Trazodone kinetics: effect of age, gender, and obesity

Single 25 mg intravenous and 50 mg oral doses of trazodone were given to 43 healthy subjects, divided into young men and women (aged 18 to 40 years) and elderly men and women (aged 60 to 76 years). Among men, trazodone volume of distribution (Varea) was increased in elderly vs. young subjects (1.15 vs. 0.89 L/kg; P less than 0.05), and clearance decreased (1.65 vs. 2.31 ml/min/kg; P less than 0.05), thereby increasing elimination half-life (t1/2) in elderly men (8.2 vs. 4.7 hours; P less than 0.001). Varea in women was also increased in the elderly (1.5 vs. 1.27 L/kg; P less than 0.02), causing increased t1/2 (7.6 vs. 5.9 hours; P less than 0.05), but clearance was unrelated to age. Absolute bioavailability of oral trazodone averaged 70% to 90% and was unrelated to age or sex. In 23 obese subjects (mean weight 112 kg) vs. 23 matched control subjects of normal weight (mean 65 kg), Varea was greatly increased (162 vs. 67 L; 1.43 vs. 1.04 L/kg; P less than 0.001) and was highly correlated with body weight (r = 0.91). Clearance was unchanged between groups (146 vs. 136 ml/min), but the increased Varea caused prolonged t1/2 in obese subjects (13.3 vs. 5.9 hours; P less than 0.001). Reduced clearance of trazodone among elderly men may indicate a need for dosage reduction during chronic therapy. In obese individuals, choice of dosage during chronic treatment should be based on ideal rather than total body weight.

Pharmacokinetics of diphenhydramine and a demethylated metabolite following intravenous and oral administration

Ten healthy volunteers received a single 50-mg dose of diphenhydramine (DP) hydrochloride intravenously and orally on two separate occasions. Kinetics of DP and a major demethylated metabolite (DMDP) were determined from multiple plasma samples drawn during a 24- to 48-hour period after dosage. Modification of a gas chromatographic (GC) technique allowed simultaneous quantitation of DP and DMDP. Mean kinetic variables for DP after intravenous (IV) dosage were: volume of distribution, 4.5 L/kg; elimination half-life, 8.4 hours; clearance, 6.2 mL/min/kg. After oral DP administration, a peak plasma level of 66 ng/mL was reached 2.3 hours after dosage. Systemic availability was 72%, nearly identical to the predicted estimate (71%) based on clearance of IV DP relative to hepatic blood flow. Appearance of the metabolite, DMDP, mirrored disappearance of DP; the area under the plasma concentration-time curve (AUC) for DMDP was highly correlated (r = .79, P less than .05) with a clearance of IV DP. However, metabolite AUC was significantly higher after oral as opposed to IV DP (218 vs 145 hr-ng/mL, P less than .05). Because DP and DMDP elute nearly identically on standard GC systems, methodologic modifications are needed to resolve them. Coelution of the two compounds could bias kinetic data based on plasma concentration presumed to be specific for intact DP.

Pharmacokinetics of antipyrine, acetaminophen and lidocaine in fed and fasted horses

Previous studies demonstrated that plasma clearance of organic anions such as bilirubin, bile acid, sulfobromophthalein (BSP) and indocyanine green (ICG), was reduced from 36% (bile acid) to 55% (ICG) in fasted (3 days) horses. It is believed that a general decline in carrier-mediated hepatic uptake may have accounted for those changes. However, fasting may also affect hepatic blood flow, thereby contributing to reduced clearance of these compounds. In order to test this hypothesis, plasma clearance of antipyrine, acetaminophen and lidocaine, drugs known to be cleared by the liver yet not suspected of undergoing carrier-mediated hepatic uptake, were investigated in nine healthy adult mares (three horses/drug group) before and following a 3-day fast. Results demonstrate that fasting decreased clearance of organic anions from previous studies more than clearance of drugs used in these studies. In addition, clearance of lidocaine, the drug with the highest plasma clearance and therefore the drug most likely to be affected by reduced hepatic blood flow, was affected least by fasting. Therefore, reductions in clearance of these compounds due to fasting must not be due entirely to reductions in hepatic blood flow, but must also involve reductions in intrinsic hepatic clearance.

