Treatment of hypertensive urgencies and emergencies with nifedipine

How well do muscle biomechanics predict whole-animal locomotor performance? The role of Ca2+ handling

It is important to determine the enabling mechanisms that underlie locomotor performance to explain the evolutionary patterns and ecological success of animals. Our aim was to determine the extent to which calcium (Ca2+) handling dynamics modulate the contractile properties of isolated skeletal muscle, and whether the effects of changing Ca2+ handling dynamics in skeletal muscle are paralleled by changes in whole-animal sprint and sustained swimming performance. Carp (Cyprinus carpio) increased swimming speed by concomitant increases in tail-beat amplitude and frequency. Reducing Ca2+ release from the sarcoplasmic reticulum (SR) by blocking ryanodine receptors with dantrolene decreased isolated peak muscle force and was paralleled by a decrease in tail-beat frequency and whole-animal sprint performance. An increase in fatigue resistance following dantrolene treatment may reflect the reduced depletion of Ca2+ stores in the SR associated with lower ryanodine receptor (RyR) activity. Blocking RyRs may be detrimental by reducing force production and beneficial by reducing SR Ca2+ depletion so that there was no net effect on critical sustained swimming speed (Ucrit). In isolated muscle, there was no negative effect on force production of blocking Ca2+ release via dihydropyridine receptors (DHPRs) with nifedipine. Nifedipine decreased fatigue resistance of isolated muscle, which was paralleled by decreases in tail-beat frequency and Ucrit. However, sprint performance also decreased with DHPR inhibition, which may indicate a role in muscle contraction of the Ca2+ released by DHPR into the myocyte. Inhibiting sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) activity with thapsigargin decreased fatigue resistance, suggesting that SERCA activity is important in avoiding Ca2+ store depletion and fatigue. We have shown that different molecular mechanisms modulate the same muscle and whole-animal traits, which provides an explanatory model for the observed variations in locomotor performance within and between species.

Sublingual nifedipine in elderly patients: even a low dose induces myocardial ischaemia

1. Low doses of sublingual nifedipine are still used for the treatment of hypertensive crises, although recent studies have raised concerns that sublingual nifedipine may cause serious dose-dependent adverse effects. The present study was performed to test the safety of low-dose sublingual nifedipine administered to elderly hypertensive patients. 2. Systemic blood pressure measurements and electrocardiographic (ECG) examinations were performed before and 45-60 min after a 5 mg dose of sublingual nifedipine in 93 consecutive hypertensive patients, 65 years of age or older, who were without coronary artery disease. In 33 patients, the effects of nifedipine on myocardial lactate metabolism were studied during cardiac catheterization. 3. In all patients, following nifedipine administration, blood pressure (BP) decreased significantly, while heart rate (HR) increased, and symptoms associated with elevated BP disappeared. However, changes consistent with myocardial ischaemia appeared on the ECG in six of 55 patients with left ventricular hypertrophy (LVH) and in one of 38 patients without LVH, although only two of these seven patients experienced angina-like precordial tightness. Sublingual nifedipine decreased myocardial lactate extraction from 52 +/- 13 to 38 +/- 19% in 20 patients with LVH (P = 0.02), but myocardial lactate extraction remained stable in 13 patients without LVH (49 +/- 7 to 50 +/- 5%; NS). The change in lactate extraction was significantly correlated with the percentage change in diastolic arterial pressure (r = 0.77, P < 0.001). 4. These results suggest that sublingual nifedipine, even at the low dose of 5 mg, may cause myocardial ischaemia in some elderly patients with LVH that is associated with a marked reduction in coronary perfusion pressure.

