Toxicology of octabromobiphenyl and decabromodiphenyl oxide.

Decabromodiphenyl oxide (DBDPO) and octabromobiphenyl (OBBP) perform well as fire-retardant additives for thermoplastics. Both compounds have low acute oral toxicity and low skin absorption toxicity. They are neither primary skin irritants or skin sensitizers and are only mildly irritating to the eyes. A 30-day dietary feeding study in rats established 8 mg DBDPO/kg-day as an unequivocal no-effect level and 80 mg/kg-day as a marginal effect level. A no-effect level was not established for OBBP in a comparative study. A 2-yr rat study providing 0.1 mg DBDPO/kg-day in the diet revealed the bromine concentration reached a plateau in the liver within 30 days, while the concentration in adipose tissue slowly increased. A comparable OBBP study revealed bromine concentration in the liver and adipose tissue increased steadily and rapidly with no attainment of a plateau during 180 days of the study. Neither compound produced an accumulation of bromine in other tissues. After administration of 14C DBDPO, all 14C activity was eliminated via the feces within 2 days. After administration of 14C OBBP, 62% was eliminated with a half-life of less than 24 hr; the half-life for the remainder was greater than 16 days. In a teratology study, 10, 100, or 1000 mg DBDPO/kg-day had no effect in rats. Reproductive capacity of rats was not effected at 3, 30, or 100 mg DBDPO/kg-day. No effects were observed on cytogenetic examination of bone marrow cells of parents and weanlings from the reproduction study.

Pharmacokinetics of probucol in male rats.

The bioavailability and pharmacokinetic behavior of 10 mg/kg of [14C]probucol in an oil-water emulsion was determined after oral and intravenous administration to rats. The bioavailability of the oral formulation was approximately 6%. For the first 12-h interval after the intravenous bolus, plasma probucol concentrations increased after an initial decrease. This effect may be attributed to the formulation or precipitation of the drug in the vasculature. The terminal plasma half-life was 6 d. By 7 d, 45 and 4.65% of the labeled intravenous bolus was excreted in the feces and in the urine, respectively. Although most of the labeled dose was excreted in the bile, any enterohepatic recirculation that did occur did not contribute to the atypical plasma concentration versus time profile. The tissue distribution of the label and elimination rates in the bile differed between the two routes of administration. Either the total body burden, precipitation of the drug, or the emulsion vehicle may be responsible for the nonlinear distribution and clearance of the intravenous dose.

Monitoring prednisone and prednisolone.

Their common clinical use, frequency of adverse effects, serious therapeutic indications, treatment failures, and availability of sensitive assays make corticosteroids such as prednisone and prednisolone candidates for therapeutic drug monitoring. Complicating the interpretation of plasma drug concentrations are the first-pass metabolism of inactive prednisone to active prednisolone and reconversion. Also, the volume of distribution, metabolic clearance, and renal clearance of prednisolone increase with dose. This is due partly to saturable binding of prednisolone to transcortin in plasma, which provides more unbound drug at higher plasma concentrations of steroid. This effect plus the probable uptake of only unbound drug into intracellular receptor sites provides the rationale for measuring free prednisolone in plasma. Drug interactions between prednisolone and anticonvulsants are common. Liver and kidney disease have only limited effects on prednisolone disposition. Changes in clinical efficacy and appearance of side effects have been related to altered prednisolone clearance. Plasma concentrations may be used to determine disease and drug interactions, bioavailability, and patient compliance. The role of pharmacokinetic factors in governing the indirect and variable pharmacodynamic response to corticosteroids at various tissue sites and in disease states currently needs clarification.

Corticosteroid analysis in biological fluids by high-performance liquid chromatography.

A sensitive, specific, and reproducible high-performance liquid chromatographic assay for the simultaneous determination of prednisone, prednisolone and cortisol in biological fluids was developed with dexamethasone as the internal standard. Samples are extracted with methylene chloride, washed with sodium hydroxide and then water, and chromatographed on a microparticulate silica gel column with UV detection at 254 nm. Sensitivity was greater than 15 ng for all four steroids. Specificity was supported by use of dual wave-length UV detection and/or radioimmunoassay. The assay has been applied in pharmacokinetic studies and a typical plasma concentration--time profile for the three steroids is presented for one subject who received 50 mg of prednisone.

Ethosuximide pharmacokinetics in a pregnant patient and her newborn.