Oxaprozin pharmacokinetics in the elderly

A series of 42 healthy male and female volunteers aged 21 to 89 years received a single 1200 mg oral dose of oxaprozin. Kinetics were determined from multiple plasma oxaprozin concentrations measured by h.p.l.c. during 14 days after the dose. Peak plasma oxaprozin concentrations were reached between 3 and 6 h after dosage the majority of subjects, probably reflecting slow absorption from the gastrointestinal tract. Elimination also was slow with a mean half-life of 59 h (range 36 to 92 h). Owing in part to extensive protein binding (mean free fraction 0.0023%), oxaprozin distribution was limited, with apparent volume of distribution averaging 0.25 l/kg. Apparent volume of distribution declined with increasing age, probably reflecting the reduction in lean mass relative to total weight that occurs in the elderly. Total apparent oxaprozin clearance declined with age in men (r = -0.58, P less than 0.01), but was not significantly related to age in women (r = -0.25, NS). This is consistent with the previously described gender-specific reduction in hepatic oxidizing capacity association with increasing age. Thus oxaprozin is a slowly eliminated nonsteroidal anti-inflammatory agent that should be suitable for once daily or every other day administration.

Metronidazole impairs clearance of phenytoin but not of alprazolam or lorazepam

Healthy volunteers received single doses of either phenytoin (300 mg IV), alprazolam (1 mg orally) or lorazepam (2 mg IV) on two occasions in random sequence. One of the two trials was a control; for the other trial, subjects ingested metronidazole, 250 mg three times daily beginning 4 days prior to and continuing for the duration of each kinetic study. Compared with control, metronidazole significantly prolonged phenytoin half-life (23 versus 16 hours, P less than .02) and reduced its clearance (.28 versus .33 mL/min/kg, P less than .005), known to depend on aromatic hydroxylation. However, metronidazole did not significantly alter kinetic variables for either alprazolam (metabolized by aliphatic hydroxylation) or lorazepam (metabolized by glucuronide conjugation). Thus, metronidazole has the capacity to impair the clearance of certain oxidatively metabolized drugs, but there is no apparent way to predict which drugs will be so influenced.

Effect of ciclosporin on rat liver and kidney glutathione content

The effect of ciclosporin (CS) on hepatic and renal glutathione was investigated in 36 male Sprague-Dawley rats weighing 200-250 g each. CS (120 micrograms/kg/day, i.p.) treatment caused a significant decrease in both hepatic and renal glutathione content. The rat hepatic glutathione levels decreased by 16% within 1 h of a single CS treatment and continued decreasing to 50% following chronic treatment with CS for 7 days. Renal glutathione content decreased only marginally (3%) within 1 h of CS treatment. However, it decreased by 17% within 24 h and continued to decrease during the 7 days of chronic treatment. This decrease in the content of both hepatic and renal glutathione may contribute to the toxicity observed during treatment with CS.

Effect of cyclosporin A on rat kidney catecholamines

The immunosuppressive agent, Cyclosporin A, (CsA) has been associated with nephrotoxicity and hypertension. The mechanism for these effects are not known. We therefore determined the levels of the catecholamines; epinephrine (EPI), norepinephrine (NE) and dopamine (DA) and some of their metabolites; epinine, dihydroxyphenyl-acetic acid (DOPAC), homovanillic acid (HVA), metanephrine (ME) and 3-methoxy-4-hydroxy-phenylglycol (MHPG) in the kidneys of rats treated intraperitoneally with either CsA (120 micrograms/kg/body wt/day) or control vehicle (1 ml olive oil/kg body wt/day). Six control or CsA treated rats were sacrificed at 1 hour or 24 hours after a single treatment or after 7 days of daily treatment. Renal catecholamine levels were determined using HPLC-amperometric detector. Treatment with CsA increased renal NE and EPI levels by 59% and 70% respectively within 1 hour. In the rats sacrificed 24 hours after treatment, renal NE, EPI and DA levels were similar to or less than the control levels. Treatment with CsA for 7 days resulted in marginal increases in renal NE (22%) and EPI (30%). These changes were associated with a significant decrease in the levels of catecholamine metabolites in the CsA treated kidneys as compared to the controls. The above findings suggest that increases in renal catecholamines may be involved in the CsA-induced hypertension and nephrotoxicity, perhaps by increasing renovascular resistance.

