Severe infantile axonal neuropathy with respiratory failure

We describe 5 infants (4 male, 1 female) with a severe intractable form of motor-sensory axonal neuropathy. All became ventilator-dependent, 4 have since died and 1 remains static. Diaphragmatic paralysis was an early feature with generalized neuropathy evolving rapidly. Nerve conduction studies and biopsies were consistent with axonal disease. This disorder could be a new condition or part of the spectrum of inherited neuropathies of the axonal degenerative type. It may be that there is a "switching-off" in the infant's Schwann cell-axonal interactions in utero or in the early postnatal period, resulting in severe progressive deterioration and then a static period without recovery.

Health-related quality of life and occurrence of intestinal side effects after pelvic radiotherapy--evaluation of long-term effects of diagnosis and treatment

Health-related quality of life (HRQOL) and occurrence of late intestinal side effects were assessed 3-4 years after pelvic radiotherapy for carcinoma of the endometrium and cervix. During 1988-1990, 143 women were included in a clinical trial to evaluate the effect of a low fat, low lactose diet on radiation-induced diarrhoea. Of 94 survivors, 79 (84%) answered the request. HRQOL was assessed by the EORTC QLQ-C36 and compared with population-based norms. The women scored lower than the general population on role functioning (81.5 versus 90.6 (p < 0.01)) and higher on diarrhoea (23.8 versus 9.5 (p < 0.01)). Compared with pre-treatment conditions, an increase in cases with pain in the lower back, hips and thighs was seen. Substantial pain and diarrhoea were associated with deterioration in HRQOL. In conclusion, few treatment and/or disease-related effects were detected 3-4 years after radiotherapy, with the exception of increased bowel frequency and pain in the lower back, hips and thighs.

Use of drug effect interaction modeling with Monte Carlo simulation to examine the impact of dosing interval on the projected antiviral activity of the combination of abacavir and amprenavir

The delineation of optimal regimens for combinations of agents is a difficult problem, in part because, to address it, one needs to (i) have effect relationships between the pathogen in question and the drugs in the combination, (ii) have knowledge of how the drugs interact (synergy, antagonism, and additivity), and (iii) address the issue of true between-patient variability in pharmacokinetics for the drugs in the population. We have developed an approach which employs a fully parametric assessment of drug interaction using the equation of W. R. Greco, G. Bravo, and J. C. Parsons (Pharmacol. Rev. 47:331-385, 1995) to generate an estimate of effects for the two drugs and have linked this approach to a population simulator, using Monte Carlo methods, which produce concentration-time profiles for the drugs in combination. This software automatically integrates the effect over a steady-state dosing interval and produces an estimate of the mean effect over a steady-state interval for each simulated subject. In this way, doses and schedules can be easily evaluated. This software allows for a rational choice of dose and schedule for evaluation in clinical trials. We evaluated different schedules of administration for the combination of the nucleoside analogue abacavir plus the human immunodeficiency virus type 1 protease inhibitor amprenavir. Amprenavir was simulated as either 800 mg every 8 h (q8h) or 1,200 mg q12h, each along with 300 mg q12h of abacavir. Both regimens produced excellent effects over the simulated population of 500 subjects, with average percentages of maximal effect (as determined from the in vitro assays) of 90.9%+/- 11.4% and 80.9%+/-18.6%, respectively. This difference is statistically significant (P<<0.001). In addition, 68.8 and 46.0% of the population had an average percentage of maximal effect which was greater than or equal to 90% for the two regimens. We can conclude that the combination of abacavir plus amprenavir is a potent combination when it is given on either schedule. However, the more fractionated schedule for the protease inhibitor produced significantly better effects in combination. Clinicians need to explicitly balance the improvement in antiviral effect seen with the more fractionated regimen against the loss of compliance attendant to the use of such a regimen. This approach may be helpful in the preclinical evaluation of multidrug anti-infective regimens.

