Pharmacokinetics of calcium antagonists under development

Designing an extended release waxy matrix tablet containing nicardipine-hydroxy propyl β cyclodextrin complex

AIM

The current study aimed to prepare a sustained release tablet for a drug which has poor solubility in alkaline medium using complexation with cyclodextrin. Nicardipine hydrochloride (NC) a weak basic drug was chosen as a model drug for this study.

METHOD

Firstly the most suitable binary system NC-HPβCD was selected in order to improve drug solubility in the intestinal media and then embedding the complexed drug into a plastic matrix, by fusion method, consists of glycerol monostearate (GMS) as an inert waxy substance and polyethylene glycol 4000 (PEG4000) as a channeling agent, after that the final solid dispersion [(NC:HPβCD):GMS:PEG4000] which was prepared at different ratios was mixed with other excipients, avicel PH101, lactose, and talc, to get a tablet owning dissolution profile complying with the FDA and USP requirements for the extended release solid dosage forms.

RESULTS

Infrared spectroscopy (IR), differential scanning colorimetry (DSC), polarized microscopy and X-ray diffractometry proved that the coevaporation technique was effective in preparing amorphous cyclodextrin complexes with NC and trapping of NC within the HPβCD cavity by dissolving both in ethanol and evaporate the solvent using a rotavapor at 65 °C. Dissolution profile of NC enhanced significantly in pH 6.8 from NC:HPβCD inclusion complex prepared by the rotavapor (t-test Student p < 0.05). The release of NC from tablet containing [(NC:HPβCD):GMS:PEG4000] [(1):0.75:0.5] (w/w/w) solid dispersion (F8) was complying with the FDA dissolution requirements for extended release dosage forms, and studying the kinetics of the release showed that the diffusional contribution is the major factor controlling the drug release from that formula.

CONCLUSION

The prepared waxy matrix tablet containing NC complexes with CD shows promising results as extended release tablets.

Flutamide inhibits nifedipine- and interleukin-1 beta-induced collagen overproduction in gingival fibroblasts

BACKGROUND AND OBJECTIVE

To understand the role of the androgen receptor in gingival overgrowth, the effects of flutamide on interleukin-1 beta- and nifedipine-induced gene expression of connective tissue growth factor (CTGF/CCN2) and collagen production in gingival fibroblasts were examined.

MATERIAL AND METHODS

Gingival fibroblasts from healthy subjects and patients with dihydropyridine-induced gingival overgrowth (DIGO) were used. Confluent cells were treated with nifedipine, interleukin-1 beta or both. The mRNA expression was examined using real-time polymerase chain reaction, and the concentration of total soluble collagen in conditioned media was analysed by Sircol Collagen Assay. In addition, the protein expressions of androgen receptor, CTGF/CCN2 and type I collagen in gingival tissue were determined by western blot.

RESULTS

Interleukin-1 beta was more potent than nifedipine in stimulating CTGF/CCN2 and procollagen alpha1(I) mRNA expression, and there was an additive effect of the two drugs. Healthy cells exhibited an equal or stronger response of procollagen alpha1(I) than those with DIGO, but DIGO cells displayed a stronger response in the secretion of soluble collagen in the same conditions. Flutamide, an androgen receptor antagonist, inhibited stimulation by nifedipine or interleukin-1 beta. Additionally, the protein expressions of androgen receptor and type I collagen were higher in DIGO gingival tissue than those in healthy gingival tissue.

CONCLUSION

The data suggest that both nifedipine and interleukin-1 beta play an important role in DIGO via androgen receptor upregulation and that gingival overgrowth is mainly due to collagen accumulation. Flutamide decreases the gene expression and protein production of collagen from dihydropyridine-induced overgrowth cells.

Structure-activity relationships of 1,4-dihydropyridines that act as enhancers of the vanilloid receptor 1 (TRPV1)

Vanilloid agonists such as capsaicin activate ion flux through the TRPV1 channel, a heat- and ligand-gated cation channel that transduces painful chemical or thermal stimuli applied to peripheral nerve endings in skin or deep tissues. We have probed the SAR of a variety of 1,4-dihydropyridine (DHP) derivatives as novel 'enhancers' of TRPV1 activity by examining changes in capsaicin-induced elevations in (45)Ca(2+)-uptake in either cells ectopically expressing TRPV1 or in cultured dorsal root ganglion (DRG) neurons. The enhancers increased the maximal capsaicin effect on (45)Ca(2+)-uptake by typically 2- to 3-fold without producing an action when used alone. The DHP enhancers contained 6-aryl substitution and small alkyl groups at the 1 and 4 positions, and a 3-phenylalkylthioester was tolerated. Levels of free intracellular Ca(2+), as measured by calcium imaging, were also increased in DRG neurons when exposed to the combination of capsaicin and the most efficacious enhancer 23 compared to capsaicin alone. Thus, DHPs can modulate TRPV1 channels in a positive fashion.