Differential effect of cigarette smoking on antipyrine oxidation versus acetaminophen conjugation

The effect of cigarette smoking on drug oxidation and conjugation was studied using antipyrine and acetaminophen as marker compounds. For the antipyrine study, healthy cigarette smokers (n = 30) and nonsmoking controls (n = 53) received a single 1.0-gram intravenous dose of antipyrine. For the acetaminophen study, 14 smokers and 15 nonsmokers received a 650-mg intravenous dose of acetaminophen. The clearance of antipyrine was significantly increased (0.93 vs. 0.60 ml/min/kg, p less than 0.0001) and elimination half-life was correspondingly reduced (8.9 vs. 13.0 h, p less than 0.0001) in smokers compared to nonsmoking controls. Total recovery of antipyrine and metabolites excreted in urine did not differ between groups, but there was a significantly increased fractional clearance of antipyrine via formation of 4-hydroxyantipyrine and 3-hydroxymethyl metabolites in smokers. Fractional clearance via formation of norantipyrine did not differ significantly between groups. Comparison of acetaminophen kinetics between smokers and nonsmokers indicated no significant differences in elimination half-life, clearance or volume of distribution. Thus, cigarette smoking is more likely to induce drug oxidation rather than drug conjugation. However, not all oxidative pathways are equally influenced; induction effects of smoking are highly substrate selective and pathway specific.

Lack of effect of influenza vaccine on the pharmacokinetics of antipyrine, alprazolam, paracetamol (acetaminophen) and lorazepam

31 healthy male (n = 17) and female (n = 14) volunteers, aged 20 to 45 years, were divided into 4 groups and received on 3 separate occasions either: paracetamol (acetaminophen) 650mg intravenously (n = 9); alprazolam 1mg orally (n = 7); antipyrine (phenazone) 1g intravenously (n = 8); or lorazepam 2mg intravenously (n = 7). Doses were administered prior to influenza vaccine (0.5ml, intramuscularly) and at 7 and 21 days post-vaccination. The overall differences among the 3 trials in clearance of antipyrine were of borderline significance (p less than 0.0611), with a trend towards reduced clearance in both of the post-vaccination trials. There were no overall differences observed in the elimination half-life of antipyrine, nor were there significant differences between trials in cumulative urinary excretion or fractional recovery of intact antipyrine, 4-hydroxyantipyrine, norantipyrine, or 3-hydroxymethyl antipyrine. For paracetamol and alprazolam, there were no significant differences among the 3 trials in any of the kinetic variables. The elimination half-life of lorazepam varied significantly among trials, but differences were small and not systematic. Lorazepam clearance did not vary significantly among trials. Thus, clearance of drugs which undergo hepatic conjugative reactions such as glucuronidation and sulphation are unlikely to be affected by the coadministration of influenza vaccine. Furthermore, not all drugs which are biotransformed by hepatic microsomal oxidation necessarily have impaired clearance due to coadministration of influenza vaccine.

Antipyrine pharmacokinetics in women receiving conjugated estrogens

The pharmacokinetics of a single 1.0 to 1.2-g intravenous dose of antipyrine was studied in 22 healthy female volunteers aged 28 to 70 years (mean, 45 years). Eleven subjects had been taking a conjugated estrogen preparation for at least 3 months; the other 11 subjects who were not taking conjugated estrogens and who were matched for age, weight, and smoking patterns, served as a control group. Plasma antipyrine concentrations were determined by high-pressure liquid chromatography (HPLC) in multiple plasma samples drawn 24 to 48 hours after dosage. Mean +/- SE pharmacokinetic variables in control and conjugated-estrogen groups were volume of distribution, 0.57 +/- 0.02 versus 0.56 +/- 0.02 L/kg; elimination half-life, 11.0 +/- 0.82 versus 12.6 +/- 0.89 hours; and clearance, 0.63 +/- 0.06 versus 0.54 +/- 0.03 mL/min/kg. None of the differences was significant. Although antipyrine clearance is significantly impaired by oral contraceptives, there is no evidence of altered antipyrine pharmacokinetics from treatment with conjugated estrogens.