Asymptomatic hypertension in the ED

A retrospective study in an urban, municipal, teaching hospital emergency department (ED) was conducted to evaluate (1) the frequency of asymptomatic hypertension in the ED, (2) the initial assessment and patterns of treatment by physicians, and (3) the changes in blood pressure (BP) in these patients. Patients with systolic BP > or = 180 mm Hg or diastolic BP > or = 110 mm Hg were included. Patients with cardiovascular, renal, or central nervous system dysfunction were excluded. Of the 11,531 charts reviewed, 269 (2.3%) met inclusion criteria. Of the 269 patients, 56 patients (20.8%) received antihypertensive treatment in the ED. The treatment group had a higher systolic BP (P < .001), diastolic BP (P < .001), and mean arterial blood pressure (MAP) (P < .001) than the nontreatment group. Fundoscopy was also performed more frequently in the treatment group (30.2% v 8.9%, P < .001). MAP decreased for both groups in the ED, but was higher in the treatment group (-20+/-21 v -11+/-21 mm Hg, P=.02). Despite the lack of support in the literature for the emergency treatment of asymptomatic hypertension in the ED, the individual physician's decision for treatment correlated with the degree of hypertension. Significantly elevated BP readings in the ED tended to decrease over time independent of any antihypertensive treatment, although the decrease was larger in the treated patients.

Controlling the hemodynamic response to laryngoscopy and endotracheal intubation

The hemodynamic response to the stress of laryngoscopy and endotracheal intubation does not present a problem for most patients. However, patients with cardiovascular or cerebral disease may be at increased risk of morbidity and mortality from the tachycardia and hypertension resulting from this stress. These hemodynamic effects gained notice after the introduction and use of muscle relaxants, such as curare and succinylcholine, for endotracheal intubation at the time of anesthesia induction. A variety of anesthetic techniques and drugs are available to control the hemodynamic response to laryngoscopy and intubation. The method or drug of choice depends on many factors, including the urgency and length of surgery, choice of anesthetic technique, route of administration, medical condition of the patient, and individual preference. The possible solutions number as many as the medications and techniques available and depend on the individual patient and anesthesia care provider. This paper reviews these medications and techniques to guide the clinician in choosing the best methods.

Arterial hemodynamics in human hypertension. Effects of the calcium channel antagonist nifedipine

Previous studies have shown some distinct hemodynamic alterations in essential hypertension, including increased resistance, wave reflections, and pulse wave velocity and decreased arterial compliance. These abnormalities are completely normalized by nonspecific smooth muscle dilation with nitroprusside but not by combined alpha- and beta-adrenergic blockade or angiotensin-converting enzyme inhibition, suggesting an enhanced smooth muscle tone that cannot be attributed solely to the sympathetic nervous or renin-angiotensin systems. Since hypertensive patients have an enhanced calcium influx-dependent vasoconstriction, we performed the present study to examine the extent to which the dihydropyridine calcium channel antagonist nifedipine could normalize the hemodynamic abnormalities in essential hypertension. An essential hypertensive patient group was compared with a normotensive group similar in age, body size, and proportion of men and women. During diagnostic cardiac catheterization, ascending aortic micromanometer pressures and electromagnetic flows were measured at baseline and after sufficient sublingual nifedipine (mean, 24 mg) to normalize blood pressure. From the pressures and flows, aortic input impedance, wave reflection magnitude, and compliance were computed. In the hypertensive group, the hemodynamic alterations were indistinguishable from those summarized above. Nifedipine produced sufficient vasodilation to completely normalize all of these hemodynamic alterations, including wave reflections. From these results, together with those reported in our previous studies, it is clear that the various classes of antihypertensive agents affect hemodynamics differently. All are capable of decreasing blood pressure to normotensive levels, but only nitroprusside and nifedipine can also completely normalize all the other pulsatile hemodynamic alterations. Thus, these hemodynamic effects of the different classes of antihypertensive agents should be considered in choosing a therapeutic modality.

Evaluation of the efficacy and safety of oral nicardipine in treatment of urgent hypertension: a multicenter, randomized, double-blind, parallel, placebo-controlled clinical trial

This study was a prospective, randomized, double-blind, placebo-controlled clinical trial designed to evaluate the safety and efficacy of oral nicardipine for the treatment of urgent hypertension in the emergency department. Of 57 patients with urgent hypertension 53 patients were enrolled: 36 men and 17 women, 43 black and 10 white, age range 48 +/- 11 years, and diastolic blood pressure 128 +/- 7 mm Hg. Patients were randomly assigned to receive 30 mg nicardipine or placebo in blind fashion followed by 30 mg open-label nicardipine in nonresponders. Responders to one or two doses of nicardipine received 30 or 40 mg nicardipine three times a day for 1 week after discharge from the emergency department. Adequate blood pressure reduction, defined as a reduction of diastolic blood pressure to less than 100 mm Hg or by at least 20 mm Hg, was achieved in 65% and 22% of patients who received 30 mg nicardipine or placebo (p = 0.002). Adequate blood pressure reduction after administration of open-label nicardipine occurred in 76% of the nonresponders to placebo. Blood pressure reductions were maintained at 1 week after discharge. The drug was well tolerated, and no significant adverse events occurred. We conclude that oral nicardipine is a safe and effective drug for the initial treatment of urgent hypertension.

