Enhancement of B cell and monocyte populations in rats exposed to chlorpheniramine

Chlorpheniramine is an anti-histamine agent on IgE-mediated inflammation. In order to investigate the immunomodulatory effects of chlorpheniramine, we assessed the changes of peripheral mononuclear cell populations and other general clinical parameters, including hematology and clinical chemistry, following chlorpheniramine administration in rats. Since prednisolone is commonly co-prescribed with anti-histamine in many hypersensitive reactions, we also examined the changes to compare the results after the prednisolone administration. Chlorpheniramine (50, 100 and 200 μg/kg) and prednisolone (1, 2 and 4 mg/kg) were intramuscularly administered to female Sprague-Dawley (SD) rats 3 times, at intervals of 1 week. Except the clinical signs, such as stiffness and abnormal gait due to the local toxicity at injection sites, no other significant changes in body weights, urinalysis, and macroscopic examination were noted in the animals given chlorpheniramine. On the other hand, white blood cells, especially B cells and monocytes, showed a dose-dependent increase in the chlorpheniramine-treated animals; whereas, the numbers of both B and T cells (helper T and cytotoxic T, NKT cells) were decreased in the prednisolone-treated animals. Taken together, these results suggest that chloropheniramine administration enhances white blood cells in the peripheral blood, mostly due to increases of the B cells and monocytes, but no T cells and NK cells.

The Optical Resolution of Racemic Chlorpheniramine and Its Stereoselective Pharmacokinetics in Rat Plasma

An ovomucoid-conjugated column has been developed for the chiral stationary-phase liquid chromatographic resolution of racemic chlorpheniramine with a quantitation limit of 0·05 μg mL−1. The assay was used to study the stereoselective kinetics of chlorpheniramine enantiomers in rats. After bolus intravenous administration of racemic chlorpheniramine maleate (20 mg kg−1), plasma concentration of the (–)-form was higher than that of the (+)-form. In the elimination phase, the concentrations of (+)- and (–)-chlorpheniramine in the plasma declined biexponentially with half-lives of 18·2 and 50·0 min, respectively. Although there was no significant difference in blood-to-plasma concentration ratio of both enantiomers, the apparent total blood clearance of (+)-chlorpheniramine was twice as large as that of the (–)-isomer. Binding of (–)-chlorpheniramine to rat plasma protein was stronger than that of (+)-chlorpheniramine suggesting stereoselective pharmacokinetics may be due to a difference in the plasma protein binding.

Peripheral and central H1 histamine receptor occupancy by levocetirizine, a non-sedating antihistamine; a time course study in the guinea pig

BACKGROUND AND PURPOSE

The H(1) receptor occupancy (H1RO) in brain is an indicator of central side effects of antihistamines. Here, we determined the kinetics of central and peripheral H1RO by levocetirizine in relation to its brain and plasma concentration, and investigated the role of the blood-brain barrier in any delay in brain H1RO.

EXPERIMENTAL APPROACH

Concentration-time profiles in plasma and brain were obtained after 0.1 and 1 mg kg(-1) oral doses of levocetirizine in guinea pigs. H1RO in brain was measured ex vivo using [3H]-mepyramine and, in the periphery, by measuring the degree of inhibition of histamine-induced contractions of isolated guinea pig ileum.

KEY RESULTS

The concentration-time profile of levocetirizine indicated lower levels (partition coefficient, K(p)=0.06-0.08), higher t(max) (2-4 h vs 1-1.5 h) and longer terminal half-life (4-5.6 h vs 2.1-2.8 h) in brain than plasma. The H1RO at 0.1 and 1 mg kg(-1) were 75% and 97%, respectively, at 1 hr in the periphery and, in the brain, were <20% and 28-67% respectively, at all time points studied. Brain H1RO vs plasma concentrations profile showed a delay, but not when compared to brain concentrations.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates an effective peripheral antihistamine effect of levocetirizine without central adverse effects at the dose close to human therapeutic dose. The slow increase in H1RO in the brain with time was caused by slow blood-brain barrier transport of levocetirizine. This demonstrates the importance of measuring time course of brain H1RO in relation to brain concentrations of drugs.

[Simultaneous determination of ephedrine and chlorpheniramine in human plasma by a highly sensitive liquid chromatography-tandem mass spectrometric method]

AIM

To develop and validate a liquid chromatography-tandem mass spectrometric (LC/MS/MS) method for the simultaneous quantification of ephedrine and chlorpheniramine in human plasma after oral administration of a compound preparation.

METHODS

The analytes and the internal standard, diphenhydramine, were isolated from plasma by protein precipitation with methanol, then chromatographied on a Zorbax SB-C18 column (150 mm x 4.6 mm ID) using a mobile phase consisted of methanol-water-formic acid (80: 20: 0.5, v/v), at a flow rate of 0.5 mL x min(-1). A tandem mass spectrometer equipped with electrospray ionization source was used as detector and was operated in the positive ion mode. Selected reaction monitoring (SRM) using the precursor to produce ion combinations of m/z 166-->115, m/z 275-->230 and m/z 256-->167 were used to quantify ephedrine, chlorpheniramine and the internal standard, respectively. Results The linear concentration ranges of the calibration curves for ephedrine and chlorpheniramine were 0.50 - 200 microg x L(-1) and 0.050 - 20.0 microg x L(-1), respectively. The lower limits of quantification were 0. 50 microg x L(-1) for ephedrine and 0.050 microg x L(-1) for chlorpheniramine, individually. The intra- and inter-day relative standard deviation (RSD) across three validation runs over the entire concentration range was less than 9.3% for both ephedrine and chlorpheniramine. The inter-day accuracy (RE) was within +/- 3.4% for the analytes. Each sample was chromatographied within 3.3 min. The method was successfully used in pharmacokinetics study of ephedrine and chlorpheniramine in human plasma after oral administration of a compound preparation containing 5 mg ephedrine hydrochloride, 1 mg chlorpheniramine maleate, 50 mg phenytoin, 12.5 mg theophylline, 12.5 mg theobromine and 7.5 mg caffeine. No interaction among the six components was observed on their pharmacokinetic parameters.