Pulmonary function and airway responsiveness in mild to moderate asthmatics given repeated inhaled doses of zanamivir

Zanamivir is a potent and specific inhibitor of influenza A and B virus neuraminidase, that is now approved for the treatment, and is currently under development for the prophylaxis of influenza. To assess the safety of this drug in asthmatics, 13 subjects with mild/moderate asthma [forced expiratory volume in 1 sec (FEV1)> or =70% predicted, reversibility of FEV1 to salbutamol > or =15%, concentration of methacholine causing a drop of 20% in the FEV1 (PC20FEV1)< or =8 mg ml(-1)], were recruited to a double-blind, randomized, placebo controlled, two way cross-over study. Subjects received 10 mg zanamivir as a dry powder (2 x 5 mg blisters via a Diskhaler Sovnn Plastics Ltd., Berkshire, U.K.), or a matching placebo, twice daily on day 1 and then four times daily from day 2 to day 14, in two separate periods separated by a washout period of 7 days. PC20FEV1 to methacholine was determined pre-study, on day 1 after the evening dose and on day 14 after the last dose of the study drug. FEV1 was measured pre-study and at regular intervals on days 1 and 14. Laboratory safety tests were performed on days 1, 7 and 15. Morning and evening peak expiratory flow rate (PEFR) and any adverse events were recorded in a diary card. Eleven subjects completed the study. One was withdrawn due to non-compliance, and one due to an adverse event that occurred during the placebo period. On day 1 the geometric mean PC20 for zanamivir was 36% lower than for placebo [ratio to placebo 0.64, (90% CI 0.44, 0.93)] and on day 14 this was 33% lower with zanamivir [ratio to placebo 0.67 (90% CI 0.38, 1.15)]. Both these confidence intervals were within the pre-defined interval of 'no clinically significant effect' of 0.25-4 (i.e. a change of two doubling doses of methacholine PC20FEV1 which was considered clinically significant). The time weighted mean FEV1 was 0.15 l (5.4%) lower for zanamivir on day 1 compared to placebo (90% CI 0.03, 0.28; P=0.050) and 0.01 l higher compared to placebo on day 14 (90%CI -0.12, 0.10; P=0.912). The day 1 changes were not associated with any significant symptoms or requirement for rescue bronchodilator therapy. Furthermore there was no apparent treatment difference over the 14 day dosing period in FEV1 data (90% CI: -0.11, 0.05, P=057). The mean morning PEFR was 4 l min(-1) less for zanamivir than for placebo (90% CI: -11, 3) and mean evening PEFR was 9 l min(-1) less (90% CI: -24, 5). The study treatments were well tolerated by the subjects with no clinically significant adverse events attributable to zanamivir treatment. Zanamivir inhaled as a dry powder does not significantly affect the pulmonary function and airway responsiveness of subjects with mild/moderate asthma and therefore its use in such patients subjects is not precluded.

Pharmacoscintigraphic evaluation of lung deposition of inhaled zanamivir in healthy volunteers

OBJECTIVE

The objective of this study was to determine the sites of zanamivir deposition in the respiratory tract and the pharmacokinetics of zanamivir after oral inhalation from the Diskhaler device and from a prototype of a novel breath-activated device.

DESIGN

This was a 2-period block-randomised study in which participants inhaled zanamivir from a Diskhaler and/or the prototype device on separate days.

STUDY PARTICIPANTS

13 healthy volunteers (5 men and 8 women) aged 20 to 42 years (mean age 29 years) and weighing 54.0 to 94.0 kg (mean bodyweight 69.2 kg) entered the study.

INTERVENTIONS

Participants were given dry powder zanamivir 10 mg formulated with 99mTc from the Diskhaler or the prototype device on separate days. Scintigraphic images of the chest and oropharynx were recorded. Blood samples for determination of serum zanamivir and urine for excretion studies were taken up to 8 hours after drug administration. Safety was evaluated by monitoring lung function tests, adverse events and laboratory parameters.

RESULTS

Orally inhaled zanamivir was well tolerated, as demonstrated by lung function tests. A mean of 13.2% (n = 11) of the 10 mg dose from the Diskhaler was deposited in the bronchi and lungs. The deposition pattern varied between individuals, showing a preferentially central deposition pattern in some and a uniform distribution pattern in others. The major deposition site was the oropharynx (mean 77.6%), with a mean of 1.2% deposited on the trachea and a mean of 3.2% retained in the blister. Similar data were obtained with the prototype device. Inhalation of zanamivir gave a broad peak of systemic absorption with mean maximum serum concentrations of approximately 30 to 40 micrograms/L after 1.5 hours. The rate and extent of absorption were similar irrespective of inhalation device. Less than 5% of drug was excreted unchanged in urine within 8 hours of inhalation, confirming the low bioavailability of zanamivir after pulmonary delivery. A significant correlation existed between systemic exposure and peripheral lung deposition.

