine patients were treated with high-dose CVVH for acute kidney injury and one patient for sepsis. The mean delivered CVVH dose was 52 ± 14 ml/kg/hour (range 32-74 ml/kg/hr). The imipenem CL_HF was 3.27 ± 0.48 L/hour, which accounted for 23 ± 4% of the CL_Total (14.74 ± 4.75 L/hr). Cilastatin CL_HF was 1.98 ± 0.56 L/hour, which accounted for 45 ± 19% of the CL_Total (5.16 + 2.44 L/hr). The imipenem and cilastatin half-lives were 1.77 ± 0.38 hours and 4.21 ± 2.31 hours, respectively. Imipenem and cilastatin Vd_ss were 35.1 ± 10.3 and 32.8 ± 13.8 L, respectively.

CONCLUSION

Efficient removal of I/C by high-dose CVVH, a high overall clearance, and a high volume of distribution in burn intensive care unit patients undergoing this CRRT method warrant aggressive dosing to treat serious infections effectively depending on the infection site and/or pathogen.

Effects of alcohol on human carboxylesterase drug metabolism

BACKGROUND AND OBJECTIVE

Human carboxylesterase-1 (CES1) and human carboxylesterase-2 (CES2) play an important role in metabolizing many medications. Alcohol is a known inhibitor of these enzymes but the relative effect on CES1 and CES2 is unknown. The aim of this study was to determine the impact of alcohol on the metabolism of specific probes for CES1 (oseltamivir) and CES2 (aspirin).

METHODS

The effect of alcohol on CES1- and CES2-mediated probe drug hydrolysis was determined in vitro using recombinant human carboxylesterase. To characterize the in vivo effects of alcohol, healthy volunteers received each probe drug alone and in combination with alcohol followed by blood sample collection and determination of oseltamivir, aspirin, and respective metabolite pharmacokinetics.

RESULTS

Alcohol significantly inhibited oseltamivir hydrolysis by CES1 in vitro but did not affect aspirin metabolism by CES2. Alcohol increased the oseltamivir area under the plasma concentration-time curve (AUC) from 0 to 6 h (AUC0 → 6 h) by 27% (range 11-46%, p = 0.011) and decreased the metabolite/oseltamivir AUC0 → 6 h ratio by 34% (range 25-41%, p < 0.001). Aspirin pharmacokinetics were not affected by alcohol.

CONCLUSIONS

Alcohol significantly inhibited the hydrolysis of oseltamivir by CES1 both in vitro and in humans, but did not affect the hydrolysis of aspirin to salicylic acid by CES2. These results suggest that alcohol's inhibition of CES1 could potentially result in clinically significant drug interactions with other CES1-substrate drugs, but it is unlikely to significantly affect CES2-substrate drug hydrolysis.

Physiologically based pharmacokinetic modeling of impaired carboxylesterase-1 activity: effects on oseltamivir disposition

BACKGROUND AND OBJECTIVE

Human carboxylesterase-1 (CES1) is an enzyme that is primarily expressed in the liver, where it plays an important role in the metabolism of many commonly used medications. Ethanol (alcohol)-mediated inhibition of CES1 and loss-of-function polymorphisms in the CES1 gene can markedly reduce this enzyme's function. Such alterations in CES1 activity may have important effects on the disposition of substrate drugs. The aim of this study is to develop a physiologically based pharmacokinetic (PBPK) model to predict changes in CES1 substrate drug exposure in humans with CES1 activity impaired by ethanol or loss-of-function CES1 genetic polymorphisms.

METHODS

The antiviral drug oseltamivir, an ethyl ester prodrug that is rapidly converted in vivo to the active metabolite oseltamivir carboxylate (OSC) by CES1 was used as a probe drug for CES1 activity. Oseltamivir PBPK models integrating in vitro and in vivo data were developed and refined. Then the changes in oseltamivir and OSC exposure in humans with CES1 impaired by ethanol or polymorphisms were simulated using a PBPK model incorporating in vitro inhibition and enzyme kinetic data. Model assumptions were verified by comparison of simulations with observed and published data. A sensitivity analysis was performed to gain a mechanistic understanding of the exposure changes of oseltamivir and OSC.

RESULTS

The simulated changes in oseltamivir and OSC exposures in humans with CES1 impaired by ethanol or polymorphism were similar to the observed data. The observed exposures to oseltamivir were increased by 46 and 37 % for the area under the plasma concentration-time curve from time zero to 6 h (AUC6) and from time zero to 24 h (AUC24), respectively, with co-administration of ethanol 0.6 g/kg. In contrast, only a slight change was observed in OSC exposure. The simulated data show the same trend as evidenced by greater change in exposures to oseltamivir (27 and 26 % for AUC(6) and AUC(24), [corrected] respectively) than OSC (≤6 %).

CONCLUSIONS

The PBPK model of impaired CES1 activity correctly predicts observed human data. This model can be extended to predict the effects of drug interactions and other factors affecting the pharmacokinetics of other CES1 substrate drugs.

Identification of alcohol-dependent clopidogrel metabolites using conventional liquid chromatography/triple quadrupole mass spectrometry

RATIONALE

Clopidogrel (CLO) is a prodrug used to prevent ischemic events in patients undergoing percutaneous coronary intervention or with myocardial infarction. A previous study found ethyl clopidogrel (ECLO) is formed by transesterification of CLO when incubated with alcohol in human liver microsomes. We hypothesize that ECLO will be subject to further metabolism and developed an assay to identify its metabolites.

METHODS

A liquid chromatography/triple quadrupole mass spectrometry (LC/MS/MS) method was developed to identify metabolites of ECLO. According to the predicted metabolic pathway of ECLO, precursor-product ion pairs were used to screen the possible metabolites of ECLO in human liver S9 fractions. Subsequently, the detected metabolites were characterized by the results of product ion scan.

RESULTS

In the presence of alcohol, CLO was tranesterified to ECLO, which was further oxidized to form ethylated 2-oxo-clopidogrel and several ethylated thiol metabolites including the ethylated form of the H4 active metabolite.

CONCLUSIONS

The ECLO formed by transesterification with alcohol is subject to metabolism by CYP450 enzymes producing ethylated forms of 2-oxo-clopidogrel and the active H4 thiol metabolite.

