Drugs online research references
Am J Med. 1986 May 23;80(5B):100-4.
Role of selective alpha 1 blockers in the therapy of hypertension.
Kaplan NM.
As millions more patients with mild hypertension are being brought into active drug therapy, the need for effective medications that are safe for long-term use has increased. This is, in part, as a result of the adverse effect on coronary heart disease mortality observed in two of the major therapeutic trials, the Oslo Study and the Multiple Risk Factor Intervention Trial. In both of these, the diuretic-first, stepped-care approach was used. Administration of diuretics is frequently associated with such biochemical abnormalities as hypokalemia, hypercholesterolemia, and hyperglycemia. Thus, the wisdom of the routine use of a diuretic as the first choice of therapy is being questioned. Alternative drugs for initial therapy include beta blockers and selective alpha 1 blockers. With beta blockers, there is a tendency for serum triglycerides to increase and high-density lipoprotein cholesterol to decline, as well as a tendency for an undesirable reduction in cardiac output and an increase in peripheral resistance. Selective alpha 1 blockers, because they lower blood pressure in a hemodynamically more favorable manner and have a tendency to improve the lipid profile, are becoming increasingly attractive as initial therapy for mild hypertension and also as part of the combination needed for more severe disease. The favorable results noted with the new selective alpha 1 blocker terazosin strongly support its addition to the list of preferred drugs for initial therapy.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2872800&dopt=Abstract
Am J Med. 1986 May 23;80(5B):12-9.
Pharmacology of terazosin.
Kyncl JJ.
Terazosin is a quinazoline antihypertensive agent that is chemically similar to prazosin. The saturated furan ring of terazosin distinguishes these two compounds. Terazosin (0.1 to 3.0 mg/kg) lowered blood pressure without increasing heart rate when given orally to spontaneously hypertensive rats. No tolerance was observed during five days of repeated oral administration. Although equally efficacious in spontaneously hypertensive rats as its congener prazosin, terazosin exhibited a more gradual onset of action than prazosin, a more uniform and linear dose-response curve, and a less variable duration of action. When administered intravenously to dogs, terazosin lowered blood pressure primarily by decreasing peripheral vascular resistance. Pretreatment with phenoxybenzamine but not with atropine or propranolol resulted in a greatly reduced hypotensive response to terazosin, demonstrating that this effect of terazosin is mediated by a sympatholytic mechanism of the alpha type. The nature of the alpha-blocking properties of terazosin was evaluated in vitro using both radioligand binding studies and functional tests in rabbit aorta and pulmonary artery. These studies demonstrated that terazosin is highly selective for alpha1 receptors. The affinity for alpha1 receptors was approximately one-third that of prazosin. Like prazosin, terazosin displayed minimal interaction with alpha2 receptors. Median lethal dose values in rats ranged from 0.255 to 0.270 g/kg for intravenous administration and from 5.5 to 6.0 g/kg, for oral administration. Oral administration of high doses of the compound to rats did not produce any gastrointestinal irritation and/or apparent abnormal behavioral effects. Comparison of the oral activity of terazosin in spontaneously hypertensive rats with the oral toxicity values in normal rats revealed a high efficacy/safety ratio. Terazosin given intravenously to rats and mice was 2.6 to 5.0 times less toxic than prazosin. The absorption of terazosin appeared to be slower than that of prazosin in rats. However, from eight to 16 hours after dosing, terazosin concentrations in plasma exceeded those of prazosin, suggesting the possibility of once-daily dosing with terazosin. In addition, terazosin exhibited statistically significant cholesterol lowering effects in gerbils.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2872801&dopt=Abstract
Am J Med. 1986 May 23;80(5B):20-4.
Pharmacokinetics of terazosin.
Sonders RC.
The pharmacokinetics of terazosin have been assessed in human volunteers, hypertensive patients, a limited number of elderly volunteers, and a small number of patients with congestive heart failure. Terazosin was administered intravenously and orally in doses ranging up to 7.5 mg. Following intravenous administration, the disposition of terazosin is characteristic of a two-compartment, open model that is linear and independent of dose. Orally administered terazosin is rapidly, consistently, and almost completely absorbed into the bloodstream. Peak plasma drug levels occur within one to two hours after ingestion. Approximately 90 to 94 percent of the drug is bound to plasma proteins, with the volume of distribution estimated to be 25 to 30 liters. Terazosin undergoes extensive hepatic metabolism, and the major route of elimination is via the biliary tract. Small amounts of terazosin are excreted in the urine. Plasma and renal clearances are 80 and 10 ml per minute, respectively. The mean beta-phase half-life is approximately 12 hours. The pharmacokinetics of terazosin were not influenced by age, congestive heart failure, or hypertension (other than plasma clearance). In contrast to prazosin, terazosin is completely and consistently bioavailable and has a half-life that is three to four times longer than that of prazosin. The prolonged half-life of terazosin allows once-daily dosing, which may facilitate patient compliance with drug therapy for hypertension.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2872802&dopt=Abstract
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