Hydroxychloroquine for the management of recalcitrant oral lichen planus

OBJECTIVE

The objective of this study is to describe the efficacy of hydroxychloroquine (HCQ) in patients with oral lichen planus (OLP) refractory to conventional therapy.

STUDY DESIGN

In this single-center retrospective study, patients were prescribed HCQ 200 mg twice daily. Pain, reticulation, erythema, and ulceration scores were recorded. Two-sample and paired t tests were used to evaluate mean and paired pain scores and paired t test to determine substantial differences in paired REU scores, at HCQ initiation visit and final follow-up at 12 to 24 months.

RESULTS

Thirty-six patients (69.4% female) with a median age of 70 ± 12.0 (range 48-99) were initiated on HCQ. Only 30 patients were evaluable because pruritus developed in 5 patients (13.9%) and gastrointestinal symptoms in 1 (2.8%). The mean follow-up was 23.2 months (range 1-74). In 19 patients, there was a significant decline in the worst pain score from a mean of 3.9 (SD± 2.8, n = 19) to 1.9 (SD ± 2.4, n = 19) (t = 2.837, P < .006). Paired reticulation, erythema, and ulceration (REU scores) decreased from a weighted mean score of 16.0 (SD ± 8.0, n = 12) to 12.0 (SD ± 6.3, n = 12) (t = 2.07, P < .032).

CONCLUSION

Hydroxychloroquine was a suitable option and effective in reducing symptoms and disease severity in patients with recalcitrant OLP who do not adequately respond to standard therapy.

Some clinical implications of the protein binding of digoxin

1 The binding of [(3)H]-digoxin to human plasma proteins was studied using both ultrafiltration and frontal analysis, to establish a suitable method for the measurement of digoxin-protein interaction, and to assess the effect of variations in digoxin protein binding on its distribution. 2 Using ultrafiltration, [(3)H]-digoxin was found to bind to plasma proteins to the extent of 30-40% over a concentration range of 0.001-1 ng/ml. Frontal analysis was unsuccessful in the measurement of digoxin protein binding. 3 Dilution experiments using plasma and human serum albumin suggested that variations in digoxin protein binding would be unlikely to cause significant alterations in the levels of free drug in the body. 4 The possible clinical implications of these results are discussed.

Cochlear nucleus neurons redistribute synaptic AMPA and glycine receptors in response to monaural conductive hearing loss

Neurons restore their function in response to external or internal perturbations and maintain neuronal or network stability through a homeostatic scaling mechanism. Homeostatic responses at synapses along the auditory system would be important for adaptation to normal and abnormal fluctuations in the sensory environment. We investigated at the electron microscopic level and after postembedding immunogold labeling whether projection neurons in the cochlear nucleus responded to modifications of auditory nerve activity. After unilaterally reducing the level of auditory inputs by approximately 20 dB by monaural earplugging, auditory nerve synapses on bushy cells somata and basal dendrites of fusiform cells of the ventral and dorsal cochlear nucleus, respectively, upregulated GluR3 AMPA receptor subunit, while inhibitory synapses decreased the expression of GlyRalpha1 subunit. These changes in expression levels were fully reversible once the earplug was removed, indicating that activity affects the trafficking of receptors at synapses. Excitatory synapses on apical dendrites of fusiform cells (parallel fibers) with different synaptic AMPA receptor subunit composition, were not affected by sound attenuation, as the expression levels of AMPA receptor subunits were the same as in normal hearing littermates. GlyRalpha1 subunit expression at inhibitory synapses on apical dendrites of fusiform cells was also found unaffected. Furthermore, fusiform and bushy cells of the contralateral side to the earplugging upregulated the GluR3 subunit at auditory nerve synapses. These results show that cochlear nucleus neurons innervated by the auditory nerve, are able to respond to small changes in sound levels by redistributing specific AMPA and glycine receptor subunits.