Identification of carboxylesterase-dependent dabigatran etexilate hydrolysis

Dabigatran etexilate (DABE) is an oral prodrug that is rapidly converted to the active thrombin inhibitor, dabigatran (DAB), by serine esterases. The aims of the present study were to investigate the in vitro kinetics and pathway of DABE hydrolysis by human carboxylesterase enzymes, and the effect of alcohol on these transformations. The kinetics of DABE hydrolysis in two human recombinant carboxylesterase enzymes (CES1 and CES2) and in human intestinal microsomes and human liver S9 fractions were determined. The effects of alcohol (a known CES1 inhibitor) on the formation of DABE metabolites in carboxylesterase enzymes and human liver S9 fractions were also examined. The inhibitory effect of bis(4-nitrophenyl) phosphate on the carboxylesterase-mediated metabolism of DABE and the effect of alcohol on the hydrolysis of a classic carboxylesterase substrate (cocaine) were studied to validate the in vitro model. The ethyl ester of DABE was hydrolyzed exclusively by CES1 to M1 (Km 24.9 ± 2.9 μM, Vmax 676 ± 26 pmol/min per milligram protein) and the carbamate ester of DABE was exclusively hydrolyzed by CES2 to M2 (Km 5.5 ± 0.8 μM; Vmax 71.1 ± 2.4 pmol/min per milligram protein). Sequential hydrolysis of DABE in human intestinal microsomes followed by hydrolysis in human liver S9 fractions resulted in complete conversion to DAB. These results suggest that after oral administration of DABE to humans, DABE is hydrolyzed by intestinal CES2 to the intermediate M2 metabolite followed by hydrolysis of M2 to DAB in the liver by CES1. Carboxylesterase-mediated hydrolysis of DABE was not inhibited by alcohol.

The role of human carboxylesterases in drug metabolism: have we overlooked their importance?

Carboxylesterases are a multigene family of mammalian enzymes widely distributed throughout the body that catalyze the hydrolysis of esters, amides, thioesters, and carbamates. In humans, two carboxylesterases, hCE1 and hCE2, are important mediators of drug metabolism. Both are expressed in the liver, but hCE1 greatly exceeds hCE2. In the intestine, only hCE2 is present and highly expressed. The most common drug substrates of these enzymes are ester prodrugs specifically designed to enhance oral bioavailability by hydrolysis to the active carboxylic acid after absorption from the gastrointestinal tract. Carboxylesterases also play an important role in the hydrolysis of some drugs to inactive metabolites. It has been widely believed that drugs undergoing hydrolysis by hCE1 and hCE2 are not subject to clinically significant alterations in their disposition, but evidence exists that genetic polymorphisms, drug-drug interactions, drug-disease interactions and other factors are important determinants of the variability in the therapeutic response to carboxylesterase-substrate drugs. The implications for drug therapy are far-reaching, as substrate drugs include numerous examples from widely prescribed therapeutic classes. Representative drugs include angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, antiplatelet drugs, statins, antivirals, and central nervous system agents. As research interest increases in the carboxylesterases, evidence is accumulating of their important role in drug metabolism and, therefore, the outcomes of pharmacotherapy.

Nonvolatile salt-free stabilizer for the quantification of polar imipenem and cilastatin in human plasma using hydrophilic interaction chromatography/quadrupole mass spectrometry with contamination sensitive off-axis electrospray

A hydrophilic interaction chromatography/mass spectrometry (HILIC-MS)-based assay for imipenem (IMP) and cilastatin (CIL) was recently reported. This orthogonal electrospray ion source-based (ORS) assay utilized nonvolatile salt (unremovable) to stabilize IMI in plasma. Unfortunately, this method was not applicable to conventional MS with off-axis spray (OAS-MS) because MS sensitivity was rapidly deteriorated by the nonvolatile salt. Therefore, we aimed to find a nonvolatile salt- and ion suppression-free approach to stabilize and measure the analytes in plasma using OAS-MS. Acetonitrile and methanol were tested to stabilize the analytes in the plasma samples. The recoveries, matrix effects and stabilities of the analytes in the stabilizer-treated samples were studied. The variations in MS signal intensities were used as the indicator of the assay ruggedness. The results show that a mixture of methanol and acetonitrile (1:1) is best for the storage and measurement of IMP and CIL in human plasma. Utilization of this precipitant not only blocked the hydrolysis of the analytes in plasma but also resulted in an ion suppression-free, fast (120 s per sample) and sensitive detection. The sensitivity obtained using the less sensitive OAS-MS (API3000, 4 pg on column) is much greater than that of the published ORS-MS-based assay (API4000, 77 pg on column). The ruggedness of the assay was demonstrated by its constant MS signal intensity. In conclusion, an improved HILIC/MS-based assay for IMP and CIL was established. The approach presented here provides a simple solution to the challenge of analyzing hydrolytically unstable β-lactam antibiotics in biological samples.

In vivo information-guided prediction approach for assessing the risks of drug-drug interactions associated with circulating inhibitory metabolites

The in vivo drug-drug interaction (DDI) risks associated with cytochrome P450 inhibitors that have circulating inhibitory metabolites cannot be accurately predicted by conventional in vitro-based methods. A novel approach, in vivo information-guided prediction (IVIP), was recently introduced for CYP3A- and CYP2D6-mediated DDIs. This technique should be applicable to the prediction of DDIs involving other important cytochrome P450 metabolic pathways. Therefore, the aims of this study were to extend the IVIP approach to CYP2C9-mediated DDIs and evaluate the IVIP approach for predicting DDIs associated with inhibitory metabolites. The analysis was based on data from reported DDIs in the literature. The IVIP approach was modified and extended to CYP2C9-mediated DDIs. Thereafter, the IVIP approach was evaluated for predicting the DDI risks of various inhibitors with inhibitory metabolites. Although the data on CYP2C9-mediated DDIs were limited compared with those for CYP3A- and CYP2D6-mediated DDIs, the modified IVIP approach successfully predicted CYP2C9-mediated DDIs. For the external validation set, the prediction accuracy for area under the plasma concentration-time curve (AUC) ratios ranged from 70 to 125%. The accuracy (75-128%) of the IVIP approach in predicting DDI risks of inhibitors with circulating inhibitory metabolites was more accurate than in vitro-based methods (28-805%). The IVIP model accommodates important confounding factors in the prediction of DDIs, which are difficult to handle using in vitro-based methods. In conclusion, the IVIP approach could be used to predict CYP2C9-mediated DDIs and is easily modified to incorporate the additive effect of circulating inhibitory metabolites.