Antipyrine and lidocaine are cleared faster in horses than in humans: acetaminophen may be handled similarly

The following studies were designed to evaluate plasma elimination kinetics of intravenously administered antipyrine, acetaminophen and lidocaine among 9 healthy adult horses and 9 healthy drug-free humans (3 each per drug group), in order to compare potential species differences in drug-metabolizing ability. Acetaminophen is largely biotransformed in humans by hepatic glucuronide and sulfate conjugation, whereas both antipyrine and lidocaine are oxidized by hepatic microsomal mixed-function oxidases. Thus, plasma clearances of these drugs are thought to reflect differences in hepatic oxidative and conjugative activity, and possibly hepatic blood flow in the case of lidocaine. Results showed that mean (+/- SD, n = 3) acetaminophen clearance was similar in both horses (4.84 +/- 0.637 ml/min/kg) and humans (4.68 +/- 0.691 ml/min/kg). However, antipyrine clearance was 10 times greater in horses (5.83 +/- 2.21 ml/min/kg) than in humans (0.536 +/- 0.110 ml/min/kg), which may reflect enhanced hepatic microsomal activity in horses. Although lidocaine clearance in humans was similar to estimated hepatic blood flow (20.6 +/- 5.81 ml/min/kg), clearance in horses was more than 2 times greater (52.0 +/- 11.7 ml/min/kg). The cause of the higher clearance of lidocaine in horses (like dogs) remains unexplained, and may involve significant metabolism of lidocaine at extrahepatic, extravascular sites, for intravascular degradation and renal excretion of intact lidocaine in horses was negligible. Although precise biochemical mechanisms underlying pharmacokinetic parameters for these drugs in horses were not determined, it is nonetheless concluded from antipyrine results that horses may have an enhanced ability (compared with humans) to clear drugs from the circulation that are primarily metabolized in the liver by phase I oxidative reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine blood concentrations determined by specific versus nonspecific assay methods

Cyclosporine blood concentrations were simultaneously determined by radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC) at multiple points in time in two patients receiving cyclosporine for immunosuppression following liver transplantation. Radioimmunoassay levels always exceed those determined by HPLC; however, the divergence between the two methods increased as serum bilirubin concentration increased, with HPLC:RIA ratios generally less than 0.3 when serum bilirubin concentrations exceeded 10.0 mg/dL. These preliminary results suggest that retention of immunoactive cyclosporine metabolites due to imparied liver function may account for RIA-determined cyclosporine concentrations that greatly exceed those measured by HPLC.

Large theophylline requirements due to high theophylline clearance: verification by the antipyrine test

An asthmatic patient required very high doses of theophylline (2.88 g/day by intravenous infusion) to maintain an adequate serum theophylline concentration (12 micrograms/ml). His cigarette smoking and concurrent treatment with phenytoin were suspected to have produced hepatic microsomal enzyme induction, causing unusually high theophylline clearance. The intravenous antipyrine test demonstrated an unusually short half-life (5.5 h) and high clearance (95 ml/min) of antipyrine, consistent with induced clearance of antipyrine. Formation of the 4-hydroxy metabolite of antipyrine was disproportionately induced. Thus the antipyrine test can be of clinical value for documenting hepatic microsomal enzyme induction in patients with low steady-state theophylline concentrations despite high maintenance doses.

Simplified approaches to the determination of antipyrine pharmacokinetic parameters

