Samson Symchowicz

Pharmacokinetics and Dose Proportionality of Loratadine

The dose proportionality and pharmacokinetics of loratadine, a new nonsedating antihistamine, were studied in 12 normal volunteers. In a three‐way cross‐over, each volunteer received a single 10‐, 20‐, or 40‐mg loratadine capsule. Blood was collected up to 96 hours after dosing. Plasma loratadine concentrations were determined by radioimmunoassay (RIA), and those of a minor, but active metabolite, descarboethoxyloratadine, by high performance liquid chromatography (HPLC). Concentrations in the disposition phase were fitted to a biexponential equation for pharmacokinetic analysis. For dose proportionality, AUC‐ and Cmax‐dose relationships were evaluated by linear regression. Also, pharmacokinetic parameters and dose‐adjusted AUCs were compared by analysis of variance. Loratadine was rapidly absorbed, reaching Cmax values (4.7, 10.8, and 26.1 ng/mL) at 1.5, 1.0 and 1.2 hours for the 10‐, 20‐, and 40‐mg doses, respectively. The loratadine t1/2β ranged from 7.8 to 11.0 hours. Descarboethoxyloratadine reached Cmax values (4.0, 9.9, and 16.0 ng/mL) at 3.7, 1.5, and 2.0 hours for the 10‐, 20‐, and 40‐mg doses, respectively. Its t1/2β ranged from 17 to 24 hours. For both compounds, AUC‐ and Cmax‐dose relationships were linear and there were no differences in the t1/2β, CL/F, or dose‐adjusted AUC values among the treatments. Loratadine and descarboethoxyloratadine plasma concentrations and pharmacokinetics were not dose dependent.

Pharmacokinetics of Interferon α-2b in Healthy Volunteers

In a three‐way crossover design, 12 healthy male volunteers received 5 × 106 IU/m2 body surface area interferon α‐2b(IFN α‐2b) by intravenous (IV) infusion over 30 minutes, intramuscular (IM) injections, and subcutaneous (SC) injections. Blood and urine samples were collected at specified times, and analysis of IFN α‐2b concentrations was performed by immunoradiometric assay. “Flulike” symptoms were the most frequently reported adverse experiences and were independent of the route of administration. After a 30‐minute IV infusion, IFN α‐2b disappeared rapidly from serum, with distribution and elimination phase half‐lives of 0.1 hour and 1.7 hours, respectively. Interferon α‐2b was absorbed slowly after IM and SC administration, with similar absorption half‐lives of 5.8 and 5.5 hours, respectively. The observed maximal concentrations after IM and SC administration were 42.1 IU/mL at six hours and 45.8 IU/mL at eight hours, respectively. Interferon α‐2b was eliminated with half‐lives of 2.2 hours after IM administration and 2.9 hours after SC administration. The areas under the serum concentration‐time curves for the SC and IM doses were higher than those obtained for the IV infusion. Measurable amounts of IFN α‐2b were not found in urine regardless of the route of administration.

Plasma binding of betamethasone3H, dexamethasone-3H, and cortisol-14C— A comparative study

Abstract The binding of betamethasone (16β-methyl-9α-fluoroprednisolone) and dexamethasone (16α-methyl-9α-fluoroprednisolone) to the proteins of cow, dog, rat and human plasma has been studied in vitro by an equilibrium dialysis technique. These synthetic steroids were appreciably bound to the plasma proteins of all species, and the degree of binding did not change substantially over a wide range of concentration. Neither of the synthetic steroids was detectably bound to corticosteroid-binding globulin (CBG) in human plasma, nor did it compete with cortisol for its binding protein. In human and cow plasma, betamethasone was bound to protein to a lesser extent than was dexamethasone; while this condition held for dog plasma, the difference in binding was not as pronounced. In contrast to the other species, betamethasone was bound to a greater extent than was dexamethasone in the rat. The synthetic steroids were bound mainly to the albumin fraction of human plasma. Chromatography on Sephadex gel demonstrated that, although albumin has a high capacity for binding dexamethasone, the affinity constant of the steroid-protein complex is of a low order.