CONCLUSION

The method was proved to be highly sensitive, selective, and suitable for pharmacokinetics investigations of different compound preparations containing low dosage of both ephedrine and chlorpheniramine.

New approaches with two cyano columns to the separation of acetaminophen, phenylephrine, chlorpheniramine and related compounds

The development of new pharmaceutical forms with classical active compounds generates new analytical problems. That is the case of sugar-free sachets of cough-cold products containing acetaminophen, phenylephrine hydrochloride and chlorpheniramine maleate. Two cyanopropyl stationary phases have been employed to tackle the problem. The Discovery cyanopropyl (SUPELCO) column permitted the separation of the three actives, maleate and excipients (mainly saccharine and orange flavour) with a constant proportion of aqueous/ organic solvent (95:5, v/v) and a pH gradient from 7.5 to 2. The run lasted 14 min. This technique avoids many problems related to baseline shifts with classical organic solvent gradients and opens great possibilities to modify selectivity not generally used in reversed phase HPLC. On the other hand, the Agilent Zorbax SB-CN column with a different retention profile permitted us to separate not only the three actives and the excipients but also the three known related compounds: 4-aminophenol, 4-chloracetanilide and 4-nitrophenol in an isocratic method with a run time under 30 min. This method was validated following ICH guidelines and validation parameters showed that it could be employed as stability-indicating method for this pharmaceutical form.

Simultaneous determination of chlorpheniramine and pseudoephedrine in human plasma by liquid chromatography–tandem mass spectrometry

A sensitive and specific procedure for simultaneous quantitation of chlorpheniramine and pseudoephedrine in human plasma has been developed and validated. Analytes were extracted from plasma samples by liquid-liquid extraction, separated on a Diamonsil C18 column (250 x 4.6 mm i.d.) and detected by tandem mass spectrometry with an atmospheric pressure chemical ionization interface. Diphenhydramine was used as the internal standard. The method has a lower limit of quantitation of 0.2 and 2.0 ng/mL for chlorpheniramine and pseudoephedrine, respectively. The intra- and inter-day relative standard deviation, calculated from quality control (QC) samples were below 4.3% for chlorpheniramine and below 9.5% for pseudoephedrine. The inter-day relative error as determined from QC samples was within 4.7% for each analyte. The overall extraction recoveries of chlorpheniramine and pseudoephedrine were 77 and 61% on average, respectively. The method was successfully applied to pharmaockinetic study of chlorpheniramine and pseudoephedrine in volunteers receiving formulations containing 4 mg of chlorpheniramine maleate and 60 mg of pseudoephedrine hydrochloride.

[Simultaneous determination of pseudoephedrine and chlorpheniramine in human plasma by HPLC-UV detection method]

AIM

To establish a sensitive and specific method to simultaneous determination of pseudoephedrine and chlorpheniramine in human plasma.

METHODS

Pseudoephedrine and chlorpheniramine were extracted from alkaline plasma with t-butyl methyl ether as the base form, and were back-extracted into 1.5% hydrochloride solution. The two drugs were simultaneous determined by RP-HPLC with ultraviolet detection at 200 nm, using dextromethorphan as internal standard. A C18 column (250 mm x 46 mm ID) and a mobile phase containing acetonitrile-water-triethylamine (46:54:0.2, containing 10 mmol x L(-1) sodium dodecyl sulfate (SDS) and 60 mmol x L(-1) NaH2 PO4, adjusted pH to 2.6 with H3PO4) were used.

RESULTS

The limit of quantification was 10.0 and 0.5 microg x L(-1), the linear range was 1.5 - 0.01 mg x L(-1) and 75 - 0.5 microg x L(-1), for pseudoephedrine and chlorpheniramine, respectively. The within-day and between-day RSD were less than 12.4%, and the average recovery was between 97.3% - 109.4%.

CONCLUSION

The method was sensitive, specific, simple, and suitable for drug level monitoring in clinical pharmacokinetic study.

Investigation of EDTA anticoagulant in plasma to improve the throughput of liquid chromatography/tandem mass spectrometric assays

In this study, EDTA and heparin are compared as anticoagulants with respect to their efficiency in preventing clot formation in plasma samples that were subsequently analyzed by liquid chromatography/tandem mass spectrometry (LC/MS/MS). A pilot in vivo pharmacokinetic study for the drug chlorpheniramine was conducted in which both EDTA and heparin plasma samples were collected simultaneously. All conditions except the anticoagulant were held constant during the pharmacokinetic study. Bioanalytical results were compared from samples transferred by manual pipette and by an automated liquid handler workstation. The concentration of chlorpheniramine in samples was determined by LC/MS/MS. Results from the analysis of variances (ANOVA) of log-transformed plasma chlorpheniramine concentrations were used to calculate 90% confidence intervals for the ratio least-squares mean values for anticoagulants and for transfer methods. Analytical concentrations of the drug chlorpheniramine were equivalent in heparin- and EDTA-containing plasma. Results suggest that the failure rate for transfer of EDTA plasma (50 micro L by automated workstation or manually) is less than that for heparinized plasma. As a consequence of these results, the vast majority of plasma samples in our laboratories are now collected in EDTA, which allows for use of automated sample transfer resulting in a three-fold timesaving over manual transfer using a single-channel pipette. The ability to use automation has resulted in improved efficiency and cost savings.