Ethosuximide concentration in serum was monitored during the last trimester of pregnancy in a patient. After delivery, the decline in serum concentration of ethosuximide was observed in the nonnursing neonate. The half-life of elimination of transplacentally acquired ethosuximide in this neonate was 41.3 hr. The ratio of breast milk to maternal serum concentration of ethosuximide was approximately 1. A total daily exposure to ethosuximide of 12.8 to 38.4 mg (3.6 to 11.0 mg/kg) as a result of nursing was predicted.

Dose dependent pharmacokinetics of prednisone and prednisolone in man.

Six healthy male volunteers were given 5, 20, and 50 mg of oral prednisone and 5, 20, and 400 mg doses of intravenous prednisolone. Plasma and urine concentrations of prednisone and prednisolone were determined by HPLC, and the binding of prednisolone to plasma proteins was measured by radioisotopic and equilibrium dialysis techniques. The pharmacokinetics of both oral prednisone and intravenous prednisolone were dose-dependent. The mean oral dose plasma clearances of prednisone ranged from 572 ml/min/1.73 m 2 for the 5 mg dose to 2271 ml/min/1.73 m 2 for the 50 mg dose. Changes in prednisone half-life were insignificant, but increases in the half-life of its metabolite were dose-dependent. The systemic plasma clearance of i.v. prednisolone was dose-dependent and increased from 111 to 194 ml/min/1.73 m 2 over the 5 to 40 mg i.v. dosage range. The steady-state volume of distribution also increased, but little change in mean transit time and half-life was found. The binding of prednisolone to plasma proteins was markedly concentration-dependent, and a two compartment, nonlinear equation was used to characterize the effective binding of prednisolone to transcortin and albumin. The apparent pharmacokinetic parameters of protein-free and transcortin-free prednisolone were relatively constant with dose. The interconversion of prednisone and prednisolone varied with time and dose, although prednisolone concentrations dominated by 4- to 10-fold over prednisone. In urine, 2-5% of either administered drug was excreted as prednisone and 11-24% as prednisolone. The apparent renal clearances of both steroids were also nonlinear and unrelated to protein binding. These studies indicate that the pharmacokinetics of prednisone and prednisolone are dose-dependent and that protein binding does not fully explain their apparent nonlinear distribution and disposition.

Phenytoin disposition in smokers and nonsmokers.

Smoking habit did not affect the disposition kinetics of intravenously administered phenytoin. Phenyoin was given to 8 smokers and 8 nonsmokers and plasma concentrations of phenytoin were determined over a three day period by GLC and RIA techniques. Nonlinear least squares computer fit of the plasma concentration-time data yielded coefficients of a biexponential equation for calculation of half-lives (t1/2beta), clearances (ClB) and volumes of distribution. There were no statistically significant differences in these parameters with respect to either sex or smoking habit. However, more variable t1/2beta's were noted in the smoking group. No differences in serum protein binding between smoking and nonsmoking groups were found. Serum thiocyanate concentrations were used as a measure of smoking habit. There was no significant correlation between thiocyanate concentrations and t1/2beta or ClB. Attemps to correlate phenytoin ClB with basal metabolic rate also failed.

Effect of smoking on prednisone, prednisolone, and dexamethasone pharmacokinetics.

The pharmacokinetics of oral prednisone and oral dexamethasone were examined in 18 healthy male adults. Eight subjects also received intravenous prednisolone and intravenous dexamethasone. Half of each group were cigarette smokers as confirmed by plasma thiocyanate concentrations. Plasma and urine concentrations of prednisone and prednisolone were assayed by high performance liquid chromatography, while plasma dexamethasone was measured by radioimmunoassay. There were no statistically significant differences between smokers and nonsmokers in the systemic availability of prednisolone (75 versus 84%), oral dose clearance of prednisone (29 verus 27 ml/min/kg), systemic prednisolone clearance (2.8 versus 2.9 ml/min/kg), or in the interconversion rates, volumes of distribution, or urinary recoveries of prednisone and prednisolone. Similarly, the pharmacokinetics of dexamethasone were unaffected by smoking. A limited correlation (r = 0.55) was found between the high oral dose clearances of prednisone and the lower values of dexamethasone (6.73 and 5.71 ml/min/kg in smokers and nonsmokers). A two- to threefold variability occurred in oral dose clearances of each steroid with partial intrasubject covariance. Unlike the anticonvulsants, which markedly induce corticosteroid metabolism, smoking has no effect on their pharmacokinetics and should not complicate therapy with these drugs.

Prednisolone disposition in steroid-dependent asthmatic children.