Application of liquid chromatography-two-dimensional nuclear magnetic resonance spectroscopy using pre-concentration column trapping and liquid chromatography-mass spectrometry for the identification of degradation products in stressed commercial amlodipine maleate tablets

Application of the HPLC hyphenated techniques of LC-two-dimensional (2D) NMR using pre-concentration column trapping and LC-MS was demonstrated by the identification of two major degradation products, DP-1 and DP-2, in stressed commercial tablets of amlodipine maleate. The molecular formulas were estimated by LC-MS. Sample pre-concentration by column trapping was conducted to obtain adequate 2D-NMR signals by reducing the peak widths of the degradation products and making sure that the maximum amount of each component was inside the flow cell for NMR detection. Double-quantum filtered correlation spectroscopy (DQF-COSY) was applied to identify DP-1 as beta-N-lactosylamlodipine by suppressing the residual water signal without affecting the sample signal and by measuring the coupling constant of the lactose anomeric proton. Heteronuclear multiple bond coherence spectroscopy (HMBC) was applied to characterize DP-2 as an aspartic acid derivative of amlodipine by detecting long-range CH correlations. The chemical structures of the degradation products could be successfully elucidated unambiguously without an isolation process.

A rapid and sensitive liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the estimation of amlodipine in human plasma

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the estimation of amlodipine in human plasma. Amlodipine was extracted from human plasma by using a solid-phase extraction technique. Imipramine was used as the internal standard. A Hypersil BDS C18 column provided chromatographic separation of analytes followed by detection with mass spectrometry. The method involves a rapid solid-phase extraction from plasma, simple isocratic chromatography conditions and mass spectrometric detection that enables detection at sub-nanogram levels. The proposed method has been validated for a linear range of 0.1-10.0 ng/mL with correlation coefficient >or=0.9990. The intrarun and interrun precision and accuracy were within 10.0%. The overall recovery for amlodipine was 63.67%. Total run time was 3.2 min only.

Quantitative structure-activity relationship and quantitative structure-pharmacokinetics relationship of 1,4-dihydropyridines and pyridines as multidrug resistance modulators

PURPOSE

The aim of this study was to develop quantitative structure-activity/pharmacokinetic relationships (QSAR/QSPKR) for a series of synthesized 1,4-dihydropyridines (DHPs) and pyridines as P-glycoprotein (P-gp) inhibitors.

METHODS

Molecular descriptors of test compounds were generated by 3D molecular modeling using SYBYL and KowWin programs. Forward inclusion coupled with multiple linear regression (MLR) was used to derive a QSAR equation for Ca2+ channel binding. A multivariate statistical technique, partial least square (PLS) regression, was applied to derive a QSAR model for P-gp inhibition and QSPKR models. Cross-validation using the "leave-one-out" method was performed to evaluate the predictive performance of models.

RESULTS

For Ca2+ channel binding, the MLR equation indicated a good correlation between observed and predicted values (R2 = 0.90), and cross-validation confirmed the predictive ability of the model (Q2 = 0.67). For P-gp reversal, the model obtained by PLS could account for most of the variation in P-gp inhibition (R2 = 0.76) with fair predictive performance (Q2 = 0.62). Nine structurally related 1,4-DHP drugs were used for QSPKR analysis. The models could explain the majority of the variation in clearance (R2 = 0.90), and cross-validation confirmed the prediction ability (Q2 = 0.69).

CONCLUSION

QSAR/QSPKR models were developed, and the QSAR models were capable of identifying synthesized 1,4-DHPs and pyridines with potent P-gp inhibition and reduced Ca2+ channel binding. The QSPKR models provide insight into the contribution of electronic, steric, and lipophilic factors to the clearance of DHPs.

Optimization of pH-independent release of nicardipine hydrochloride extended-release matrix tablets using response surface methodology

The purpose of this study was to optimize the pH-dependent release of nicardipine hydrochloride extended release formulations by using simultaneously combination two hydrophilic polymers: hydroxypropylmethylcellulose (HPMC) and sodium alginate as retardant and avicel as additive. The constrained mixture experimental design was used to prepare systematic model formulations which were composed of three formulation variables: the content of HPMC (X1), avicel (X2), and sodium alginate (X3). The response surface methodology (RSM) and multiple response optimization utilizing the polynomial equation were used to search for the optimal formulation with specific release rate at different time intervals and to quantify the effect of each formulation variables. The drug release percent at 3, 6 and 12 h were the target responses and were restricted to 10-30% (Y3h), 40-65% (Y6h) and not less than 80% (Y12h), respectively. The results showed that the effect of combination of HPMC and sodium alginate was the most influence factor on the drug release from extended-release matrix tablets. The observed results of Y3h, Y6h and Y12h coincided well with the predictions in the RSM optimization technique, indicating it was quite useful for optimizing pharmaceutical formulation. The mechanism of drug release from extended-release matrix tablets was dependent on the added amount of alginate. The release kinetic of drug from HPMC matrix tablets with alginate was followed the zero-order release pattern.

Treatment of mild-to-moderate hypertension with calcium channel blockers: a multicentre comparison of once-daily nifedipine GITS with once-daily amlodipine

BACKGROUND

Hypertension is one of the most important causes of cardiovascular disease, and treatment of hypertension leads to a significant reduction in cardiovascular mortality and morbidity. Although calcium channel blockers are regarded as an important part of the therapeutic armamentarium against cardiovascular diseases, and are among the most frequently prescribed antihypertensive medications, concern has been aroused about these drugs, particularly the short-acting dihydropyrldine derivatives. However, the value of nifedipine GITS(Adalat-Crono), the long-acting dihydropyrldine, is in need of being re-established.

OBJECTIVE

To compare the effectiveness, safety and tolerability of once-daily nifedipine and amlodipine treatment in patients with mild-to-moderate essential hypertension.