Simple and sensitive method for the determination of chlorpheniramine maleate in human plasma using liquid chromatography-mass spectrometry

A convenient liquid chromatographic-single quadrupole mass spectrometric (LC-MS) method was developed and validated for the determination of chlorpheniramine maleate (INN name: chlorphenamine) in human plasma. The method had advantages of a single liquid-liquid extraction with diethylether and high sensitivity. The linearity was also excellent over the concentration range of 0.52-20.8 ng/ml of chlorpheniramine maleate. The intra- and inter-day precision and accuracy ranged between 0.0 and 13.9%, showing a good reproducibility. This developed method was successfully applied to analysis of chlorpheniramine maleate in clinical studies.

The roles of CYP2D6 and stereoselectivity in the clinical pharmacokinetics of chlorpheniramine

AIMS

To examine the stereoselective disposition of chlorpheniramine and to evaluate the role of CYP2D6 in chlorpheniramine pharmacokinetics in humans.

METHODS

Eight healthy volunteers (six extensive metabolizers with respect to CYP2D6 and two poor metabolizers) received a single 8 mg oral dose of rac-chlorpheniramine either given alone or following administration of quinidine 50 mg every 6 h for 2 days prior to the study day and every 6 h thereafter until the end of the study. Plasma concentrations of (S)-(+)- and (R)-(-)-enantiomers of chlorpheniramine were determined using liquid chromatography/mass spectrometry.

RESULTS

In extensive metabolizers, mean Cmax was greater (12.55+/-1.51 ng ml-1vs 5.38+/-0.44 ng ml-1) and CLoral was lower (0.49+/-0.08 l h-1 kg-1vs 1.07+/-0.15 l h-1 kg-1) for (S)-(+)- than for (R)-(-)-chlorpheniramine (P<0.005). For (S)-(+)-chlorpheniramine, administration of quinidine, an inhibitor of CYP2D6, resulted in an increase in Cmax to 13.94+/-1.51 (P<0.01), a reduction in CLoral to 0.22+/-0.03 l h-1 kg-1 (P<0.01), and a prolongation of elimination half-life from 18.0+/-2.0 h to 29.3+/-2.0 h (P<0.001). Administration of quinidine decreased CLoral for (R)-(-)-chlorpheniramine to 0.60+/-0.10 l h-1 kg-1 (P<0.005). In CYP2D6 poor metabolizers, systemic exposure was greater after chlorpheniramine alone than in extensive metabolizers, and administration of quinidine resulted in a slight increase in CLoral.

CONCLUSIONS

Stereoselective elimination of chlorpheniramine occurs in humans, with the most pharmacologically active (S)-(+)-enantiomer cleared more slowly than the (R)-(-)-enantiomer. CYP2D6 plays a role in the metabolism of chlorpheniramine in humans.

Differential cognitive effects of ebastine and (+)-chlorpheniramine in healthy subjects: correlation between cognitive impairment and plasma drug concentration

AIMS

It has been widely recognized that classical antihistamines induce sedation as an adverse effect, while second-generation antihistamines have few if any sedative effects. In order to evaluate the sedative properties of ebastine, a second-generation antihistamine, its effect on cognitive performance in healthy subjects was compared with placebo and (+)-chlorpheniramine.

METHODS

Twelve healthy male subjects were instructed to perform six types of attention-demanding cognitive tasks, and objective measurements of reaction times and accuracy was made before and after drug administration. Their sleepiness levels were also monitored. Test drugs were ebastine 10 mg, placebo and two doses of (+)-chlorpheniramine 2 mg and 6 mg, as positive controls. Plasma drug concentrations at the end of the study were analysed.

RESULTS

After treatments with (+)-chlorpheniramine, the reaction times of the tasks were significantly prolonged (e.g. ratios of after/before dosing: placebo (0.998 +/- 0.113) vs (+)-chlorpheniramine 2 mg (1.103 +/- 0.083; P<0.05) or (+)-chlorpheniramine 6 mg (1.170 +/- 0.139; P<0.001) in a 7 ms visual discrimination time task) and the accuracy was significantly decreased (e.g. ratios: placebo (1.038 +/- 0.158) vs (+)-chlorpheniramine 2 mg (0.792 +/- 0.202; P<0.01) or (+)-chlorpheniramine 6 mg (0.837 +/- 0.222; P<0.05) in a 7 ms task). On the other hand, performance was not affected by ebastine or placebo treatment (e.g. ebastine 10 mg (reaction time ratio; 1.014 +/- 0.067 and accuracy ratio; 0.990 +/- 0.146) in a 7 ms task). Subjective sleepiness was also not affected by ebastine but (+)-chlorpheniramine significantly increased sedation. With respect to the relationship between plasma drug concentrations and task performance, the latter deteriorated with an increase in plasma (+)-chlorpheniramine concentration (e.g. r=0.439 (P=0.007) in a 5 ms and r = 0.352 (P=0.039) in a 7 ms task), but it did not correlate with the plasma concentration of carebastine, an active metabolite of ebastine.

