Comparative pharmacology and clinical efficacy of newer agents in treatment of heart failure

Prediction of Human Disproportionate and Biliary Excreted Metabolites Using Chimeric Mice with Humanized Liver

The PXB-mouse is potentially a useful in vivo model to predict human hepatic metabolism and clearance. Four model compounds, [¹⁴C]desloratadine, [³H]mianserin, cyproheptadine, and [³H]carbazeran, all reported with disproportionate human metabolites, were orally administered to PXB- or control SCID mice to elucidate the biotransformation of each of them. For [¹⁴C]desloratadine in PXB-mice, O-glucuronide of 3-hydroxydesloratadine was observed as the predominant metabolite in both the plasma and urine. Both 3-hydroxydesloratadine and its O-glucuronide were detected as major drug-related materials in the bile, whereas only 3-hydroxydesloratadine was detected in the feces, suggesting that a fraction of 3-hydroxydesloratadine in feces was derived from deconjugation of its O-glucuronide by gut microflora. This information can help understand the biliary clearance mechanism of a drug and may fill the gap in a human absorption, distribution, metabolism, and excretion study, in which the bile samples are typically not available. The metabolic profiles in PXB-mice were qualitatively similar to those reported in humans in a clinical study in which 3-hydroxydesloratadine and its O-glucuronide were major and disproportionate metabolites compared with rat, mouse, and monkey. In the control SCID mice, neither of the metabolites was detected in any matrix. Similarly, for the other three compounds, all human specific or disproportionate metabolites were detected at a high level in PXB-mice, but they were either minimally observed or not observed in the control mice. Data from these four compounds indicate that studies in PXB-mice can help predict the potential for the presence of human disproportionate metabolites (relative to preclinical species) prior to conducting clinical studies and understand the biliary clearance mechanism of a drug. SIGNIFICANCE STATEMENT: Studies in PXB-mice have successfully predicted the human major and disproportionate metabolites compared with preclinical safety species for desloratadine, mianserin, cyproheptadine, and carbazeran. In addition, biliary excretion data from PXB-mice can help illustrate the human biliary clearance mechanism of a drug.

Hemodynamic effects of isoxsuprine in cardiac failure

Isoxsuprine, a peripheral arteriolar vasodilator, was given to 12 patients with congestive heart failure. Cardiac index increased up to 31 percent; pulmonary artery wedge pressure fell by as much as 33 percent; mean arterial pressure fell by 17 percent; mean pulmonary artery pressure fell by 29 percent; systemic pulmonary vascular resistance fell by 37 percent; and pulmonary vascular resistance fell by 33 percent. All patients showed clinical improvement in the signs and symptoms of congestive heart failure during the three-hour observation period. This initial report documents the short-term salutary effects of isoxsuprine in congestive heart failure. The long-term efficacy of the drug remains to be evaluated.

A double-blind study of trimazosin and methyldopa in hypertensive patients receiving polythiazide

Data are presented on 22 hypertensive patients in an 18-week, double-blind comparison of trimazosin and methyldopa during which treatment with polythiazide was continued. Maximum daily doses of trimazosin and methyldopa were 800 and 2000 mg, respectively. Eight of nine patients receiving trimazosin and 8 of 12 receiving methyldopa had excellent or good overall responses. (One trimazosin patient was not evaluated for overall response.) Quantitative criteria of blood pressure response indicated that trimazosin was as effective as methyldopa. There were no clinically significant changes in results of Holter monitor recordings, ECGs, chest x-ray films, cardiopulmonary tests, or ophthalmoscopy. There were no abnormalities in laboratory tests of trimazosin patients. One patient receiving methyldopa had a positive Coombs' test. Significant side effects developed in two methyldopa patients-syncope in one patient and postural hypotension in the other. No significant side effects occurred in the patients taking trimazosin.

