Drugs and the heart. VI. Vasodilating drugs

Continuous infusion of drugs: a simple and rational system

Continuous infusion of potent, often short-acting drugs particularly affecting the cardiovascular system is becoming more common in the operating room and intensive care unit. Accuracy and, hence, safety are always important in drug therapy, and never more so than when using the potent vasoactive and cardioactive drugs, yet the multiplicity of methods for preparing these drugs for infusion creates a situation in which mistakes may easily occur. A series of decimally related dilutions for drug preparation is presented, which has been in use for the past 5 years in the cardiac intensive care units at this hospital. It is believed that this system is easy to understand and remember and it thereby simplifies the process. This system may enhance the accuracy of dosage and improve the safety for patients.

Cardiovascular alterations in dogs treated with hydralazine

Groups of 5 male beagle dogs were treated orally with hydralazine tablets in gelatin capsules at a dose of 12 or 24 mg/kg twice a day (6 hours apart) for 2 consecutive days. Five male dogs treated with empty gelatin capsules served as untreated controls. Clinical findings and heart rate changes during treatment and terminal body weight, hematology, and blood chemistry changes were evaluated. The heart, liver, kidneys, spleen, and thymus of each animal were examined microscopically. Dogs in the 12 mg/kg group ate less than control group. Dogs treated with 24 mg/kg did not eat and vomited. Heart rates in both of the treated groups increased by 60% to 80% within 2 hours of treatment and remained high during the entire treatment period. Significant hematologic change was confined to a slight increase in platelet number of dogs treated with 24 mg/kg. Serum glucose was increased in the hydralazine treated dogs. Conjugated serum bilirubin was increased and serum potassium, chloride and phosphorus were decreased in the 24 mg/kg group. Blood urea nitrogen and serum chloride were slightly increased in dogs treated with 12 mg/kg. Treatment-related pathologic alterations were confined to the heart. Two dogs from each of the hydralazine groups experienced acute localized hemorrhage into the epicardium and subepicardium of the right atrium. The media of the muscular branches of the coronary arteries, especially the left coronary artery, was hemorrhagic in 3 dogs from the 24 mg/kg group. Medial necrosis, when seen, tended to be proportional to the severity of medial hemorrhages. There was no necrosis in the papillary muscles of the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

New concepts and drugs in the treatment of congestive heart failure

This article seeks to make clear the basic differences in the treatment of heart failure between therapeutic maneuvers that are aimed at improving the mechanical loading conditions of the heart and those that are aimed at augmenting the fundamental contractile or inotropic state of the myocardium. Emphasis is placed on recognizing that treatment expectations must be viewed within an age- or maturity-dependent framework, since a diminished margin of cardiocirculatory reserve exists in the smallest and youngest patients that limits the extent of benefit that may be derived from diverse treatment approaches.

Endralazine, a new peripheral vasodilator: absence of effect of acetylator status on antihypertensive effect

50 patients with confirmed hypertension were treated with endralazine, a new peripheral vasodilator, in addition to the beta-blocker, pindolol, to which they had not responded adequately. The blood pressure was lowered from 173/115 mm Hg to 143/87 mm Hg in the 34 slow acetylators and from 175/111 mm Hg to 140/84 mm Hg in the 16 fast acetylators. The dosages of both pindolol and endralazine were the same in both groups. It is concluded that the acetylator phenotype does not affect the therapeutic efficacy or dosage requirement of endralazine. It is suggested that this is because endralazine is metabolised mainly by hydrazone formation and only to a minor extent by acetylation.

The transdermal administration of nitrates: an overview

Nitroglycerin has been the mainstay of the medical management of angina pectoris for over 100 years. The long-held clinical impression of the efficacy of nitroglycerin has now been clearly documented in controlled clinical trials designed to evaluate objective response to antianginal agents. Advances in scientific methodology and improved experimental design have contributed to continuing interest in nitrates. Newer uses of nitroglycerin and other nitrates in congestive heart failure and acute myocardial infarction are the result of a developing understanding of the pharmacology of nitrates.

Effects of vasodilators on hypoxic pulmonary vasoconstriction in normal man

A reduction of arterial PO2 is generally observed when vasodilators are given to patients with cardiac or pulmonary disease. This has been attributed to a release of preexisting hypoxic pulmonary vasoconstriction (HPV). We investigated the effects of hemodynamics and blood gases of IV nitroglycerin, IV nitroprusside and sublingual nifedipine, at dosages currently used in clinical practice, in 23 healthy volunteers at normoxic conditions (fraction of inspired O2, FIO2 0.21) and at acute inspiratory hypoxia (FIO2 0.125 during 10 min). Breathing FIO2 0.125 elicited pulmonary vasoconstriction in all the subjects. At FIO2 0.21, nitroglycerin reduced preload, nifedipine reduced afterload, nitroprusside had balanced effects, but none of the drugs induced pulmonary vasodilation and only nitroglycerin deteriorated arterial oxygenation. At FIO2 0.125, nitroglycerin did not at all affect the pulmonary pressor response, while both nitroprusside and nifedipine decreased it. An inhibition of HPV was obtained with certainty in only one subject who received nitroprusside. In all the subjects in whom HPV was partially inhibited by vasodilator administration, the alveolar-arterial PO2 gradients remained significantly lowered, suggesting that the pulmonary vascular tone adaptation to alveolar hypoxia still was effective in improving ventilation/perfusion relationships. The role of impaired HPV in the reduction of arterial PO2 in patients under vasodilator therapy may have to be reevaluated.

Cardiovascular effects in man of intravenous prizidilol hydrochloride (SK&F 92657); a new antihypertensive agent

1 Cardiovascular responses to intravenous prizidilol hydrochloride (SK&F 92657) 0.86 mg/kg were studied in eight supine resting healthy volunteers. Five subjects were slow and the remaining three were fast acetylators of sulphamethazine. Compared with pre-infusion values, mean resting systolic and diastolic blood pressures were significantly reduced, while mean resting pulse rate was significantly increased at 30 min after the start of the twenty minute infusion. 2 During the 6 h study period the lowest mean +/- s.e. mean systolic blood pressure (108.8 +/- 1.7) was recorded 30 min after the start of the infusion. This represented a mean reduction of 5.2 mmHg. Reductions in mean diastolic blood pressure were greater and of longer duration, the lowest mean value (44.8 +/- 2.0 mmHg) being recorded 3.5 h after the start of the infusion and representing a reduction of 18.5 mmHg from the pre-dosing value. At 6 h after the start of the infusion mean diastolic blood pressure was still significantly reduced (by 15.3 mmHg). 3 The maximum mean +/- s.e. mean resting pulse rate (79.3 +/- 4.4 beats/min) occurred 3 h after the start of the infusion, an increase of 23.0 beats/min over the pre-infusion value. At the end of the study the pulse rate was still significantly raised (by 17.7 beats/min). 4 The left ventricular ejection fraction, evaluated in five subjects, 45 min after the start of the infusion, was not altered by prizidilol hydrochloride, but the left ventricular area decreased significantly. 5 Intravenous prizidilol hydrochloride decreases resting blood pressure and left ventricular area, increases pulse rate and has virtually no effect on left ventricular ejection fraction.

Hydrallazine alone in acute left ventricular failure

A patient presented with severe acute left ventricular failure and was treated with hydrallazine and oxygen alone. He made a rapid and full recovery as judged by clinical, radiological and blood gas evidence.