Pharmacokinetics of single-dose oral stavudine in subjects with renal impairment and in subjects requiring hemodialysis.

Two open-label studies assessed the pharmacokinetics of single orally administered doses of 40 mg of stavudine in subjects with renal impairment. In one study (study I), 15 subjects with selected degrees of renal impairment, but not requiring hemodialysis, were stratified into three groups of five subjects each according to creatinine clearance (CL(CR)) normalized by body surface area (ml/min/1.73 m(2)): mild (CL(CR), 60 to 80), moderate (30 to 50), and severe (/= 90) were also enrolled. The stavudine area under the curve from 0 h to infinity (AUC(0-infinity)) increased nonlinearly with declining renal function: 1,864, 2,215, 3,609, and 5,928 ng. h/ml for normal renal function and for mild, moderate, and severe renal impairment, respectively (P = 0.0001 between renal impairment groups). The following stavudine dosage recommendations for renal impairment were proposed for subjects weighing >/=60 kg: CL(CR) of >50 ml/min/1.73 m(2), 40 mg every 12 h; CL(CR) of 21 to 50 ml/min/1. 73 m(2), 20 mg every 12 h; and CL(CR) of 10 to 20 ml/min/1.73 m(2), 20 mg every 24 h. For subjects weighing <60 kg, the proposed doses were 30, 15, and 15 mg, respectively, with the same dosing intervals specified above. In a second study (study II), 12 subjects with end-stage renal disease requiring hemodialysis three times a week were enrolled in a randomized, open-label crossover study (dialysis 2 h after dosing and lasting 4 h or dosing without dialysis). There were no statistically significant differences for AUC(0-infinity), AUC(2-6), time to maximum concentration of drug in serum, half-life, or apparent oral clearance when the two treatment dosage regimens were compared. As a result of study II, the recommended dosing rate for subjects requiring hemodialysis was the same as that proposed for those with severe renal impairment not requiring hemodialysis; however, dosing was recommended to follow hemodialysis and to occur at the same time each day.

A single-dose study to assess the penetration of stavudine into human cerebrospinal fluid in adults.

Penetration of stavudine into the cerebrospinal fluid (CSF) was studied in healthy humans. In this open, randomized study, a single oral dose of 40 mg of stavudine was given to 12 fasting volunteers > or = 18 years of age. Subjects were divided into three groups based on the time of CSF sampling (i.e., 0.75-1.25, 2-3, or 4-5 hours after dosing). Blood samples were collected over an 8-hour period after dosing and included a sample simultaneous with CSF collection to permit an estimate of CSF : plasma ratios. Stavudine concentrations in plasma and CSF were determined by a validated high-performance liquid chromatography method. Repeated measurements of vital signs, physical examination, and clinical laboratory tests indicated that the stavudine dose was well tolerated. CSF levels were not detected 0.75 to 1.25 hours after dosing. Thereafter, levels were detected in the CSF of five subjects; the mean concentration was 61 ng/ml. The mean CSF: plasma ratio increased with time, from 0.16 at 2 to 3 hours postdose in one subject to 0.40 at 4 to 5 hours postdose in four subjects. In conclusion, the mean stavudine concentration of 61 ng/ml achieved in the CSF of five subjects exceeds the ED50 of clinical isolates of HIV (230 nM, 52 ng/ml).

A comparison of the pharmacokinetics of meropenem after administration by intravenous injection over 5 min and intravenous infusion over 30 min.

The pharmacokinetics of meropenem were determined in healthy volunteers after intravenous injection over 5 min or iv infusion over 30 min. Five volunteers received meropenem 500 mg and six volunteers received 1000 mg. For both doses, administration over 5 rather than 30 min doubled the plasma concentrations observed at the end of the dosing period. Comparison of the other data derived from the two modes of administration indicated that rapid administration of meropenem did not appreciably alter its disposition pharmacokinetics. Plasma clearance, renal clearance, non-renal clearance, terminal half-life and volume of distribution were unchanged. Within 1 h of dosing, the plasma concentrations were very similar indicating that dosing over either time period would result in similar antimicrobial cover and thus should not affect efficacy. There were no changes in tolerability of meropenem associated with more rapid administration.