DESIGN

Randomised multicentre trial with an open comparison of treatments for 12 weeks, with a preceding placebo run-in period of 2 weeks (patients on beta-blockers at the time of enrollment entered a mandatory 2-week wash-out period before being allowed In the placebo run-in period;this wash-out period was one week for patients using any antihypertensive medication other than beta-blockers).

SETTING

Nine centres (all university hospitals) in Turkey.

PATIENTS

155 patients with essential hypertension(diastolic blood pressure 95-109 mmHg).

INTERVENTIONS

Initial treatment (step 1) consisted of 30 mg nifedipine GlTS (n = 76; (Adalat-Crono tablets), or 5 mg amlodipine (n = 79; Norvasct5-mg tablets), either administered once daily, as a morning dose, or f the blood pressure was not below 140/90 mmHg, or the reduction In diastolic blood pressure was lower than 10 mmHg after a treatment period of 6 weeks, the dose was increased (Step 2) to 60 mg once daily in the nifedipine group, or 10 mg once daily in the amlodipine group. MAIN EFFICACY PARAMETER: Diastolic blood pressure at trough after 12 weeks of active compound therapy adjusted to baseline.

RESULTS

After 12 weeks of treatment, the mean diastolic blood pressure was 83.1 and 81.9 mmHg,in the nifedipine and amlodipine groups, respectively (p = 0.436). The mean decrease in systolic blood pressure (28.5 +/- 11.9 and 28.2 +/- 11.2 mmHg in the nifadipine and amlodipine groups, respectively) and the mean decrease in diastolic blood pressure (16.4A +/- 7.0 and 17.5 +/- 6.9 mmHg in the nifedipine and amlodipine groups, respectively), as well as the responder rates (88.1%and 92.1%, in the nifediplne and amlodipine groups, respectively) were comparable at the end of the study. No significant differences between groups were detected In the efficacy parameters assessed in this study. Both drugs were well tolerated. The overall incidence of adverse events was 7.9% in the nifadipine group and 10.1% In the amlodipine group. However, more patients discontinued treatment prematurely in the amlodipine group (13 patients; 19.7%), than in the nifedipine group (four patients; 5.6%).

CONCLUSIONS

The results of this study demonstrated that once-daily nifedipine in GITS formation and amlodipine are comparably safe and effective treatment options in patients with mild-to-moderate essential hypertension.

MDR1-mediated interaction of digoxin with antiarrhythmic or antianginal drugs

The multidrug transporter, MDR1-mediated interaction of digoxin with antiarrhythmic or antianginal drugs was examined in vitro by using the MDR1-overexpressing LLC-GA5-COL150 cells, which were established by transfection with human MDR1 cDNA into porcine kidney epithelial LLC-PK(1) cells. Amiodarone, its active metabolite monodesethyl-amiodarone (DEA), and quinidine markedly inhibited the basal-to-apical transport (renal secretion) of [(3)H]digoxin and increased the apical-to-basal transport (reabsorption), but cibenzoline and lidocaine showed slight inhibition of the transport, and disopyramide and mexiletin had no such effects. The IC(50) values for amiodarone, DEA and quinidine on [(3)H]digoxin transport in LLC-GA5-COL150 cells were 5.48 microM, 1.27 microM and 9.52 microM, respectively. These were comparable to, or only several times the achievable concentration in clinical use, suggesting that MDR1 could be responsible for the drug interaction between digoxin and amiodarone found in clinical reports and that DEA contributes the elevation of digoxin serum concentration. Similarly, dipyridamole altered the transport, but isosorbide showed only slight modification of the transport. The IC(50) value for dipyridamole was 40.0 microM, also only several times the achievable concentration in clinical use, indicating a risk of interaction.

Calcium channel blockers as tocolytics

This article reviews the clinical and basic science investigations regarding the safety and efficacy of calcium channel blockers as tocolytic agents. The authors reviewed the English language literature on the pharmacology and clinical applications of calcium antagonists in obstetrics. A MEDLINE (1966-2000) search was performed with the terms "calcium channel blockers," "randomized controlled trial," "preterm labor," "calcium antagonist," "tocolysis," and "nifedipine." References from these data sources were then used to find additional studies. Animal data and clinical trials in humans were included. The safety of these agents was researched in published data from the nonobstetric as well as obstetric literature. The calcium channel blockers most commonly used as tocolytics are nifedipine and nicardipine. These agents act to inhibit calcium influx across cell membranes, thereby decreasing tone in the smooth muscle of the vasculature. They act as profound vasodilatory agents and have minimal effect on the cardiac conduction system. Numerous randomized clinical trials have shown them to be as effective as beta-mimetics and magnesium in achieving tocolysis. When used for tocolysis, calcium antagonists have fewer maternal side effects than other tocolytics and have no adverse effect on fetal outcome.

Systematic toxicological analysis procedures for acidic drugs and/or metabolites relevant to clinical and forensic toxicology and/or doping control

This paper reviews systematic toxicological analysis (STA) procedures for acidic drugs and/or metabolites relevant to clinical and forensic toxicology or doping control using gas chromatography, gas chromatography-mass spectrometry, liquid chromatography, thin-layer chromatography and capillary electrophoresis. Papers from 1992 to 1998 have been taken into consideration. Screening procedures in biosamples (whole blood, plasma, serum, urine, vitreous humor, brain, liver or hair) of humans or animals (horse, or rat) are included for the following drug classes: angiotensin-converting enzyme (ACE) inhibitors and angiotensin II (AT-II) blockers, anticoagulants of the 4-hydroxy coumarin type, barbiturates, dihydropyridine calcium channel blockers (calcium antagonists), diuretics, hypoglycemic sulfonylureas and non-steroidal anti-inflammatory drugs (NSAIDs). Methods for confirmation of preliminary results obtained by screening procedures using immunoassay or chromatographic techniques are also included. Furthermore, procedures for the simultaneous detection of several drug classes are reviewed. The toxicological question to be answered and the consequences for the choice of an adequate method, the sample preparation and the chromatography itself are discussed. The basic information about the biosample assayed, work-up, separation column, mobile phase or separation buffer, detection mode and validation data of each procedure is summarized in 16 tables. They are arranged according to the drug class and the analytical method. Examples of typical applications are presented. Finally, STA procedures are reviewed and described allowing simultaneous screening for different (acidic) drug classes.