X-ray CT metal artifact reduction using wavelets: an application for imaging total hip prostheses

Traditional computed tomography (CT) reconstructions of total joint prostheses are limited by metal artifacts from corrupted projection data. Published metal artifact reduction methods are based on the assumption that severe attenuation of X-rays by prostheses renders corresponding portions of projection data unavailable, hence the "missing" data are either avoided (in iterative reconstruction) or interpolated (in filtered backprojection with data completion; typically, with filling data "gaps" via linear functions). In this paper, we propose a wavelet-based multiresolution analysis method for metal artifact reduction, in which information is extracted from corrupted projection data. The wavelet method improves image quality by a successive interpolation in the wavelet domain. Theoretical analysis and experimental results demonstrate that the metal artifacts due to both photon starving and beam hardening can be effectively suppressed using our method. As compared to the filtered backprojection after linear interpolation, the wavelet-based reconstruction is significantly more accurate for depiction of anatomical structures, especially in the immediate neighborhood of the prostheses. This superior imaging precision is highly advantageous in geometric modeling for fitting hip prostheses.

Health surveillance of Glasgow medical undergraduates pursuing elective studies abroad (1992-1998)

BACKGROUND

An integral part of the training for many UK medical undergraduates involves a period of elective study abroad. There is concern about the health risks this poses to the students, and uncertainty regarding the responsibility this places on medical schools.

METHODS

Annually since 1992, medical undergraduates at Glasgow University have been asked to complete and return a confidential questionnaire on return from their elective studies. This records personal demographic details, the countries visited, and information about illnesses experienced. Analyses were conducted on the students' health experiences, lifestyle, the health precautions taken, and the climates experienced.

RESULTS

Global statistics were compiled on 750 respondents. A subset of 267 completed a more extensive, post-1996, questionnaire enabling detailed study of comparative illness rates. A majority took pretravel health advice, visited only one country, stayed for 1 to 2 months, and experienced a tropical climate. Forty-five percent reported symptoms of illness, and alimentary symptoms predominated (77% of those ill). Higher illness rates were reported in those who experienced a hot desert or tropical climate compared with those who did not. There was correlation between taking professional pretravel health advice and exposure to a more hazardous climate.

CONCLUSIONS

The attack rate for medical students on electives compares favorably to that for package holidaymakers; similarly the attack rate for students staying in the tropics compared with other travelers. A preexisting health problem did not predispose to a higher attack rate. Attack rates can be minimized by avoiding climatically extreme locations. This surveillance provides a focus of interest to the students, insight on minimizing avoidable health problems, evidences social responsibility by the Medical Faculty, and has the potential for expansion to other medical schools. Current Scottish medical school policies on HIV risk management would be strengthened by a more coordinated approach.

The effect of cimetidine on the pharmacokinetics of epirubicin in patients with advanced breast cancer: preliminary evidence of a potentially common drug interaction

Epirubicin is known to be metabolized in the liver. Therefore, drugs such as cimetidine, which inhibit the cytochrome P-450 enzyme system or reduce liver blood flow, may reduce the plasma clearance of epirubicin. In a small study, epirubicin 100 mg/m2 every 3 weeks was administered intravenously to eight patients, who also received oral cimetidine (400 mg b.d. for 7 days starting 5 days before chemotherapy) with either the first or second cycles. Epirubicin pharmacokinetics and liver blood flow (idocyanine green clearance) were assessed at each course. The areas under the plasma concentration time curves (AUCs) were used to compare the systemic exposure to epirubicin and its metabolites with each course. The estimated median percentage increase (95% confidence interval CI) in the AUC with cimetidine were: epirubicin 50% (95% CI -18 to 193, epirubicinol 41% (95% CI 1 to 92). Despite the small numbers studied, the increase in the active metabolite epirubicinol was significant (P < 0.05). These changes in exposure were not explained by reduced cytochrome P-450 activity as the 7-deoxy-doxorubicinol aglycone AUC was not reduced (357% increase: 95% CI 17 to 719) or by a decrease in liver blood flow (17% increase: 95% CI -39 to 104). Cimetidine is likely to be coprescribed or self-administered with epirubicin and therefore clinicians should be aware of this potential interaction.

Analysis of animal pharmacokinetic data: performance of the one point per animal design

A simulation study was carried out to determine the impact of various design factors on the accuracy and precision with which population pharmacokinetic parameters are estimated in preclinical pharmacokinetic studies. A drug given by intravenous bolus injection and having mono-exponential disposition characteristics was assumed. The factors investigated were (i) number of animals sampled at specified times with one observation taken per animal, (ii) error in observed concentration measurements, and (iii) doubling the number of observations per animal while varying the number of animals. Data were analyzed with the NONMEM program, and the least number of animals per time point (where each animal supplied one concentration-time point) required for accurate and precise parameter estimation was determined. The one observation per animal design yielded biased and imprecise estimates of variability, and residual variability could not be estimated. Increasing the error in the concentration measurement led to a significant deterioration in the accuracy and precision with which variability was estimated. Obtaining a second sample from each animal practically eliminated bias and facilitated the partitioning of interanimal variability and residual intraanimal variability, by introducing information about the latter. Doubling the total number of observations per animal required using half (i.e., 50) the total number of animals required for accurate and precise parameter estimation with the one sample per animal design.

