Repeated dosing of piperine induced gene expression of P-glycoprotein via stimulated pregnane-X-receptor activity and altered pharmacokinetics of diltiazem in rats.

This study investigated the effect of piperine on the gene expression of P-glycoprotein (P-gp) as well as pregnane-X-receptor (PXR) activity and also its implication on the bioavailability of diltiazem, a P-gp substrate. The effect of piperine on the systemic exposure of diltiazem was examined in rats after the intravenous and oral administration of diltiazem with/without 2 week pretreatment with piperine. Compared with the control group given diltiazem (20 mg/kg) alone, the pretreatment with piperine (10 or 20 mg/kg, once daily for 2 weeks) decreased the oral exposure of diltiazem by 36-48% in rats. Consequently, the bioavailability of oral diltiazem was significantly lower (p < 0.05) after the 2 week pretreatment with piperine. The pretreatment with piperine for 2 weeks also reduced the systemic exposure of desacetyldiltiazem, a major active metabolite of diltiazem by approximately 73%, accompanied by a significant decrease in the metabolite-parent ratio. In contrast to the oral pharmacokinetics, piperine did not affect the intravenous pharmacokinetics of diltiazem in rats. Immunoblot analysis indicated that the protein expression level of intestinal P-gp was significantly enhanced after the 2 week pretreatment with piperine in rats. In addition, piperine increased the PXR reporter activity in human hepatoma cells. Taken together, the 2 week pretreatment with piperine significantly induced intestinal P-gp expression in conjunction with stimulated PXR activity and decreased the oral exposure of diltiazem and desacetyldiltiazem in rats.

Development and characterization of transdermal drug delivery systems for diltiazem hydrochloride.

Transdermal drug delivery system of diltiazem hydrochloride was developed to obtain a prolonged controlled drug delivery. Both the matrix diffusion controlled (MDC) and membrane permeation controlled (MPC) systems were developed. The matrix diffusion controlled systems used various combinations of hydrophilic and lipophillic polymers, whereas membrane permeation controlled systems were developed using the natural polymer chitosan. The MDC systems were prepared using the cast film method and the MPC systems by an adhesive sealing technique. Both the systems were characterized for in vitro and in vivo performance. The MDC systems were characterized for physicochemical properties such as tensile strength, moisture content, and water vapor transmission. The in vitro release studies showed that the release from the matrix diffusion controlled transdermal drug delivery systems follows a nonfickian pattern and that from the membrane permeation controlled transdermal drug delivery systems follow zero-order kinetics. The release from the matrix systems increased on increasing the hydrophilic polymer concentration, but the release from the membrane systems decrease on cross-linking of the rate controlling membrane and also on addition of citric acid to the chitosan drug reservoir gel. The in vivo studies of the selected systems showed that both systems are capable of achieving the effective plasma concentration for a prolonged period of time. The MPC system achieved effective plasma concentration a little more slowly than the MDC system, but it exhibited a more steady state plasma level for 24 hr.

An investigation of pulsatile release tablets with ethylcellulose and Eudragit L as film coating materials and cross-linked polyvinylpyrrolidone in the core tablets.

To develop new pulsatile release tablets, which can suppress drug release in stomach and release the drug rapidly after a predetermined lag time of about 3 h in intestine, the use of tablets with ethylcellulose/Eudragit L as a coating film and cross-linked polyvinylpyrrolidone in the core tablets was investigated. The release of diltiazem hydrochloride (DIL) as a model drug in the core tablets was investigated in vitro. The lag time (t10) was prolonged with an increase of the coating level, whereas the drug release rate was almost constant, irrespective of the coating level. The water-uptake study and electron microscope photographs suggested the mechanism of pulsatile release of drug. Pulsatile release tablets containing 60 mg DIL with 4.4 h of lag time (t10) in vitro were administrated to eight volunteers. The mean plasma concentration curves showed 4.9 h of lag time (tlag), 8.0 h of time to maximum concentration (tmax) and 3.1 h of time between tmax and tlag (t(psi)) in vivo. Relative bioavailability was 1.05 for pulsatile release tablets compared to conventional tablets.