Grapefruit juice-drug interactions

The novel finding that grapefruit juice can markedly augment oral drug bioavailability was based on an unexpected observation from an interaction study between the dihydropyridine calcium channel antagonist, felodipine, and ethanol in which grapefruit juice was used to mask the taste of the ethanol. Subsequent investigations showed that grapefruit juice acted by reducing presystemic felodipine metabolism through selective post-translational down regulation of cytochrome P450 3A4 (CYP3A4) expression in the intestinal wall. Since the duration of effect of grapefruit juice can last 24 h, repeated juice consumption can result in a cumulative increase in felodipine AUC and Cmax. The high variability of the magnitude of effect among individuals appeared dependent upon inherent differences in enteric CYP3A4 protein expression such that individuals with highest baseline CYP3A4 had the highest proportional increase. At least 20 other drugs have been assessed for an interaction with grapefruit juice. Medications with innately low oral bioavailability because of substantial presystemic metabolism mediated by CYP3A4 appear affected by grapefruit juice. Clinically relevant interactions seem likely for most dihydropyridines, terfenadine, saquinavir, cyclosporin, midazolam, triazolam and verapamil and may also occur with lovastatin, cisapride and astemizole. The importance of the interaction appears to be influenced by individual patient susceptibility, type and amount of grapefruit juice and administration-related factors. Although in vitro findings support the flavonoid, naringin, or the furanocoumarin, 6',7'-dihydroxybergamottin, as being active ingredients, a recent investigation indicated that neither of these substances made a major contribution to grapefruit juice-drug interactions in humans.

Pharmacokinetic behaviour of R-(+)- and S-(-)-amlodipine after single enantiomer administration

Amlodipine, 3-ethyl 5-methyl-2-[(2-aminoethoxymethyl]-4-(2-chlorophenyl)-1,4-dihydro-6-methy l-3,5-pyridinedicarboxylate, is a chiral calcium antagonist, currently on the market and in therapeutic use as a racemate. The pharmacokinetic behaviour of R-(+)- and S-(-)-amlodipine after single enantiomer administration to healthy male human volunteers together with comparative administration of the racemic mixture of both enantiomers were studied. Plasma levels were studied as a function of time and assayed using an enantioselective chromatographic method (coupled chiral and achiral HPLC) with on-line solid-phase extraction and UV absorbance detection. The method was validated separately for the R-(+)- and S-(-)-enantiomer, respectively. Results of the study indicate that the pharmacokinetic behaviour of R-(+)- and S-(-)-amlodipine after single enantiomer administration is comparable to that of each enantiomer after administration of the racemate. No racemization occurs in vivo in human plasma after single enantiomer administration.

Pharmacologic and pharmacokinetic profile of mibefradil, a T- and L-type calcium channel antagonist

Mibefradil is a recently introduced calcium antagonist that, as a tetralol derivative, is chemically distinct from previous calcium antagonists. This article will review pertinent results from in vitro, animal, and clinical investigations to report the pharmacologic properties that distinguish mibefradil from all of the calcium channel antagonists in use today, all of which operate on the "L-type" calcium channel. Mibefradil's pharmacokinetic profile indicates it can be used as a once-daily oral treatment for hypertension and chronic stable angina pectoris.

Clinical evaluation of serum amlodipine level in patients with angina pectoris

Serum amlodipine levels were determined in 18 patients with vasospastic angina. Patients were divided into two groups: Group A (n = 9) received amlodipine 5 mg by single daily administration, and Group B (n = 9) received 10 mg given by single daily administration for the first 3 days, then 5 mg from the 4th day on. The serum amlodipine concentration in Group A took 7 days to reach a steady state of around 8 ng/ml. The level in Group B was 8.9 ng/ml at 3 days. From these results, the optimal dosage of amlodipine in the treatment of angina pectoris is 10 mg for the initial 3 days followed by 5 mg thereafter.

Hypoglycaemic brain damage: effect of a dihydropyridine calcium channel antagonist in rats

Hypoglycaemic brain damage consists of selective necrosis of cerebral neurons related to the extracellular release of excitatory amino acids. Neuronal excitatory amino acid receptors are activated and calcium channels are opened. The present investigation was designed to test the effectiveness of dihydropyridine blockade of voltage-sensitive calcium channels in hypoglycaemic brain damage. Sixty-four rats were given either high-dose nimodipine, consisting of an initial bolus of 300 micrograms/kg nimodipine administered at the stage of EEG slowing (blood glucose levels of 1.0-1.5 mmol/l), followed by continuous intravenous nimodipine infusion at 1.5 micrograms.kg-1.min-1, low-dose nimodipine, consisting of an initial bolus of 30 micrograms/kg at the time of EEG slowing, followed by 0.15 microgram.kg-1.min-1, an equal volume of vehicle solution, or 154 mmol/l NaCl. Animals receiving either low- or high-dose nimodipine had higher mortality, and increased brain damage compared with controls. Examination of the perfusion-fixed brains 1 week after recovery with glucose revealed that quantitated neuronal necrosis was worsened by nimodipine in the hippocampus, caudate nucleus and cerebral cortex. The present results in profound hypoglycaemia (accompanied by a flat EEG) contrast with the beneficial effect of nimodipine in brain ischaemia.