CONCLUSIONS

Ebastine 10 mg did not cause any cognitive impairment or subjective sleepiness. On the other hand, (+)-chlorpheniramine impaired cognitive function and induced sleepiness even at 2 mg, the recommended dose in over-the-counter medication. In addition, impaired CNS performance was significantly correlated with plasma (+)-chlorpheniramine concentration.

The enantioselective determination of chlorpheniramine and its major metabolites in human plasma using chiral chromatography on a beta-cyclodextrin chiral stationary phase and mass spectrometric detection

A sensitive enantioselective high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of plasma concentrations of (-)(R)- and (+)(S)-chlorpheniramine (CP) and their metabolites, desmethyl-chlorpheniramine (DCP), didesmethyl-chorpheniramine (DDCP) and chlorpheniramine N-oxide (CPNO). Enantioselective separations were achieved on a beta-cyclodextrin chiral stationary phase (CYCLOBOND I 2000) with a mobile phase consisting of diethylamine acetate (0.25%, pH 4.4):methanol:acetonitrile [85:7.5:7.5, (v/v/v)]and a flow-rate of 0.5 ml/min. For CP, the enantioselectivity (alpha) of the separation was 1.12 with a resolution factor (R(s)) of 1.17. The method was validated for CP by using mass spectroscopy detection (MSD). Concentrations of each enantiomer could be measured down to 125 pg/ml from a 1-ml plasma sample. Extracted calibration curves were linear from 0.13 to 50.00 ng/ml for each enantiomer. The method was applied to samples from two clinical studies.

Postmortem diffusion of drugs from the bladder into femoral venous blood

We describe significantly elevated drug concentrations in the femoral venous blood due probably to postmortem diffusion from the bladder. A 16-year-old deceased male was found in a shallow ditch in winter. The estimated postmortem interval was 9 days and putrefaction was not advanced. The cardiac chambers contained fluid and coagulated blood and a small amount of buffy coat clots. Diffused hemorrhages were found in the gastric mucosa. The bladder contained approximately 600 ml of clear urine. Gas chromatographic-mass spectrometric analysis of the urine disclosed allylisopropylacetylurea (a fatty acid ureide sedative), diphenhydramine, chlorpheniramine and dihydrocodeine. The cause of death was considered to be drowning due to a drug overdose and cold exposure. The concentrations of diphenhydramine, free dihydrocodeine and total dihydrocodeine in the femoral venous blood (1.89, 3.27 and 3.30 microg/ml, respectively) were much higher than those in blood from the right cardiac chambers (0.294, 0.237 and 0.240 microg/ml, respectively). Urine concentrations of diphenhydramine, free dihydrocodeine and total dihydrocodeine were 22.6, 37.3 and 43.1 microg/ml, respectively. The stomach contained negligible amounts of diphenhydramine, free dihydrocodeine and total dihydrocodeine (0.029, 0.018 and 0.024 mg, respectively); concentrations of these drugs in the femoral muscle were 0.270, 0.246 and 0.314 microg/g, respectively. These results indicate that postmortem diffusion of diphenhydramine and dihydrocodeine from the bladder resulted in the elevated concentrations of these drugs in the femoral venous blood. Not only high urinary drug concentrations but also a large volume of urine in the bladder might accelerate the postmortem diffusion.

Binding of chlorpheniramine enantiomers to human plasma proteins

The in vitro binding of RS-chlorpheniramine to human proteins was studied by equilibrium dialysis. The binding to total plasma proteins and to individual albumin and alpha-glycoprotein acid is stereoselective. (+)S-chlorpheniramine is more extensively bound than its antipode to total plasma proteins (38% vs. 23%), to albumin (20% vs. 15%) and to alpha-glycoprotein acid (23% vs. 5%).

Simultaneous determination of paracetamol and chlorpheniramine in human plasma by liquid chromatography-tandem mass spectrometry

An analytical method for the determination of paracetamol and chlorpheniramine in human plasma has been developed, validated and applied to the analysis of samples from a phase I clinical trial. The analytical method consists in the extraction of paracetamol and chlorpheniramine with diethyl ether, followed by the determination of both drugs by an LC-MS-MS method, using 2-acetamidophenol as internal standard. The intra-assay and inter-assay precision and accuracy of this technique were good and the limit of quantitation was 0.5 microg/ml of plasma for paracetamol and 0.2 ng/ml for chlorpheniramine. The concentration working range was established between 0.5 microg/ml and 25 microg/ml for paracetamol and between 0.2 ng/ml and 50 ng/ml for chlorpheniramine. This method has been used for analyzing more than 1200 human plasma samples from a clinical study with 24 volunteers.

Pharmacokinetics of chlorpheniramine, phenytoin, glipizide and nifedipine in an individual homozygous for the CYP2C9*3 allele

Genetic polymorphisms in the cytochrome P450 (CYP) family are widely known to contribute to interindividual differences in the pharmacokinetics of many drugs. Several alleles for the CYP2C9 gene have been reported. Individuals homozygous for the Leu359 variant (CYP2C9*3) have been shown to have significantly lower drug clearances compared with Ile359 (CYP2C9*1) homozygous individuals. A male Caucasian who participated in six bioavailability studies in our laboratory over a period of several years showed extremely low clearance of two drugs: phenytoin and glipizide (both substrates of CYP2C9), but not for nifedipine (a CYP3A4 substrate) and chlorpheniramine (a CYP2D6 substrate). His oral clearance of phenytoin was 21% of the mean of the other 11 individuals participating in the study, and his oral clearance of glipizide, a second generation sulfonylurea structurally similar to tolbutamide, was only 188% of the mean of the other 10 individuals. However, his oral clearance of nifedipine and chlorpheniramine did not differ from individuals in other studies performed at our laboratories. An additional blood sample was obtained from this individual to determine if he possessed any of the known CYP2C9 or CYP2C19 allelic variants that would account for his poor clearance of the CYP2C9 substrates (phenytoin and glipizide) compared with the CYP3A4 (nifedipine) and CYP2D6 (chlorpheniramine) substrates. The results of the genotype testing showed that this individual was homozygous for the CYP2C9*3 allele and did not possess any of the known defective CYP2C19 alleles. This study establishes that the Leu359 mutation is responsible for the phenytoin and glipizide/tolbutamide poor metabolizer phenotype.