Effects of cigarette smoke inhalation on plasma diltiazem levels in rats.

A rapid and sensitive method for the assay of plasma diltiazem was developed using a solid-phase extraction technique followed by high-performance liquid chromatography. The effects of cigarette smoke on plasma levels of orally administered diltiazem was investigated in rats. The animals were exposed to cigarette smoke for 10 min using a Hamburg II smoking machine, immediately after oral administration of diltiazem (10 mg/kg). In the nonsmoking nonrestrained rats, plasma diltiazem levels increased rapidly and reached the maximum (7.1 micrograms/kg) 2 h after administration and decreased gradually thereafter. In the nonsmoking restrained rats, plasma diltiazem levels increased rapidly, but showed almost constant levels between 1 h and 8 h after administration. The maximum level (5.4 micrograms/kg) was shown after 2 h. On the other hand, plasma diltiazem levels in the rats exposed to cigarette smoke reached the maximum (4.3 micrograms/kg) after 4 h. These results suggest that absorption of orally administered diltiazem is inhibited and delayed by cigarette smoke.

Cardioprotective effects of diltiazem during acute rejection on heterotopic heart transplants.

In the presence of severe rejection, cardiac allograft perfusion has been shown to be impaired. Since a functionally reversible vasoconstrictor component has been identified in this condition and rejection does not reverse if ischemia does not, we hypothesized that diltiazem may be beneficial in this condition. Experiments were performed on dogs with heterotopic heart transplants and chronic instrumentation for the assessment of allograft perfusion. Two groups of cardiac allograft recipients were studied: untreated recipients and recipients treated with the calcium antagonist diltiazem (180 mg twice daily, orally). Allograft blood flow was monitored daily along with plasma diltiazem levels. The lymphoproliferative response to mitogens was studied at selected intervals until terminal rejection. Contractile function of the graft was assessed daily by palpation. Without immunosuppression, terminal rejection was observed within 7 days. Rejection was confirmed by histology; cellular infiltration and myocyte necrosis were present in all cardiac allografts but to a significantly lesser degree in diltiazem-treated recipients. The mean blood flow of heterotopically implanted hearts was in the range of 35-50 ml/min, which decreased steadily in untreated recipients. In contrast, significant improvement of allograft perfusion was observed in diltiazem-treated recipients at days 4-6 after transplantation. Diltiazem also significantly attenuated mitogen-induced lymphocyte proliferation at peak sensitivity (2 days after transplantation). Diltiazem plasma concentrations were in the therapeutic range (30-60 ng/ml) before and after cardiac transplantation. Results of the present study demonstrate beneficial effects of diltiazem in the course of severe cardiac rejection. Such findings support its use during rejection when maintenance of graft blood flow and myocyte protection may be important for myocardial function and viability.

Effect of cardiopulmonary bypass on plasma concentrations of diltiazem and its two active metabolites.

Diltiazem is often used to prevent myocardial ischaemia during the perioperative period of coronary artery bypass surgery. The purpose of this study was to investigate the effect of cardiopulmonary bypass (CPB) on plasma concentrations of diltiazem and of its two main and active metabolites (N-monodemethyldiltiazem (N-desmethyldiltiazem) and desacetyldiltiazem). The patients were administered their usual treatment during the preoperative days. The last dose was administered immediately before anaesthesia. At the onset of CPB, a significant decrease in the plasma concentrations of diltiazem and its metabolites was observed, whereas the variation was slight and not significant when the plasma concentrations were corrected for haemodilution. These results confirm that the decrease observed at the initiation of the bypass procedure can be ascribed to the haemodilution induced by the CPB. During CPB, the concentrations of diltiazem and its metabolites remained constant suggesting that the rate of metabolism and excretion of the drug was altered during the bypass procedure. At the end of CPB, there was no increase of drug plasma concentrations suggesting that no redistribution of diltiazem from tissues to plasma occurred. Furthermore, this study shows that only 33% of subjects have therapeutic levels of diltiazem before anaesthesia, and that all subjects have subtherapeutic levels during and after the CPB. These results suggest that a higher chronic oral dose of the drug should be given in patients undergoing cardiac surgery with CPB.