1. The pharmacokinetics of single intravenous doses of antipyrine were determined in 96 volunteers using multiple (12 or more) plasma antipyrine concentrations measured by high-pressure liquid chromatography during 24-48 h after dosage. These kinetic estimates were compared with those based on: A, the 4 h and 12 h points only; B, the 4 h through 12 h points; C, the 8 h and 24 h points only. 2. Mean clearance values for the complete study (48.0 ml min-1) were nearly identical to abbreviated approaches A, B, and C (49.1, 49.3, and 46.4 ml min-1), and were highly correlated (r = 0.99). 3. Coefficients of variation (CV) between individual clearance values for complete vs abbreviated studies averaged 5.5%, 5.8% and 2.9%, and CVs were less than 15% in 95.8%, 93.7% and 98.9% of subjects, respectively, for methods A, B, and C. 4. Overall mean values of elimination half-life (11.9, 12.1, 12.0 and 12.5 h) and volume of distribution (43.7, 45.1, 45.2, and 44.71) were likewise very similar for complete A, B and C analyses respectively. 5. The best correlation with the complete study was observed for the 8 and 24 h sampling scheme, for which clearance values were within 5% of the reference method in 84% of subjects, and within 10% in 97% of subjects. 6. Antipyrine pharmacokinetic parameters can be estimated with reasonable precision using a simplified two-point blood sampling procedure following a single intravenous dose. Estimates of elimination half-life, volume of distribution and clearance based on 8 h and 24 h data points correlated best with complete pharmacokinetic studies.

Effect of antipyrine coadministration on the kinetics of acetaminophen and lidocaine

Pharmacokinetic interactions between antipyrine and acetaminophen were evaluated in 7 healthy volunteers. On 3 occasions subjects received: 1, antipyrine 1.0 g intravenously (i.v.); 2, acetaminophen 650 mg i.v.; 3, antipyrine 1.0 g and acetaminophen 650 mg i.v. simultaneously. Between Trials 1 and 3, antipyrine elimination t1/2 (17.2 vs 17.4 h), clearance (0.44 vs 0.43 ml.min-1.kg-1) and 24-h recovery of antipyrine and metabolites (313 vs 293 mg) did not differ significantly. Between Trials 2 and 3, acetaminophen VZ was reduced (1.14 vs 1.00 l.kg-1), t1/2 prolonged (2.7 vs 3.3 h), clearance reduced (4.8 vs 3.6 ml.min-1.kg-1), and fractional urinary recovery of acetaminophen glucuronide reduced. Eight additional subjects received 50 mg of lidocaine hydrochloride i.v. in the control state, and on a second occasion immediately after antipyrine 1.0 g given i.v. The two trials did not differ significantly in lidocaine VZ (2.6 vs 2.7 l.kg-1), t1/2 (2.0 vs 2.4 h) or clearance (15.0 vs 13.5 ml.min-1.kg-1). Although acetaminophen does not alter antipyrine kinetics, acute administration of antipyrine appears to impair acetaminophen clearance, possibly via inhibition of glucuronide formation. However, antipyrine has no significant effect on the kinetics of a single i.v. dose of lidocaine.

Validity of a two-point acetaminophen pharmacokinetic study

The pharmacokinetics of a single 650-mg intravenous dose of acetaminophen were determined in 82 volunteers using multiple (13 or more) plasma acetaminophen concentrations measured by high pressure liquid chromatography during 24 h after dosage. Kinetic values from the complete study were compared with kinetic estimates based on only two data points: (a) the 2- and 6-h points only; and (b) the 3 and 6-h points only. For elimination half-life, values from the complete study (mean 2.42 h) were highly correlated (r = 0.87 and 0.84) with methods a and b (means 2.41 and 2.43 h), with regression slopes of 1.00 and 0.99, respectively. For clearance, the complete study values (mean 312 ml/min) were highly correlated (r = 0.97 and 0.97) with method a and b values, but both two-point methods significantly overestimated clearance (means 350 and 355 ml/min) by an average of 13 and 14%, respectively. Results for volume of distribution were similar to those for clearance. Although acetaminophen elimination half-life can be estimated with reasonable precision using a two-point blood-sampling procedure, clearance and volume of distribution values using the two-point method overestimate the actual values.

Effect of cyclosporin A on the content of glutathione in the brain of the rat

The effect of cyclosporin A on the content of glutathione was investigated in various regions of the brain of male Sprague-Dawley rats, weighing 275-300 g each. Treatment of rats with cyclosporin A (120 micrograms/kg/day, i.p.) resulted in approximately 50% decrease in the content of glutathione of the cerebellum within 1 hr, relative to time-matched controls, treated with olive oil vehicle. During the same period, cyclosporin A also caused an apparent, but statistically insignificant, decrease in the content of glutathione of the hypothalamus (37%), pontine nucleus (37%) and medulla oblongata (10%) and had no apparent effect on that of the cerebral cortex and the caudate nucleus. Within 24 hr of a single treatment, the content of glutathione of the rats treated with cyclosporin A returned to the control concentrations in all the regions of the brain. After 7 days of daily treatment with cyclosporin A, the content of glutathione of the hypothalamus remained within control levels, whereas that of the pontine nucleus showed an apparent decrease (30%) and those of the medulla oblongata and cerebellum decreased significantly, again by 58% and 64%, respectively, relative to their controls. This selective depletion of the content of glutathione in brain may contribute to some of the neurological side effects of cyclosporin A.