The pharmacokinetics of a 40-mg intravenous dose of prednisolone were determined in 10 steroid-dependent asthmatic children with highly variable prednisone requirements (5 mg every other day to 40 mg a day). Concentrations of prednisolone and cortisol in plasma over a 24-hr test period were measured by high-performance liquid chromatography. Eosinophil concentrations and the concentration-dependent protein binding of prednisolone were also determined. The mean (+/-SD) apparent half-life of prednisolone in these children was 2.5 +/- 0.5 hr. The mean total volume of distribution was 52.8 +/- 14.5 L/1.73 m2 and mean plasma clearance was 246 +/- 62 ml/min/1.73 m2. These pharmacokinetic parameters, as well as the protein binding and eosinopenic response, were similar to values from healthy and steroid-dependent asthmatic adults. The data were also similar in both responsive and relatively resistant patients. The pharmacokinetics and protein binding of prednisolone are not responsible for the highly variable prednisone requirement and clinical response of these children to prednisone therapy.

Effect of charcoal and sorbitol-charcoal suspension on the elimination of intravenous phenobarbital.

The effects of two different oral charcoal suspensions on the elimination of a 200 mg/70 kg, 1 h intravenous (i.v.) infusion of phenobarbital and the tolerances of the two regimens were determined in a randomized crossover study in six healthy male volunteers. Phenobarbital was given i.v. alone or together with 105 g of oral activated charcoal suspension or with 105 g of a commercially available sorbitol-charcoal suspension over a 36-h period. A 13-34% decrease in the area under the serum concentration time curve (AUC) for 0-60 h occurred with the administration of the activated charcoal, and a 19-52% decrease occurred with the commercial sorbitol-charcoal regimen. The mean apparent systemic clearance of total phenobarbital increased from 0.089 +/- 0.019 ml/min/kg to 0.141 +/- 0.029 and 0.146 +/- 0.036 ml/min/kg with the charcoal and sorbitol-charcoal treatments, respectively. No significant change in the fraction of phenobarbital bound to protein was detected. The charcoal regimen caused constipation in one subject. All subjects taking the sorbitol-charcoal preparation experienced diarrhea; there were no changes in electrolytes with either charcoal suspension. All subjects preferred the sorbitol-charcoal preparation.

Disposition and cardioselectivity of MDL 74,405, a vitamin E-like free radical scavenger, in rats and dogs after intravenous infusion.

The disposition kinetics of MDL 74,405, a potent free radical scavenger for cardiac reperfusion and a vitamin E analog, was investigated in rats (1.2, 6.0, and 12 mg/kg) and dogs (1 and 10 mg/kg) after an intravenous infusion. Because the heart is the target site of drug action, a tissue distribution study was also conducted in rats (1.2 mg/kg) to explore the affinity of the drug to rat heart. In both animal species, plasma drug concentrations declined rapidly in the early distribution phase and exhibited a multiexponential pattern of elimination. Of the total excretion (95-96% of the dose) in 120 hr in rats, 45-51% was excreted in urine and 45-50% in feces. Of the total excretion (86-89% of the dose) in 120 hr in dogs, 41-43% of the dose was excreted in urine and 41-43% in feces. The dose was excreted mainly unchanged (62-78% in rat and 80-86% of the dose in dog urine) with several potential minor metabolites, indicating that renal and biliary excretions are the two major, equally important, routes of drug elimination in both species. Rats cleared the drug from the body markedly faster than dogs: the mean residence time in rats. (1.9-3.2 hr) was 15-20 times shorter, the terminal elimination half-life in rats (3.6-7.0 hr) was 10 times shorter; and the total clearance in rats (148-216 ml/min/kg) was 6-9 times greater. The steady-state volume of distribution was very large for both species. (19-37 liters/kg for rats and 59-64 liters/kg for dogs), which is consistent with the extensive tissue uptake of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of troleandomycin on methylprednisolone elimination.

Troleandomoycin (TAO), a macrolide antibiotic, has an apparent "steroid-sparing" effect when used in the treatment of severe steroid-dependent asthma. This study was designed to investigate the effect of TAO on methylprednisolone elimination. Pharmacokinetic studies were performed before and 1 wk after starting TAO in 10 severe steroid-dependent asthmatics. Baseline total body clearance of methylprednisolone was 406 +/- 139 (mean +/- SD) ml/min/1.73 m2 and decreased significantly (p < 0.001) to 146 +/- 57 ml/min/1.73 m2 1 wk after TAO therapy was initiated. Methylprednisolone half-life was 2.46 +/- 0.75 hr before TAO and increased significantly (p < 0.01) to 4.63 +/- 1.35 hr after 1 wk on TAO therapy. A follow-up evaluation of methylprednisolone pharmacokinetics in three patients after at least 1 mo on TAO therapy demonstrated continuation of the reduced methylprednisolone elimination. TAO inhibition of methylprednisolone clearance may contribute to the beneficial effects observed initially with combined methylprednisolone-troleandomycin therapy in severe steroid-dependent asthma.

