The effect of felodipine on bile flow in pentobarbital anaesthetized rats and conscious rats receiving bile salt supplementation.

Felodipine, a vasoselective dihydropyridine calcium antagonist, has been given i.v. (0.2 mumol/kg) to anaesthetized and conscious male rats. There was no effect of pentobarbital anaesthesia on bile flow over a 6 h observation period. Felodipine increased the 6 h recovery of bile by approximately 25% in the conscious rat but in the anaesthetized rat there was a 20% decrease in bile flow following i.v. felodipine. A positive effect of Na-taurocholate infusion (1 mumol/min/100 g body weight) on bile flow in conscious rats was reinforced by concomitant felodipine dosing. Accumulated 6 h recoveries were 2.32 +/- 0.80 g/100 g body weight (control), 3.09 +/- 0.91 g/100 g body weight (taurocholate) and 5.00 +/- 0.80 g/100 g body weight. (taurocholate plus felodipine). The excretion of felodipine in the bile was significantly reduced during anaesthesia and during infusion of 2% bovine serum albumin (0.01 ml/min/100 g body weight) to conscious rats.

Biliary secretion of felodipine metabolites in man after intravenous [14C]felodipine.

The biliary secretion of [14C]felodipine in 4 healthy human subjects was studied by use of the multiple marker dilution principle with double lumen tubes placed in the stomach and intestine. Insignificant amounts of 14C activity were recovered from gastric aspirates. The individual recovery from intestinal aspirates varied from 2.9 to 8.5% of the dose of radioactivity over the period of 4.5 h after dosing. Less than 0.1% was identified as unchanged felodipine. The results show that biliary secretion is a minor route of elimination of felodipine or its metabolites. Bile collection for 4.5 h had no significant effect on the pharmacokinetics of felodipine, although the 72 h urinary recovery of radioactivity tended to be lower when bile was collected (59%) than in the control experiment (66%).

Contribution of the intestine to the first-pass metabolism of felodipine in the rat.

The systemic availability of intraduodenally (i.d.) administered felodipine in the rat is about 10%. The purpose of this study was to determine to what extent intestinal metabolism contributes to the first-pass elimination of felodipine in the rat. Four different types of experiments were performed. 1) [3H]Felodipine was given i.v. and i.p.; 2) the uptake of i.p. administered [3H]felodipine by the lymph was studied for 3 hr after dosing; 3) portal blood was collected quantitatively for 40 min after i.d. administration of [3H]felodipine; and 4) the in vitro metabolism of felodipine was studied in intestinal cell suspensions. The mean bioavailability of the i.p. dose was approximately 48%. The uptake via the lymph was negligible as an insignificant amount of the radioactive i.p. dose was recovered in lymph from a main lymph vessel in the peritoneal cavity. An average of 21 +/- 12% of given radioactive dose was recovered in portal blood during the first 40 min after i.d. dosing. The recovered radioactivity was to 40 to 70% due to felodipine and 9 to 16% was due to dehydro-felodipine. These results indicate that substantial first-pass elimination occurs in the intestine of the rat. Further support for gastrointestinal metabolism of felodipine in the rat was obtained from incubations with intestinal cells.

Multiple-dose pharmacokinetics of imipramine and its major active and conjugated metabolites in depressed patients.

Imipramine (IMI) and its active metabolites, desipramine (DMI), 2-hydroxyimipramine (2-OH-IMI), and 2-hydroxydesipramine (2-OH-DMI), were assayed by high pressure liquid chromatography in the serum and urine of 14 depressed patients after 1 week of twice-daily treatment with 100 mg of IMI. The concentrations of the glucuronide conjugates of 2-hydroxyimipramine (GA-O-IMI) and 2-hydroxydesipramine (GA-O-DMI) were assessed via enzyme hydrolysis. The range of serum concentrations of IMI and DMI was 65 to 1,064 ng/ml with slight elevation in total active components caused by inclusion of the unconjugated hydroxy metabolites. The average of total active compounds in smokers (239 ng/ml) was less (p less than 0.1) than in nonsmokers (524 ng/ml). The mean serum concentration ratios were 0.24 for 2-OH-IMI/IMI and 0.50 for 2-OH-DMI/DMI ratios, whereas the DMI/IMI ratio was 1.88, indicating more extensive accumulation of DMI. Appreciable glucuronide conjugate accumulation occurred with average serum concentration ratios of 8.13 for GA-O-IMI/2-OH-IMI and 6.22 for GA-O-DMI/2-OH-DMI. Covariance occurred in metabolite/precursor ratios indicating intrapatient similarities in formation/disposition rates of the hydroxy pairs and the conjugate metabolite pairs. Renal clearances of 2-OH-DMI were 35 to 267 ml/min, whereas those of the conjugates were only 10 to 110 ml/min. Total urinary recovery of these metabolites was similar to that reported previously for single IMI doses. The data indicate accumulation of substantial serum concentrations of glucuronide conjugates after therapeutic doses of IMI in depressed patients and similarities within patients in disposition of metabolite pairs.

Effects of biliary excretion on the disposition of felodipine and metabolites in the rat.

1. After i.v. and intraduodenal administration of 3H-felodipine to rats, approx. 50% of the dose was excreted in bile in the first 6 h. Total urinary and biliary recoveries after both administration routes were similar. 2. Neither unchanged felodipine nor oxidized pyridine metabolite was detected in bile. Bile collection had no effect on the blood concentration-time profiles of either compound. 3. Bile collection decreased the area under the blood concentration-time curve (AUC) of total, unidentified felodipine metabolites by 30%, and their urinary recovery by 50%. 4. Of the total metabolites excreted in bile, 40% was calculated to be subject to enterohepatic recycling. 5. The dose-normalized AUC of both felodipine and pyridine metabolite were decreased after intraduodenal administration of drug, indicating pre-systemic elimination of drug, and possibly of the pyridine, in the gut. Route of administration had no effect on the AUC of total unidentified metabolites.