Profile of trimazosin: an effective and safe antihypertensive agent

Trimazosin, a selective alpha-1-adrenoceptor-blocking agent, has been extensively evaluated in over 1000 patients. In hypertensive patients, reduction in elevated blood pressure in both supine and standing positions, consequent to a reduction in systemic vascular resistance, persisted in long-term therapy. Progression of hypertension target organ damage did not occur. Improvement in blood lipids with decreased total serum cholesterol was noted in long-term therapy. In long-term studies, 74% of patients responded at a trimazosin dose of 300 mg/day or less; the maximum dose was 300 mg/day or less in 52% of patients and 200 mg/day or less in 36%. Most patients received twice a day therapy. The side effect profile of trimazosin was comparable to placebo and significantly better than that of either methyldopa or propranolol. Concomitant disease or therapy did not adversely affect the trimazosin safety profile. Hematology, clinical chemistry, and urinary parameters did not indicate deleterious effects. Because of its excellent safety and toleration profile, trimazosin may be particularly suitable in first-line therapy of patients with mild or moderate hypertension.

Symptoms, haemodynamics, and exercise capacity during long term treatment of chronic heart failure. Experience with pirbuterol

An open study of long term treatment with an oral beta 2 agonist (pirbuterol 20 mg three times daily) was undertaken in 63 patients with severe chronic heart failure. During three months of treatment 20 (32%) patients died, of whom 16 were taking the drug at the time of death. Mortality was related to initial functional class (New York Heart Association classification: 23% in grade III and 75% in grade IV). Concomitant treatment with digoxin did not affect mortality. The drug was well tolerated by most patients but unwanted side effects necessitated withdrawal of the drug in six (10%). Thirty-five patients were continuing to take the drug after three months, of whom 22 reported symptomatic improvement and only four deterioration. There was a relation between symptomatic improvement and increase in exercise capacity. At initial haemodynamic assessment a single dose of pirbuterol increased the cardiac index by 34% and the stroke index by 21%. Left ventricular filling pressure fell by 23% and systemic vascular resistance by 22%. Haemodynamic reassessment after three months of continuous treatment in 29 patients showed maintained improvement in the group as a whole, although individual variation was considerable. There was no apparent relation between haemodynamic improvement and improvement in exercise duration and symptoms. Severe heart failure has a poor prognosis. Identification of those patients who may derive benefit from treatment with a particular drug is not yet possible.

Acute haemodynamic comparison of amrinone and pirbuterol in chronic heart failure. Additional effects of isosorbide dinitrate

A randomised, within patient comparison was made in patients with severe chronic heart failure, to study the acute haemodynamic effects of oral agents which have inotropic and vasodilator properties. A non-glycosidic non-adrenergic positive inotropic agent with vasodilator properties (amrinone) was compared with a beta-agonist which has vasodilator and positive inotropic effects (pirbuterol). To assess whether combined treatment with a venodilator might be advantageous, the effect of adding isosorbide dinitrate was studied. Oral amrinone or pirbuterol were given in random order to each of 13 patients, on successive days, and oral isosorbide dinitrate was added after two-and-a-half hours. Control values before amrinone or pirbuterol were similar, and both drugs increased cardiac index while reducing left ventricular filling pressure, right atrial pressure, and systemic vascular resistance. Heart rate and blood pressure were unchanged. The magnitude of the changes caused by amrinone and pirbuterol were not significantly different. The addition of isosorbide dinitrate caused further falls in left ventricular filling pressure and right atrial pressures, and a fall in heart rate with each drug. Other measurements remained unchanged. Although amrinone and pirbuterol have different pharmacological properties, their acute haemodynamic effects in patients with chronic heart failure are indistinguishable.

Immediate and sustained haemodynamic effects of prazosin during upright exercise in man

To ascertain the immediate pharmacodynamic and long-term haemodynamic effects of prazosin in chronic ambulant heart failure, measurements were made during sitting, standing, and walking in 12 patients with severe ischaemic left ventricular failure before and after their first dose of prazosin (2 mg) and in six of these patients after a further 12 weeks of sustained treatment (2 mg tds). When first added to treatment with digoxin and frusemide, prazosin was followed within an hour by substantial reductions in systemic arterial, pulmonary arterial, and pulmonary venous pressures in both postures at rest and also during walking. These changes were significantly attenuated after continued treatment. Cardiac output while sitting and standing at rest was reduced in both instances but the response to exercise was unchanged. The pharmacodynamic effects of prazosin in heart failure are explicable in terms of blockade of alpha1 adrenoceptors in arterial resistance and venous capacitance vessels augmented perhaps by lessening of reflex vasoconstriction secondary to the reduction in pulmonary venous pressure. The cause of the attenuation of the acute haemodynamic effects of the drug during sustained treatment is unknown.