CONCLUSIONS

The local concentrations of zanamivir that result from oral inhalation via the Diskhaler are estimated to be > 10 mumol/L throughout the respiratory tract, well in excess of the concentrations observed to inhibit influenza virus neuraminidases by 50% (0.64 to 7.9 nmol/L). Similar deposition data were obtained with the Diskhaler and the prototype device, which was consequently not developed further. Pharmacoscintigraphy was confirmed as being a reliable technique for measuring zanamivir deposition in the respiratory tract.

Deposition and disposition of [11C]zanamivir following administration as an intranasal spray. Evaluation with positron emission tomography

OBJECTIVE

This study used positron emission tomography (PET) to investigate the deposition and disposition of zanamivir administered as a nasal spray.

DESIGN

This was an open-label single-dose study in healthy volunteers.

STUDY PARTICIPANTS

Six healthy male volunteers, aged 19 to 33 years (mean age 25 years) with a bodyweight of 65 to 94 kg (mean bodyweight 76 kg), took part in the study.

INTERVENTIONS

Each participant received by nasal spray zanamivir 6.4 mg mixed with, on average, 2.5 MBq of [11C]zanamivir. The amount of radioactivity was recorded sequentially in 5 different sectors of the body, starting with a short dynamic sequence over the nasal passage. Each of the regions was examined 1 to 4 times at different times after inhalation. The duration of the examination was 90 minutes. During this time, multiple blood samples were taken for analysis of radioactivity in whole blood. Serum samples for pharmacokinetic determinations were collected for 8 hours after administration.

RESULTS

Immediately after administration, about 90% of the drug was deposited in the nasal passage, decreasing to 48% at 90 minutes after administration. Less than 2% was detected in the lower respiratory tract. The major elimination route was via the oesophagus to the stomach. Approximately 2% of the dose was absorbed; the median maximum drug concentration in serum was 15 micrograms/L, and occurred around 1.75 hours after inhalation.

CONCLUSIONS

The major deposition site for zanamivir administered by nasal inhalation is the nasal passage; half of the drug remains there for at least 1.5 hours after administration. PET seems to be an excellent tool for this type of kinetic study, allowing imaging and measurements of inhaled drugs with high quantitative accuracy and good spacial resolution.

Effect of renal impairment on the pharmacokinetics of intravenous zanamivir

OBJECTIVE

Zanamivir is eliminated almost exclusively by renal excretion. This study evaluated the effect of renal impairment on the pharmacokinetics of intravenous zanamivir.

DESIGN

This open-label study compared individuals with mild/moderate or severe renal impairment, as defined by creatinine clearance (CLCR), with healthy participants.

STUDY PARTICIPANTS

There were 17 participants (9 men and 8 women), of whom 7 had normal renal function (CLCR > 70 ml/min), 5 had mild/moderate renal impairment (CLCR 25 to 70 ml/min) and 5 had severe renal impairment (CLCR < 25 ml/min).

INTERVENTIONS

Single 4 mg doses of zanamivir were administered intravenously to healthy participants and those with mild/moderate renal impairment; participants with severe renal impairment received 2 mg. Zanamivir concentrations were determined in blood and urine. Safety was evaluated by monitoring adverse events, vital signs and laboratory parameters.

RESULTS

Zanamivir was well tolerated both in participants with renal impairment and in healthy volunteers. There were no clinically significant changes attributable to zanamivir treatment. Renal dysfunction had marked effects on the pharmacokinetics of zanamivir. Although no statistically significant differences were detected between either renal impairment group and the normal renal function group for the maximum serum concentration (Cmax) or the time this occurred (tmax), a strong relationship was detected between CLCR and total body clearance (CL), renal clearance (CLR) and the terminal phase elimination rate constant (lambda z). Each 2-fold increase in CLCR produced average increases of 100, 121 and 85% in CL, CLR and lambda z, respectively. The area under the serum concentration-time curve from zero to infinity (AUC infinity) was on average increased 2-fold in individuals with mild/moderate renal impairment (4 mg dose) and 3.5-fold in those with severe impairment (2 mg dose) compared with healthy individuals (4 mg dose).