Distribution of antihistamines into the CSF following intranasal delivery

The preferential absorption of certain drug compounds from the nasal cavity into the cerebrospinal fluid (CSF) raises questions regarding the transport processes controlling drug disposition following intranasal delivery. The disposition characteristics of several structurally similar antihistamine compounds, hydroxyzine, chlorpheniramine, triprolidine, and chlorcyclizine, into the CSF following nasal administration were studied using the rat as an animal model. The antihistamines were administered either intranasally or intra-arterially, and serial CSF and plasma samples were collected from the cisterna magna and the femoral artery, respectively. The drug levels in CSF and plasma were assayed by HPLC. Hydroxyzine concentrations in plasma and CSF were found to be significantly greater than most of the other compounds tested. In addition, hydroxyzine also showed the most rapid systemic absorption following nasal administration. Interestingly, the hydroxyzine levels in CSF following intranasal administration were significantly higher than those following intra-arterial administration. The AUC ratios between CSF and plasma for hydroxyzine after intranasal and intra-arterial administration were 4.0 and 0.4, respectively. The AUC ratios for triprolidine, the other antihistamine with measurable CSF concentrations, were 0.5 and 0.7, respectively. The distribution of antihistamines from the nasal membrane into the CSF appears to be controlled by a combination of their molecular properties. It also appears that the intranasal delivery of drugs with optimal physicochemical characteristics can result in an improved CNS bioavailability compared to those achieved from an equivalent parenteral dose.

Bioequivalence and pharmacokinetics of chlorpheneramine in healthy human volunteers

This study was carried out to evaluate the bioavailability of a new regular release tablet formulation of chlorphenamine (CPA) (Histop) relative to a reference formula (Piriton) using 13 human healthy volunteers. Each one received the two formulations as two 4 mg tablets in a two-way double-blind, crossover study. The concentration of CPA was measured with a sensitive high performance liquid chromatography (HPLC). The geometric mean for the area under the curve up to the last concentration (AUC0-t), to infinity (AUC0-oo) and the maximum concentration (Cp max) were 316.5, 315 + 439.8, 431.2 (ngh/ml) and 22, 20.5 (ug/ml) for the test (T) and reference (R) formulations, respectively. The parametric 90% confidence intervals of T/R ratio of the above parameters were within the bioequivalence acceptable range of 80-125%. The mean time to the maximum concentration Tmax (h) were 2.5 and 2.08 for the two formulations respectively and the parametric 90% confidence intervals of the Tmax difference (T-R) were in the range of -0.26-1.14 h, with point estimate of 0.44 h. The two formulations were found to be bioequivalent by the Schuirmann two one-sided t-test. Based on the pharmacokinetic results obtained frequent (ie, Q 4-6 h) CPA daily dosing may not be required particularly for the adults because of its long elimination half-life.

Chlorpheniramine plasma concentration and histamine H1-receptor occupancy

The plasma concentration-response relationship of the antihistamine chlorpheniramine is poorly characterized. This study examined concurrently the concentrations of chlorpheniramine and presence of H1-receptor antagonist in plasma after administration of 8 mg chlorpheniramine in normal volunteers. Six extensive metabolizers and five poor metabolizers, as judged by CYP2D6 phenotype (dextromethorphan metabolic ratio), were enrolled in the study. More than 80% occupancy of H1-receptors by antagonist in plasma was observed for 12 hours after the dose in extensive metabolizers and greater than 60% from 12 to 30 hours in poor metabolizers, when plasma concentrations had fallen below those that should result in 50% occupancy of receptors. The results suggest that (+/-)-chlorpheniramine plasma concentrations do not predict H1-receptor antagonist in plasma. In addition, a role is suggested for CYP2D6 in formation of a potent active metabolite of chlorpheniramine.

Sensitive high-performance liquid chromatographic determination of chlorpheniramine in human serum using column switching

A sensitive method for the determination of chlorpheniramine in human serum was developed using column-switching high-performance liquid chromatography (HPLC) with ultraviolet detection at 210 nm. The analyte was extracted with diethyl ether from alkalinized serum. After evaporation of the organic layer, the reconstituted residue was analyzed by HPLC using a heart-cut technique. Good recoveries of the analyte from spiked human serum samples were obtained with a coefficient of variation below 7%. A good linear response was obtained for the concentration range 0.5-50 ng/ml, with a correlation coefficient higher than 0.999. The lower limit of quantitation for chlorpheniramine in human serum was 0.5 ng/ml. The method was satisfactorily applied to the determination of chlorpheniramine in human serum after oral administration of chlorpheniramine maleate.