Experimental design and efficient parameter estimation in preclinical pharmacokinetic studies

Monte Carlo simulation technique used to evaluate the effect of the arrangement of concentrations on the efficiency of estimation of population pharmacokinetic parameters in the preclinical setting is described. Although the simulations were restricted to the one compartment model with intravenous bolus input, they provide the basis of discussing some structural aspects involved in designing a destructive ("quantic") preclinical population pharmacokinetic study with a fixed sample size as is usually the case in such studies. The efficiency of parameter estimation obtained with sampling strategies based on the three and four time point designs were evaluated in terms of the percent prediction error, design number, individual and joint confidence intervals coverage for parameter estimates approaches, and correlation analysis. The data sets contained random terms for both inter- and residual intra-animal variability. The results showed that the typical population parameter estimates for clearance and volume were efficiently (accurately and precisely) estimated for both designs, while interanimal variability (the only random effect parameter that could be estimated) was inefficiently (inaccurately and imprecisely) estimated with most sampling schedules of the two designs. The exact location of the third and fourth time point for the three and four time point designs, respectively, was not critical to the efficiency of overall estimation of all population parameters of the model. However, some individual population pharmacokinetic parameters were sensitive to the location of these times.

Evaluation of a Bayesian approach to the pharmacokinetic interpretation of cyclosporin concentrations in renal allograft recipients

The utility of a Bayesian parameter estimation program in the interpretation of cyclosporin concentrations was investigated in a group of 32 patients following renal transplantation. The program was evaluated by comparing concentrations predicted from individual estimates of pharmacokinetic parameters with measured concentrations. A one-compartment model incorporating an exponential, time-related change in clearance was used for data collected in the first 4 weeks after transplantation, and predictions of concentrations measured during weeks 5-14 were made using three schemes: a changing clearance model using all data from week 1 onward; a changing clearance model using data from week 4 onward; and a nonchanging clearance model using data from week 4 onward. Results demonstrated that predictions made by the Bayesian program were unreliable during the first 4 weeks of therapy, but that there was a progressive improvement as time after transplantation increased. The changing clearance model was superior to the constant clearance model and its performance was not compromised by including data from the first 4 weeks of therapy. Although the Bayesian approach may help with the interpretation of blood cyclosporin concentrations during maintenance therapy, the large variability in the pharmacokinetics of orally administered cyclosporin limits the usefulness of the approach in the early weeks following transplantation.

The consequences of H2 receptor antagonist--piroxicam coadministration in patients with joint disorders

A randomised crossover study was performed in subjects with rheumatoid arthritis (or other arthropathies) to investigate if any alteration in the steady pharmacokinetics of the NSAID piroxicam (a drug which is extensively metabolised via cytochrome P450) or its major metabolites occurred as a result of coadministering either cimetidine or nizatidine. Twelve females and 2 males with mean age, weight, and albumin concentrations of 58 years, 61 kg, and 40 g.L-1 respectively, completed the study. Comparisons were made between the following parameters: plasma piroxicam AUCs [AUC0-24(P)], plasma 5-hydroxypiroxicam AUCs [AUC0-24(5-OHP)], the ratio of these i.e. AUC0-24(5-OHP):AUC0-24(p), the % piroxicam daily dose excreted in urine as 5-hydroxypiroxicam (before and after glucuronidase incubation); and the mean of the steady state trough piroxicam, and 5-hydroxypiroxicam concentrations (obtained during each study phase in addition to the wash-out period). A statistically significant difference as a result of initiating either cimetidine or nizatidine was obtained only for the ratio AUC0-23(5-OHP):AUC0-24(P). This was indicative of a weak potential to inhibit piroxicam hydroxylation. No clinically significant alteration in the steady state pharmacokinetics of piroxicam occurred in these subjects as a result of cimetidine or nizatidine coadministration. Consequently it is unlikely that any adverse events would arise from these combinations.