Excretion of Loratadine in Human Breast Milk

The excretion of loratadine, a new nonsedating antihistamine, into human breast milk was studied in six lactating nonpregnant volunteers. Each volunteer received one 40‐mg loratadine capsule. Milk and blood were collected before and at specified times (to 48 hours) after dosing. Plasma and milk loratadine concentrations were determined by a specific radioimmunoassay, and those of an active but minor metabolite, descarboethoxyloratadine, by high performance liquid chromatography (HPLC). Breast milk concentration‐time curves of both loratadine and descarboethoxyloratadine paralleled the plasma concentration‐time curves. For loratadine, the plasma Cmax was 30.5 ng/mL at 1.0 hour after dosing and the milk Cmax was 29.2 ng/mL in the 0 to 2 hour collection interval. Through 48 hours, the loratadine milk‐plasma AUC ratio was 1.2 and 4.2 μg of loratadine was excreted in breast milk, which was 0.010% of the administered dose. For descarboethoxyloratadine, the plasma Cmax was 18.6 ng/mL at 2.2 hours after dosing, whereas the milk Cmax was 16.0 ng/mL, which was in the 4 to 8‐hour collection interval. Through 48 hours, the mean milk‐plasma descarboethoxyloratadine AUC ratio was 0.8 and a mean of 6.0 μg of descarboethoxyloratadine (7.5 μg loratadine equivalents) were excreted in the breast milk, or 0.019% of the administered loratadine dose. Thus, a total of 11.7 μg loratadine equivalents or 0.029% of the administered dose were excreted as loratadine and its active metabolite. A 4‐kg infant ingesting the loratadine and descarboethoxyloratadine excreted would receive a dose equivalent to 0.46% of the loratadine dose received by the mother on a mg/kg basis. An estimated “worst‐case” dose (i.e., the maximum dose that could be expected under any circumstances) of loratadine and descarboethoxyloratadine to an infant was calculated to be only 1.1% of the adult loratadine dose on a mg/kg basis. The adult dose has been reported to be safe and well tolerated, so it is unlikely that this dose presents a hazard to infants.

Loratadine: multiple-dose pharmacokinetics

The steady‐state pharmacokinetics of loratadine (L), a new long‐acting antihistamine devoid of CNS activity, was investigated in 12 healthy male volunteers. Each volunteer received 40‐mg L capsules q24h for ten days. Blood samples were collected at various times on day 1, 5, 7, and 10 and assayed for L by radioimmunoassay (RIA) and for descarboethoxyloratadine (DCL), a known active metabolite, by high‐performance liquid chromatography (HPLC). The plasma L and DCL concentration‐time data in the disposition phases were fitted to a biexponential equation for pharmacokinetic analysis. Steady‐state plasma L Cmax concentrations were reached at 1.5 hour (Tmax) after each dose. DCL steady‐state Cmax values ranged 26 to 29 ng/mL at a Tmax ranging from 1.8 to 3 hours. The AUC at steady state, AUCτ, was 80 to 96 and 349 to 421 h × ng/mL for L and DCL, respectively. The accumulation indexes (Ra) based on AUCτ ratios, did not change for either compound after day 5. Ra values for L and DCL after the fifth dose were 1.4 and 1.9, respectively, indicating that there is little accumulation of either L or DCL after a multiple (once‐a‐day) dosage regimen. The t1/2β at steady state were 14.4 and 18.7 hours for L and DCL, respectively, which were similar to those reported following a single‐dose L administration. Observed plasma drug concentrations were in good agreement with predicted values derived for pharmacokinetic parameters.

Single and Multiple Dose Pharmacokinetic Evaluation of Flutamide in Normal Geriatric Volunteers

Single dose and steady‐state pharmacokinetics of flutamide (F) and its active plasma metabolite, hydroxyflutamide (HF) were studied in twelve healthy geriatric volunteers administered 250 mg flutamide capsules on day 1 and 250 mg flutamide capsules three times a day on days 2 through 9. After oral administration, F was rapidly absorbed and metabolized. It was present in the plasma in small and variable concentrations, which precluded quantitative assessment of pharmacokinetic parameters for individual subjects. Steady‐state plasma concentrations were reached on or before Day 6. The mean steady state Cmax (Day 9), 112.7 ng/ml, occurred at 1.3 hr. Pharmacokinetic analysis of mean data at steady‐state gave a distribution and elimination half‐life of 0.8 hr and 7.8 hours, respectively. The plasma levels for HF were much higher and less variable than F. The mean Cmax for HF averaged 894 ng/ml at 2.7 hours after a single dose and 1719 ng/ml (Day 9) at 1.9 hr after multiple doses. The distribution and elimination half‐lives of HF at steady‐state were 1.9 and 9.6 hours, respectively. The steady‐state HF plasma concentrations were also achieved on or before Day 6 and were approximately twice those obtained after a single dose. From this study, it has been demonstrated that the pharmacokinetics of F and HF do not change appreciably upon multiple dosing of 250 mg F capsule given three times a day.