The effect of isradipine administration on existing fatty streaks in the cholesterol-fed rabbit: a morphometric study

Previous studies have shown that the administration of certain calcium channel blocking drugs (at an appropriate time point) can reduce the severity of atherosclerotic lesion formation. This study was undertaken to determine if the administration of isradipine would reverse established lesions produced by feeding rabbits an atherogenic diet. Rabbits were fed cholesterol for three weeks and examined directly, or after being left for a four week washout period, with or without a daily oral supplement of isradipine. Fatty streaks were well established after three weeks of cholesterol feeding and were more extensive at the end of the washout period, as indicated by gross changes in the volume of the intima per unit length of aorta. When isradipine was administered during the washout period, the volume of the intima per unit length of aorta fell to levels below those produced by cholesterol feeding for three weeks alone. The major components of the lesions affected to accommodate these changes were the foam cells and myointimal cells; these were examined in detail using morphometry and lipid cytochemistry. The mean volume of intima/cm of aorta occupied by foam cells and myointimal cells both fell by more than 60% to levels lower than those found after three weeks of cholesterol feeding alone. The volume of the extracellular space of the intima occupied by cytochemically demonstrable unesterified and esterified cholesterol was reduced by isradipine administration as was that of foam cells, all to levels lower than those found after three weeks of cholesterol feeding alone. These data indicate that the administration of isradipine during a washout period, after cholesterol feeding, can promote the regression of fatty streak lesions.

Stereoselective pharmacokinetics of dihydropyridine calcium antagonists

Many dihydropyridine calcium antagonists are widely used for the treatment of angina and hypertension, and many more are under development. Most of these drugs have one or more chiral centre, and the pharmacological activity between the enantiomers for these drugs is known to be markedly different. First, the stereospecific assay methods for these drugs in plasma or serum are reviewed with emphasis on chiral stationary phase high-performance liquid chromatography for their determination. Next, the stereoselective pharmacokinetics of these drugs (nilvadipine, nitrendipine, felodipine, nimodipine, manidipine, benidipine and nisoldipine) in animals, healthy subjects and patients with hepatic disease is reviewed. Enantiomer-enantiomer interaction, enantiomeric inversion and the stereochemical aspects of pharmacokinetic drug interactions in these drugs are also described.

An overview of the pharmacokinetics and pharmacodynamics of amlodipine in elderly persons with systemic hypertension

Pharmacokinetic and pharmacodynamic data were compared between elderly and young patients with hypertension who received single intravenous doses of amlodipine, a dihydropyridine calcium antagonist, followed by oral administration of amlodipine up to 10 mg once daily for 12 weeks. After intravenous administration, elderly patients had prolonged elimination half-life values (58 +/- 11 vs 42 +/- 8 hr; p < 0.05) caused by decreased clearance (19 +/- 5 vs 7 liters/hr; p < 0.05). Systolic and diastolic blood pressures were significantly decreased from baseline throughout the 3-month treatment period in both groups. After long-term oral administration, elderly and young patients had comparable decreases in mean blood pressure at a given drug plasma concentration. The antihypertensive effect of amlodipine is well correlated with plasma concentration and, at a given concentration, is similar in both elderly and young patients.

Effects of nimodipine on the amphetamine- and methamphetamine-induced decrease in tryptophan hydroxylase activity

The effects of nimodipine on the amphetamine- and methamphetamine-induced decrease in central tryptophan hydroxylase activity was examined. Rats were administered 4 or 5 injections of amphetamine or methamphetamine at 6-h intervals with or without nimodipine (1 mg/kg), and killed 1 or 18 h after the last drug administration. The decrease in hippocampal tryptophan hydroxylase activity induced by amphetamine and methamphetamine was potentiated by the administration of nimodipine. Moreover, while hippocampal tryptophan hydroxylase activity was not altered by 2.5 mg/kg methamphetamine alone, the coadministration of 1 mg/kg nimodipine decreased the enzymatic activity to 68% of control. The decrease in striatal tryptophan hydroxylase activity caused by these amphetamine analogues was not significantly altered by the coadministration of nimodipine. Interestingly, nimodipine increased hippocampal and striatal amphetamine concentrations to 187 and 162%, respectively, of the concentrations measured in animals treated with amphetamine alone. Nimodipine also increased by 2-fold the plasma concentration of methamphetamine and amphetamine measured 3 h after a single administration of methamphetamine, whereas the hippocampal concentrations of these compounds were raised to 354 and 516%, respectively, of that in animals treated with methamphetamine alone. These results suggest that nimodipine altered drug distribution and potentiated the methamphetamine-induced decrease in hippocampal tryptophan hydroxylase activity by increasing the cerebral methamphetamine concentration.