Direct injection assay of drug enantiomers in serum on ovomucoid-bonded silica materials by liquid chromatography

A high-performance liquid chromatographic (HPLC) method for the determination of drug enantiomers in serum was developed. The method involves direct injection of serum samples on to an ovomucoid-bonded column, which is prepared by bonding of ovomucoid proteins to an aminopropyl-silica gel by the N,N'-disuccinimidyl carbonate activation method and separation of drug enantiomers on the column using a mixture of phosphate buffer and an organic solvent. High recoveries of serum proteins were obtained using eluent pH values of 3, 4, 6 and 7 at phosphate buffer concentrations above 50 mM, whereas the recovery was ca. 70% at an eluent pH of 5. The recovery of each enantiomer of basic and acidic drugs from serum was almost 100%.

Pharmacokinetics and pharmacodynamics of terfenadine and chlorpheniramine in the elderly

In a double-blind, randomized, crossover study, the H1-receptor antagonists, terfenadine and chlorpheniramine, were investigated in eight healthy, fasting female subjects, aged 67.8 +/- SD 0.8 years, who ingested single doses of terfenadine, 1 mg/kg (mean dose, 69.6 +/- 11.2 mg), and chlorpheniramine, 0.12 mg/kg (mean dose, 8.4 +/- 1.3 mg). The mean serum-elimination half-life of terfenadine metabolite I was 8.7 +/- 3.7 hours. After terfenadine ingestion, significant wheal suppression occurred from 2 to 24 hours compared to predose wheal size, with maximum wheal suppression, 42 +/- 13% to 60 +/- 16% from 2 to 12 hours. Significant flare suppression occurred from 2 to 24 hours, with maximum flare suppression, 75 +/- 15% to 78 +/- 13% from 4 to 8 hours. The mean serum-elimination half-life of chlorpheniramine was 22.6 +/- 11.0 hours. After chlorpheniramine ingestion, significant wheal suppression occurred from 1 to 10 hours, inclusive, compared to predose wheal size, with maximum wheal suppression, 36 +/- 11% to 37 +/- 11% from 5 to 6 hours. Significant flare suppression occurred from 1 to 12 hours, with maximum flare suppression of 43 +/- 14% to 46 +/- 19% at 2, 5, and 6 hours (p less than 0.01). Adverse effects, chiefly sedation, occurred in five of eight patients after receiving terfenadine, and in all eight patients after receiving chlorpheniramine; but, since no placebo control was administered, these adverse effects could not be definitely attributed to H1-receptor-antagonist ingestion.

[Behavior of chlorpheniramine in vivo after administration of d- and l-chlorpheniramine maleate]

A high performance liquid chromatographic (HPLC) method was developed for the determination of chlorpheniramine (I) in the plasma. By this method, 1 ng of I could be measured. Plasma levels of I were determined by the HPLC method after oral administration of d-chlorpheniramine maleate (II) or l-chlorpheniramine maleate (III) to healthy subjects and dogs. Plasma levels of I brought about by oral administration of II were evidently higher than those by III both in humans and dogs. On the other hand, there was no difference in plasma levels of I when II or III was injected intravenously into dogs. Therefore, it was considered that the discrepancy in plasma levels of I after oral administration of II and III to dogs was neither due to a difference in elimination rate nor a distribution volume but rather in first-pass effect in absorption process. The result observed in the human study could be also explained in the same way as that in dogs.

Chronic chlorpheniramine therapy: subsensitivity, drug metabolism, and compliance

To investigate whether patients develop true subsensitivity to antihistamines during chronic therapy, we studied 14 adult subjects who received chlorpheniramine for 3-day and 3-week trials of therapy. Titrated skin tests to histamine and compound 48/80, chlorpheniramine blood levels (by HPLC), compliance, and side effects were monitored and compared during the two courses of therapy and their respective 72-hour washout periods. We found a significant correlation between chlorpheniramine blood levels and skin test suppression during both the 3-day and 3-week therapies. The 3-day chlorpheniramine therapy was more clinically effective (measured by skin test suppression corrected for serum chlorpheniramine concentration) than the 3-week therapy (P less than .01). Chlorpheniramine serum half-lives and 2-hour chlorpheniramine blood levels were not significantly different after the 3-day and 3-week trials. Compliance was significantly worse (P less than .01) during 3-week therapy. Medication side effects (particularly drowsiness) were frequently reported during both courses of therapy. We conclude that subsensitivity to chlorpheniramine does develop in adult patients receiving 3 weeks of therapy. This subsensitivity is not explained by changes in drug metabolism. In addition to subsensitivity, poor compliance may contribute to sub-therapeutic results during chronic antihistamine therapy. Side effects from antihistamines may also require individualization of therapy for certain patients.

Highly sensitive determination of chlorpheniramine as fluorescence derivative by high-performance liquid chromatography

A new method has been developed for the quantitative analysis of chlorpheniramine in human blood using high-performance liquid chromatography with a fluorescence detector. Benzyl chloroformate was found to be suitable as a fluorometric derivatizing reagent. A linear calibration curve ranging from 0 to 40 ng was obtained for chlorpheniramine, and the minimum detectable concentration was 0.1 ng/ml (whole blood) at a signal-to-noise ratio of 2. It was confirmed that chlorpheniramine levels in the blood of healthy adult volunteers could be precisely determined up to 96 h after a single oral administration of a tablet containing 4 mg of chlorpheniramine.