A new preparation of nifedipine for sublingual application in hypertensive urgencies

A new preparation of nifedipine for sublingual application in hypertensive urgencies was investigated in a prospective study. Patients admitted to the Emergency Department with a persistent elevation of systolic blood pressure (SBP) greater than 190 mmHg and/or a diastolic blood pressure (DBP) greater than 100 mmHg received nifedipine 10 mg sublingual with a sprayer. A second dose was administrated fifteen minutes later if an adequate response defined as a stable reduction of SBP below 180 mmHg and DBP below 100 mmHg had not occurred. Of 30 patients, 21 (70%) responded to the first nifedipine application, 7 responded to the second dose, and 2 nonresponders had to be treated with urapidil. Overall mean SBP was 206 +/- 19 mmHg and mean DBP was 113 +/- 15 mmHg before treatment, and a significant antihypertensive effect was noted within fifteen minutes after nifedipine spray (p < 0.05). The maximum antihypertensive effect was for SBP in sixty minutes (146 +/- 19 mmHg) and for DBP after one hundred twenty minutes (78 +/- 18 mmHg). The average reduction in SBP was 29% and in DBP 31%. In first-dose responders (n = 21) a significant antihypertensive effect was noted within fifteen minutes. SBP declined from 205 +/- 21 to a minimum of 142 +/- 15 mmHg (22.3%) after sixty minutes and DBP from 113 +/- 13 to a minimum of 77 +/- 11 mmHg (22.2%) after one hundred twenty minutes. In second-dose responders (n = 7) a significant antihypertensive effect was noted within thirty minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Advances in pharmacotherapy: treatment of hypertensive crisis

A hypertensive crisis can be caused by many factors. Frequently, the mechanism involved is complex and highly variable among patients. Without drug therapy, this condition is associated with very high mortality and morbidity. There are a number of oral and intravenous hypotensive agents available, which can effectively control blood pressure in a hypertensive crisis. The relative advantages and disadvantages of each treatment option is discussed.

Oral antihypertensives for hypertensive urgencies

OBJECTIVE

To review the data describing the use of oral antihypertensive agents in the treatment of hypertensive urgencies (HU).

DATA SOURCES

A MEDLINE search of the English-language literature and fan searches of papers evaluating oral antihypertensives in HUs and emergencies were conducted.

STUDY SELECTION

Controlled and uncontrolled studies in humans are reviewed. Emphasis was placed on recent trials evaluating individual agents and comparative trials.

DATA SYNTHESIS

Comparative trials have demonstrated that four currently available oral agents can lower blood pressure rapidly and predictably. Nifedipine, the most extensively studied, and clonidine have served traditionally as the oral agents of choice for the treatment of HUs. All the agents can lower blood pressure effectively within the first few hours after dosing, but their use also has been associated with adverse effects. Nifedipine and captopril are the two agents with the most rapid onset, within 0.5-1 hour, and may treat hypertensive emergencies as well as urgencies. Clonidine and labetalol have maximal blood pressure lowering effects at 2-4 hours.

CONCLUSIONS

Captopril, clonidine, labetalol, and nifedipine are all effective agents for the treatment of HUs. Agent selection should be based on the perceived need for urgent blood pressure control, the cause of HU, and concomitant conditions. A definite benefit from acute blood pressure lowering in HUs has yet to be demonstrated, especially in asymptomatic patients. More controlled trials with less aggressive dosing regimens and placebo controls need to be performed to assess the most appropriate treatment for HUs with the fewest adverse effects.