A comparative assessment of amlodipine and felodipine ER: pharmacokinetic and pharmacodynamic indices

This study investigated potential therapeutic differences between Amlodipine 5 mg and Felodipine ER 10 mg in 12 normotensive/borderline hypertensive subjects by comparison of the plasma drug concentration-time profiles and the blood pressure and heart rate responses. There was significantly less trough-to-peak variability in plasma drug concentrations with amlodipine with a ratio of 67%, compared to 37% for felodipine. Correspondingly there was less variability with amlodipine in the blood pressure reductions across the dosage interval. Overall, amlodipine displayed a more consistent hypotensive effect across 24 hours and lower blood pressure values at trough, i.e. 24 hours post-dose.

Calcium antagonists in the elderly

The calcium antagonists are associated with a number of advantages over other antihypertensive agents, such as a lack of metabolic, vascular and respiratory adverse events, yet are effective in reducing blood pressure. The currently available calcium antagonists are widely used, and new members, particularly of the dihydropyridine group, continue to emerge. These agents may well be considered for use in the management of hypertension and angina in elderly people. They undergo significant first-pass metabolism and tend to have high values of hepatic clearance with minimal amounts of unchanged drug in the urine. Plasma concentrations tend to be higher in elderly people and for that reason it may be prudent to initiate therapy with lower dosages. With this caveat, adverse effect profiles seem to be qualitatively and quantitatively similar in younger and older people. At equivalent plasma concentrations, the antihypertensive effect appears similar in young and elderly patients, and clinical studies point to comparable efficacy with other drug classes. Calcium antagonists do not have adverse renal, respiratory, cardiovascular, metabolic or peripheral vascular effects and therefore may be useful in patients with relevant concomitant disease.

Use of calcium channel antagonists for cardiovascular disease

Until recently, only three calcium channel antagonists--verapamil, diltiazem and nifedipine--were available for managing cardiovascular disorders such as hypertension and ischemic heart disease. In the past few years, however, several dihydropyridine calcium channel antagonists, including nicardipine, isradipine, felodipine, nimodipine, and amlodipine, have been marketed. Others are currently awaiting FDA approval. In addition, bepridil, which belongs to a new class of calcium channel antagonists, has recently been marketed for refractory angina pectoris. Clinical uses of calcium channel antagonists have been expanded since the 1970s to include management of cardiovascular disorders such as supraventricular arrhythmias, CHF secondary to diastolic dysfunction, and myocardial reinfarction in selected patients. Calcium channel antagonists are also being investigated for prevention of atherosclerosis. Calcium channel antagonists are a heterogeneous group of pharmacologic agents. Differences in tissue selectivity are largely responsible for the variations in hemodynamic and electrophysiologic properties of these agents. Thus, their clinical uses and side effect profiles differ. These differences must be taken into consideration in the selection of the most appropriate agent for a specific indication. Potential advantages of some of the newer dihydropyridine calcium channel antagonists include less frequent dosing (amlodipine and isradipine) and little or no negative inotropic effect (nicardipine, felodipine, amlodipine, isradipine) compared with the prototype calcium channel antagonists. Additional clinical experience with these newer agents is required, however, before their role in the management of cardiovascular disorders can be fully delineated. The availability of sustained-release formulations of verapamil, diltiazem, nifedipine, felodipine, and nicardipine, as well as the recent marketing of calcium channel antagonists with relatively long half-lives (amlodipine and isradipine), makes once- or twice-daily dosing possible with most calcium channel blockers. However, selection of a particular agent will depend on several factors, including clinical efficacy, side effect profile, cost, and patient characteristics such as concomitant disease states and baseline hemodynamic status.

Double-blind evaluation of the dose-response relationship of amlodipine in essential hypertension

To determine the dose-response efficacy of once-daily administration of placebo or a new long-acting calcium channel blocker amlodipine in patients with mild to moderate hypertension, a randomized, multicenter, placebo-controlled, double-blind trial was conducted. The study included 210 patients with diastolic hypertension (blood pressure 95 to 114 mm Hg) without major hematologic, renal, hepatic, cardiac, or endocrine abnormalities. After a 4-week single-blind placebo run-in period, patients were given placebo or amlodipine (1.25, 2.5, 5, or 10 mg) daily for 4 weeks. To assess the antihypertensive effect of amlodipine over a 24-hour period, blood pressure and pulse rate at weeks 0 and 4 were recorded for 12 hours after the dose and then again at 24 hours. At the end of the study patients treated with all doses of amlodipine greater than 1.25 mg daily had significantly reduced diastolic blood pressure in both supine and standing than 1.25 mg daily had significantly reduced diastolic blood pressure in both supine and standing positions. Amlodipine, 1.25 mg daily, was also associated with a decrease in standing diastolic blood pressure. Response to treatment was greater in all amlodipine-treated patients than in those receiving placebo. Pulse rate in both the supine and standing positions was not significantly affected by amlodipine. At doses of 2.5, 5.0, or 10.0 mg daily, amlodipine maintained blood pressure below values obtained with placebo throughout the 24-hour period. Treatment with amlodipine was well tolerated and the incidence of side effects was low.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic management of childhood hypertension

Antihypertensive drug therapy is used in children primarily to treat secondary forms of hypertension, because the prevalence of essential hypertension in the first decade of life is considerably less than 1% of the childhood population. This prevalence increases during the second decade of life, but the percentage of teenagers with essential hypertension continues to be low. Pharmaceutical companies have been able to target drug development to specific physiologic and biochemical systems. The converting enzyme inhibitors and calcium-channel blockers have greatly improved the success of therapy concomitant with a reduction in the incidence of adverse effects. The result has been a major change during the past decade in the recommendations for antihypertensive drug therapy.