A compilation of meropenem tissue distribution data.

Meropenem body fluid and tissue concentration data from both published studies and samples obtained during efficacy evaluation have been compiled and presented according to a consistent format to facilitate comparison. The concentration data have been compared with the mode MIC data available for the pathogens isolated during the clinical evaluation of meropenem. These data support the widespread and rapid penetration of meropenem into the interstitial fluid of those tissues not protected by a tight epithelial barrier. Furthermore, they suggest that the proposed dosages of meropenem 500 mg or 1 g tds would provide an adequate duration of cover at tissue sites for the treatment of a range of commonly occurring pathogens. A higher dosage of 40 mg/kg or 2 g in adults given tds would be recommended for meningitis based on the penetration of meropenem into CSF. Overall, the tissue and body fluid data presented confirm the expectation, based on the plasma concentrations and theoretical arguments, that meropenem is rapidly and readily distributed into the interstitial fluid, thereby producing concentrations in tissues likely to be clinically effective. This is consistent with the available clinical data on the therapeutic efficacy of meropenem.

The disposition and metabolic fate of 14C-meropenem in man.

1. The metabolism and pharmacokinetics of 14C-meropenem were studied in five volunteers who received 0.5 g (40 microCi) of the radiolabelled drug by i.v. infusion. 2. The maximum concentration of drug in plasma was 27 +/- 2 micrograms/ml (70 microM) corresponding to 98% of plasma radioactivity at the end of a 30 min infusion. The elimination half-life for meropenem in plasma was 1 h and meropenem remained the major radioactive component up to 6 h, but represented a decreasing proportion of the plasma radioactivity with time. One metabolite (the ring-open lactam) accounted for most of the remaining plasma radioactivity. The maximum concentration of metabolite was 1 +/- 0.1 micrograms/ml and the concentration of total radioactivity decreased to 2% of the peak value by 8 h. 3. Over the 5 days of the study, urinary excretion of radioactivity accounted for 99 +/- 0.5% dose, most of which was recovered in the first 8 h. There was negligible excretion in faeces. 4. Structural confirmation of the drug-related components in urine was accomplished by h.p.l.c.-mass spectrometry. Meropenem accounted for 71 +/- 2% dose of 14C and the ring-open lactam metabolite for most of the remainder, no other metabolites were detected. 5. Meropenem was the major radioactive component in urine up to 8 h after dosing and is therefore remarkably stable to human renal dehydropeptidase (DHP-1) compared with other carbapenems in clinical use.

Pharmacokinetics of meropenem in subjects with various degrees of renal impairment.

Five healthy volunteers and 18 patients with various degrees of renal impairment received 500 mg of meropenem intravenously as a 30-min infusion. Five dialysis patients were dosed 2 h prior to hemodialysis, and four of them were also dosed between hemodialysis treatments. Plasma and urine samples were collected for up to 48 h and 12 h, respectively. Concentrations of meropenem and its open ring metabolite ICI 213,689 were determined by high-performance liquid chromatography and radioimmunoassay, respectively. The subjects were divided into four groups with glomerular filtration rates (GFR) of greater than 80, 30 to 80, 5 to 29, or less than 5 ml/min. There were linear correlations between the GFR and the rates for total plasma clearance as well as renal clearance of meropenem (group mean values for total clearance of 186, 74, 53, and 19 ml/min/1.73 m2, respectively). In subjects with normal renal function, nonrenal clearance accounted for approximately 20% of total elimination, increasing to about 50% in patients with GFR between 5 and 29 ml/min/1.73 m2. The terminal half-life of meropenem increased from 0.9 h in the healthy volunteers to 6.8 h in patients with end-stage renal disease. The half-life of ICI 213,689 was 2.31 h in the healthy volunteers and increased to 23.6 h in patients with GFR of 5 to 29 ml/min. In patients with end-stage renal disease, half-lives could not be measured, as concentrations were hardly declining during the 48-h observation period. The area under the concentration-time curve for meropenem increased more than 10-fold. Both meropenem and its open ring metabolite were readily dialyzable, with dialysis clearances of 79 and 81 ml/min/1.73 m2, respectively.

