Determination of amoxapine and its metabolites in human serum by high-performance liquid chromatography.

The simultaneous quantitative determination of amoxapine, 7-hydroxyamoxapine and 8-hydroxyamoxapine in human serum was established, with good recoveries, using reversed-phase high-performance liquid chromatography (HPLC). Prior to analysis by high-performance liquid chromatography, the enzymic hydrolysis with beta-glucuronidase/arylsulphatase of sera from healthy volunteers receiving the drug showed that each conjugate of two hydroxyamoxapines was 75-90% of the amount determined by the present method. The concentrations of amoxapine and its hydroxylated metabolites were measured against time in sera from the volunteers who were given the antidepressant orally for 2 weeks. The serum levels of 8-OH-amoxapine were markedly higher than the drug itself and the 7-OH-derivative. Whereas the levels of the drug were little increased during the continuous administration, the levels of 8-OH-amoxapine were linearly increased until the fourth day after the administration was started. In addition, the ratio of each hydroxylated metabolite to the drug and the time-course of their serum levels varied interindividually.

Amoxapine and amitriptyline: serum levels and clinical response in patients with primary unipolar depression.

Amoxapine, a new antidepressant of the dibenzoxazepine class, was compared with amitriptyline in 80 patients with primary unipolar depressive disorders. In a four-week double-blind trial, the two medications were equally effective and had similar onsets of therapeutic action. The range of side effects was similar, although there was a trend for fewer side effects in the amoxapine group. Serum levels were not related to therapeutic response for either medication.

Clinical and plasma level characteristics of intramuscular and oral loxapine.

The intramuscular and oral forms of loxapine succinate were compared in their clinical, side effect, and blood level characteristics in ten hospitalized chronic schizophrenic patients. The first phase of the study determined the single dose that produced moderate sedation (i.e., the sedation threshold), and this dose was essentially the same for the two forms. Continuous administration of the two forms using the individualized sedation threshold dosage also failed to indicate any clinical or side effect differences in the two forms. The blood level characteristics, however, did differ between the two forms. The kinetic studies indicated that there was a larger are under the loxapine curve with the intramuscular form than with the oral form, while the 8-OH loxapine area was larger with the oral form. The steady-state studies also showed that the i.m. form had higher loxapine levels than the oral form. The significance of these findings, both clinically and in terms of the relative activity of loxapine and its metabolites, is discussed.

GLC determination of 7-chloro-5,11-dihydrodibenz[b,e][1,4]-oxazepine-5-carboxamide in serum or plasma.

This report describes the isolation, derivative formation, GLC, and quantitation of unmetabolized 7-chloro-5,11-dihydrodibenz[b,e][1,4]oxazepine-5-carboxamide (I) in blood serum or plasma. Carbamazepine is used as the internal standard to compensate for losses of I during extraction and handling. Essentially complete recovery (100 +/- 6%) was demonstrated over a concentration range of 1-30 mug of I/ml of serum.

Isocratic liquid chromatographic method for the determination of amoxapine and its metabolites.

An isocratic reverse-phase liquid chromatographic method for the determination of amoxapine and its major metabolites in human plasma utilizing UV detection is described. Plasma samples were extracted with ethyl acetate after pH adjustment. The reconstituted extracts were injected onto a cyanopropylsilane column and eluted with a mobile phase consisting of 65% acetonitrile and 35% sodium acetate buffer, 0.03 M and pH 6. The minimum detectable limit was less than 10 ng/mL of plasma. Possible interferences from other drugs which might be administered concurrently were studied. The reproducibility and precision of the method are demonstrated by the analysis of samples containing 25-600 ng/mL of plasma. The method is being applied successfully in our laboratory for the analysis of plasma from patients receiving amoxapine.

GLC analysis of loxapine, amoxapine, and their metabolites in serum and urine.

A GLC analysis is presented for loxapine, amoxapine, and their major metabolites in serum and urine. Electron-capture detection is employed for serum analysis, and flame ionization is used for urine analysis. The procedure includes trifluoroacetylation of secondary amine functions, followed by trimethylsilylation of phenolic groups after ethyl acetate extraction of the sample. Urine requires prior enzymatic hydrolysis of conjugates. Data indicating the utility of the procedure in hospitalized patients and normal volunteers are presented.

Analysis of blood and tissue for amoxapine and trimipramine.

A method for the identification and quantitation of two tricyclic antidepressants, amoxapine (Asendin) and trimipramine (Surmontil) is presented here. Samples were extracted with hexane at pH 10, back-extracted with 1.0N sulfuric acid. The acidic layer was adjusted to pH 10 and re-extracted with hexane. Electron impact mass spectra were obtained. The base peak and molecular ion for amoxapine were at m/z 245 and 313, respectively. The base peak and molecular ion for trimipramine were at m/z 58 and 294, respectively. There were three forensic toxicology cases involving amoxapine in Cook County, IL, in 1980 and 1981. The concentrations of amoxapine in blood for these three cases were 1.66 mg/L, 7.16 mg/L, and 2.95 mg/L, respectively.

Liquid chromatographic separation of antidepressant drugs: II. Amoxapine and maprotiline.