Simultaneous determination of codeine and chlorpheniramine in human plasma by capillary column gas chromatography

A specific and highly sensitive capillary column gas chromatographic method was developed for the simultaneous determination of codeine and chlorpheniramine in human plasma. The method involves a solvent extraction and analysis by capillary column gas chromatography on a cross-linked 50% phenylmethyl silicone fused-silica capillary column with flame thermionic detection. A 10% solution of n-butanol in toluene was used as extraction medium and pyrilamine was used as internal standard. Reproducibility, linearity of calibration curves and specificity were all satisfactory with both drugs. The plasma concentration of codeine and chlorpheniramine could be measured at levels down to 0.9 ng/ml as codeine phosphate and 0.4 ng/ml as chlorpheniramine maleate, respectively. The method was applied to plasma samples from normal volunteers, and was confirmed to be adequate for biopharmaceutical and pharmacokinetic studies.

Subnanogram quantitation of chlorpheniramine in plasma by a new radioimmunoassay and comparison with a liquid chromatographic method

A new radioimmunoassay (RIA) procedure for the quantitation of chlorpheniramine in plasma is described. The assay allows the determination of chlorpheniramine levels up to 96 h after oral administration of a single 4-mg tablet to healthy volunteers. This procedure was sensitive to a 156-pg/mL plasma concentration when a 100-microL plasma sample was used. The mean coefficient of variation over the linear range of the assay from 0.156 to 20 ng/mL was 3.79%. The specificity of the assay was investigated, and the antisera showed 7% cross-reactivity with the N,N-didemethyl analogue and 17% cross-reactivity with the N-demethyl analogue. This high degree of specificity was also evident from the findings that the plasma concentrations determined by this newly described RIA procedure in samples of two healthy male volunteers who were administered 4 mg of chlorpheniramine maleate orally gave a strong correlation (r2 = 0.88) with values obtained by an HPLC-UV procedure. The antiserum cross-reacted 100% with brompheniramine and, thus, can be used for its analysis in plasma. The described RIA procedure is precise, simple, and capable of handling a large number of plasma samples with a minimal turnaround time.

Bioavailability of regular and controlled-release chlorpheniramine products

The bioavailability of chlorpheniramine regular-release versus controlled-release products was compared using 15 human subjects. The dosage forms evaluated were an 8-mg barrier coated-bead capsule, an 8-mg repeat action tablet, two 4-mg tablets, and 4- and 8-mg syrups. Single doses of each product were administered orally in a 5-way crossover study, plasma samples were collected at specific time intervals, and chlorpheniramine levels assayed by HPLC. Pharmacokinetic analysis was based on a two-compartment open model. The average plasma elimination half-life of chlorpheniramine was calculated to be approximately 18.3 hr. The controlled-release products gave a higher Cmax than the 4-mg syrup, but less than two 4-mg tablets. The controlled-release products also extended the time necessary to attain peak drug levels compared to the 4- and 8-mg syrups. The area under the curve (AUC) data for the controlled-release products was not equivalent to equal amounts of the regular-release products. The study indicated that while the controlled-release chlorpheniramine products were successful in prolonging the time course of absorption, this was at the expense of incomplete bioavailability of the drug.

Evaluation of activated charcoal-sorbitol suspension as an antidote

Studies in rats were performed to evaluate the effect of sorbitol on the antidotal efficacy of activated charcoal against four test drugs and to investigate the influence of storage upon the antidotal effect of activated charcoal-sorbitol suspension. The antidotal potency of activated charcoal was not diminished by sorbitol solution 70% w/v. In fact, it was enhanced by the sorbitol solution, as indicated by greater decrease in peak tissue drug concentration, compared to the effect produced by activated charcoal in aqueous suspension. Furthermore, storage of activated charcoal in sorbitol for as long as 1 year did not reduce the antidotal-efficiency of the absorbent.

Blood levels following multiple oral dosing of chlorpheniramine conventional and controlled release preparations

An examination of steady-state performance of chlorpheniramine conventional versus controlled release products was conducted using 15 male subjects in a 3-way crossover study with a 2-week washout period between studies. The study was designed to determine if chlorpheniramine formulations provide consistent pharmacokinetic performance between individual units upon going from single dose to multiple dose therapy. In addition, the validity of predicting steady-state levels for these kinds of products using only single oral dose data was examined. The dosage forms evaluated were a conventional 4 mg tablet, and 8 mg barrier coated-bead capsule, and an 8 mg repeat action tablet. Multiple doses of each product were orally administered to each subject for 6 days prior to the study day to achieve steady-state levels and on the actual study day. Serum samples were collected at specific time intervals on the study day, and chlorpheniramine levels assayed by HPLC. Pharmacokinetic analysis was based on a two-compartment open model. The mean plasma elimination half-lives of the various dosage forms were in the range 24.5-25.4 h. There was no rapid release of drug from the controlled release products nor did they have drug release problems during the dosing interval. Good agreement was obtained between predicted average drug concentration at steady-state and drug concentration actually present for all the formulations studied. Based upon comparative examination of AUC, Cmax, and fraction of dose absorbed data, the controlled release products administered every 12 h were comparable in performance to a conventional release tablet administered every 6 h. Since the half-life of chlorpheniramine is approximately 1 day, therapeutic management may possibly be gained with dosing the patient once daily with a controlled release product or twice daily with a conventional tablet.

