Drugs online research references
Ann Allergy. 1987 Dec;59(6 Pt 2):20-4.
The comparative pharmacokinetics of H1-receptor antagonists.
Simons FE, Simons KJ, Chung M, Yeh J.
University of Manitoba, Winnipeg, Canada.
H1-receptor antagonists appear to be absorbed rapidly after oral administration, with peak serum concentrations being reached one to three hours after a dose. For most of these drugs, the absolute bioavailability is unknown because no intravenous formulations are available for comparative purposes. The serum elimination half-life values of these agents are variable: a few hours for terfenadine and triprolidine; about 9 hours for cetirizine, azatadine, and loratadine; from 20 to 25 hours for hydroxyzine, chlorpheniramine, and brompheniramine; and from 5 to 14 days for astemizole. Few pharmacokinetic studies of H1-receptor antagonists in children have been reported. However, it is known that chlorpheniramine, hydroxyzine, cetirizine, and terfenadine have shorter elimination half-life values in children than in adults. Regardless of the age of patients, for most of the H1-receptor antagonists the apparent volumes of distribution and total body clearances appear to be large (3.4 to 18.5 L/kg and 4.4 to 32.1 mL/min/kg, respectively). Cetirizine is an exception, with values of 0.8 L/kg and 0.5 mL/min/kg. Urinary excretion of unchanged antihistamine is higher after cetirizine (60% of dose) than any other H1 blocker. For H1-receptor antagonists with long half-life values, steady state may not be reached for several days (chlorpheniramine and brompheniramine) or several weeks (astemizole), and significant accumulation of drug occurs if the dosing interval is more frequent than every half-life. There is no evidence for the introduction of metabolism of H1-receptor antagonists, even after months of treatment.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2892445&dopt=Abstract
word match zyrtec online literature
Ann Allergy. 1987 Dec;59(6 Pt 2):25-30.
Pharmacokinetics of cetirizine in the elderly and patients with renal insufficiency.
Matzke GR, Yeh J, Awni WM, Halstenson CE, Chung M.
Drug Evaluation Unit, Hennepin County Medical Center, Minneapolis, Minnesota.
The disposition of cetirizine, a new H1-receptor antagonist, was evaluated in 30 healthy adults of various ages and in 15 adults with various degrees of renal insufficiency. The purpose of the evaluation was to determine whether dosage schedules of cetirizine will require modification in the elderly or patients with renal insufficiency. We found that the elimination half-life of cetirizine was prolonged in patients with mild and moderate renal insufficiency, compared with age-matched individuals with normal renal function (19.0 +/- 3.3 and 20.9 +/- 4.4 hours, vs 7.4 +/- 3.0 hours, respectively). However, the mean apparent steady-state volume of distribution did not differ significantly between these subject groups (range 0.41 to 0.47 L/kg). Total body clearance and renal clearance of the drug were both significantly lower in the patients with renal insufficiency. In elderly subjects, the elimination half-life of cetirizine was significantly prolonged compared with younger adults, and apparent total body clearance was significantly reduced. Again, there was no significant difference in the volume of distribution between the groups. Linear regression showed good correlations between the disposition characteristics of cetirizine and age as well as creatinine clearance. However, we found no relationship between age and the ratio of apparent total body clearance of cetirizine to creatinine clearance. Thus the disposition of cetirizine is independent of age but dependent on renal function. The relationship between apparent total body clearance of cetirizine and creatinine clearance was significant only in patients with creatinine clearances greater than 40 mL/min. Progressive decrements in creatinine clearance were not associated with similar changes in the pharmacokinetic parameters of cetirizine.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2892446&dopt=Abstract
word match zyrtec online literature
Ann Allergy. 1987 Dec;59(6 Pt 2):31-4.
The metabolism and pharmacokinetics of 14C-cetirizine in humans.
Wood SG, John BA, Chasseaud LF, Yeh J, Chung M.
Department of Metabolism and Pharmacokinetics, Huntingdon Research Centre Ltd., Cambridgeshire, England.
This study investigated the metabolism and pharmacokinetics of cetirizine, a new H1-receptor antagonist. Single oral doses of 14C-cetirizine dihydrochloride (10 mg) in aqueous solution were administered to six healthy male volunteers. The drug was rapidly absorbed: The peak mean concentration of radioactivity (359 ng-equivalents/mL) and of unchanged drug (341 ng/mL) were achieved within one hour. Mean concentrations of cetirizine declined biexponentially and had a mean elimination half-life of 7.4 hours. The drug was excreted quite rapidly, with 60% of the dose recovered in the 24-hour urine. An additional 10% was excreted in urine over the next four days. Approximately 10% of the dose was excreted in feces over the five-day study period. The dose was excreted mainly as the unchanged drug. Examination of the radioactive compounds present in the plasma, and excreted in the urine and feces indicate that there is little metabolism of cetirizine. One minor metabolite, formed by oxidative O-dealkylation of the cetirizine side chain, was detected in plasma and feces.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2892447&dopt=Abstract
word match zyrtec online literature
Herbs and Pharmaceuticals Online ||
Hair Million herbal formula for hair loss and hair growth ||
Antibiotics and prescription medications online literature ||