A comparison of the acute hypotensive effects of two different doses of nifedipine

To determine whether a dose of 5 mg of nifedipine would be useful in the treatment of hypertensive emergencies, we compared the acute hypotensive effects of two different doses of nifedipine, 5 mg and 10 mg, in patients with severe hypertension. In this prospective, randomized, double-blind study, 30 consecutive black patients with diastolic blood pressure that was equal to or greater than 115 mm Hg received either a 5 mg or 10 mg nifedipine capsule and a placebo capsule, which matched that of the alternative strength. Patients were asked to bite the capsules and swallow the contents. Blood pressure response over 4 hours and adverse effects were monitored. Mean systolic blood pressure was reduced from 191.7 mm Hg (95% confidence interval 170.8 to 212.7 mm Hg) to 157.9 mm Hg (137.0 to 178.9 mm Hg) and 206.1 mm Hg (185.1 to 227.0 mm Hg) to 153.7 mm Hg (132.8 to 174.7 mm Hg) in patients who were given 5 mg and 10 mg doses of nifedipine, respectively. Mean diastolic blood pressure in the group of patients that received 5 mg doses of nifedipine decreased from 128.2 mm Hg (115.6 to 140.7 mm Hg) to 105.2 mm Hg (92.7 to 117.7 mm Hg); the corresponding values in the group that received 10 mg doses of nifedipine were 129.9 mm Hg (117.4 to 142.5 mm Hg) and 97.5 mm Hg (85.0 to 110.1 mm Hg), respectively. The minimum mean systolic blood pressures occurred 20 and 25 minutes after administration of the 5 mg and 10 mg capsules, respectively; the minimum diastolic blood pressures were reached after 20 and 30 minutes, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral labetalol versus oral clonidine in the emergency treatment of severe hypertension

This study was designed to compare the clinical efficacy and safety of oral clonidine and oral labetalol in the treatment of severe hypertension in an emergency department setting. Thirty-six patients with severely elevated blood pressure (mean baseline blood pressure 199/132 mm Hg) without acute end-organ dysfunction were treated with either oral labetalol or oral clonidine in a randomized double-blind prospective study. Labetalol was administered as an initial dose of 200 mg, followed by hourly 200 mg doses up to 1,200 mg. Clonidine was administered as an initial dose of 0.2 mg, followed by hourly 0.1 mg doses up to 0.7 mg. Labetalol reduced diastolic blood pressure in 94% of the patients within 6 hours, with a mean reduction in blood pressure of 54/37 mm Hg. Clonidine reduced diastolic blood pressure in 83% of the patients within 6 hours, with a mean reduction in blood pressure of 57/32 mm Hg. The authors conclude that oral labetalol was comparable to clonidine in efficacy, had a similar incidence of side effects, and offered the clinician a useful alternative for the treatment of severe hypertension in an emergency department setting. Further studies are indicated to determine appropriate dosing regimens for oral labetalol in the acute treatment of severe hypertension.

Nifedipine pharmacokinetics and pharmacodynamics during the immediate postpartum period in patients with preeclampsia

Pharmacokinetic and pharmacodynamic parameters of oral nifedipine were studied in the immediate postpartum period in eight women with preeclampsia. Peak serum concentrations of 18 +/- 2.1 micrograms/L occurred 40 minutes after ingestion of nifedipine (10 mg). The terminal elimination half-life (mean = 1.35 +/- 0.3 hours) was found to be shorter than that reported for normotensive volunteers or nonpregnant hypertensive women (mean, 3.4 +/- 0.4 hours). A mean apparent oral elimination clearance of 3.3 +/- 1.3 L/hr/kg was more rapid than that found in normal volunteers (mean, 0.49 +/- 0.09 L/hr/kg) or in women with pregnancy-induced hypertension in the third trimester (mean, 2.0 +/- 0.8 L/hr/kg). Initial nadirs in mean arterial pressure were noted at 50 minutes after ingestion of nifedipine, with an average reduction in mean arterial pressure of 13.8 mm Hg. A dosing interval of every 3 to 4 hours is suggested when rapid-release nifedipine is used in the postpartum patient with preeclampsia.