Interpretation of simulation studies for efficient estimation of population pharmacokinetic parameters

OBJECTIVE

To develop new approaches for evaluating results obtained from simulation studies used to determine sampling strategies for efficient estimation of population pharmacokinetic parameters.

METHODS

One-compartment kinetics with intravenous bolus injection was assumed and the simulated data (one observation made on each experimental unit [human subject or animal]), were analyzed using NONMEM. Several approaches were used to judge the efficiency of parameter estimation. These included: (1) individual and joint confidence intervals (CIs) coverage for parameter estimates that were computed in a manner that would reveal the influence of bias and standard error (SE) on interval estimates; (2) percent prediction error (%PE) approach; (3) the incidence of high pair-wise correlations; and (4) a design number approach. The design number (phi) is a new statistic that provides a composite measure of accuracy and precision (using SE).

RESULTS

The %PE approach is useful only in examining the efficiency of estimation of a parameter considered independently. The joint CI coverage approach permitted assessment of the accuracy and reliability of all model parameter estimates. The phi approach is an efficient method of achieving an accurate estimate of parameter(s) with good precision. Both the phi for individual parameter estimation and the overall phi for the estimation of model parameters led to optimal experimental design.

CONCLUSIONS

Application of these approaches to the analyses of the results of the study was found useful in determining the best sampling design (from a series of two sampling times designs within a study) for efficient estimation of population pharmacokinetic parameters.

Effect of misspecification of the absorption process on subsequent parameter estimation in population analysis

A prospective simulation study has been carried out to evaluate the effect of potential misspecification of the absorption rate constant (ka) in population pharmacokinetic analysis when few to no concentration-time data were available in the absorption phase and estimation of ka was not possible. Data were simulated for 100 subjects using a one-compartment model at steady state with first-order input. Data were generated over a range of ka values: ka was misspecified in the NONMEM analysis by factors of 0.25, 0.5, 1, 2, 3, and 4. In general, clearance (CL) was typically estimated with a small, constant underprediction, regardless of the range of misspecification of ka or whether data were present in the absorption phase. The same was not true for volume of distribution (V), values were biased and sensitive to the degree of misspecification, but only when the data contained even a little information about absorption. If studies are to be designed in which information absorption is either not required or is of no therapeutic use, then blood samples could be concentrated in the postabsorption phase and the absorption input fixed according to the best a priori information available.

Value of theophylline treatment in patients handicapped by chronic obstructive lung disease

BACKGROUND

It is still not certain whether it is worth using theophylline in addition to inhaled bronchodilators and corticosteroids to treat obstructive airways disease. This trial was designed to test whether the addition of prescribed theophylline in doses sufficient for sustained optimal steady state plasma concentrations would produce any detectable additional advantage in spirometric or functional variables in these handicapped patients.

METHODS

A randomised, double blind, placebo controlled, crossover study of added theophylline treatment was aimed at steady state plasma concentrations of 10 and 17 mg/l, the dose being calculated individually by Bayesian parameter estimation and maintained for six weeks along with the patient's previously prescribed bronchodilators and steroids. Of 20 patients sequentially recruited, 15 provided data that could be analysed. All had chronic obstructive lung disease with a mean forced expiratory volume in the first second (FEV1) up to about 30% of the predicted value and gave no history of being treated with theophylline. The protocol included spirometry, whole body plethysmography, and treadmill exercise. Measurements also included steady state plasma theophylline concentrations and trapped gas volume. Quality of life was assessed by an established questionnaire method covering breathlessness in everyday activities, fatigue, emotional function, and control over the disease.

RESULTS

Both target plasma concentrations were achieved. Improvements in peak flow (PEF; mean 20%), trapped gas volumes (38%), two stage vital capacity (15%), distances walked (48%), breathlessness in everyday activities (32%), and fatigue (18%) were found at the higher plasma concentration only. FEV1, forced vital capacity (FVC), emotional function, and control did not change.

CONCLUSION

Theophylline treatment with sustained steady state concentrations about 17 mg/l provides worthwhile objective and subjective further benefits for patients handicapped by chronic obstructive lung disease when it is added to bronchodilators and corticosteroids.