CONCLUSIONS

The proposed total daily dosage of zanamivir by oral inhalation is 20 mg. Given the tolerability (observed in a separate study to be reported in this supplement) after daily intravenous dosages of 1200 mg, and the limited systemic absorption after oral inhalation, the increased drug exposure in patients with severe renal failure is not considered clinically significant. Furthermore, the local concentrations in the lung following oral inhaled delivery are essential for efficacy. Therefore, for orally inhaled zanamivir, no dosage adjustment is required in patients with renal impairment.

Pharmacokinetics of zanamivir after intravenous, oral, inhaled or intranasal administration to healthy volunteers

OBJECTIVE

The objective of these studies was to examine the clinical pharmacokinetics and safety of zanamivir, an influenza A and B virus neuraminidase inhibitor, when administered to healthy volunteers.

DESIGN

The safety, tolerability and pharmacokinetics of zanamivir administered by a number of routes were assessed in randomised, double-blind and placebo-controlled studies. The study of absolute oral bioavailability had an open design.

STUDY PARTICIPANTS

The participants in these studies were healthy male or female volunteers.

INTERVENTIONS

Zanamivir was administered as single or multiple doses by the intravenous, oral, inhaled (nebuliser and dry powder) and intranasal routes. Serum and urine samples were obtained for determination of pharmacokinetic parameters, and nasal washes and throat gargles were performed to assess drug concentrations in the nose and throat. Safety was evaluated by monitoring adverse events, vital signs and laboratory parameters.

RESULTS

Zanamivir was well tolerated at all doses by all routes; no serious adverse events were reported. The kinetics of zanamivir were linear with single intravenous doses up to 600 mg, and there was no evidence of modification in the kinetics after repeated twice-daily administration. Approximately 90% of zanamivir was excreted unchanged in the urine. The elimination of zanamivir from the serum was a first-order process with a half-life of approximately 2 hours and, at 16 L, the volume of distribution was similar to that of extracellular water. The absolute oral bioavailability of zanamivir was low, averaging 2%. After intranasal or oral inhaled administration, a median of 10 to 20% of the dose was systemically absorbed, with maximum serum concentrations generally reached within 1 to 2 hours. The median serum half-life ranged between 2.5 and 5.05 hours, suggesting that the elimination rate is limited by absorption. There was no evidence of modification in the kinetics after repeated inhaled administration.

CONCLUSIONS

Zanamivir is a well tolerated drug. The low level of absorption of the drug after inhaled administration results in low serum concentrations, and therefore there is modest systemic exposure to zanamivir after inhalation. Zanamivir is not metabolised, and the potential for clinically relevant drug-drug interactions is very low.