Pharmacokinetics and tissue distribution of chlorpheniramine in rabbits after intravenous administration

Intravenous studies of chlorpheniramine (CPM) were conducted in six New Zealand White male rabbits (mean wt. 3.88 kg). CPM and its two demethylated metabolites in arterial serum and urine were assayed by HPLC. Triexponential equations were needed to fit the i.v. CMP serum data in three rabbits, while biexponential equations were required in the other three rabbits. Harmonic mean of V1, Mss, Varea, CL, and terminal t 1/2 were 2.84, 10.8, and 15.5 liters/kg, and 4.14 liters/kg/hr and 2.57 hr, respectively. The average serum protein binding was 44%. The average blood to plasma concentration ratio was 1.85. Estimated mean hepatic blood extraction ratio based on i.v. studies was 0.88. Tissue distribution studies showed rapid and extensive uptake of CPM by various organs such as lung, kidneys, and brain after i.v. bolus injection, and their concentrations were 160-, 80-, and 31-fold higher than the plasma level. The amount of CPM in the muscle was calculated to represent about 50% of CPM present in the body near the steady state. Variation in plasma protein and tissue binding was postulated to be an important factor for the observed marked interspecies difference in the apparent volume of distribution of CPM. Only 2% of the dose was excreted unchanged in the urine.

Sensitive GLC-mass spectrometric determination of chlorpheniramine in serum

A new method was developed for the quantitative analysis of chlorpheniramine in serum using the high sensitivity and selectivity of GLC-mass spectrometry with selected-ion monitoring. Intense fragment ions at m/e 203 and 207 from the drug and a tetradeuterated analog, respectively, are monitored continuously. The deuterated quantitation standard can be prepared by a simple exchange reaction. A linear calibration curve was obtained over the range of 0-160 ng/ml of serum using 85 ng of the standard/ml. The sensitivity limit is 1-2 ng/ml, and each serum extract can be analyzed in less than 2 min. The method was applied to a measure chlorpheniramine concentrations through at least 1.5 biological half-lives.

Chlorpheniramine. II. Effect of the first-pass metabolism on the oral bioavailability in dogs

The pharmacokinetics of chlorpheniramine has been studied in six dogs by following the time course of plasma concentration of the drug after intravenous and oral administration of its maleate salt in solution form. After intravenous dosing the decline in chlorpheniramine plasma concentration was typically biexponential. The drug distributed rapidly and extensively to the extravascular tissues. The mean distribution phase half-life was 12.5 min, and the mean apparent volume of distribution, Vdb, was 525% of the body weight in four dogs with normal hematocrits. The mean half-life of elimination was 1.7 hr. The percent absolute availability following oral administration of the drug in the aqueous solution form was found to be dose dependent. At 100-mg dose, in six dogs, an average of 36% of the orally administered dose was found to be systemically available. At 50-mg dose, in one of the four dogs studied, no measurable plasma levels of chlorpheniramine were obtained, and the average bioavailability was only 9.4%. The average availability in four dogs at 200-mg dose was 39.4%. Even at 200-mg oral dose, the dogs did not show any signs of sedation and remained alert all through the experiment. Saturable first-pass gut and/or hepatic elimination has been postulated. The possible implications of these findings on the therapeutic effectiveness of the usual dosing regimen of chlorpheniramine in dogs are discussed.

Chlorpheniramine. I. Rapid quantitative analysis of chlorpheniramine in plasma, saliva and urine by high-performance liquid chromatography

A method was developed for the rapid quantitative analysis of chlorpheniramine in plasma, saliva and urine using high-performance liquid chromatography. A diethyl ether or hexane extract of the alkalinized biological samples was extracted with dilute acid which was chromatographed on a reversed-phase column using mixtures of acetonitrile and ammonium phosphate buffer as the mobile phase. Ultraviolet absorption at 254 nm was monitored for the detection and brompheniramine was employed as the internal standard for the quantitation. The effects of buffer, pH, and acetonitrile concentration in the mobile phase on the chromatographic separation were investigated. A mobile phase 20% acetonitrile in 0.0075 M phosphate buffer at a flow-rate of 2 ml/min was used for the assays of plasma and saliva samples. A similar mobile phase was used for urine samples. The drug and internal standard were eluted at retention volumes of less than 17 ml. The method can also be used to quantify two metabolites, didesmethyl- and desmethylchlorpheniramine, in the urine. The method can accurately measure chlorpheniramine levels down to 2 ng/ml in plasma or saliva using 1 ml of sample, and should be adequate for biopharmaceutical and pharmacokinetic studies. Various precautions for using the assay are discussed.

Trace determination of chlorpheniramine in plasma by GLC using a nitrogen-phosphorous (N-P) detector

A fast, sensitive and specific method for the determination of chlorpheniramine in plasma is described. The drug was extracted with diethylether, back extracted in hydrochloric acid and reextracted in diethylether. The extract was evaporated to dryness and reconstituted in isopropyl alcohol. The isopropyl alcoholic solution was gas chromatographed without any derivatization and the detection was carried out using a nitrogen sensitive detector. The mean recovery of chlorpheniramine was found to be 96% and a drug level as low as 0.5 ng/ml can be accurately measured.

Determination of nanogram amounts of aromatic compounds by spectrophotometry on thin-layer chromatograms

A highly sensitive method is described for the simultaneous determination of codeine and chlorpheniramine in plasma. Thin-layer chromatography is used for the separation of the drugs. The spots are then rendered visible by nitration of the substances on the thin-layer plate. Codeine can be quantified by direct measurement of the resulting fluorescence. After reduction, the aromatic amines are diazotized and coupled with N-(1-naphthyl)ethylenediamine on the thin-layer plate. For codeine the fluorimetric measurement is more reliable than the colorimetric determination. The sensitivity limits are 8 ng/ml of plasma for codeine phosphate and 1-2 ng/ml of plasma for chlorpheniramine maleate. This procedure is also applicable to other aromatic compounds which can be nitrated by the described method. The method has been applied to compare a determination of the plasma levels of codeine and chlorpheniramine after administration in normal capsules and retard tablets.