[Plasma concentrations of diltiazem and its metabolites in coronary surgery: relation with preoperative treatment]. / Concentrations plasmatiques du diltiazem et de ses métabolites en chirugie coronarienne: relation avec le traitement préopératoire.

Preoperative oral administration of calcium channel blocking agents has been found ineffective to prevent perioperative myocardial ischaemia. Our hypothesis was that low plasma concentrations may account for this inefficiency. Twenty-three male patients, scheduled for surgical myocardial revascularisation, were administered their usual anti-anginal treatment, including 180 to 360 mg of diltiazem since more than one week. The usual dosage was given at 8.00 p.m. on the day before surgery. On the morning of surgery, after withdrawal of a first blood sample, 60 mg of diltiazem were administered per month before the induction of anaesthesia. The anaesthesia was obtained with fentanyl, midazolam or flunitrazepam, pancuronium and isoflurane as required. The cardiopulmonary bypass (CPB) was associated with total haemodilution with Ringer's Lactate and a membrane oxygenator. A second blood sample was withdrawn after CPB. Plasma concentrations of diltiazem and its two active metabolites, N-monodemethyldiltiazem (MA) and desacetyldiltiazem (M1), were assessed by HPLC. Plasma diltiazem concentrations decreased from 78 +/- 66 (mean +/- SD) to 51 +/- 42 micrograms.l-1 (p < 0.05) with wide individual variations. These concentrations were under therapeutic levels in 18 out of 23 patients before (p < 0.05) with wide individual variations. These concentrations were under therapeutic levels in 18 out of 23 patients before induction and in 22 patients after CPB. The metabolite/diltiazem ratios remained constant. A dosage-plasma concentration relationship was observed preoperatively with diltiazem and MA. It is concluded that plasma concentrations of diltiazem should be optimized preoperatively in order to prevent myocardial ischaemia.

Pharmacokinetics of diltiazem in patients undergoing coronary artery bypass grafting.

The pharmacokinetics of oral diltiazem (DZ) were studied in 10 patients on the day before cardiac surgery and on the next day during surgery and cardiopulmonary bypass (CPB). Six patients were taking DZ 60 mg q.i.d. and four patients were taking DZ 90 mg q.i.d. All had been receiving DZ treatment for at least 3 months. The plasma concentration profile of DZ on the day before surgery was assumed to reflect the steady-state condition. DZ showed dose-dependent kinetics. On the day of surgery, the levels of total DZ (TDZ) at 15 min and 1 h after the initiation of CPB were significantly reduced (approximately 50%) when compared with the pre-CPB level. The levels of unbound DZ (FDZ) and the two major metabolites, N-demethyl DZ (MA) and deacetyl-DZ (M1) were not changed significantly by CPB. The plasma unbound fraction value increased sharply from 0.43 +/- 0.12 before the onset of CPB to a peak value of 0.83 +/- 0.12 during CPB, and returned to baseline level 24 h after dosing. We conclude that CPB decreases the TDZ concentration but has little effect on FDZ, MA, and M1 levels. The lack of effect of CPB on FDZ was related to the reduction of plasma protein binding of DZ.

Hemodynamic effect of calcium channel blockade during anesthesia for coronary artery surgery.