Clinical pharmacokinetics of lamivudine

Lamivudine (3TC), the negative enantiomer of 2'-deoxy-3'-thiacytidine, is a dideoxynucleoside analogue used in combination with other agents in the treatment of human immunodeficiency virus type 1 (HIV-1) infection and as monotherapy in the treatment of hepatitis B virus (HBV) infection. Lamivudine undergoes anabolic phosphorylation by intracellular kinases to form lamivudine 5'-triphosphate, the active anabolite which prevents HIV-1 and HBV replication by competitively inhibiting viral reverse transcriptase and terminating proviral DNA chain extension. The pharmacokinetics of lamivudine are similar in patients with HIV-1 or HBV infection, and healthy volunteers. The drug is rapidly absorbed after oral administration, with maximum serum concentrations usually attained 0.5 to 1.5 hours after the dose. The absolute bioavailability is approximately 82 and 68% in adults and children, respectively. Lamivudine systemic exposure, as measured by the area under the serum drug concentration-time curve (AUC), is not altered when it is administered with food. Lamivudine is widely distributed into total body fluid, the mean apparent volume of distribution (Vd) being approximately 1.3 L/kg following intravenous administration. In pregnant women, lamivudine concentrations in maternal serum, amniotic fluid, umbilical cord and neonatal serum are comparable, indicating that the drug diffuses freely across the placenta. In postpartum women lamivudine is secreted into breast milk. The concentration of lamivudine in cerebrospinal fluid (CSF) is low to modest, being 4 to 8% of serum concentrations in adults and 9 to 17% of serum concentrations in children measured at 2 to 4 hours after the dose. In patients with normal renal function, about 5% of the parent compound is metabolised to the trans-sulphoxide metabolite, which is pharmacologically inactive. In patients with renal impairment, the amount of trans-sulphoxide metabolite recovered in the urine increases, presumably as a function of the decreased lamivudine elimination. As approximately 70% of an oral dose is eliminated renally as unchanged drug, the dose needs to be reduced in patients with renal insufficiency. Hepatic impairment does not affect the pharmacokinetics of lamivudine. Systemic clearance following single intravenous doses averages 20 to 25 L/h (approximately 0.3 L/h/kg). The dominant elimination half-life of lamivudine is approximately 5 to 7 hours, and the in vitro intracellular half-life of its active 5'-triphosphate anabolite is 10.5 to 15.5 hours and 17 to 19 hours in HIV-1 and HBV cell lines, respectively. Drug interaction studies have shown that trimethoprim increases the AUC and decreases the renal clearance of lamivudine, although lamivudine does not affect the disposition of trimethoprim. Other studies have demonstrated no significant interaction between lamivudine and zidovudine or between lamivudine and interferon-alpha-2b. There is limited potential for drug-drug interactions with compounds that are metabolised and/or highly protein bound.

Evaluation of different partial AUCs as indirect measures of rate of drug absorption in comparative pharmacokinetic studies

The performance of different partial AUCs, including partial AUC from zero to t(max) of the reference formulation (AUC(r)) and partial AUC from zero to tmax of test or reference formulation, whichever occurs earliest (AUC(e), as indirect measures of rate of absorption have been evaluated using simulated experiments. The performance of these metrics relative to C(max), t(max) and C(max)/AUC(infinity) was further assessed using the results of actual studies involving a Glaxo drug. The normalised metrics AUC(r)/AUC(infinity) and AUC(e)/AUC(infinity) have also been evaluated. Our provisional conclusions were: (1) AUC(r)/AUC(infinity) and AUC(e)/AUC(infinity) had greater statistical power than C(max) and the non-normalised partial AUCs at detecting true differences in rate of absorption. Using real data, the performance of AUC(e)/AUC(infinity) was poor, however, the performance of AUC(r)/AUC(infinity) was good; (2) C(max)/AUC(infinity) was more precisely estimated than AUC(r)/AUC(infinity) or AUC(e)/AUC(infinity) and may be a superior metric for assessing absorption rates of highly variable drugs.

Nucleoside analog 1592U89 and human immunodeficiency virus protease inhibitor 141W94 are synergistic in vitro

The use of combinations of anti-human immunodeficiency virus (anti-HIV) agents targeted to different molecular targets will most likely result in increased viral suppression and may also delay or prevent the emergence of resistant HIV strains. The purpose of the present study was to develop information on the in vitro anti-HIV activities of combinations of the reverse transcriptase inhibitor 1592U89 and the protease inhibitor 141W94 to help guide the choice of dosages in clinical trials. Triplicate in vitro dose-response matrices were prepared with MT-2 cells infected with HIV type 1 (HIV-1) strain IIIB. In order to account for the effects of protein binding, tissue culture medium with 10% fetal bovine serum was supplemented with the human serum proteins alpha1 acid glycoprotein (1 mg/ml) and albumin (40 mg/ml). The three-dimensional drug interaction surface for 1592U89 and 141W94 was constructed with the program MacSynergy II. As analyzed relative to a Bliss Independence null reference model, this combination was synergistic, with volumes of synergy exceeding 100 (99% confidence). Analysis of the data set with a fully parametric form of an equation for the quantitation of drug interaction developed by Greco et al. (W. R. Greco, G. Bravo, and J. C. Parsons, Pharmacol. Rev. 47:331-385, 1995) resulted in an interaction term statistically significantly greater than 0.0, indicating true synergy. Both methods concur that this combination is significantly synergistic. These data, with favorable findings from phase I/II trials for each drug alone, suggest that the combination of 1592U89 plus 141W94 should be further evaluated in clinical trials.

