Single dose pharmacodynamics of thioridazine and remoxipride in healthy younger and older volunteers

Phenothiazines are widely used in older patients, but little experimental work has been carried out in this age group. Two groups of healthy volunteers, a younger group (Y: six males and six females, aged 20-42 years) and an older group (O: six males and eight females, aged 65-77 years) took part in a randomized double-blind three-period crossover study in which they received by mouth single doses of thioridazine (Y: 50 mg; O: 25 mg) remoxipride (Y: 100 mg; O: 50 mg) or placebo. Measures of central nervous system (CNS) and haemodynamic function were carried out before drug administration and at 1.5-h intervals up to 9 h post-dose, and blood samples were collected over a 24-h period. No significant differences in dose-corrected pharmacokinetic variables were found between the two groups. There was evidence of marked CNS depressant effects of thioridazine from both objective and subjective measures. The effects for remoxipride were similar, though generally less marked. After allowance was made for dose, there was little indication of any difference in degree of CNS depression between the two age groups. Haemodynamic measures showed orthostatic reductions in blood pressure with thioridazine which were particularly marked in the older group, who also showed lower compensatory increases in pulse rate. These results indicate potential problems with orthostatic hypotension with thioridazine in older patients. CNS depression may also be a problem, especially in patients with compromised cholinergic function.

Effect of L-arginine on renal blood flow in normal subjects and patients with hypoxic chronic obstructive pulmonary disease

BACKGROUND

L-arginine is the precursor of endothelium derived nitric oxide (NO) and increasing the available substrate may increase the production of NO. This has been shown by local infusion in peripheral vascular beds but there are few studies of the effects during systemic infusion. Renal vasoconstriction is known to be important in the pathogenesis of cor pulmonale in patients with hypoxic chronic obstructive pulmonary disease (COPD). The effects of a systemic infusion of L-arginine on renal and aortic haemodynamics were therefore investigated in normal subjects and in patients with hypoxic COPD.

METHODS

Ten normal volunteers were recruited from the research staff of King's College Hospital Six patients with COPD and hypoxia (arterial oxygen tension (PaO2) < 8.5 kPa) were recruited from the thoracic medicine outpatient clinic at King's College Hospital and five age and sex matched normal subjects were recruited from a group of normal subjects recruited from the database of the Department of Health Care for the Elderly as volunteers for medical research. There was no history of renal, cardiac, or hepatic disease. Baseline values of time averaged mean of the maximum instantaneous velocity (Tamx) and maximum velocity (Vmax) of blood flow in intrarenal arteries were obtained using colour flow Doppler ultrasound. Using the same technique, Vmax was obtained from the abdominal aorta just distal to the xiphisternum before and after infusion of L-arginine via a large peripheral vein (20 g in 100 ml sterile water over 30 minutes).

RESULTS

In normal subjects L-arginine increased blood velocity in the intrarenal vessels from a mean of 0.22 m/s to 0.26 m/s, an increase of 19.8%. There was no effect on arterial blood pressure, heart rate, or aortic blood velocity. L-arginine had no effect on intrarenal or aortic blood velocity in patients with hypoxic COPD. In age matched controls L-arginine increased blood velocity in the intrarenal vessels from a mean of 0.20 m/s to 0.26 m/s, an increase of 36.8%. There was no effect on arterial blood pressure, heart rate, or aortic blood velocity.

CONCLUSIONS

L-arginine, at the doses administered, increased renal blood flow, as assessed by renal arterial velocity. This effect was not seen in patients with hypoxic COPD but was present in age matched controls. This suggests that the abnormal renal vascular control seen in hypoxic patients with COPD may reflect a disturbance of the L-arginine/nitric oxide pathway.

Hawksley random zero sphygmomanometer versus the standard sphygmomanometer: an investigation of mechanisms

There has been recent controversy over the accuracy of the Hawksley random zero sphygmomanometer (RZS). In most instances, there has been a bias towards lower recordings with the RZS. In an attempt to identify the mechanism, we designed a study to test the hypothesis that biased error is due to: (1) the magnitude of the random zero; and (2) the magnitude of the pressure being recorded. A RZS (60 mm Hg zero UK version) was connected via a Y-tube to a standard mercury sphygmomanometer (SMS). The circumference of the cam responsible for the variable reservoir size in the RZS was marked into quarters. Within each 10 mm Hg band from 300 to 60 mm Hg, 12 paired readings were taken randomly: three within each of the four quarters of the cam circumference. The mean SMS value was 148.8 vs. 148.2 mm Hg for the RZS. Although of minimal biological significance this difference was highly significant (t = 6.2; p < 0.0001). Our findings fail to confirm the difference between RZS and SMS previously reported and we did not find any evidence of a relation in the difference between SMS and RZS and either the random zero value or the height of the blood pressure. Our findings suggest that if the RZS does under record BP versus the SMS it may relate to a patient-machine interaction not detectable in our system.

The association of age with gastric emptying

Gastric emptying is important as a rate-limiting step in the absorption of orally administered drugs. Paracetamol absorption kinetics were used to compare gastric emptying in 19 fit elderly and 19 fit young volunteers. The results showed no significant difference in any of the derived parameters (t1/2abs, tlag and tmax) between the two groups. These results suggest that ageing does not impair this rate-limiting step in drug absorption.