The effect of ethanol on oral cocaine pharmacokinetics reveals an unrecognized class of ethanol-mediated drug interactions

Ethanol decreases the clearance of cocaine by inhibiting the hydrolysis of cocaine to benzoylecgonine and ecgonine methyl ester by carboxylesterases, and there is a large body of literature describing this interaction as it relates to the abuse of cocaine. In this study, we describe the effect of intravenous ethanol on the pharmacokinetics of cocaine after intravenous and oral administration in the dog. The intent is to determine the effect ethanol has on metabolic hydrolysis using cocaine metabolism as a surrogate marker of carboxylesterase activity. Five dogs were administered intravenous cocaine alone, intravenous cocaine after ethanol, oral cocaine alone, and oral cocaine after ethanol on separate study days. Cocaine, benzoylecgonine, and cocaethylene concentrations were determined by high-performance liquid chromatography. Cocaine had poor systemic bioavailability with an area under the plasma concentration-time curve that was approximately 4-fold higher after intravenous than after oral administration. The coadministration of ethanol and cocaine resulted in a 23% decrease in the clearance of intravenous cocaine and a 300% increase in the bioavailability of oral cocaine. Cocaine behaves as a high extraction drug, which undergoes first-pass metabolism in the intestines and liver that is profoundly inhibited by ethanol. We infer from these results that ethanol could inhibit the hydrolysis of other drug compounds subject to hydrolysis by carboxylesterases. Indeed, there are numerous commonly prescribed drugs with significant carboxylesterase-mediated metabolism such as enalapril, lovastatin, irinotecan, clopidogrel, prasugrel, methylphenidate, meperidine, and oseltamivir that may interact with ethanol. The clinical significance of the interaction of ethanol with specific drugs subject to carboxylesterase hydrolysis is not well recognized and has not been adequately studied.

Pharmacodynamic evaluation of the cardiovascular effects after the coadministration of cocaine and ethanol

One of the most common drug dependencies occurring with alcoholism is cocaine dependence. This combination is particularly worrisome because of the increased risk of cardiovascular events associated with their coabuse. Although it is well known that ethanol increases the cardiovascular effects of cocaine by inhibiting cocaine clearance and the formation of cocaethylene, it has also been postulated that ethanol enhances the cardiovascular effects of cocaine independent of the two latter mechanisms. In this study, we investigated the cardiovascular pharmacodynamics of the cocaine-ethanol interaction to determine whether ethanol directly enhanced the cardiovascular effects of cocaine. Dogs (n = 6) were administered cocaine alone (3 mg/kg i.v.) and in combination with ethanol (1 g/kg i.v.) on separate study days. Blood pressure, heart rate, and the electrocardiogram were monitored continuously, and blood samples were collected periodically after drug administration. Concentration-time data were fitted to a two-compartment model, and concentration-effect data were fitted to a simple E(max) model using WinNonlin software. Pharmacokinetic and pharmacodynamic parameters were compared between the two treatment phases by a paired t test. The administration of ethanol before cocaine resulted in a decrease in cocaine clearance, but there were no differences in any of the other pharmacokinetic or pharmacodynamic parameter values between the cocaine alone and cocaine plus ethanol phases. As has been demonstrated in previous animal and human studies, the clearance of cocaine was decreased by prior administration of ethanol. However, ethanol did not change the concentration-effect relationship of the cardiovascular response to cocaine administration. It is concluded from this study that ethanol does not directly enhance the cardiovascular effects of cocaine.

Selective serotonin reuptake inhibitors for migraine prophylaxis

The objective of this study was to assess the efficacy of sertraline in migraine prophylaxis. Other selective serotonin reuptake inhibitors have been studied for migraine prophylaxis, but this is the first report with sertraline. Twenty-seven subjects were enrolled and baseline assessment of migraine frequency and severity were measured over a 4-week period. Subjects were then randomized to receive placebo or sertraline in a double-blind fashion with headache frequency and severity measured over an 8-week period. Subjects completed a daily diary reporting the occurrence, severity, and degree of impairment associated with migraine. The headache index, a composite measure of migraine frequency and severity, scores did not significantly improve between assessments at baseline (20.8 +/- 14.88), 8 weeks (17.6 +/- 12.27), and 12 weeks (16.7 +/- 6.38) in the treatment group (n=6) (P=0.956). This finding is compared to other studies with the serotonin selective reuptake inhibitors, fluoxetine, fluvoxamine, and paroxetine. The authors believe that the selective serotonin reuptake inhibitors are not as effective as conventional migraine prophylaxis medications such as beta-blockers, tricyclic antidepressants, or divalproex sodium, but that in patients with comorbid depression who have failed conventional therapy selective serotonin reuptake inhibitors may be effective.

P-glycoprotein modulates aldosterone plasma disposition and tissue uptake

Aldosterone plays an important role in the pathophysiology of numerous cardiovascular disorders including heart failure and hypertension. Because aldosterone's actions are primarily mediated by its interaction with an intracellular mineralocorticoid receptor, factors affecting the cellular uptake and distribution of aldosterone may be important determinants of the hormone's activity. P-glycoprotein (P-gp) is an ATP-binding cassette efflux transporter encoded by the ABCB1 (also known as MDR1) gene in humans. P-gp is expressed on the luminal membrane of the capillary endothelial cells of tissues that are targets for aldosterone, including the brain and heart, where it attenuates cellular uptake of substrates. Recent in vitro evidence indicates P-gp transports aldosterone. Therefore, in this study we tested the hypothesis that P-gp modulates the uptake of aldosterone into the brain and heart by comparing the plasma and tissue distribution of [3H]-aldosterone in wild-type and P-gp-deficient [mdr1a/1b (-/-)] mice. Compared with wild-type mice, [3H]-aldosterone activity in the plasma, brain, and heart was significantly (P < 0.05) higher in the mdr1a/1b (-/-) animals. The area under the plasma or tissue concentration-time curves in the mdr1a/1b (-/-) mice was 2.0, 1.6, and 1.6-fold higher in the brain, heart, and plasma, respectively, than in wild-type controls. Our results demonstrate that P-gp plays an important role in aldosterone plasma disposition and modestly limits its uptake into the brain. The increased exposure of the brain and heart to aldosterone in the absence of P-gp suggests P-gp may play a key role in modulating aldosterone's effects in these organs.