The simultaneous serum analysis of amoxapine (AMOX) and its major metabolite 8-hydroxyamoxapine (8-OH AMOX), and maprotiline (MAP) and its major metabolite desmethylmaprotiline (D-MAP) by high-performance liquid chromatography (HPLC) and ultraviolet detection is described here. AMOX and 8-OH AMOX were detected at 254 nm at 0.01 absorbance units full scale (AUFS). MAP and D-MAP were detected at 214 nm at 0.05 AUFS. Serum (1.0 ml collected in plastic) extraction was by Bond-Elut C18 columns. The compounds of interest were eluted from the columns with 10 mM methanolic ammonium acetate. The eluates are evaporated at 56-58 degrees C and reconstituted with 200 microliter of mobile phase. The mobile phase was absolute ethanol-acetonitrile-tert-butylamine (98:2:0.05, vol/vol), and the flow rate was 2.0 ml/min. Absolute recoveries range from 97 to 100% for all compounds. HPLC was done on a 5-micron (4.6 X 250 mm) silica-packing column (normal phase). Separations on a 10-micron silica column (3.9 X 300 mm) are also discussed. Peak height ratios using trimipramine as the internal standard were linear for each drug between 25 and 1080 ng/ml. AMOX and 8-OH AMOX ratios with promazine as the internal standard were linear between 25 and 1080 ng/ml. Detection limits were 3 ng/ml for AMOX and 8-OH AMOX, 12 ng/ml for D-MAP, and 15 ng/ml for MAP. Coefficients of within-day and day-to-day variation at three concentration levels were less than 10.8% and 10.5%, respectively, for all compounds. Correlations of AMOX, 8-OH AMOX, and MAP sample assays using gas chromatography (or gas chromatography-mass spectrometry) and this method were compared. Steady-state daily dosages and corresponding serum levels are presented for seven patients. AMOX and 8-OH AMOX concentrations for 37 patients are given; these show that the ratios of these compounds are highly variable between patients. MAP and D-MAP concentrations for 30 patients show that D-MAP can be a significant fraction of the circulating drug. Assay time for 8-OH AMOX/AMOX was 6.5 min and less than 13 min for D-MAP/MAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Liquid-chromatographic determination of amoxapine and 8-hydroxyamoxapine in human serum.

We describe a liquid-chromatographic procedure for amoxapine and 8-hydroxyamoxapine, its active metabolite, in serum. We used a mu-Bondapak C18 reversed-phase column and a mobile phase of acetonitrile/water (74/26 by vol) plus 26 microL of n-butylamine per liter. The compounds were measured at 254 nm, with 8-methoxyloxapine as internal standard. Necessary pre-analysis purification consisted of adsorbing the drug from serum onto extraction columns, eluting with 1-butanol/hexane (1/5 by vol), re-extracting into aqueous acid, and from that re-extracting again into the elution-solvent mixture. We prefer this procedure for monitoring both therapeutic and toxic concentrations of amoxapine, because parent drug and metabolite are measured separately.

Pharmacokinetics of amoxapine and its active metabolites.

The plasma concentrations of amoxapine and its active metabolites, 8-hydroxyamoxapine and 7-hydroxyamoxapine were determined in 8 healthy volunteers receiving a single oral dose of 100 mg of the drug. Considerable interindividual variation was seen in the plasma levels of the three substances. Amoxapine reached maximum levels of 67.4 +/- 35.8 ng/ml between 1 and 2 h after administration. The decline of amoxapine levels in plasma was biphasic. The mean elimination half-life was 9.8 +/- 2.6 h and the estimated first-pass loss ranged between 0.18 and 0.54. The peak levels of the metabolites were reached between 1 and 3 h after administration, with 8-hydroxyamoxapine levels significantly higher than those of 7-hydroxyamoxapine. The mean elimination half-lives were 30.8 and 5.1 h for 8-hydroxyamoxapine and 7-hydroxyamoxapine respectively. The margins of the plasma concentrations reached at steady-state were calculated according to pharmacokinetics parameters for a dosage interval of 8 h.

Analysis of amoxapine, 8-hydroxyamoxapine, and maprotiline by high-pressure liquid chromatography.

Two high-pressure liquid chromatography procedures are presented for the routine analysis of two new antidepressant drugs, amoxapine (Asendin) as well as its active metabolite and maprotiline (Ludiomil). Recovery rates were excellent with both methods of extraction. Method 1, for amoxapine and its metabolites, was linear up to 1,000 ng/ml. Sensitivity for the parent drug was 10 ng/ml and, for the active metabolite, 25 ng/ml. Within-run coefficients of variation (CV) were 4.57% for 8-hydroxyamoxapine and 3.84% for amoxapine. Method 2, for maprotiline, was linear from 10 to 1,000 ng/ml. Intraassay CV was 3.2%. Reliable, yet simple, methods for monitoring these drugs are needed in order to establish firmly the pharmacological data important to appropriate patient therapy.

Clinical pharmacology of SQ 10,996, a potential antidepressive agent.