Bayesian parameter estimation and population pharmacokinetics

The widespread application of Bayesian parameter estimation in the area of therapeutic drug monitoring (TDM) has prompted the need for well conducted population studies to obtain relevant prior pharmacokinetic parameter estimates. In many cases the population has consisted of a relatively small number of subjects. This may be unavoidable for drugs used in cancer chemotherapy or in small, specific populations of patients. In contrast, information about drugs which are used extensively, such as the aminoglycosides, can be obtained by population studies which involve a large number of individuals. Indeed, this technique has proved particularly useful for determining parameter estimates which can be employed in neonatal TDM. Bayesian parameter estimation has been most frequently used for drugs with narrow therapeutic ranges such as the aminoglycosides, cyclosporin, digoxin, anticonvulsants (especially phenytoin), lithium and theophylline. However, the technique has now been extended to cytotoxic drugs, Factor VIII and warfarin. Bayesian methods have also been used to limit the number of samples required in more conventional pharmacokinetic studies with new drugs. Further advances in the use of these methods are likely to include measures of drug response and toxicity requiring population studies which also include relevant pharmacodynamic information.

Variability in the pharmacokinetics of epirubicin: a population analysis

Population pharmacokinetic analysis of the anticancer agent epirubicin was carried out using the program NONMEM. Data were available from 36 patients aged 20-73 years, of whom 23 were women. All subjects exhibited normal liver and renal function. Epirubicin was given as a short-term i.v. infusion over the dose range of 25-100 mg/m2, and an average of 11 plasma samples/subject were taken for a period of up to 72 h after each dose. A Two compartment model was fitted to the data, characterised by the parameters clearance, volume of the central compartment, alpha and beta. Clearance was tested as a linear function of various demographic and/or biochemical features. A significant proportion of the variability in clearance could be attributed to sex, and also to age in women. For example, a 25-year-old man would display an average clearance of 95 l/h, whereas a 70-year-old woman would exhibit an average clearance of 64 l/h. Such differences in clearance might be important in the selection of epirubicin dose regimens.

Cyclosporine pharmacokinetics in liver transplant recipients: evaluation of results using both polyclonal radioimmunoassay and liquid chromatographic analysis

Pharmacokinetic variables were derived from cyclosporine measurements using liquid chromatography (HPLC) and radioimmunoassay with a non-selective polyclonal antibody (PARIA) in 11 orthotopic liver transplant recipients studied in paired oral and intravenous studies both before and after permanent clamping of the biliary T-tube. After oral drug administration, mean areas under blood cyclosporine concentration versus time curves before clamping were around 5.2-fold greater by PARIA than HPLC but 2.9-fold greater after clamping and closer to comparable values after intravenous cyclosporine (2.5 and 2.3-fold, respectively). Cyclosporine clearance was smaller by PARIA than HPLC (mean 7.3 versus 3.3 ml.min-1.kg-1, respectively, before clamping). Both values decreased by 25% after clamping (to 5.5 and 2.4 ml.min-1.kg-1, respectively), although there was no significant change in distribution or elimination half-lives (around 0.5 and 8 h, respectively). The mean bioavailability of oral cyclosporine increased significantly after clamping in 9 patients (from 10.6% to 28.1% by HPLC and from 14.8 to 35.1% by PARIA) but in two patients who developed the vanishing bile duct syndrome values fell to less than 10% and the proportional overestimation of cyclosporine concentrations by PARIA increased. Clamping had no singificant effect on the mean apparent volumes of distribution but values of Vz were approximately twice those of Vss (around 2.6 and 1.31.kg-1 by PARIA and HPLC respectively). Mean half lives after clamping were shorter following oral than intravenous cyclosporine (t 1/2 lambda 2 around 15 h enterally versus 8 h parenterally).(ABSTRACT TRUNCATED AT 250 WORDS)

Altered pharmacokinetics of cyclosporin in heart-lung transplant recipients with cystic fibrosis

The cyclosporin dose versus blood concentration relationship for 11 heart-lung transplant recipients with cystic fibrosis was studied retrospectively. Eleven patients, closely matched for age and gender, who received heart-lung transplantation for other diseases were selected as controls. Cystic fibrosis patients received 16.7 (SD 7.2) mg/kg/day of oral cyclosporin compared with 8.2 (SD 1.9) mg/kg/day given to the control patients (p less than 0.01). Nine of the cystic fibrosis patients received higher mean daily doses of cyclosporin. Mean blood cyclosporin concentrations were, however, not significantly different (p = 0.58), and there were no apparent differences in clinical outcome in terms of rejection, infection, and nephrotoxicity in the two groups. The apparent oral clearance of cyclosporin was significantly higher (p less than 0.01) in cystic fibrosis patients. Cyclosporin dosage individualization with the aid of cyclosporin blood concentration measurements is critically important in this subpopulation of heart-lung transplant recipients.