Evaluation of an automatic seizure detection method for the newborn EEG

In another publication, we described a set of methods for automatic detection of EEG seizures in the newborn. We describe here the evaluation of these methods using a completely new set of data, which were not used in developing the method. This testing data set consisted of recording from 54 patients, lasting an average of 4.4 h. Recordings had 8-16 channels and were obtained, in approximately equal numbers, from 3 institutions in Canada, the USA and Australia. Recording conditions varied from short recordings fully attended by a technologist to overnight recordings largely unattended. The average seizure detection rate was 69% (77%, 53%, 84% in the 3 institutions). False detections occurred at the average rate of 2.3/h (4.1, 1.0, 2.7 in the 3 institutions), with fluctuations that reflected largely the technical quality and level of supervision of the recordings. The results are similar to those obtained in the commonly used method of epilepsy monitoring in adults and allow us to envisage clinical application.

[Computer analysis of life style. A tool for reduction of cardiovascular diseases]

In accordance with the concept of total risk assessment for preventing coronary heart disease we have developed, over a ten-year period, three data programs for risk analysis (LIVDA). The patient is given a copy of his risk profile diagram and a written evaluation, together with advice and suitable literature. By means of this additional knowledge, and by establishing motivation and a consensus plan for improvement, the responsibility for change of lifestyle is transferred to the patient. The data system is flexible and the counsellor can adjust the risk factor system ad lib. Systematic quality adjustments of the advice to patients can be made continuously and in accordance with the treatment procedures. The risk data from selected patient groups can be used in scientific studies.

[Risk factors analysis of cardiovascular diseases. Is the Life Style Assessment useful?]

The Norwegian Medical Association's Health Control Handbook (1993) has introduced a lifestyle risk analysis-a paper-based way of assessing risk factors for cardiovascular disease and transferring them into pedagogic risk scores. By using the lifestyle risk analysis in our data based risk profile system LIVDA, we compared and evaluated the two systems through 437 consultations at our Occupational Health Clinic. The lifestyle risk analysis is a pedagogic tool, as compared with the unsystematic clinical information recorded in journals. We found only small differences between the lifestyle risk analysis and LIVDA, except when assessing total cholesterol and physical exercise. Lifestyle risk analysis does not, however, allow categorisation of risk factor values without adjustments, and does not include all relevant risk factors. Further, there are no possibilities of measuring motivation, or for selecting patients for group intervention.

Constant infusion and bolus injection of stable-label tracer give reproducible and comparable fasting HGO

We have investigated the reproducibility of fasting hepatic glucose output (HGO) estimates by use of isotope dilution methodology of stable-label tracers. Six normal subjects were studied on two occasions 1 wk apart. After an overnight fast, the subjects received a bolus injection of 7 mg/kg of [U-13C]glucose and, simultaneously, a primed constant infusion of 0.05 mg.kg-1.min-1 of [6,6(-2)H]glucose. The bolus injection provided one estimate of HGO (HGOBOL), and the constant infusion provided two estimates of HGO, namely, HGO at 2 h (HGOINF2) and HGO at 4 h (HGOINF4), both with the assumption of steady-state conditions. All estimates were similar in value; HGOBOL was highest, followed by HGOINF2 and HGOINF4 [2.30 +/- 0.11 (SE), 2.17 +/- 0.12, and 2.01 +/- 0.13 mg.kg-1.min-1]. The constant infusion gave highly reproducible results. In the case of HGOINF2, the within-subject coefficient of variation (CV) was only 3% compared with 5% of HGOINF4. The reproducibility of HGOBOL was comparable with the within-subject CV of 7%. We conclude that a constant infusion and a bolus injection of stable-label tracer give reproducible and comparable estimates of HGO.

