Tolerability and Safety of Felodipine

A randomized, double-blind, parallel-group study to compare the anti-hypertensive effects of imidapril and nifedipine in the treatment of mild-to-moderate essential hypertension

This 12-week, multicentre, double-blind, placebo-controlled, parallel-group study compared efficacy of the angiotensin-converting enzyme (ACE) inhibitor imidapril 5 - 10 mg/day and the calcium channel blocker nifedipine slow-release (SR) formulation 20 - 40 mg twice daily. In total 320 patients aged 18 - 75 years, with mean sitting diastolic blood pressures of 95 - 115 mmHg, were randomized to treatment with imidapril (n = 157) or nifedipine SR (n = 163). Efficacy evaluations were based on the intent-to-treat principle. On study completion, there was no difference between the groups with respect to the primary efficacy variable of response to treatment (imidapril 63.1%; nifedipine SR 61.3%). After 2 weeks' treatment, clinically relevant decreases in blood pressure were observed in both groups, with a trend towards further reductions until study end. Fewer patients in the imidapril-treated group than the nifedipine group withdrew due to adverse events that occurred on treatment with study medication (3.2% versus 16.0%) or experienced adverse events (40.1% versus 49.7%). In addition, fewer adverse events were causally related to imidapril (24.2%) compared with nifedipine SR (41.7%). These results show that imidapril is effective in the treatment of essential hypertension and is better tolerated than nifedipine SR.

Clinical and pharmacokinetic results with a new ultrashort-acting calcium antagonist, clevidipine, following gradually increasing intravenous doses to healthy volunteers

AIMS

To investigate the tolerability and safety of clevidipine in healthy male volunteers during intravenous infusion at gradually increasing dose rates and to obtain preliminary information on the pharmacokinetics and pharmacodynamic effects of the drug.

METHODS

Twenty-five subjects were enrolled in the study and twenty-one of them were included twice, resulting in a total of forty-six study entries encompassing 20 min infusions of clevidipine at target dose rates ranging from 0.12 to 48 nmol min-1 kg-1. Haemodynamic variables and adverse events were recorded throughout the study. Concentrations of clevidipine and its primary metabolite, H 152/81, were followed in whole blood, and the pharmacokinetics were evaluated by non-compartmental and compartmental analysis. An Emax model was fitted to the effect on mean arterial pressure (MAP) over heart rate (HR) and the corresponding blood concentrations of clevidipine.

RESULTS

Clevidipine was administered up to a target dose rate of 48 nmol min-1 kg-1, where a pre-determined escape criterion was reached (HR>120 beats min-1 ) and the study was stopped. The most common adverse events were flush and headache, which can be directly related to the mechanism of action of clevidipine. There was a linear relationship between blood concentration and dose rate in the range studied. The median clearance value determined by non-compartmental analysis was 0.125 l min-1 kg-1. Applying the population approach to the sparse data on clevidipine concentrations, an open two compartment pharmacokinetic model was found to be the best model in describing the disposition of the drug. The population mean clearance value determined by this method was 0.121 l min-1 kg-1, and the volume of distribution at steady state was 0.56 l kg-1. The initial half-life, contributing by more than 80% to the total area under the blood concentration-time curve following i.v. bolus administration, was 1.8 min, and the terminal half-life was 9.5 min. At the highest dose rates, MAP was reduced by approximately 10%, and the HR reached the pre-determined escape criterion for this study (>120 beats min-1 ).

CONCLUSIONS

Clevidipine is well tolerated and safe in healthy volunteers at dose rates up to at least 48 nmol min-1 kg-1. The pharmacokinetics are linear over a wide dose range. Clevidipine is a high clearance drug with extremely short half-lives. The effect of clevidipine on the blood pressure was marginal, probably due to a compensatory baroreflex activation in this population of healthy volunteers. A simple Emax model adequately describes the relationship between the pharmacodynamic response (MAP/HR) and the blood concentrations of clevidipine.

omega-Conotoxin GVIA and prazosin, but not felodipine, cause postural hypotension in rabbits

1. The aim was to compare the effect of N-type calcium channel blockade by omega-conotoxin GVIA (omega-CTX) with alpha 1-adrenoceptor or L-type calcium channel blockade on postural adaptation in conscious rabbits. 2. Orthostatic responses were assessed by rapidly tilting the rabbits through 90 degrees for 1 min. Tilts were performed before, 30 and 60 min after i.v. bolus administration of vehicle (propylene glycol 0.17 mL/kg; n = 8), prazosin (0.5 mg/kg; n = 8), felodipine (30 micrograms/kg; n = 8) or omega-CTX (3 & 7 micrograms/kg; n = 9). 3. Prazosin, felodipine or omega-CTX caused significant falls in mean arterial pressure (MAP) with corresponding increases in heart rate (HR). Vehicle administration had no effect on MAP but caused a small fall in HR. 4. Before drug or vehicle administration, a small rise in MAP and HR occurred in response to tilt in all rabbits. In the vehicle treatment group, similar responses were observed to tilt at 30 and 60 min. Postural hypotension was observed in the prazosin treatment group, but not following administration of felodipine. Tilts 30 and 60 min after omega-CTX (3 micrograms/kg) caused an increase in HR but no change in MAP, different to the small pressor response observed following vehicle administration. However, following administration of omega-CTX 7 micrograms/kg (total dose, 10 micrograms/kg), significant falls in MAP with tachycardia were observed in response to tilt. 5. In conclusion, orthostatic hypotension was observed following acute alpha 1-adrenoceptor or N-type calcium channel blockade in the conscious rabbit. These findings are compatible with the expectation that agents which are directly sympatholytic interfere with postural adaptation. In contrast, L-type calcium channel antagonism with felodipine did not elicit postural hypotension.

Force and intracellular Ca2+ during NANC-mediated relaxation of rat anococcygeus muscle and the effects of cyclopiazonic acid

1. Simultaneous recordings of tension and [Ca2+]i during NANC-mediated relaxation were made in the rat anococcygeus muscle under various conditions. 2. In muscles precontracted with guanethidine, nitrergic stimulations at 2 Hz produced a rapid decrease in both the tension and [Ca2+]i. 3. The nitric oxide synthase inhibitor, NG-nitro-L-Arginine (NOLA, 100 mumol/L) completely abolished the decreases in the [Ca2+]i and force response of the NANC-mediated relaxation. 4. Noradrenergic-mediated contractions elicited by electrical field stimulation were potentiated by the addition of NOLA. In the absence of NOLA, the motor responses were larger in magnitude at 10 Hz stimulation than at 2 Hz. After NOLA, both the force response and the associated rise in [Ca2+]i were substantially increased in comparison to the control stimulations. Proportionately the potentiation of the 2 Hz response was of a far greater magnitude than that of the 10 Hz response. 5. The guanylate cyclase inhibitor methylene blue (10 mumol/L), partially inhibited the force and [Ca2+]i response of the NANC relaxation. 6. Following exposure of the muscles to the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor, cyclopiazonic acid, (10 mumol/L) the responses to NANC stimulation were inhibited. The attenuated relaxation response displayed a bi-phasic timecourse and the Ca2+ change in comparison to that of the control was markedly smaller. In some cases, a relaxation was observed with no detectable change in the [Ca2+]i. 7. The results suggest that part of the relaxation response observed with NANC-mediated relaxation in the rat anococcygeus is dependent on Ca2+ sequestration into the sarcoplasmic reticulum. However, other Ca2+ lowering mechanisms and possible Ca2+ independent mechanisms may also contribute to the NANC relaxation response.