Pharmacokinetics of buprenorphine after intravenous administration in the mouse

Buprenorphine is a potent partial m-opioid agonist that is used as an analgesic in animals and humans to ameliorate moderate to severe pain and in the treatment of opiate addiction as an alternative to methadone maintenance. The purpose of this study was to characterize the pharmacokinetics of buprenorphine after intravenous administration in mice. Mice (n=48) were given 2.4 mg/kg buprenorphine (HCl salt) by intravenous bolus injection, and groups of 4 mice were euthanized at 5, 15, and 30 min and 1, 2, 3, 5, 7, 9, 12, 18, and 24 h after drug administration. Plasma concentrations of buprenorphine and norbuprenorphine were determined using liquid chromatography-tandem mass spectrometry. By using the mean concentrations at each time point (n=4), pharmacokinetic parameters were estimated for buprenorphine using a 3-compartment model with the reciprocal of the predicted concentration as the weight factor. The estimated values for the exponents of the 1st, 2nd, and terminal compartments; volume of distribution at steady state; clearance; and area under the concentration-time curve were 12.8/h, 2.13/h, 0.239/h, 6.5 l/kg, 4.3 l/h/kg, and 559 microg/lxh, respectively. In addition, we compare the pharmacokinetic disposition of buprenorphine in the mouse with that previously reported for other species.

Studies on itraconazole delivery and pharmacokinetics in mallard ducks (Anas platyrhynchos)

Avian aspergillosis is commonly treated with itraconazole (ITZ). This paper describes two studies using mallard ducks (Anas platyrhynchos). The first study evaluated in vivo release of ITZ from subcutaneously injected controlled-release gel formulations and the second study compared pharmacokinetic parameters for two ITZ oral suspensions. ITZ-A suspension was prepared by mixing contents of commercially available capsules with hydrochloric acid and orange juice. ITZ-B suspension was prepared by dispersing the complex of the drug with hydroxypropyl-beta-cyclodextrin in water. Concentrations of ITZ and its active metabolite, hydroxyitraconazole (OH-ITZ), in plasma and tissue samples were measured using high-performance liquid chromatography. In the second study, drug concentrations in plasma samples were also analyzed using a bioassay. After administration of two ITZ controlled-release formulations, plasma and tissue concentrations of ITZ and OH-ITZ were either very low (< or = 52 ng/mL) or undetectable. Exceptions included skin, subcutaneous fat, and muscle adjacent to the injection site. The drug from ITZ-A and ITZ-B suspensions was absorbed after oral administration. ITZ pharmacokinetic parameters for both suspensions in mallard ducks were similar and the bioassay successfully measured ITZ equivalents in plasma samples from ducks.

Effects of grapefruit juice on intestinal P-glycoprotein: evaluation using digoxin in humans

STUDY OBJECTIVES

To determine the effects of grapefruit juice on the pharmacokinetics of oral digoxin, a P-glycoprotein substrate not metabolized by cytochrome P450 3A4, in healthy volunteers, and to assess whether polymorphic multidrug-resistance-1 (MDR1) expression contributes to interindividual variability in digoxin disposition.

DESIGN

Prospective, open-label, unblinded, crossover study.

SETTING

University research center.

SUBJECTS

Seven healthy adult volunteers (four men, three women).

INTERVENTION

Each subject received a single oral dose of digoxin 1.0 mg with water or grapefruit juice with at least a 2-week washout between treatments. During the grapefruit juice phase, juice was administered 3 times/day for 5 days before digoxin administration to maximize any effect on P-glycoprotein.

MEASUREMENTS AND MAIN RESULTS

Digoxin pharmacokinetics in the presence and absence of grapefruit juice were compared. The MDR1 exon 26 C3435T genotype was determined by real-time polymerase chain reaction. Compared with water, grapefruit juice significantly reduced the digoxin absorption rate constant (3.0 +/- 2.4 to 1.2 +/- 1.0 hr(-1), p<0.05) and increased absorption lag time (0.32 +/- 0.12 to 0.53 +/- 0.34 hr, p<0.05). Grapefruit juice did not affect digoxin maximum concentration (Cmax), area under the curve (AUC), elimination half-life, or renal clearance. The effect of grapefruit juice on digoxin Cmax (-45% to +41%) and AUC(0-4) (-29% to +25%) varied substantially among subjects and was inversely correlated with the values during the water phase. Trends toward higher digoxin Cmax AUC, and absorption rate constant during the water phase were found in CC homozygotes compared with subjects carrying a T allele.

CONCLUSION

Inhibition of intestinal P-glycoprotein does not appear to play an important role in drug interactions involving grapefruit juice. Interindividual variability in response to grapefruit juice may be related to the balance of intestinal drug uptake and efflux transport.

Cocaethylene metabolism and interaction with cocaine and ethanol: role of carboxylesterases

Carboxylesterases are important in the metabolism of cocaine, catalyzing the hydrolysis of cocaine to its two major metabolites, benzoylecgonine and ecgonine methyl ester. In the presence of ethanol, some cocaine undergoes transesterification with ethanol instead of hydrolysis with water producing the active metabolite, cocaethylene. The metabolic fate of cocaethylene is unknown, but given its structural similarity to cocaine, it was hypothesized that cocaethylene would also be metabolized by carboxylesterases and its elimination decreased in the presence of ethanol, as is cocaine's. Dogs were given cocaine alone, cocaethylene alone, cocaine and ethanol, cocaethylene and ethanol, and cocaine and cocaethylene on separate study days and sequential blood samples drawn. Plasma concentrations of cocaine, benzoylecgonine, and cocaethylene were determined by high-performance liquid chromatography. The pharmacokinetic dispositions of cocaine and cocaethylene were similar with clearance values of 0.91 +/- 0.22 and 0.79 +/- 0.16 l/min, and volumes of distribution of 2.6 +/- 0.82 and 2.7 +/- 0.47 l/kg, respectively. Both cocaine and cocaethylene clearances were decreased about 20% when given with ethanol. Following administration of cocaethylene alone, benzoylecgonine achieved similar plasma concentrations as those attained following cocaine alone, which indicates that benzoylecgonine is a major metabolite of cocaethylene. Carboxylesterases play an important role in the elimination of both cocaine and cocaethylene.