Mixed effect modeling of sumatriptan pharmacokinetics during drug development. I: Interspecies allometric scaling

Allometric scaling is an empirical examination of the relationships between the pharmacokinetic parameters and size (usually body weight), but it can also involve brain weight for metabolized drug. Through all species, the protein binding of sumatriptan is similar (14-16%), and its metabolic pathway undergoes extensive oxidative deamination involving the monoamine oxidase A isoenzyme. These similarities across species suggested the possible relevance of an allometric analysis. Toxicokinetic data were collected from rats, pregnant rabbits, and dogs in animal pharmacokinetic studies where sumatriptan was administered intravenously to the animals at doses of 5 mg/kg. 0.25 mg/kg, and 1 mg/kg, respectively. Animal data were pooled and analyzed in one step using a mixed effect modeling (population) approach. The kinetic parameters predicted in any species were close to the observed values by species: 77 L/hr vs. 80 L/hr in man for total clearance, 137 L vs. 119 L for distribution volume at steady state. The value of the mixed effect modeling approach compared to the two-step method was demonstrated especially with the possibility of including covariates to describe the status of animal (e.g., pregnancy) in the model. Knowledge of the animal kinetics, dynamics, and metabolism of a drug contributes to optimal and expeditious development. Valuable information for the design of the first-dose-in-man study may emerge from more creative data analysis based on all the information collected during the preclinical and ongoing nonclinical evaluation of a new drug.

Common noncompartmental pharmacokinetic variables: are they normally or log-normally distributed?

We investigated the hypothesis that distributions of continuous pharmacokinetic variables are positively skewed in nature and that logarithmic transformation of these variables restores normality. The distributions of common continuous noncompartmental pharmacokinetic variables were investigated for four different Glaxo Wellcome compounds, administered by three different routes of administration: ranitidine (po), sumatriptan (sc), ondansetron (iv), and bismuth, from ranitidine bismuth citrate (po). The distributions of all the investigated noncompartmental pharmacokinetic variables were adequately described by a log-normal distribution, whereas statistically significant departures from normality occurred in the majority of cases. Thus, unless there is strong and consistent evidence for a departure from log-normality, the parametric statistical analysis of common noncompartmental pharmacokinetic variables should be carried out after a priori log transformation.

Dynamic modeling of cortisol reduction after inhaled administration of fluticasone propionate

Fluticasone propionate (FP) is a new corticosteroid that has been developed for the treatment of asthma. The compound has a very high receptor affinity, 18 times that of dexamethasone. After inhalation, FP is systemically available because of inhaled bioavailability. In healthy subjects this may lead to measurable systemic effects, such as cortisol reduction. A clinical study was conducted in 12 healthy volunteers to determine the systemic effects after inhaled administration of single 500-micrograms, 1,000-micrograms, and 2,000-micrograms doses of FP. Blood samples were collected over a 24-hour period after administration. Concentrations of FP and cortisol were measured in plasma by immunoassay. Cortisol reduction was chosen as the pharmacodynamic parameter. A novel linear release rate model was used to parameterize the cortisol data. The pharmacokinetics of FP were linear over the dose range studied. The cortisol release parameters were determined from baseline data (before drug administration). Based on these results, the E50 values for cortisol reduction were then determined for each dose of FP. The average E50 was 0.134 ng/mL for total FP concentrations and 0.013 ng/mL for unbound FP concentrations; these results were not dose dependent. These in vivo pharmacodynamic values measured in healthy subjects are in good agreement with the relatively high receptor affinity of FP.

Pharmacokinetics of intravenous fluticasone propionate in healthy subjects

1. Fluticasone propionate (FP) is a potent glucocorticoid used in the treatment of asthma. Prior to reporting the pharmacokinetics following the inhaled and oral routes, the pharmacokinetics need to be established following intravenous dosing. The present study determines the intravenous pharmacokinetics of FP, using non-compartmental analysis, in healthy male subjects over the 250 to 1000 micrograms dose range. 2. The pharmacokinetics of FP can be regarded as being linear over this dosing range. FP was extensively distributed within the body (Vss 3181), rapidly cleared (CL 1.1 l min-1) with a terminal elimination half-life of 7.8 h and a mean residence time of 4.9 h. 3. In order that future pharmacokinetic/pharmacodynamic and other modelling can be carried out, the plasma concentration-time profiles were parameterized using a model based on sums of exponentials, the appropriateness of this model was justified as the secondary kinetic parameters from the model were similar to those obtained using non-compartmental analysis.