Experimental design and efficient parameter estimation in population pharmacokinetics

A computer simulation technique used to evaluate the influence of several aspects of sampling designs on the efficiency of population pharmacokinetic parameter estimation is described. Although the simulations are restricted to the one-compartment one-exponential model, they provide the basis for a discussion of the structural aspects involved in designing a population study. These aspects include number of subjects required, number of samples per subject, and timing of these samples. Parameter estimates obtained from different sampling schedules based on two- and three-point designs are evaluated in terms of accuracy and precision. These simulated data sets include noise terms for both inter- and intraindividual variability. The results show that the population fixed-effect parameters (mean clearance and mean volume of distribution) for this simple pharmacokinetic model are efficiently estimated for most of the sampling schedules when two or three points are used, but the random-effect parameters (describing inter- and intraindividual variability) are inaccurate and imprecise for most of the sampling schedules when only two points are used. This drawback was remedied by increasing the number of data points per individual to three.

Pharmacokinetics of an ACE inhibitor, S-9780, in man: evidence of tissue binding

Pharmacokinetic data from 20-min constant rate infusions of the ACE inhibitor S-9780 1 mg to 16 subjects were studied for evidence of nonlinearity. A hierarchy of standard compartmental models and of nonlinear binding models was fitted to the data by least squares nonlinear regression and the most appropriate model was chosen on the basis of F-ratio tests, Schwarz criteria, and residual plots. A one-compartment model which included saturable tissue and plasma binding components allowed the best overall description of the data. Median parameter estimates from this model suggest that approximately 308 nmol of plasma binding sites and 572 nmol of tissue binding sites were present and that the total plasma concentration of S-9780 at 50% saturation of binding sites was 16.5 nmol L-1. The elimination half-life for free drug in plasma was only 30 min. This model describes the discrepancy previously noted between accumulation and apparent elimination half-lives for long-acting ACE inhibitors and offers a noninvasive method for assessment of tissue-bound ACE inhibitor in vivo.

Rhabdomyolysis and listeria monocytogenes

Non-traumatic rhabdomyolysis occurs as a complication of a wide variety of infections and is often discovered as a result of the associated renal failure. We report a case of meningitis due to Listeria monocytogenes, an uncommon cause of infection in adults which was associated with rhabdomyolysis. This confirms a recent first case report of this association.

Population pharmacokinetic analysis of bisoprolol

The technique of population pharmacokinetic analysis was employed to study the variability in the dose concentration relationship of bisoprolol during its clinical development. The influence of demographic factors on the variability of clearance was investigated in 3 different populations: group I, patients (including an elderly group) with essential hypertension receiving multiple oral doses of bisoprolol 10 or 20mg for 3 months; group II, patients with different degrees of renal impairment and healthy controls; and group III, patients with different types of hepatic impairment and healthy controls. Patients and controls in groups II and III received only a single oral dose of bisoprolol 10mg. The 3 data sets were analysed separately, using a non-linear mixed effects model (the NONMEM program). A 2-compartment pharmacokinetic model with first-order absorption described the data adequately. The typical values of volume of central compartment, volume of distribution at steady-state and the absorption rate constant for the 3 populations were: for group I, 68L, 235L, and 0.7h-1; for group II, 28L, 179L, and 0.3h-1; and for group III, 55L, 256L, and 0.4h-1, respectively. Plasma clearance was related to age in group I, to serum creatinine in group II and to aspartate transaminase activity in group III. The 68% confidence limits for clearance and elimination half-life were 8.2 to 21.5 L/h and 7.6 to 19.7h, respectively, for 50-year-old patients in group I. The analysis predicted that progressive increases in serum creatinine or aspartate transaminase activity will result in only a 50% reduction of clearance.