Pharmacokinetic and clinical studies in patients with cimetidine-associated mental confusion.

15 cases of cimetidine-associated mental confusion have been reported. In order that this syndrome might be investigated changes in mental status (M.S.) were correlated with serum concentrations and renal and hepatic function in 36 patients, 30 patients had no M.S. change on cimetidine and 6 had moderate to severe changes. These 6 patients had both renal and liver dysfunction (P less than 0.05), as well as cimetidine trough-concentrations of more than 1.25 microgram/ml (P less than 0.05). The severity of M.S. changes increased as trough-concentrations rose, 5 patients had lumbar puncture. The cerebrospinal fluid: serum ratio of cimetidine concentrations was 0.24:1 and indicates that cimetidine passes the blood-brain barrier; it also raises the possibility that M.S. changes are due to blockade of histamine H2-receptors in the central nervous system. Patients likely to have both raised trough-concentrations and mental confusion are those with both severe renal and hepatic dysfunction. They should be closely observed and should be given reduced doses of cimetidine.

Prednisolone disposition in steroid-dependent asthmatics.

A 40-mg intravenous dose of prednisolone was given as prednisolone phosphate to seven severe steroid-dependent asthmatics and to 13 healthy volunteers to determine if the large prednisone requirements of these patients were a function of the disease, cellular response, or rapid clearance of prednisolone. Plasma concentrations of prednisolone, prednisone, and cortisol were determined by high-performance liquid chromatography over an 8-hr test period. Circulating eosinophil concentrations were monitored concurrently. The apparent half-lifes of prednisolone in the asthmatics and normals were 3.33 +/- 0.71 and 3.25 +/- 0.58 hr (mean +/- SD). The apparent plasma clearances of prednisolone were 201 +/- 54 and 198 +/- 38 ml/min/1.73 m2 and the apparent volumes of distribution were 50.8 +/- 11.7 and 53.5 +/- 13.5 L/1.73 m2 for the asthmatic and normal groups, respectively. When the concentration-dependent binding of prednisolone to plasma protein was examined, no differences in the apparent clearances of unbound drug were found between the two groups. The eosinopenic response to prednisolone was similar in the steroid-dependent asthmatics and healthy normal volunteers. These studies indicate that binding, distribution, and clearance of prednisolone are not responsible for the large prednisone requirement of some steroid-dependent asthmatics. Differences in steroid-receptor sensitivity or in severity or pathophysiology of the disease state more likely account for the need for large prednisone dosages in these patients.

Intoxication caused by interaction of chloramphenicol and phenytoin.

A patient with a brain tumor and seizures who was receiving maintenance doses of phenytoin was given chloramphenicol on three occasions. Her neurological status was both complicated and obscured by the reoccurrence of phenytoin intoxication. Retrospective drug analysis showed a marked elevation of serum concentrations of phenytoin during each course of chloramphenicol.

Steroid-specific and anticonvulsant interaction aspects of troleandomycin-steroid therapy.

Troleandomycin (TAO) is a macrolide antibiotic that has an apparent "steroid-sparing" effect when used in the treatment of severe steroid-dependent asthmatic patients. Recent observations demonstrated the effect of TAO on inhibiting methylprednisolone elimination, possibly contributing to its beneficial effects. Prednisolone and methylprednisolone disposition were studied before and 1 wk after initiation of TAO therapy in three patients. Methylprednisolone elimination was characteristically impaired in the presence of TAO therapy; however, there was no apparent effect on prednisolone elimination. Methylprednisolone elimination was also evaluated before and after initiation of TAO therapy in three patients receiving concomitant anticonvulsant therapy with phenobarbital-1, phenytoin-2. Methylprednisolone clearance before TAO was at least 4 times faster than normal and was probably related to enzyme induction by the anticonvulsant medication. Methylprednisolone clearance was subsequently reduced by approximately 70% in the presence of TAO therapy. The effect of TAO on corticosteroid disposition is steroid-specific and TAO can diminish the effect of certain drugs on the induction of corticosteroid metabolism.