Treatment of hypertensive urgencies with oral nifedipine, nicardipine, and captopril

Sixty-five patients with uncomplicated hypertensive urgencies were treated in the emergency and cardiology departments with 20 mg nifedipine, 20 mg nicardipine, or 25 mg captopril in a randomized study. The study population consisted of 65 patients ranging in age from forty-one to seventy-one. Blood pressure and heart rate were assessed for six hours after intake of the antihypertensive agents. Within sixty minutes nifedipine reduced blood pressure by an average of 74.7 mmHg for the systolic and 35.4 mmHg for the diastolic. Average heart rate increased significantly by 11.6 beats/min at within thirty minutes. Nicardipine and captopril produced equivalent falls in systolic (-81.6 and -79.4 mmHg) and diastolic (-37.3 and -33 mmHg) blood pressure respectively, but did not increase heart rate significantly. The antihypertensive effect of each drug was maintained until six hours after medication. In conclusion, nifedipine, nicardipine, and captopril show similar efficacy in the treatment of hypertensive urgencies. The authors believe that these drugs can be used as first-line therapy in the treatment of hypertensive urgencies safely and effectively.

Dose-response evaluation of oral labetalol in patients presenting to the emergency department with accelerated hypertension

STUDY OBJECTIVE

Dose-response evaluation of oral labetalol (100, 200, or 300 mg) on heart rate and systemic blood pressure in emergency department patients with hypertensive urgency (diastolic blood pressure, 110 to 140 mm Hg, and no end-organ evidence of hypertensive emergency).

METHODS

This acute-treatment, dose-ranging study used a randomized, double-blind, parallel design. Patients with supine diastolic blood pressure of 110 to 140 mm Hg after 30 minutes of bedrest received an oral dose of labetalol. Supine blood pressure and heart rate were measured manually and recorded hourly for four hours after dose. Diastolic blood pressure of 100 mm Hg or less or a 30-mm Hg reduction in diastolic blood pressure was considered a treatment success.

RESULTS

Two hundred fifty-five patients were evaluated for inclusion, and 36 patients (19 women and 17 men; mean age, 44 years; age range, 23 to 67 years) were studied. The most frequent reason for exclusion was a spontaneous decrease in diastolic blood pressure to less than 110 mm Hg (31%) with bedrest. There were 12 patients in each treatment group. Compared with baseline, the 100-mg dose significantly (P less than .05) reduced heart rate at three and four hours after dose, and the 300-mg dose significantly (P less than .05) reduced heart rate at one, two, and three hours after dose; the 200-mg dose did not significantly affect heart rate. All doses produced a significant decrease in systolic and diastolic blood pressures at one, two, three, and four hours after dose compared with baseline. There were no statistically significant differences between treatment groups with regard to systolic or diastolic blood pressure or heart rate at baseline or one, two, three, or four hours after dose. At two hours after dose, diastolic blood pressure control was observed in 75%, 58%, and 67% of patients receiving 100, 200, and 300 mg, respectively (P = .903). At four hours after dose, diastolic blood pressure control was observed in 50%, 64%, and 67% of patients receiving 100, 200, and 300 mg, respectively (P = .755). A comparison of treatment success rates between the two time periods showed a waning of response with the 100-mg dose of labetalol at hour 4 compared with hour 2 (P less than .05). No adverse effects were observed.

CONCLUSION

Labetalol provides safe and effective treatment for hypertensive urgencies when administered orally in doses of 100 to 300 mg.

The use of nifedipine during the postpartum period in patients with severe preeclampsia

Nifedipine is a calcium channel blocker that reduces blood pressure and increases renal blood flow. This double-blind investigation evaluated the effect of nifedipine in postpartum patients with severe preeclampsia. Thirty-one patients were randomized to receive either nifedipine (10 mg) or placebo every 4 hours beginning immediately after delivery. Data analysis revealed a significantly higher urine output in the nifedipine group during the first 24 hours after delivery (3834 versus 2057 ml; p less than 0.05). A significant reduction in mean arterial pressure was also noted in the nifedipine group between 18 and 24 hours postpartum (93.9 versus 100.2 mm Hg; p less than 0.05). There were no significant differences in the systolic or diastolic blood pressures, pulse, laboratory study results, or the need to administer hydralazine to control blood pressure. Nifedipine appears to have a beneficial effect on urinary output and mean arterial pressure during the first 24 hours post partum in patients with severe preeclampsia.