The effects of a 5-HT2 receptor antagonist (ICI 169,369) on changes in waking EEG, pupillary responses and state of arousal in human volunteers.

1. ICI 169,369 (2-(2-dimethylamino ethylthio)-3-phenyl quinoline) is a potent selective competitive antagonist of the 5-HT2 receptor in animal models. Effects of ICI 169,369 as single oral doses (80 and 120 mg) separated by 1 week, on the power spectrum of waking EEG, dark adapted pupil responses and sedation score, were studied in a double-blind, placebo controlled, randomised cross over within subject comparison, in six healthy male volunteers. 2. Pupillary responses were measured using a portable infrared pupillometer following 15 min dark adaptation, assessing resting vertical pupil diameter (RPD), light constricted diameter (MPD) and recovered final diameter (FPD) at the end of a 3 s measurement cycle. 3. Both doses of ICI 169,369 produced a mean 36% (range 10-54%) decrease in log 10 power of the waking EEG alpha activity with eyes closed (P less than 0.02), and mean 38% (range 2-86%) increase in theta activity at 2 h compared with placebo. 4. Both 80 and 120 mg doses of ICI 169,369 reduced RPD by approximately 30% from a predose value of 6.25 mm (+/- 0.87; 95% CI) and from placebo values 6.41 mm (+/- 1.06) and 7.48 mm (+/- 1.49) at 3 and 5 h after dosing. MPD was reduced by 50% with the 120 mg dose at 5 h after dosing (placebo 5.2 mm; ICI 169,369 2.7 mm; P less than 0.05). FPD was significantly reduced (P less than 0.01) by both doses at 3 h after dosing.(ABSTRACT TRUNCATED AT 250 WORDS)

Dapsone in low doses prevents Pneumocystis carinii pneumonia in the rat model.

Less toxic drugs are needed for the prophylaxis and treatment of Pneumocystis carinii pneumonia (PCP) in patients with AIDS. Rats immunosuppressed with cortisone were given dapsone, chlorproguanil (CPG) and chlorcycloguanil (CCG), alone or in combination, in the diet and the P. carinii attack rate was compared with that of untreated controls. Dapsone alone at doses of 25 and 5 mg/kg/day was 100% effective in preventing PCP. The efficacy of CPG and CCG, however, could not be properly assessed because of the lack of acceptance of the diet by the animals. Even so, as a result of the findings with dapsone in this study, and because of its pharmacokinetics and minimum inhibitory concentration for P. carinii in vitro, a clinical trial of reduced dosage of dapsone given prophylactically to human beings is suggested. Such a trial may show a decrease in the toxicity of the drug that usually accompanies its long-term administration but retention of its efficacy.

Pharmacokinetics of meropenem compared to imipenem-cilastatin in young, healthy males.

Imipenem combined with cilastatin and meropenem was given as intravenous infusions of 1 g to eight young, healthy males on two separate occasions. Blood and urine samples were collected for up to 12 h. The terminal half-lives in plasma were 0.98 h and 1.11 h for meropenem and imipenem, respectively. The volume of distribution was smaller for meropenem than for imipenem (12.5 l and 14.4 l, respectively). The plasma clearance for meropenem was 188 (SD 31) ml/min and for imipenem 183 (SD 25) ml/min. Renal clearance was on average 139 (SD 24) ml/min and 135 (SD 11) ml/min, respectively. About 75% of the administered dose of both compounds was eliminated unchanged in urine. Non-renal clearance accounted for approximately 25% of the total clearance for both drugs. The kinetics of meropenem are very similar to those of imipenem given with cilastatin, and meropenem is as stable against renal metabolic degradation as imipenem combined with cilastatin.

Pharmacokinetics of meropenem and its metabolite ICI 213,689 in healthy subjects with known renal metabolism of imipenem.