Controlled release of oxytetracycline in sheep

A novel biodegradable injectable formulation of oxytetracycline (OTC) was administered subcutaneously to sheep at a dose of 40 mg/kg. Blood samples were collected from the jugular vein at predetermined time intervals. The concentration of OTC in plasma was analyzed by an HPLC method. The concentrations of OTC in plasma were maintained at or above 0.5 microg/ml (minimum inhibitory concentration) for approximately 6 days. The pharmacokinetic parameters of OTC in sheep were also determined by monitoring the plasma concentration of OTC after a single intravenous injection of a commercially available OTC formulation at 10 mg/kg body weight. The in vivo release profiles of OTC from the biodegradable injectable formulations in sheep were determined from the plasma concentration time profiles by the deconvolution method using PCDCON software. The in vitro release of OTC from the biodegradable injectable formulation was tested in phosphate buffer (pH 7.4), containing 0.686% w/v of sodium sulfite as antioxidant. The correlation between the in vitro and in vivo release of OTC from the injectable formulation was also evaluated. The results of the in vivo evaluation of the formulation in sheep indicated that a controlled release biodegradable injectable dosage form of OTC for food animals is feasible.

Increased lithium dose requirement in a hyperglycemic patient

OBJECTIVE

To report a case of apparent increased lithium clearance in a patient with persistent hyperglycemia.

METHODS

Lithium doses, blood glucose concentrations, and lithium plasma concentrations were evaluated in a patient during a 53-day inpatient admission for exacerbation of bipolar disorder. The lithium dose required to increase the lithium plasma concentration by 0.1 mEq/L was computed from the lithium dose and corresponding lithium plasma concentration. This value was correlated with the blood glucose concentration.

RESULTS

A plot of the lithium dose required to increase the lithium plasma concentration by 0.1 mEq/L versus the blood glucose concentration exhibited a direct linear relationship (r2 = 0.62). This plot indicates that higher lithium doses are needed during hyperglycemic states compared with euglycemic states to achieve equivalent plasma concentrations.

CONCLUSIONS

Glycosuria associated with hyperglycemia induces an osmotic diuresis that increases the renal clearance of lithium, necessitating higher lithium doses to maintain therapeutic lithium plasma concentrations.

Nefazodone: An update

Nefazodone is an antidepressant with some novel characteristics in regard to its putative mechanism of action. Although the clinical significance of these properties is not clear, nefazodone is unique in that it is associated with minimal effects on sleep architecture and sexual functioning. Use of nefazodone to treat anxiety disorders appears to have promise, although placebo-controlled studies are still needed. Nefazodone is a potent inhibitor of CYP3A4, and thus numerous potential drug interactions must be carefully considered in order to avoid potential therapeutic misadventures. Recent reports indicate that nefazodone can cause severe hepatic toxicity. Evaluation of hepatic function before, and periodically after, therapy with nefazodone is initiated would be prudent. Nefazodone may be an appropriate antidepressant when potential anxiolytic activity would be beneficial and there is a need to avoid adverse effects on sexual functioning or sleep architecture.

Disposition of morphine in tissues of the pregnant rat and foetus following single and continuous intraperitoneal administration to the mother

Foetal exposure to maternally administered opiates such as morphine represent a serious human health problem but disposition studies in man are difficult to perform. Morphine disposition was therefore investigated in pregnant rats and their foetuses near term as a model. Disposition was examined either following intraperitoneal dosing as a single dose or continuous infusion. A high-pressure liquid chromatography assay for morphine in plasma and tissue was developed and validated. Following the single morphine dose, foetal distribution was rapid and concentrations in foetal and placental tissue were from 2.6 (whole foetus) to 27.6 (placenta) times higher compared with maternal plasma. The rank order of the area under the concentration vs time curve (AUC) of morphine in tissues was: placenta > or = foetal liver > foetal brain > whole foetus > maternal brain. The foetal brain to maternal brain AUC ratio for morphine was 9.5, suggesting large differences in their blood-brain barrier permeability. Following continuous administration of morphine there were significant linear relationships between maternal plasma and tissue concentrations with the same rank order as the single dose study. However, following continuous administration the relative amount of morphine in placenta and foetal liver was reduced by half and one-third, respectively, compared with the single dose study. These results document why the rat foetus is particularly susceptible to the pharmacodynamic effects of morphine following maternal administration.

Cocaethylene formation in rat, dog, and human hepatic microsomes

The dog and rat are important animal models for studying the role of cocaethylene in the pharmacodynamic interaction between cocaine and ethanol. In a previous study in our laboratory it was found that a cocaine dose of 3 mg/kg IV and ethanol 1 g/kg IV failed to produce detectable concentrations of cocaethylene in the plasma of dogs. In follow up to this result, the pharmacokinetic disposition of cocaine and cocaethylene in the dog were determined to be similar. These results suggested significant differences between animal and human cocaethylene formation may occur. To test this possibility the in vitro formation of cocaethylene was determined in rat, dog and human hepatic microsomal preparations containing cocaine (0-7 mM) and ethanol (50 mM). Nonlinear least-squares regression was used to estimate Km and Vmax and the results were compared statistically. The mean +/- standard deviation for Km and Vmax in the rat, dog and human were 0.53 +/- 0.04, 0.97 +/- 0.07, and 0.56 +/- 0.08 mM, and 390 +/- 9, 233 +/- 6, and 60 +/- 3 pmol/minute/mg protein, respectively. The Km in the dog was significantly greater (p<0.05) than the Km in the rat and human. The Vmax was statistically different among all three species (rat>dog>human; p<0.05). These results demonstrate that cocaethylene formation is greater in dog than human hepatic microsomes, which is in contrast to in vivo studies that appear to show that humans produce more cocaethylene than dogs. It is suggested by the authors that route of cocaine administration may be an important factor in the formation of cocaethylene when cocaine and ethanol are co-administered.