Nifedipine in the treatment of hypertensive episodes in the coronary care unit

The effectiveness of nifedipine for the treatment of acute hypertensive episodes in patients already taking chronic calcium-channel blocker therapy is unknown. We report our experience with 43 consecutive patients who received nifedipine for acute hypertensive episodes in the coronary care unit. Of the 43 patients (24 men, 19 women), 23 (53 percent) were taking chronic (greater than 2 mo) calcium-channel blocker therapy. Nifedipine 10 mg capsules were chewed and swallowed with repeat doses given at hourly intervals if necessary. Target BP was 140/90 mm Hg, which was achieved in 31 of 43 patients (72 percent). In patients already taking calcium-channel blockers, target BP was achieved in 18 of 23 patients (78 percent). Response in patients not taking chronic calcium-channel blockers was observed in 13 of 20 patients (65 percent). Overall, adverse effects occurred in 16 of 43 patients (37 percent): 11 of 23 patients (48 percent) taking calcium-channel blockers, and 5 of 20 patients (25 percent) not taking calcium-channel blockers. Nifedipine is equally effective in lowering BP in patients taking calcium-channel blockers as it is in patients not taking them. Although associated with a higher incidence of adverse effects in patients already taking calcium-channel blockers, these effects were not considered serious. Nifedipine is an effective agent in acute hypertensive episodes, even in patients receiving chronic calcium-channel blocker therapy.

Dosage of nifedipine in hypertensive crises of infants and children

Eight hypertensive crises (HC) were treated with 2.5 mg of sublingual nifedipine in three children with weights below 10 kg (group A); 16 HC in 6 children between 10 and 20 kg with 5 mg (group B); and 40 HC in 10 children over 20 kg with 10 mg of nifedipine (group C). The relative decrease in both systolic and diastolic blood pressure was similar in all groups. The decrease was more rapid in groups A and B when the contents were extracted from the capsule and given directly. The hypotensive effect lasted 4 h. There were no side effects. The effective and safe single dose of nifedipine has been established to be 2.5 mg for children weighing less than 10 kg, and 5 mg for children weighing between 10 and 20 kg.

Intravenous nicardipine in severe systemic hypertension

Sixty-six patients with severe hypertension were treated with intravenous nicardipine in 3 separate protocols. Each protocol had a common end point: Diastolic blood pressure would either reduce 25 mm Hg or measure below 95 mm Hg. Each of the 66 patients studied attained the desired clinical response end point. Intravenous nicardipine produced a gradual reduction in blood pressure, was effective in maintaining blood pressure control during constant infusion and had few undesirable effects. These observations suggest that intravenous nicardipine maybe a useful addition to a limited number of therapeutic agents currently available to the physician for treatment of hypertensive urgencies.

Nifedipine potentiates cardiopulmonary baroreflex control of sympathetic nerve activity in healthy humans. Direct evidence from microneurographic studies