Six healthy male subjects who had received imipenem without cilastatin in previous studies, were given 500 mg meropenem as single 30 min intravenous infusions. Plasma and urine samples were collected for 12 h and meropenem and its metabolite were assayed by HPLC and RIA, respectively. The mean plasma half-life of meropenem was 0.8 h, mean plasma clearance 277 ml/min and the mean volume of distribution 20.4 l. The metabolite reached mean peak plasma concentrations of 1.5 mg/l. Renal clearance of meropenem averaged 200 ml/min. The mean urinary recovery of the metabolite was 20% and of unchanged drug 72% of the dose given. The recovery of meropenem ranged from 62.2% to 78.2% and was correlated to the urinary recovery of imipenem when given without cilastatin to the same subjects in previous studies (range 15.2-32.2%, rank correlation coefficient = 0.934). The results indicate that meropenem is much less susceptible to renal metabolism than imipenem. The inter-subject variability observed with meropenem correlates with the extent of urinary recovery of imipenem observed in previous studies with imipenem alone, indicating some susceptibility of meropenem to renal dehydropeptidase-I.

The pharmacokinetics of meropenem in volunteers.

Two human volunteer studies were performed with meropenem: a dose proportionality study of 0.25, 0.5 and 1.0 g and a probenecid interaction study. Six volunteers took part in each study. Meropenem was generally well tolerated: One volunteer was withdrawn from the dose proportionality study because of looseness of stool and abdominal pain after a dose of 1.0 g. The plasma concentrations of meropenem were linearly related to dose. The half-life of meropenem was approximately 1 h and the urinary recovery of unchanged drug was 79%. In the presence of probenecid the plasma half-life of meropenem was increased by 33% but the urinary recovery was unaffected.

Epstein Barr virus-specific immune defects in patients with persistent symptoms following infectious mononucleosis.

In a number of patients recovery from infectious mononucleosis (IM) following primary Epstein Barr virus (EBV) infection, is complicated by the persistence of symptoms for months or years. Normally recovery from infectious mononucleosis is associated with the development of EBV-specific antibodies and memory cytotoxic T-cells, which are present in the peripheral blood of all normal seropositive individuals. We studied four patients who had persistent symptoms for more than two years after infectious mononucleosis to determine if this abnormality was associated with a defect in EBV-specific or non-specific immune responses. All four patients had normal immunoglobulin concentrations, T- and B-cell numbers, T-cell proliferative responses and natural killer cell activity. However three of the four had reduced or absent antibodies to the EBV nuclear antigen (EBNA) although other EBV-specific antibody titres were normal. All four also had reduced EBV-specific cytotoxic T-cell activity as measured by the EBV regression assay. This defect was probably EBV-specific as alloreactive cytotoxic T-cell responses were normal. In addition, three of three patients tested had reduced in vitro antibody synthesis following pokeweed mitogen stimulation. These studies indicate that the syndrome of persistent symptoms following EBV mononucleosis may be associated with a defect in EBV-specific immunity, and thus suggest a possible immunological basis for the syndrome.

Pulmonary haemorrhage complicating Wegener's granulomatosis and microscopic polyarteritis.

The incidence and characteristics of pulmonary haemorrhage in a series of 89 patients with systemic vasculitis were analysed. Pulmonary haemorrhage occurred in 32 of these patients and was associated with haemoptysis in all 32, alveolar shadowing in the chest radiograph in 28, and a significantly raised transfer coefficient in 30. Pulmonary haemorrhage usually resolved with treatment by immunosuppressive drugs but was the cause of death in 11 patients. In contrast with patients with antibasement membrane antibodies there was no correlation between pulmonary haemorrhage and cigarette smoking. Pulmonary haemorrhage is a cause of serious morbidity in patients with systemic vasculitis.

Severe intestinal involvement in Wegener's granulomatosis.

A case of Wegener's granulomatosis is described, in which the presentation was blood stained mucus diarrhoea. Severe ileal, caecal, and rectal involvement improved rapidly after treatment with cyclophosphamide, azathioprine, and prednisolone. Although intestinal disease is an uncommon feature of Wegener's granulomatosis, both in our own experience (four of 45 cases) and in the literature, this diagnosis should be considered in view of the response to appropriate therapy.