Prenatal effects of acute harmaline exposure on fetal brain biogenic amine metabolism

Harmaline, a known type A monoamine oxidase (MAO) inhibitor in adult brain of various species was found to elevate whole brain levels of dopamine and serotonin (5-HT) in rat fetuses of mothers injected 2-4 h before Caesarean delivery. Similar stimulatory effects were observed for the norepinephrine metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG), however, no significant effect was obtained for norepinephrine. The dopamine metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) and the 5-HT metabolite 5-hydroxyindole acetic acid (5-HIAA) were decreased with the same treatment. These results imply that harmaline or one of its metabolites may cross the placental barrier to affect the fetal brain system not merely as a type A MAO inhibitor (i.e., relatively 5-HT-specific), but possibly also as a stimulatory agent for aldehyde reductase or catechol-O-methyltransferase (COMT) or alternately as an agent inhibiting the conjugation, efflux, or turnover of biogenic amine metabolites such as MHPG.

Sulfasalazine-induced agranulocytosis

We report a patient with ulcerative colitis in whom agranulocytosis was diagnosed 5 wk after the initiation of sulfasalazine therapy. Concomitant features included fever and skin rash, and bone marrow examination revealed severe myeloid hypoplasia. Antineutrophil antibodies were absent from the serum. Recovery began during the 2nd wk and was characterized by a leukemoid reaction with thrombocytosis. Subsequently, the patient received 5-aminosalicylate enemas without adverse effects. Agranulocytosis, a rare effect of sulfasalazine, appears to occur almost invariably during the first 2 months of therapy, and prompt evaluation is therefore required in patients with unexplained fever or other nonspecific illness during this period.

Ketoconazole does not impair antipyrine clearance in humans

The effect of ketoconazole on the kinetics of antipyrine was investigated. The antipyrine Vd showed an overall difference among the 4 trials, but the magnitude of the differences was small. Antipyrine half-life was slightly but not significantly shortened and the antipyrine clearance was essentially identical in the whole study. The data are commented and interpreted.

Absence of interaction of cimetidine and ranitidine with intravenous and oral midazolam

Eight healthy volunteers received a single 5-mg intravenous dose of the imidazobenzodiazepine derivative midazolam on three occasions in random sequence: a, control, with no other treatment; b, during coadministration of cimetidine, 300 mg every 6 hr; c, during coadministration of ranitidine, 150 mg every 12 hr. Midazolam kinetics in each trial were determined from multiple plasma midazolam levels measured by gas chromatography for 24 hr after each dose. High pressure liquid chromatography analysis of plasma also verified compliance with cimetidine (mean level, 0.61 microgram/ml) and ranitidine (mean level, 0.36 microgram/ml) regimens. Analysis of variance indicated no significant differences in mean values for trials a, b, and c in midazolam elimination half-life (2.25 vs 2.02 vs 2.05 hr), volume of distribution (2.13 vs 2.14 vs 2.16 L/kg) or total clearance (10.8 vs 12.2 vs 12.3 ml . min-1 . kg-1). In a second study, six subjects received a 15-mg oral dose of midazolam on three occasions identical to those described above. Again, there were no significant differences among trials a, b, and c in midazolam peak plasma level (90 vs 95 vs 117 ng/ml), time of peak level (0.65 vs 1.45 vs 0.90 hr after dose), elimination half-life (3.04 vs 3.38 vs 3.30 hr), or apparent oral clearance (16.2 vs 14.3 vs 13.8 ml . min-1 . kg-1). Thus the usual therapeutic doses of cimetidine or ranitidine do not significantly alter the kinetics of intravenous or oral midazolam in healthy individuals.