Amlodipine combined with beta blockade for chronic angina: Results of a multicenter, placebo-controlled, randomized double-blind study

Amlodipine, a potent long-acting dihydropyridine calcium antagonist, was compared with placebo in a parallel, randomized, double-blind study in 134 patients with chronic stable angina pectoris maintained on beta-adrenergic blocking agents. After a single-blind, two-week placebo period, patients were randomized to receive either amlodipine (2.5, 5, and 10 mg) or placebo once daily for four weeks. The effects of amlodipine on maximal exercise time, work, time to angina onset, and subjective indices including angina frequency, nitroglycerin tablet consumption, and patient and investigator ratings were assessed. Each dose of amlodipine produced increases in exercise time and calculated total work accomplished compared to baseline. Improvements at 5 and 10 mg were significantly greater than placebo which produced no significant change (p less than 0.05). Qualitative improvements in the severity of angina were produced by amlodipine at 5 and 10 mg daily assessed by patient-rating questionnaires (p less than 0.05). Reductions in angina frequency attacks per week and weekly nitroglycerin tablet consumption occurred but were not statistically significant when compared with placebo. Adverse effects observed during amlodipine treatment prompted discontinuation of treatment in only 2 out of 100 patients. Three patients discontinued treatment for reported lack of efficacy. No laboratory abnormalities prompted treatment discontinuation and minor side effects of dizziness, nausea, headache, and fatigue were observed infrequently. The results of this controlled, large-scale multicenter trial suggest that amlodipine significantly increased exercise capacity and was well tolerated when added to the antianginal regimen of patients remaining symptomatic while receiving beta-blocking agents.

Clinical pharmacokinetics of calcium antagonists. An update

The calcium antagonists are valuable and widely used agents in the management of essential hypertension and angina. There is an increasing number of new agents to add to the 3 prototype substances nifedipine, diltiazem and verapamil. These new agents are dihydropyridines structurally related to nifedipine. However, they tend to have longer elimination half-lives (t 1/2 beta) and may be suitable for twice-daily administration. Amlodipine is an exception with a t 1/2 beta in excess of 30h. Apart from elimination rates, however, the pharmacokinetic characteristics of the newer agents have a notable tendency to resemble those of the established agents. They are highly cleared drugs, are relatively highly protein bound. As they are subject to significant first-pass metabolism, old age and hepatic impairment will increase their plasma concentrations due to a reduced first-pass effect. Renal impairment does little to their pharmacokinetics since the fraction eliminated unchanged by the kidney is small. For most agents, plasma concentration-response relationships have been described. Interesting areas for further research include chronopharmacokinetics, stereoselective pharmacokinetics and lipid solubility. Drugs affecting hepatic blood flow and drug metabolising capacity have predictable interaction potential. Some of the newer calcium antagonists will, like verapamil, increase plasma digoxin concentrations. Verapamil and diltiazem decrease phenazone (antipyrine) metabolism and therefore tend to decrease the metabolism of other drugs.

Isradipine--another calcium-channel blocker for the treatment of hypertension and angina

OBJECTIVE

To review the pharmacology, pharmacokinetic disposition, dose recommendations, adverse effects, drug interactions, and efficacy of isradipine in patients with hypertension or ischemic heart disease.

DATA SOURCES

Data from scientific literature were extracted, evaluated, and summarized for presentation. A MEDLINE search was conducted using the following indexing terms: isradipine, calcium-channel blockers, hypertension, and angina pectoris. Experiences from studies evaluating isradipine reported in the form of articles, abstracts, or proceedings involving patients or healthy subjects were considered for inclusion.

STUDY SELECTION

Special consideration was given to clinical studies that had been designed in a blind, randomized fashion. Studies that compared the effectiveness and safety of isradipine with another antihypertensive or antianginal agent or placebo were included.

DATA EXTRACTION

Data from human studies published in the English language were evaluated. Trials were evaluated according to sample size, design, and adequacy of description of therapeutic response.

DATA SYNTHESIS

Isradipine is a new dihydropyridine calcium-channel blocker that appears to exert less negative inotropic activity than nifedipine and to selectively inhibit sinoatrial conduction. Pharmacokinetic parameters are quite variable and considerably more work is needed to better describe the kinetic disposition of isradipine. Antihypertensive efficacy has been demonstrated extensively in a number of short-term trials. Antianginal efficacy also has been observed in a few short-term trials and is comparable to that of isosorbide dinitrate and nifedipine. Extensive experience with isradipine is minimal and no clear-cut advantages over existing compounds have been noted thus far.

CONCLUSIONS

The place of isradipine in the therapy of hypertension and myocardial ischemia is unclear and its routine use cannot yet be recommended based solely on clinical grounds.

Case report: nifedipine-rifampicin interaction attenuates the effect on blood pressure in a patient with essential hypertension

A 72-year-old woman with 5-year history of essential hypertension developed peritoneal tuberculosis. The patient's hypertension, which had been well-controlled by long-acting nifedipine, deteriorated after the administration of rifampicin, an antitubercular agent. During use of nifedipine and rifampicin, both the peak plasma concentration and the area under the curve of nifedipine decreased markedly to about 40% of those without rifampicin. The findings suggest that rifampicin may increase the elimination of nifedipine, presumably by induction of its hepatic metabolism. Nisoldipine, another calcium antagonist, also failed to lower the patient's blood pressure, when given in combination with rifampicin. Taken together, these findings indicate that more caution should be urged when calcium antagonist is prescribed along with rifampicin.