Liquid-chromatographic determination of eight tri- and tetracyclic antidepressants and their major active metabolites.

A "high-performance" liquid-chromatographic method is presented for monitoring the therapeutic concentrations, in plasma, of eight tri- and tetracyclic antidepressants (amitriptyline, nortriptyline, imipramine, desipramine, doxepin, clomipramine, maprotiline, and protriptyline) and their major active metabolites. One of two internal standards is added to 0.5 mL of drug-containing plasma, the pH is adjusted to about 9.5 with borate buffer, and the sample is extracted with isoamyl alcohol in hexane. The extracts are chromatographed on a column of silica and absorbance of the effluent is measured at either 214 or 254 nm. Chromatographic response is linearly related to concentration for all components over a 5-500 ng range. Analytical recovery of the drugs and metabolites from plasma is approximately 75 to 85% at low and high concentrations. Within-run and day-to-day precision (CV) is less than 5% for both high and low concentrations of most of these drugs and metabolites. Parallel analysis of clinical samples by gas chromatography indicates that results by the two techniques are comparable. We report some results of therapeutic monitoring of clinical samples.

The analysis and disposition of imipramine and its active metabolites in man.

Single oral and intramuscular (i.m.) doses of imipramine (IMI) were administered to four normal males. Serum and urine concentrations of IMI, desipramine (DMI) and their unconjugated 2-hydroxy metabolites were measured by high-pressure liquid chromatography (HPLC). Urinary conjugated 2-hydroxy metabolites were also measured after enzyme hydrolysis. Computer analysis of serum concentration and urinary excretion rate data allowed confirmation of drug and metabolite kinetics, and calculation of pharmacokinetic parameters. The rapid appearance of the metabolites in serum indicates that sequential first-pass metabolism of IMI involves both hydroxylation and demethylation. However, the dose-normalized areas under the serum concentration-time curves indicate that the fractions of the doses converted to metabolites were similar after both routes of IMI administration. Similar total fractions of the i.m. and oral doses recovered in urine indicate complete absorption of the oral doses. Inclusion of the metabolites increased the apparent availability of active components after oral IMI from 22%-50% to 45%-94%. Both the 2-hydroxy metabolites exhibited formation rate-limited kinetics, whereas DMI kinetics were elimination rate-limited. The t1/2 of IMI and 2-hydroxyimipramine (2-OH-IMI) was 6-18 h, while that of DMI and 2- hydroxydesipramine (2-OH-DMI) was 12-36 h. The t1/2 of these compounds was 1.5-2 times longer after the i.m. doses. The metabolite/parent ratios and the disposition of the individual metabolites confirm findings that chronic dosing results in only limited accumulation of hydroxy metabolites.

Active metabolites of imipramine and desipramine in man.

Active hydroxy metabolites of imipramine (IMI) and desipramine (DMI) have been quantified in plasma and cerebrospinal fluid (CSF) from patients at steady-state. In plasma of prepubescent boys and adults the concentration of unconjugated 2-hydroxyimipramine is only 15% to 25% that of IMI; 2-hydroxydesipramine (OH-DMI) concentration, however, is usually 50% that of DMI and in some cases OH-DMI is the predominant compound. In CSF from adult patients the ratio of concentrations of OH-DMI/DMI is higher than in plasma. Judging from the CSF/plasma ratio 12% of DMI exists in the free form at steady state, whereas 16% of OH-DMI is free (P less than 0.02). There is no evidence for saturation of hydroxylation within the therapeutic dose and concentration ranges investigated. On the basis of a steady-state OH-DMI/DMI ratio of less than 1/30 in plasma 5% of the population studied could be classified as deficient DMI hydroxylators. This in the same as the incidence of deficient debrisoquine hydroxylators reported in other populations.

Excessive plasma concentration of tricyclic antidepressants resulting from usual doses: a report of six cases.

Six patients are described who achieved very high plasma concentrations of imipramine and desipramine during chronic therapy with usual doses. Side effects were minimal. Speculation as to apparent tolerance includes the presence of low metabolite concentrations. Plasma concentration monitoring may be indicated to identify the occasional patient who achieves potentially toxic plasma concentrations while taking recommended doses of tricyclics.

High-performance liquid chromatographic assay for imipramine, desipramine, and their 2-hydroxylated metabolites.

High-performance liquid chromatographic method is presented for the simultaneous determination of imipramine, desipramine, and their 2-hydroxylated metabolites in plasma. The method involves a simple plasma extraction at basic pH with organic solvent, chromatography on a silica gel column, and fluorescence detection. Correlation with a GLC-mass spectrometric method for imipramine and desipramine is illustrated. The method can detect 1 ng of each component/ml of plasma, sufficient sensitivity for pharmocokinetic studies.

Early detection of aminoglycoside nephrotoxicity with urinary beta-2-microglobulin.

We used a radioimmunoassay to evaluate the changes in the urinary excretion of beta2-microglobulin (beta2M) in 21 patients receiving aminoglycosides for treatment of infection. Excretion of this protein rose to a peak at least 5 times the baseline value in the urine, and declined rapidly to control values after drug administration ceased. In six patients who developed aminoglycoside nephrotoxicity, urinary beta2M excretion rose 5 days or more before serum creatinine rose, and 5 of 6 nephrotoxic patients excreted more than 50 mg/day (normal, less than 0.1 mg/day). Urinary beta2M is a non-specific indication of renal tubular damage, but heralds aminoglycoside-induced damage before standard tests of kidney function change.