Nifedipine augments baroreflex mechanisms in in vivo animal models. Previous studies in our laboratory demonstrate that nifedipine potentiates baroreflex control of heart rate and vascular resistance in normal human subjects. To further define the neuroeffector mechanism of the autonomic effects of nifedipine, we directly measured postganglionic sympathetic nerve activity to muscle (MSNA, microneurography), before and after drug administration, during selective unloading of cardiopulmonary baroreceptors with lower body negative pressure (-10 mm Hg, LBNP-10), and during the cold pressor test. Twenty-three normal subjects (age, 23 +/- 1 years; mean +/- SEM) were studied in the control state and 20 minutes after administration of either nifedipine (10 mg s.l., 10 subjects), during nitroprusside infusion (0.37 +/- 0.03 microgram/kg/min i.v., eight subjects), or 20 minutes after sublingual administration of placebo (five subjects). We measured systemic arterial pressure, central venous pressure, heart rate, and MSNA. Nifedipine and nitroprusside produced similar increases in resting heart rate and MSNA and similar decreases in central venous pressure, whereas placebo had no effect on resting hemodynamics. During LBNP-10, hemodynamic changes were not significantly different among the three treatment groups. However, the percentage increase in MSNA during LBNP-10 was significantly augmented from a 24 +/- 9% increase before nifedipine to a 56 +/- 7% increase after nifedipine (p less than 0.05). Decreases in central venous pressure with LBNP-10 were nearly identical before compared with after nifedipine. Thus, nifedipine increased the cardiopulmonary baroreflex sympathetic sensitivity (change in total MSNA per mm Hg decrease in central venous pressure during LBNP-10) from 26.5 +/- 10.7 units/mm Hg to 74.9 +/- 19.0 units/mm Hg (p less than 0.01). In contrast, administration of hemodynamically similar doses of nitroprusside resulted in an attenuation of MSNA responses to LBNP-10. During LBNP-10, MSNA increased 57 +/- 12% before nitroprusside but only 14 +/- 4% during nitroprusside (p less than 0.01). The cardiopulmonary baroreflex sympathetic sensitivity was not significantly altered by nitroprusside (45.1 +/- 12.4 units/mm Hg before compared with 33.1 +/- 20.8 units/mm Hg during nitroprusside, p = NS). Placebo had no effect on the responses to LBNP-10. Nifedipine did not augment MSNA responses to the cold pressor test. To evaluate the linearity of sympathetic responses to cardiopulmonary baroreceptor unloading, graded LBNP (0, -5, -10, and -15 mm Hg) was applied in three additional subjects before and after nifedipine (10 mg s.l.).(ABSTRACT TRUNCATED AT 400 WORDS)

Nifedipine does not adversely affect uteroplacental blood flow in the hypertensive term-pregnant rat

The short-term effect of the calcium channel blocker, nifedipine, on maternal hemodynamics and organ perfusion was investigated in 12 hypertensive term-pregnant, spontaneously hypertensive rats by means of the radioactive-labeled microsphere technique. The normal fall in blood pressure during pregnancy was prevented by reducing litter size to two conceptuses on day 7 of gestation. Nifedipine (200 micrograms/kg) effectively lowered mean arterial pressure 25% by decreasing total peripheral resistance 38%. Cardiac output was increased 15%. Blood flows to the splanchnic region and the reproductive organs were increased after nifedipine administration. The increase in blood flow to the reproductive organs was the result of increased ovarian and uterine wall perfusion caused by large reductions in vascular resistances. Placental blood flow was not significantly altered, but resistance was decreased. Thus, the use of nifedipine to lower maternal blood pressure in pregnancy complicated by extreme hypertension does not necessarily decrease uteroplacental perfusion.

Subcutaneous administration of nifedipine

Contents of a 10 mg nifedipine capsule (0.33 ml) were withdrawn by syringe and administered subcutaneously to a patient with hypertensive urgency due to misinterpretation of a physician's order. The drug apparently had its desired hypotensive effect and no adverse effects were noted. The literature on use of nifedipine in hypertensive urgency is reviewed. Subcutaneous administration is not recommended because of a lack of suitable controlled studies and the potential for adverse effects.

Intravenous nicardipine for the treatment of severe hypertension

PURPOSE

Severe hypertension responds to treatment with nifedipine given orally or sublingually. Nicardipine hydrochloride, a water soluble dihydropyridine analogue similar to nifedipine, has less of a negative ionotropic effect and produces less reflex tachycardia than nifedipine. Our purpose was to assess the antihypertensive efficacy and safety of intravenous nicardipine in a group of patients with severe hypertension (defined as a supine diastolic blood pressure of more than 120 mm Hg).

PATIENTS AND METHODS

Eighteen patients with severe hypertension received treatment with intravenous nicardipine. Nicardipine titration was performed using doses of 4 to 15 mg/hour to achieve therapeutic goal (diastolic blood pressure 95 mm Hg or less or decrease in diastolic blood pressure of more than 25 mm Hg). After this therapeutic end-point was reached, patients received maintainance therapy with nicardipine for varying lengths of time: one hour (Group I), six hours (Group II), or 24 hours. When blood pressure control was lost, patients in Groups I and II entered a second maintenance period lasting a maximum of 24 hours. Onset and offset of action of nicardipine at various infusion rates and times of infusion were measured.