Effect of dexamethasone on monoamine oxidase inhibition by iproniazid in rat brain

Chronic (6 days) dexamethasone administration caused a slight decrease of rat brain MAO enzyme activity which was reflected by lower levels of 14C-homovanillic acid (HVA) and increased levels of 14C-3-methoxytyramine (3MT) following intracisternal injections of 14C-dopamine (DA). Opposite results with dexamethasone were obtained in iproniazid (MAO-inhibited)-treated rats. In these animals, brain MAO enzyme activity was significantly increased by dexamethasone. This effect increased with the duration of dexamethasone treatment and appeared to be dose dependent. In the brain areas tested (hypothalamus, midbrain, cerebellum, pons and medulla, olfactory, rest of brain) increases of MAO enzyme activity were also indicated by lower levels of 14C-3MT and increased levels of 14C-HVA formed from intracisternally injected radiolabeled DA. Treatment with other glucocorticoids (16alpha-methyldichlorisone, 16beta-methylprednisone and prednisolone) had a similar effect on 14C-DA metabolism. On the other hand, desoxycorticosterone, progestone, estradiol and testosterone, did not exhibit this property. The data indicate that chronic glucocorticoid treatment may have a slight inhibitory effect on brain MAO and also has the ability to partially reverse or antagonize the inhibition of MAO caused by iproniazid.

Excretion of Quazepam Into Human Breast Milk

Abstract: Previous metabolic studies have established that two major metabolites, 2‐oxoquazepam and N‐desalkyl‐2‐oxoquazepam, are present in plasma after dosing with quazepam, a new benzodiazepine hypnotic. The excretion of quazepam, 2‐oxoquazepam, and N‐desalkyl‐2‐oxoquazepam into human breast milk was studied in four lactating nonpregnant volunteers. Each volunteer received one 15‐mg quazepam tablet following an overnight fast. Nursing of offspring was discontinued after drug administration. Milk and blood samples were collected prior to and at specified times (up to 48 hours) after dosing. Plasma and milk levels of quazepam, 2‐oxoquazepam, and N‐desalkyl‐2‐oxoquazepam were determined by specific GLC methods. The concentrations of the three compounds found in milk appeared to depend on their relative lipophilicities, which were determined by log P values. The mean milk/plasma AUC ratios of quazepam, 2‐oxoquazepam, and N‐desalkyl‐2‐oxoquazepam were 4.19, 2.02, and 0.091, respectively. Levels of quazepam and 2‐oxoquazepam declined at about the same rate in plasma and in milk. The total amount of the administered quazepam dose found in the milk as quazepam, 2‐oxoquazepam, and N‐desalkyl‐2‐oxoquazepam through 48 hours was only 0.11 per cent.

Inhibition of dopamine uptake into synaptosomes of rat corpus striatum by chlorpheniramine and its structural analogs.

Abstract Pheniramine and its structural analogs were evaluated for their ability to inhibit dopamine uptake into synaptosomes of rat corpus striatum. A structural activity relationship has been observed. A chlorine or bromine substitution greatly facilitates the inhibitory activity of pheniramine which is further enhanced by demethylation or addition of another halogen. There was no appreciable difference in activity between d- and l- optical isomers of chlorpheniramine or brompheniramine. There was also no correlation between the antihistaminic potency of the compounds and their inhibitory activity on dopamine uptake.

The Pharmacokinetics of Loratadine in Normal Geriatric Volunteers

The pharmacokinetics of loratadine, a non-sedating anti-histamine, were studied in 12 normal geriatric volunteers. In an open label fashion, each volunteer received one 40 mg loratadine capsule. Blood was collected prior to and at specified times (up to 120 h) after dosing. Plasma loratadine concentrations were determined by a specific radioimmunoassay and those of an active metabolite, descarboethoxyloratadine, by high performance liquid chromatography. Concentrations of loratadine in the disposition phase were fitted to a biexponential equation and those of descarboethoxyloratadine to either a monoexponential or biexponential equation for pharmacokinetic analysis. Loratadine was rapidly absorbed, reaching a maximum plasma concentration of 50.5 ng/ml at 1.5 h after dosing. The disposition half-lives of loratadine in the distribution and elimination phases were 1.5 and 18.2 h, respectively. The area under the plasma concentration–time curve, was 146.7 h·ng/ml. Descarboethoxyloratadine had a maximum plasma concentration of 28.0 ng/ml at 2.9 h post-dose and an area under the concentration–time curve of 394.9 h·ng/ml. Its disposition half-lives in the distribution and elimination phases were 2.8 and 17.4 h, respectively. Comparison of these data with those from a previous study of loratadine in young adults showed no clear differences in the disposition half-lives between the two groups. The clearance of loratadine tends to be lower in the elderly, but inter-individual variation within each age group appears greater than any age effect.