Pharmacokinetics and dialysability of isradipine in chronic haemodialysis patients

The pharmacokinetics of isradipine, a calcium-channel blocker, have been studied in eight patients on chronic haemodialysis. A single oral dose of 5 mg was administered on both a non-haemodialysis and a haemodialysis day and the plasma concentrations of isradipine were analyzed. The mean cmax, tmax, AUC, and t1/2 in plasma on the non-haemodialysis day were 5.2 ng.ml-1, 1.4 h, 23.8 ng.h.ml-1, and 3.1 h, respectively. The dialysis clearance of isradipine was negligible (5.0 ml.min-1). The t1/2 values during haemodialysis were not significantly different from those observed during the same period post dose on the non-haemodialysis day. The study demonstrates that supplemental doses of isradipine are not necessary in these patients since isradipine is not significantly removed by haemodialysis.

A comparative in vitro study of transdermal absorption of a series of calcium channel antagonists

The in vitro transdermal absorption of five calcium channel antagonists (nifedipine, nitrendipine, nicardipine, felodipine, and nimodipine) was studied using the skin of hairless rats as a membrane. The aim of this study was to determine the penetration parameters [permeability constant (Kp), lag time (T1, and flux (J)] as measures of the intrinsic transdermal permeabilities of these drugs, in order to predict the potential capacity of these drugs to be formulated in a therapeutical transdermal system (TTS). Reliable prediction of Kp values, using K'w (extrapolated capacity factor in 100% water) and P (n-octanol-water partition coefficient) values as independent variables in the parabolic, bilinear, and hyperbolic functions, were assayed. Nicardipine showed a higher mean transdermal penetration (Kp; 4.9 x 10(-3) cm.h-1) value than the other dihydropyridines. Nifedipine showed the shortest mean T1 value (5.1 h). The permeability rate constants of the calcium channel antagonists assayed can be predicted from their n-octanol-water partition coefficients, using the parabolic function (r = 0.984, p less than 0.01). Nicardipine would be the most suitable candidate for formulation in a TTS design.

New developments in antihypertensive drugs

New developments in antihypertensive drug treatment include optimizing the use of established drugs, the introduction of novel compounds, and a renewed appreciation that hypertension is but one of various cardiovascular risk factors that must be addressed in managing the patient with raised blood pressure. Thus, the approach used must be tailored to the individual patient both in terms of drug choice and dose as well as preventive measures. New drug development depends very much on improving our understanding of the pathophysiologic mechanisms involved in hypertension and seems likely to be applied at the level of the renin angiotensin system and other local factors governing vascular smooth muscle function.

The preparation and acute antihypertensive effects of a nanocapsular form of darodipine, a dihydropyridine calcium entry blocker

We have addressed two problems associated with the use of dihydropyridine calcium entry blockers in antihypertensive therapy, namely, potent vasodilation and short half-lives, by incorporating the representative blocker, darodipine, into a nanocapsular vehicle. In awake, renovascular hypertensive rats, darodipine nanocapsules lowered blood pressure when given orally or intramuscularly, and the initial fall in blood pressure was less marked than that observed with the same dose of darodipine dissolved in polyethylene glycol 400 (PEG). Intramuscular administration of the nanocapsular form of darodipine had an antihypertensive effect which lasted for at least 24 hr.

Pharmacokinetics of newer drugs in patients with renal impairment (Part II)

Cardiovascular diseases occur frequently in patients with renal failure. Any pharmacokinetic impairment in these diseases should be considered when individualizing drug therapy. The pharmacokinetics of new cardiovascular drugs in uraemic patients are reviewed: alpha- and beta-blocking agents, ACE inhibitors, centrally acting antihypertensive agents, calcium antagonists, antiarrhythmic agents and inotropic agents. Guidelines are proposed for adjustment of dosage regimens as a function of renal impairment. Renal or extrarenal elimination of drugs and their metabolites, and the activity of the latter, are taken into account. The disposition of new drugs such as flestolol, alacepril, delapril, propafenone, milrinone or enoximone, is not well documented in patients with renal failure. Further characterizations of the elimination of these compounds are needed and the potential therapeutic or toxic effects of the metabolites require evaluation to determine whether the dosage needs to be adjusted. Until such investigations are performed, those drugs should not be used in uraemic patients; if no therapeutic alternative is available, clinical controls are necessary at regular intervals. Relationships between pharmacological or therapeutic effects and drug plasma concentrations should be evaluated for such long term use drugs. The knowledge of a plasma concentration therapeutic window is important to provide information which will be useful in determining appropriate drug dosage in renal failure.

Evaluation of first pass effect and biliary excretion of diperdipine in the dog

Intravenous, oral and intraportal doses of diperdipine were given to bile duct cannulated dogs in order to assess the impact of first pass effect on the pharmacokinetics of this compound. After intravenous and oral doses, absolute bioavailability was calculated to be 18.7%. Biliary excretion accounted for about 0.1% of the total clearance of diperdipine and did not contribute to the overall elimination of the drug. After intraportal administration, the bioavailable fraction of diperdipine was increasing up to 44.3% suggesting a prehepatic site of loss of the drug. This was also substantiated by the fact that after oral administration a lesser fraction was excreted in the bile, than after the intraportal dose. The drug was highly bound to plasma proteins (greater than 96%) and was largely distributed in the blood cells for which a concentration dependent process was observed.