Single oral doses of SQ 10,996 ranging from 500 to 1000 mg (0.34 to 15.3 mg/kg), given once daily for 3 consecutive days to groups of healthy volunteers, were well tolerated. One of three subjects given 1250 mg (17.1 mg/kg) and two of three subjects given 1500 mg (15.6 and 21.4 mg/kg) became drowsy on the second and third days; this symptom disappeared within 24 hrs after cessation of dosage. A short-term, multiple-dose tolerance study was carried out with a formulation of SQ 10,996, the bioavailability of which was comparable to that of the formulation used earlier in the ascending-dose tolerance study. When 200-mg doses were administered every 12, 8, or 6 hrs over a 6-day period, mean steady-state serum concentrations of approximately 4, 7, and 8 mug/ml were attained within 48 hrs; unexpectedly, no subject showed any sign of drowsiness. The half-life for SQ 10,996 in serum, estimated from concentrations in serum after the last dose, was approximately 13 hrs, significantly shorter than the half-life found previously after the administration of single 10-mg doses. These clinical pharmacology studies in healthy volunteers have shown SQ 10,996 to be biologically available and well tolerated. Future studies will test its antidepressive potential in patients.

The fate of dibenz[b,f]-1,4-oxazepine (CR) in the rat, rhesus monkey and guinea-pig. Part I. Metabolism in vivo.

The fate of dibenz[b,f]-1,4-[11(14)-C]oxazepine (CR) in rats, rhesus monkey and guinea-pig and in isolated perfused rat livers has been examined. 14C-CR was administered to rats at doses from 1.56 to 3470 mumol/kg and irrespective of dose or route of administration most (59-93%) was eliminated in the urine as primarily the sulphates of the 7-, 4- and 9-hydroxylated 10,11-dihydrodibenz[b,f]-1,4-oxazepine-11(10H)-one. In blood, both in vivo and in liver perfusates, CR concentrations decreased biphasically to be replaced initially with CR-lactam (dihydrodibenz[b,f]-1,4-oxazepine-11(10H)-one), followed by the sulphates of the 7-, 4- and 9-hydroxylactams. The rate of disappearance of CR in liver perfusates was slower than in vivo. Bile contained only small amounts of sulphate conjugates and significant amounts of conjugated 2-amino-2'-hydroxymethyldiphenyl ether (amino alcohol). This was not identified in the urine or blood of rats. Preliminary studies in rhesus monkey and the guinea-pig show similar excretory patterns and metabolites. However, only free hydroxylactams were isolated from monkey urine and traces of the amino alcohol were detected in guinea-pig urine. Whole-body autoradiography of mice confirm the rapid disappearance of CR from blood into heart, liver, kidneys and small intestine with evidence of biliary excretion. It is consistent with the rat studies showing the rapid absorption of a highly lipophilic compound undergoing hepatic metabolism, biliary secretion, enterohepatic recirculation and renal excretion.

Determination of loxapine in human plasma and urine and identification of three urinary metabolites.

1. A g.l.c. method for quantitative determination of loxapine (2-chloro-11-(4-methyl-1-piperazinyl)dibenz(b,f)(1,4)oxazepine), in human plasma and urine is described. 2. Preliminary pharmacokinetic data on plasma concn of loxapine over 12 h from five psychiatric patients who received a total average dose of 80 mg of loxapine succinate per day orally for twelve weeks are presented. 3. In addition to unchanged loxapine, three urinary metabolic products, namely aromatic ring-hydroxy loxapine, desmethyl loxapine and loxapine-N-oxide, were identified using g.l.c.--mass spectrometry.

Determination of therapeutic and toxic concentrations of doxepin and loxapine using gas-liquid chromatography with a nitrogen-sensitive detector, and gas chromatography-mass spectrometry of loxapine.

A gas-liquid chromatographic procedure is presented for the determination of therapeutic and toxic serum levels of doxepin and loxapine, using a nitrogen-phosphorus-sensitive detector. Amitriptyline is used as the internal standard. The method is accurate, sensitive and specific with no derivatization required prior to analysis. An advantage of the procedure is the small serum sample size needed for analysis and the selectivity and sensitivity of the detector, with the limit of detection being 3 and 2 microgram/l for doxepin and loxapine, respectively. Nine cases of doxenin and loxapine misuse are presented. Serum doxepin concentrations ranged from 113 to 439 microgram/l, with a loxapine concentration of 192 microgram/l observed in one patient. The presence of the tricyclics was identified and confirmed by gas chromatography-mass spectrometry and the mass spectrum of loxapine is reported.

Direct microtitre plate radioimmunoassay of savoxepine in unextracted plasma.

An original solid phase method for direct radioimmunoassay of the antipsychotic savoxepine (CGP 19,486 A) in plasma has been developed which does not require the extraction of the parent drug with organic solvents. The assay showed good reproducibility over the working concentration range 1.9-30.6 nmol/l with intra- and inter-assay coefficients of variation < or = 16%. The procedure, which requires only small volumes of plasma (10 microliters), is simple to handle and well suited for routine analysis. The method allowed to investigate the pharmacokinetics of savoxepine in schizophrenic patients given low oral doses of the drug.