Evaluation of dose-dependent pharmacokinetics of cocaethylene and cocaine in conscious dogs

Cocaine use continues to be widespread in the United States. Most cocaine users co-ingest ethanol resulting in decreased elimination of cocaine and formation of the active cocaine metabolite, cocaethylene, by hepatic carboxylesterases. In a recent study from our laboratory in dogs to evaluate the cocaine-ethanol interaction, we demonstrated a similar ethanol-induced reduction in cocaine metabolism, although we were unable to detect cocaethylene when the two drugs were given together. This unexpected finding could be explained by ethanol-induced inhibition of cocaine metabolism via a pathway that does not involve hepatic carboxylesterases or formation of cocaethylene that inhibits cocaine metabolism and is then rapidly cleared. The purpose of the present study is to determine which of these mechanisms best explain our data by characterizing the pharmacokinetics of cocaine and cocaethylene over a range of doses in conscious dogs. Seven adult mongrel dogs received 1, 3, and 5 mg/kg cocaine and cocaethylene HCl base with each drug dose administered i.v. on a separate study day. Arterial blood samples were collected at various times after each dose and analyzed for cocaine and cocaethylene by HPLC. Cocaine clearance was dose-dependent with clearance decreasing from 1.53 +/- 0.31 to 1.09 +/- 0.11 l/min as the dose was increased from 1 to 5 mg/kg (p<0.05). Vmax x Vss and Km for cocaine were 0.95 +/- 0.40 l/min/kg and 11.2 +/- 6.2 mg/kg, respectively. Cocaethylene pharmacokinetics were similar to those of cocaine, but were not dose-dependent over the dose range of 1-5 mg/kg. These results suggest that cocaethylene is not formed and rapidly cleared after co-administration of cocaine and ethanol to the dog, but rather suggests that cocaethylene is not formed in appreciable quantities in the dog. Therefore, we conclude that the decrease in cocaine elimination in the dog associated with ethanol administration is due to ethanol-mediated inhibition cocaine metabolism, rather than inhibition by cocaethylene.

Decreased hypoprothrombinemic effect of warfarin associated with furosemide

The authors describe a case of furosemide possibly inhibiting the hypoprothrombinemic effect of warfarin. The initiation of furosemide dosing in a patient receiving a stable dose of warfarin was associated with an 28% decrease in the international normalized ration (INR). Using normal volunteers, two previous controlled studies of an interaction between warfarin and chlorthalidone, and between warfarin and spironolactone, assert that volume depletion produced by forced diuresis results in the inhibition of warfarin's hypoprothrombinemia. Consistent with this hypothesis, the authors found that their patient's hematocrit (believed to reflect hydration status) correlated with the INR: r2 = 0.78, p < 0.05. This case provides further evidence suggesting that acute diuresis can decrease the hypoprothrombinemic effect of warfarin.

Methazolamide-induced delirium

A 74-year-old man became delirious 2 days after beginning oral therapy with methazolamide. The delirium was manifested by intermittent psychosis, incontinence of bowel and bladder, lethargy, and disorientation. These symptoms continued for 25 days despite many changes in his drug regimen, and complete laboratory, urologic, and neurologic work-ups. The symptoms resolved completely within 1 week of discontinuing methazolamide. This is the first case reported of delirium associated with methazolamide not accompanied by a metabolic imbalance.

Effects of ethanol and cocaethylene on cocaine pharmacokinetics in conscious dogs

Coingestion of cocaine and ethanol is common among cocaine users, and this combination is reported to enhance the euphoric effects of cocaine. The cardiovascular effects of cocaine are increased in the presence of ethanol, although the mechanism(s) involved in this interaction are poorly understood. Recent studies suggest the enhanced cardiac effects may be caused by ethanol-mediated inhibition of cocaine metabolism leading to higher cocaine plasma concentrations. However, these studies were all performed in animals or humans that form cocaethylene when ethanol and cocaine are coadministered. Thus, it is also possible that cocaethylene could inhibit cocaine's metabolism. Preliminary studies in our laboratory indicate the dog does not form detectable quantities of cocaethylene after coadministration of cocaine and intravenous ethanol. Thus, the dog may be a useful model for isolating the individual contributions of ethanol and cocaethylene to this interaction. The purpose of the present study was to confirm this observation, and to determine the effects of ethanol and cocaethylene on cocaine pharmacokinetics in the conscious dog. Six dogs received cocaine (3 mg/kg i.v.) alone, ethanol (1 g/kg i.v.) followed by cocaine (3 mg/kg i.v.), and cocaine (3 mg/kg i.v.) + cocaethylene (3 mg/kg i.v.). Cocaethylene was not detected in any of the plasma samples from the six dogs after administration of cocaine and ethanol. Ethanol and cocaethylene reduced mean cocaine clearance by 47% and 26%, respectively. Inhibition of cocaine's metabolism by both ethanol and cocaethylene may play an important role in mediating the enhanced effects of cocaine in the presence of ethanol.

Quantitation of cocaine and cocaethylene in canine serum by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic procedure for the determination of cocaine and cocaethylene in canine serum has been developed. The compounds were extracted from 1 ml of alkalinized canine serum with hexane. Chromatographic separation was achieved with a cyanopropyl column (250 x 4.6 mm I.D., 5 microns) using a mobile phase of acetonitrile and phosphate buffer, pH 7.40 (38:62, v/v) flowing at 1 ml/min. Eluate was monitored by a variable-wavelength UV detector set to 230 nm. The extraction procedure yields an average recovery of 99 and 96% for cocaine and cocaethylene, respectively. The between-day coefficients of variation, at 2400 ng/ml, for cocaine and cocaethylene were both 8.6% and the within-day coefficients of variation, at 400 ng/ml, for cocaine and cocaethylene were 7.3 and 8.0%, respectively. A concentration-time profile resulting from administration of 3 mg/kg cocaine and cocaethylene to the dog revealed a similar disposition between cocaine and cocaethylene, with a clearance and volume of distribution at steady-state values of 72.8 and 61.0 ml/min/kg and 2.6 and 2.7 1/kg, respectively.

Factors affecting serum protein binding of cocaine in humans

The free (unbound) drug in serum is an important determinant of pharmacologic response. The present study was performed to more completely identify and evaluate factors affecting cocaine binding to human serum proteins. Protein binding was determined by ultrafiltration with [3H] cocaine. Cocaine binding parameters in serum from eight healthy volunteers were determined over a concentration range of 0.003 to 300 microM (0.001-100 micrograms/ml) and indicated cocaine binds to two classes of independent binding sites; one with high affinity [association constant (Ka) = 0.42 +/- 0.09 microM-1] and low capacity (N1 = 12.3 +/- 2.9 microM) and one with low affinity and high capacity (gamma = 0.41 +/- 0.05). Binding was concentration dependent with free fraction increasing from 0.16 +/- 0.05 to 0.68 +/- 0.02 over this concentration range. The binding capacity was significantly correlated with alpha-1-acid glycoprotein (AAG) concentration (r2 = 0.71, P = .0009). Binding studies were performed using AAG and human serum albumin (HSA) alone and together in phosphate buffer to determine the specific proteins responsible for cocaine binding. These studies revealed the binding of cocaine to AAG is potentiated by the presence of HSA as Ka for the first binding site increased from 0.08 microM-1 with AAG alone to 0.46 microM-1 with AAG combined with HSA 4 g/dl. Binding parameter estimates and cocaine free fraction in human serum and AAG 75 mg/dl plus HSA 4 g/dl in phosphate buffer were similar indicating that AAG and HSA are the principal binding proteins in serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Trimethoprim-sulfamethoxazole pharmacokinetics in trauma patients

STUDY OBJECTIVES

To characterize the pharmacokinetic profile of trimethoprim-sulfamethoxazole (TMP-SMX) in trauma patients and to compare these parameter estimates with those obtained in nontrauma patients.