Because the choice of anesthetic technique does not influence the incidence of perioperative myocardial ischemia, reduction of ischemic risk may require specific antianginal therapy. Calcium entry blockers are effective drugs in antianginal therapy. Diltiazem reduces myocardial oxygen demand through decreases in heart rate, inotropy, and systolic function, while increasing myocardial oxygen delivery through coronary vasodilation. These potentially beneficial effects of diltiazem were evaluated in 15 of 29 patients (diltiazem v placebo, double-blind study) scheduled for coronary artery bypass graft surgery. Continuous infusion of diltiazem (0.15 mg/kg bolus followed by 2 micrograms/kg/min), during anesthesia and surgery before cardiopulmonary bypass, significantly reduced the major MVO2 determinants during anesthesia with moderate doses of fentanyl and a benzodiazepine (midazolam in 8 of 14 control patients and 9 of 15 treated patients, or flunitrazepam in the others). Heart rate, mean arterial pressure, and inotropy were decreased during the most stressful events of surgery when plasma diltiazem concentrations were in the therapeutic range (greater than 96 ng/mL). The number of patients with perioperative ischemia was 2 of 15 in the treated group and 4 of 14 in the control group. Provided that diltiazem plasma concentrations are sufficient, it can contribute to lowering the ischemic burden during anesthesia for coronary artery surgery.

Beneficial effects of diltiazem on the natural history of hypertensive diabetic cardiomyopathy in rats.

Hypertensive diabetic rats develop a cardiomyopathy characterized by systolic and diastolic ventricular dysfunction, myocardial hypertrophy and fibrosis, pulmonary congestion and a very high mortality rate. Alterations in contractile proteins and sarcoplasmic reticular calcium (Ca2+) transport in diabetic myocardium and their partial reversal with verapamil suggest that calcium channel blockade may prevent death from congestive heart failure in hypertensive diabetic rats. A large group of rats with renovascular hypertension and streptozotocin diabetes were divided into four groups: untreated animals (Group 1) and animals treated with 100 (Group 2), 300 (Group 3) or 600 (Group 4) mg/kg per day of sustained release diltiazem mixed in their food. Treatment was begun shortly after the onset of hypertension and diabetes. Mortality rates after 4 months were 59% (19 of 32), 53% (17 of 32), 27% (7 of 26) and 35% (12 of 34) in Groups 1, 2, 3 and 4, respectively; the mortality rate in age-matched control rats was 5% (1 of 19). The reductions in mortality rates in Groups 3 and 4 were statistically significant. Diltiazem did not change systolic blood pressure, serum glucose concentration, heart rate or left ventricular mass. There was a trend to decreased left ventricular interstitial fibrosis and perivascular fibrosis in diltiazem-treated animals. Ventricular collagen concentration was similar in untreated hypertensive diabetic and control rats; levels were higher in hypertensive diabetic rats that died than in those that survived. There was a trend to decreased collagen concentration as diltiazem dose increased. Myosin isoenzyme distribution was not changed in Groups 3 and 4 (in comparison with Group 1). In all hypertensive diabetic groups, rats that died had a higher blood pressure, heart rate, relative left ventricular mass, lung weight and lung water than did survivors. The mortality rate was two to three times higher among rats with an initial blood pressure greater than or equal to 180 mm Hg. The beneficial effects of diltiazem on survival were most significant among rats with severe hypertension.

Effects of diltiazem on renin-aldosterone and ACTH-adrenocortical function during upper abdominal surgery.

STUDY OBJECTIVE: To observe the effects of continuous intravenous infusion of diltiazem on the renin-aldosterone system and ACTH-adrenocortical axis responses during surgical stimulation. DESIGN: Randomized study of intravenous diltiazem. SETTING: Operating room at the Hyogo Medical College Hospital. PATIENTS: Twenty-three patients undergoing upper abdominal surgery were divided into two groups: the control group (n = 10) and the diltiazem group (n = 13). All the patients were without any complications and classified as ASA physical status I. INTERVENTIONS: Patients in the diltiazem group received an infusion of 10 micrograms/kg/min for 90 to 120 minutes following skin incision. MEASUREMENTS AND MAIN RESULTS: Plasma adrenocorticotropic hormone, plasma aldosterone and cortisol concentrations, and plasma renin activity were determined with radioimmunoassay before the induction of anesthesia at 10, 30, 60, and 90 minutes after skin incision and at the end of anesthesia. Renin activity did not change significantly. Maximal increases in plasma adrenocorticotropic hormone, aldosterone, and cortisol observed 90 minutes after skin incision were 355 +/- 95 pg/ml, 118 +/- 30 pg/ml, and 14.2 +/- 2.3 micrograms/dl in the control group versus 246 +/- 41 pg/ml, 119 +/- 25 pg/ml, and 15.0 +/- 1.8 micrograms/dl in the diltiazem group, respectively, and there were no significant differences between these groups. Adrenocorticotropic hormone was significantly lower in the diltiazem group compared with that in the control group 60 minutes after the start of surgery (p less than 0.05). There was marked natriuresis (40 +/- 25 microEq/min vs 470 +/- 147 microEq/min at the 90-minute mark) and diuresis (0.16 +/- 0.13 ml/min vs 2.53 +/- 0.88 ml/min) in the diltiazem group. CONCLUSIONS: Diltiazem at this dose increased urine output and sodium excretion without affecting most of these hormonal responses to surgical stimulation. These findings suggest that diltiazem has beneficial renal effects independent of hormonal concentrations.