RESULTS

Onset time to achieve therapeutic response was rapid at 15 mg/hour (0.31 +/- 0.13 hours) when compared with lower doses (1.11 +/- 0.36 hours at 4 mg/hour; 0.54 +/- 0.09 hours at 5 mg/hour; 0.52 +/- 0.09 hours at 7 to 7.5 mg/hour). Those who showed a therapeutic response received maintenance infusions with nicardipine for one (n = 7), six (n = 6), or 24 (n = 5) hours. Sustained blood pressure control at a constant rate of nicardipine infusion was seen in all patients during the maintenance period. After discontinuation of nicardipine, the time for offset of action (increase in diastolic blood pressure of 10 mm Hg or more) was independent of duration of infusion. Decreases in both systolic and diastolic pressures correlated well with plasma nicardipine levels. Heart rate increased by about 10 beats/minute, but this increase did not correlate with plasma nicardipine levels. Side effects were minimal, consisting of headache and flushing. In seven patients, local phlebitis developed at the site of infusion. This occurred after at least 14 hours of infusion at a single site, and the incidence can probably be reduced by shortening the infusion time at a single site.

CONCLUSION

Nicardipine appears to be a safe and effective drug for intravenous use in the treatment of severe hypertension.

Treatment of hypertensive crisis in children with nifedipine

We report 31 episodes of hypertensive crises in children, managed with sublingual nifedipine at the following dosages: 10 mg in children with body weight (BW) higher than 20 kg, 5 mg in children with BW between 10 and 20 kg, and 2.5 mg in children with BW below 10 kg. The mean initial blood pressures were 161.41 mm Hg for the systolic pressure (mSBP) and 111.25 mm Hg for the diastolic pressure (mDBP). After nifedipine, both the mSBP and the mDBP decreased, with onset of effect five minutes after dosage and maximum decrease at 60 min (mSBP 134.93 mm Hg, mDBP 79.23 mm Hg, for decreases of 16.4 and 28.7%, respectively), and this effect persisted for 180 min. Blood pressure increased again from min 240 to min 360, yet without reaching the initial levels. One case did not respond to the first dose of nifedipine and required a second one. The effect of nifedipine was more pronounced on the DBP than on the SBP, and greater reductions of both pressures were achieved in the cases with higher initial readings. No side of medication were observed in our patients.

The use of sublingual nifedipine in a patient with a clonidine overdose

We report the case of a 46-year-old woman who took approximately 8 mg of clonidine in a suicidal gesture. She arrived in the emergency department 45 min after the overdose with severe hypertension and an altered mental status. Nitroprusside, which is the drug of choice for treating this "paradoxical hypertension," was not readily available. The patient was treated with a total of 20 mg of nifedipine sublingually. This resulted in a rapid decline in her blood pressure and an improvement in her mental status. We review the toxicology of clonidine overdose and discuss its treatment.

Influence of nifedipine on arterial baroreflex modulation of heart rate control during dynamic increases in arterial pressure: studies in normal man

Studies in animals have demonstrated that calcium channel blocking agents exert important influences on autonomic mechanisms in addition to their direct vascular effects. Previous studies in our laboratory showed that clinical doses of nifedipine sensitized baroreceptor-mediated control of peripheral vascular resistance in normal human subjects. However, baroreflex control of vascular tone does not necessarily imply parallel control of heart rate. A series of experiments was therefore performed to test the hypothesis that therapeutic doses of nifedipine would potentiate arterial baroreflex modulation of heart rate during ramp increases of arterial pressure in normal volunteers. Arterial baroreflex control was assessed by measuring heart interval (HI) responses to dynamic ramp elevation of systolic arterial pressure (SAP) with bolus administration of phenylephrine (PE) before and after nifedipine or placebo in 19 normal subjects. Arterial baroreflex control was calculated from the slope of the regression of SAP on succeeding HI during the first 18 cardiac cycles following onset of rise of SAP after PE bolus. In 13 subjects, bolus PE produced an increase in SAP from 125 +/- 3 mm Hg to 152 +/- 5 mm Hg (p less than 0.01), with a resultant increase in HI from 1110 +/- 57 msec to 1541 +/- 87 msec (p less than 0.01). The baroreflex response was linear (r greater than 0.80, p less than 0.025) and = 17.8 +/- 3.3 msec/mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)