DESIGN

Open-label, multidose, pharmacokinetic study.

SETTING

Trauma intensive care unit of a level 1 trauma center located within a regional medical center.

PATIENTS

Fifteen adult trauma patients with serious gram-negative infections. All patients were studied on day 1 of treatment, nine on day 3, three on day 5, and two on day 7. One patient was discontinued from the study because of a possible drug-induced rash.

INTERVENTIONS

Study patients received TMP 4 mg/kg and SMX 20 mg/kg intravenously every 12 hours. Serial blood sampling was performed up to 4 times per patient between treatment days 1 and 7. Serum was assayed for TMP-SMX using high-performance liquid chromatography. A one-compartment model was fit to the data using maximum likelihood estimation.

MEASUREMENTS AND MAIN RESULTS

Mean (SD) baseline parameter estimates for TMP were volume 2.1 (0.65) L/kg, half-life 9.7 (3.0) hours, and clearance 2.6 (0.80) ml/min/kg. Estimates for SMX were volume 0.51 (0.10) L/kg, half-life 7.8 (2.0) hours, and clearance 0.80 (0.29) ml/min/kg. Both volume (p < 0.01) and clearance (p < 0.001) for SMX were significantly higher and half-life (p < 0.05) significantly shorter than previously reported estimates in nontrauma patients. No significant differences in TMP parameter estimates were found. Neither TMP nor SMX clearance was significantly correlated with estimated creatinine clearance (p > 0.05).

CONCLUSION

The results indicate that the pharmacokinetics of SMX in trauma patients differ significantly from nontrauma patients, which may result in lower than expected concentrations using standard dosing guidelines.

Disposition of tirilazad (U74006F), a 21-aminosteroid, in the plasma, heart, brain, and liver of the rat

Tirilazad mesylate (Freedox, Upjohn) is the first agent of a new class of compounds called lazaroids currently under clinical investigation for its potential beneficial effects following neurotrauma. Tirilazad's therapeutic effect is due to its ability to inhibit iron-dependent lipid peroxidation. This study was conducted in Sprague-Dawley rats to determine the basic pharmacokinetics and distribution of tirilazad into the brain, heart, and liver. Rats (N = 50) were killed in groups of five at 0, 10, 20, and 40 min, and at 1.5, 2, 3, 4, 6, and 8 hr after intravenous administration of 10 mg/kg of tirilazad mesylate. Tirilazad was assayed in plasma, heart, liver, and brain tissue by HPLC. Using the mean concentrations at each time point, pharmacokinetic parameters were estimated using standard noncompartmental techniques and statistical moment theory. Tirilazad was rapidly eliminated from the plasma with a half-life of 2.4 hr and clearance of 6.1 ml/min. The volume of distribution at steady-state was large, 4.8 liters/kg. The concentrations of tirilazad were highest in the liver and heart and lowest in the plasma and brain. Elimination from tissues paralleled elimination from plasma with half-lives of 1.9, 1.6, and 1.5 hr in the brain, heart, and liver, respectively. Tirilazad appears to be a highly extracted, hepatically eliminated drug, suggesting its clearance is dependent on liver blood flow, and alterations in plasma protein binding are unlikely to affect its clearance but may affect the fraction unbound.

The disposition and cerebrospinal fluid penetration of morphine and its two major glucuronidated metabolites in adults undergoing lumbar myelogram

STUDY OBJECTIVE

To determine the pharmacokinetic disposition of morphine and its two major glucuronidated metabolites, morphine-6-glucuronide (M6G) and morphine-3-glucuronide (M3G), in serum and their penetration into cerebrospinal fluid (CSF).

DESIGN

A single-dose, open-label pharmacokinetic study.

SETTING

The Memphis Neurosciences Center at Methodist Hospital.

PATIENTS

Twenty patients undergoing a diagnostic lumbar myelogram.

INTERVENTIONS

All patients received morphine sulfate 10 mg intramuscularly approximately 1.5 hours before the procedure.

MEASUREMENTS AND MAIN RESULTS

Three blood samples were drawn after the dose and a CSF sample was drawn immediately after lumbar puncture. The mean +/- standard deviation for the half-life of morphine was 2.8 +/- 1.4 hours. The apparent half-lives of M6G and M3G were 5.7 +/- 3.1 and 6.3 +/- 2.2 hours, respectively, and were inversely related to the estimated creatinine clearance (r = -0.61, p < 0.007 and r = -0.69, p < 0.002, respectively). The mean concentrations of morphine, M6G, and M3G in the CSF (collection time 1.5 +/- 0.32 hrs, n = 19) were 3.1 +/- 3.7, 12.5 +/- 17.6, and 19.6 +/- 16.1 nmol/L, respectively.

CONCLUSIONS

Elderly patients and patients with renal dysfunction receiving morphine may experience prolonged analgesic and adverse effects secondary to a decrease in the clearance of M6G.

Multiple-dose pharmacokinetics of 12 milligrams of trimethoprim and 60 milligrams of sulfamethoxazole per kilogram of body weight per day in healthy volunteers

The disposition of 12 mg of trimethoprim and 60 mg of sulfamethoxazole per kg of body weight in six healthy male volunteers is described. The daily dose was evenly divided and administered orally every 6 h for 13 consecutive doses. Individual drug components were assayed by high-performance liquid chromatography. Steady-state concentrations in serum for trimethoprim and sulfamethoxazole were within the purported therapeutic ranges for treating Pneumocystis carinii pneumonia. Co-trimoxazole was well tolerated, and no subject withdrew from the study because of toxicity. Comparison of the pharmacokinetic parameters in this study with those of our previous findings indicates that the elimination of trimethoprim-sulfamethoxazole follows a first-order process within the dose ranges assessed. Administration of 15- to 20-mg/kg trimethoprim and 75- to 100-mg/kg sulfamethoxazole in four evenly divided doses for the first 24 h followed by 12 and 60 mg/kg/day, respectively, for the remainder of therapy rapidly attains concentrations in serum within the proposed P. carinii pneumonia therapeutic range. Clinical trials are indicated to evaluate this dosing scheme, which may decrease exposure to potentially excessive concentrations of trimethoprim and sulfamethoxazole.