Cyclosporin A pharmacokinetics in liver transplant recipients in relation to biliary T-tube clamping and liver dysfunction

Cyclosporin A pharmacokinetics were studied after oral (4-14 mg/kg body weight) and intravenous dosing (1.5-3.5 mg/kg) in 13 orthotopic liver transplant recipients before and after permanent clamping of the biliary T-tube. After T-tube clamping, cyclosporin A absorption was faster and more complete with the mean time of peak concentration, tmax, reduced to around three hours from around six hours and mean bioavailability rising from only 16.6% (n = 13) to 30% in the entire group (n = 11 after clamping) or to 35% after excluding two patients who developed severe cholestasis after the preclamping study. Bioavailability in these two patients fell below 8% and to around 1% in a further patient with severe graft dysfunction. Clamping reduced the metabolic clearance of cyclosporin A by only 25% from a mean before clamping of 2.9 ml/min/kg to 2.3 ml/min/kg (n = 11). Oral cyclosporin A becomes a reliable means of maintaining therapeutic drug concentrations only after bioavailability increases in association with T-tube clamping and in the absence of severe liver dysfunction or cholestasis.

Lisinopril population pharmacokinetics in elderly and renal disease patients with hypertension

1. The population pharmacokinetics of lisinopril were investigated using data collected from two multicentre trials of lisinopril in the treatment of hypertension in elderly patients (n = 40) and patients with renal disease (n = 20). 2. Lisinopril was started at doses of 2.5-5 mg daily and increased at 2-4 weekly intervals as required for control of blood pressure. Steady-state concentration-time profiles were measured after at least 2 weeks at a constant dose. 3. All concentration-time data were analysed simultaneously using the program NONMEM and the influence of clinical factors on clearance/F and volume of distribution/F was tested. 4. Clearance was significantly influenced by creatinine concentration, age, weight and cardiac failure. No clinical features tested were found to influence volume of distribution. 5. The influence of renal function and cardiac failure on lisinopril clearance has been confirmed using a population pharmacokinetic analysis technique.

Evaluation of a new Seralyzer assay for carbamazepine

The performance of a new dry-phase, strip immunoassay technique for the analysis of serum carbamazepine concentrations (Seralyzer), was compared to a standard high performance liquid chromatography (HPLC) method. One hundred blood samples were collected from 87 patients and analysed using both techniques. There was no significant difference between the concentrations measured by either technique, and the results were highly correlated (r = 0.97). The Seralyzer is a rapid and accurate method for use in carbamazepine therapeutic drug monitoring.

Naproxen dose and concentration: response relationship in rheumatoid arthritis

Information on the relationship between the plasma concentration of nonsteroidal anti-inflammatory drugs (NSAIDs) and clinical response in rheumatoid arthritis is sparse. As a result treatment is often relatively empirical. Standard doses are prescribed and an apparent lack of response leads either to the prescription of another drug, or an increase in the dose beyond that recommended. This study investigated 18 patients given three doses (500, 1000 and 1500 mg/day) of naproxen in a randomized double-blind design for 12 days at a time. Using a linear modelling approach we found that three out of four clinical response measurements improved linearly with increasing naproxen trough concentrations, suggesting that most patients will achieve an improvement in symptoms if the dose of naproxen is increased up to 1500 mg/day. However, since trough naproxen concentrations show a less than proportional increase with increasing dose (due to saturation of binding sites on plasma albumin), the improvement in response will be less dramatic as the dose is increased.

The effect of food on the absorption of slow-release isosorbide-5-mononitrate tablets

The influence of food on the absorption characteristics of slow release isosorbide-5-mononitrate tablets was investigated in 10 normal healthy volunteers. There were no differences in the peak concentration achieved or the area under the curve, but the peak concentration occurred later when the drug was administered after food. The apparent elimination half-life ranged from 4.7 to 10.1 h. Bioavailability of slow-release isosorbide-5-mononitrate is therefore unaffected by food, but there is a slower rate of absorption.

Population pharmacokinetics of gentamicin in neonates

The influence of a number of clinical characteristics on the population pharmacokinetics of gentamicin were examined using routine drug-monitoring data from a group of 113 neonates. The data were analyzed using the programme NONMEM. Clearance was 0.053 litres.h-1.kg-1 and was reduced in neonates with postconceptional age less than or equal to 34 weeks (X 0.83) and 5-min Apgar score less than 7 (X 0.82). Volume of distribution was 0.47 litres.kg-1. These population mean parameter estimates were used to generate dosage regimens to achieve concentrations within the therapeutic range.