Effect of ranitidine hydrochloride (150 mg twice daily) on the pharmacokinetics of increasing doses of ethanol (0.15, 0.3, 0.6 g kg-1)

1. The interaction of ranitidine hydrochloride (150 mg twice daily for 15 doses) with single doses (0.15, 0.3 and 0.6 g kg-1) of ethanol was investigated in a placebo controlled study in 24 male subjects. Ethanol was given 1 h after a standard breakfast to maximise a drug ethanol effect if there is one. A balanced incomplete block design was used in that each subject received two of the three ethanol doses in the presence or absence of ranitidine. Blood samples (n = 18) were taken for 8 h after dosing and blood ethanol concentrations (BAC) were determined by head space analysis using a validated gas liquid chromatographic method. 2. At the lowest dose of ethanol studied the pharmacokinetic profile was largely first order but at the higher doses the usual zero order kinetics were seen. Using the technique of simultaneous fitting across all doses the Km and Vmax constants were similar and close to literature value of 100 mg l-1 and 200-300 mg h l-1 respectively. 3. Ranitidine, in common with other H2-receptor antagonists tested under the same experimental conditions, caused a small rise in BAC. However this was only evident at the smallest dose of ethanol studied and in common with many other publications, no effects were seen at the higher doses. The mean rise in blood ethanol following the 0.15 g kg-1 dose was 2.6 mg dl-1 (13.3 mg dl-1 for placebo and 15.9 mg dl-1 for ranitidine) and this change is of no clinical relevance.

Electroencephalograms, clinical observations and the monitoring of neonatal seizures

OBJECTIVE

To identify neonatal seizures and evaluate the efficiency of clinical observations and short duration electroencephalograms (EEG).

METHODOLOGY

Sixty-three neonates were investigated using prolonged video/EEG monitoring. Patients with confirmed seizures were treated with sequential doses of phenobarbitone and, if seizures persisted, phenytoin. The likelihood of correct management if short duration EEG and clinical observations had been employed was determined.

RESULTS

Thirty-two patients had confirmed seizures. After administration of anticonvulsants, clinical observations identified seizures in a mean of 66% (s.d. 7.3%) of the cohort. A 60 min EEG after each stage of phenobarbitone therapy would guarantee electrographic seizure capture in a mean of 76% (s.d. 10%) of the cohort. A 60 min EEG after addition of phenytoin would guarantee capture in 50%.

CONCLUSIONS

An EEG would avoid misdiagnoses in most patients with ambiguous clinical signs. After anticonvulsant infusions, EEG add substantial information to that gained by clinical observations.

Fluticasone propionate--an update on preclinical and clinical experience

Fluticasone propionate (FP) is a novel androstane glucocorticoid with potent anti-inflammatory activity which has been effectively used, intranasally, as therapy for seasonal and allergic perennial rhinitis. When taken by the inhaled route, FP has shown significant therapeutic efficacy in the management of asthma. Fluticasone propionate is a highly lipophilic molecule with good uptake, binding and retention characteristics in human lung tissue. Fluticasone propionate has high glucocorticoid receptor selectivity and affinity, demonstrating rapid receptor association and slow receptor dissociation. In vitro, FP has been shown to potently inhibit T lymphocyte proliferation, cytokine generation, tumour necrosis factor alpha (TNF-alpha)-induced adhesion molecule expression, interleukin-5-induced eosinophilia, mucosal oedema and toluene 2,4-diisocyanate-induced mast cell proliferation, while promoting secretory leucocyte protease inhibitor production and eosinophil apoptosis. In human studies, FP has demonstrated marked vasoconstrictor potency in normal subjects and inhibited antigen-induced mucosal platelet activating factor/eicosanoid production, T lymphocytes and CD25+ cells in patients with rhinitis. Biopsy data from mild asthmatics demonstrate FP-associated reduction in CD3, CD4, CD8 and CD25 cells, with an accompanying reduction in eosinophil and mast cell markers. Clinical studies have evaluated lung function, bronchial reactivity, exacerbation rates and oral corticosteroid-sparing effect. Results show that FP has at least twice the clinical potency of beclomethasone dipropionate and budesonide. This appears to be achieved without an accompanying increase in systemic effects, suggesting a therapeutic index which may be higher than other currently available inhaled corticosteroids.