Use of low-dose trimethoprim-sulfamethoxazole thrice weekly for primary and secondary prophylaxis of Pneumocystis carinii pneumonia in human immunodeficiency virus-infected patients

We conducted an open prospective clinical trial to evaluate the efficacy and toxicity of trimethoprim-sulfamethoxazole given as one double-strength tablet thrice weekly for primary and secondary prophylaxis of Pneumocystis carinii pneumonia (PCP) in human immunodeficiency virus-infected (HIV+) patients. A total of 104 HIV+ patients were evaluated, with 74 being in the primary prophylaxis group and 30 being in the secondary prophylaxis group. All except six patients received concomitant zidovudine; five patients on primary prophylaxis and one patient on secondary prophylaxis refused zidovudine. There were 70 patients evaluated for the efficacy of primary prophylaxis. The mean CD4 count was 124.4 +/- 110.1 cells per microliter. The mean follow-up time was 11.8 +/- 5.8 months (median, 12 months; range, 1 to 32 months). Two noncompliant patients developed PCP after 1 and 3 months of chemoprophylaxis. The failure rate (under the intention to treat principle) was 2 of 70 patients (2.9%; 95% confidence interval, 0.35 to 10%), or 1 per 413 patient-months of observation. There were 27 patients evaluated for the efficacy of secondary prophylaxis. The mean follow-up time was 12.4 +/- 7.2 months (median, 11 months; range, 1 to 29 months). Two patients, one of whom was noncompliant, were treatment failures, developing PCP after 14 and 15 months of chemoprophylaxis; this gave a failure rate of 2 of 27 patients (7.4%; 95% confidence interval, 0.9 to 24.3%), or 1 per 167 patient-months of observation. Adverse reactions sufficient to permanently terminate therapy occurred in 9 of 104 patients (8.7%; 95% confidence interval, 4 to 15.7%) overall. The serum trimethoprim, sulfamethoxazole, and N4-acetyl-sulfamethoxazole concentrations measured by high-pressure liquid chromatography were uniformly low. One double-strength tablet of trimethoprim-sulfamethoxazole taken weekly on Monday, Wednesday, and Friday appeared to be well tolerated and efficacious for the prophylaxis of PCP in HIV+ patients at high risk and deserves further investigation.

Pharmacokinetics and adverse effects of 20-mg/kg/day trimethoprim and 100-mg/kg/day sulfamethoxazole in healthy adult subjects

The pharmacokinetics of trimethoprim-sulfamethoxazole were studied in 12 healthy adult subjects receiving trimethoprim at 20 mg/kg of body weight per day and sulfamethoxazole at 100 mg/kg/day, which is the conventional dose for treating Pneumocystis carinii pneumonia (PCP). Daily doses were evenly divided and orally administered every 6 h for 3 days. Trimethoprim, sulfamethoxazole, and N4-acetylsulfamethoxazole concentrations in serum and urine were measured by high-performance liquid chromatography. Five subjects withdrew from the study because of intolerable gastrointestinal and central nervous system toxicities. In the seven subjects that completed the study, the mean maximum serum drug concentrations after the last dose were 13.6 +/- 2.0, 372 +/- 64, and 50.1 +/- 10.9 micrograms/ml for trimethoprim, sulfamethoxazole, and N4-acetylsulfamethoxazole, respectively. The mean half-lives were 13.6 +/- 3.5, 14.0 +/- 2.3, and 18.6 +/- 4.3 h, respectively. Changes in absolute neutrophil count were significantly correlated with the minimum concentrations of trimethoprim and sulfamethoxazole in serum and trimethoprim area under the concentration-time curve (for all three parameters, r2 = 0.6 and P less than 0.05). Our findings add to the evidence that serum drug concentrations in adults following the conventional dose of trimethoprim-sulfamethoxazole for PCP are excessive and contribute to certain adverse reactions. Further studies are indicated in patients to optimize the dosing regimen of trimethoprim-sulfamethoxazole in the treatment of PCP.

Disposition of bupropion in healthy volunteers and subjects with alcoholic liver disease

Bupropion hydrochloride is a new monocyclic antidepressant. In humans, its disposition results in the formation of three major metabolites: the morpholinol metabolite, the erythroamino alcohol, and the threoamino alcohol metabolite. Bupropion's disposition was monitored following a single oral 200 mg dose in eight healthy volunteers and eight age- (44.5 +/- 8.4 years) and weight- (77.4 +/- 6.7 kg) matched volunteers with alcoholic liver disease. This latter group is of interest because the incidence of depression is more frequent in alcoholics than in the general population, and the liver is the major route of elimination for cyclic antidepressants. The mean elimination half-life of the morpholinol metabolite was significantly prolonged in subjects with alcoholic liver disease (32.2 +/- 13.5 vs. 21.1 +/- 4.9 hours (p less than 0.05), while the differences in bupropion (17.3 +/- 8.6 hours vs. 16.5 +/- 10.4 hours for healthy subjects and subjects with alcoholic liver disease, respectively), erythroamino alcohol (26.1 +/- 13.3 hours vs. 29.8 +/- 6.9 hours for healthy subjects and subjects with alcoholic liver disease, respectively), and threoamino alcohol (25.5 +/- 8.6 hours vs. 23.4 +/- 10.7 hours for healthy subjects and subjects with alcoholic liver disease, respectively) were minimal. Mean area under the plasma concentration time curves for bupropion and metabolites were increased in subjects with alcoholic liver disease; however, clear differences between means of these small groups did not emerge, probably due to the increased variability of bupropion pharmacokinetics in these subjects. As a therapeutic agent for the treatment of depression in chronic alcoholics who may consume alcohol in combination with their antidepressant therapy, the lack of sedation with bupropion could be advantageous.(ABSTRACT TRUNCATED AT 250 WORDS)