Determination of serum diltiazem concentrations in a pharmacokinetic study using gas chromatography with electron capture detection.

An open cross-over randomized clinical trial was performed in nine healthy humans to determine steady-state pharmacokinetics and bioavailability of three oral diltiazem preparations, tablets containing 60 and 90 mg of diltiazem hydrochloride, administered in total daily doses of 180 mg. Serum drug levels were determined by gas chromatography with electron capture detection following a simple extraction procedure. Blood samples were collected before and at several post-dosing intervals after administration of the last dose in steady state, and pharmacokinetic parameters were calculated. The steady-state diltiazem concentrations in sera were determined 48 h after the first dose, and were (mean +/- SD): 46.4 +/- 28.1, 60.8 +/- 36.3 and 36.8 +/- 22.6 micrograms l-1 for Pliva 60, Pliva 90, and Aldizem 90 diltiazem preparations, respectively. The corresponding elimination half-lives were 5.6 +/- 2.0, 5.2 +/- 1.8 and 6.9 +/- 3.2 h; peak concentrations were 88.4 +/- 29.5, 153.5 +/- 86.5 and 139.2 +/- 72.5 micrograms l-1, and areas under the concentration curves (AUC 12 h) were 477.4 +/- 172.5, 989.2 +/- 536.3 and 817.9 +/- 494.5 micrograms h-1, respectively.

Diltiazem withdrawal before coronary artery bypass surgery.

The authors studied the effects of withdrawing oral diltiazem therapy on the subsequent course of coronary artery bypass graft surgery. Patients with severe coronary artery disease were divided into three groups using a prospective, controlled, randomized protocol. In group D (diltiazem-continuation) patients, diltiazem was administered 2.1 +/- 0.1 hours (mean +/- SEM) before anesthetic induction (n = 10). Group DW (diltiazem-withdrawal) patients received their final diltiazem dose 17.3 +/- 2.9 hours before anesthesia (n = 10). Group R was a reference group of patients not receiving diltiazem (n = 11; not randomized). Anesthesia was induced and maintained with fentanyl and pancuronium without use of halogenated anesthetics. No clinically important differences were detected in measured hemodynamics or drug requirements. Group D patients did not have a lower systemic vascular resistance (SVR) index (P greater than 0.31) or mean arterial pressure (P greater than 0.08) compared with group DW. Also, no evidence for a diltiazem withdrawal response was found, because group DW did not have either a higher SVR index (P = 0.99) or a higher pulmonary vascular resistance index (P = 0.99) compared with group R, and no severe myocardial ischemia, coronary artery spasm, or postoperative heart block were seen. Plasma diltiazem concentrations decreased significantly during CPB (P less than 0.0001), but showed overlap between groups D and DW. Plasma diltiazem concentration did not correlate significantly with simultaneous SVR. These data show the benign effects of both diltiazem administration and its acute withdrawal before coronary artery bypass surgery with high-dose fentanyl anesthesia.

Beneficial effects of long-term diltiazem treatment in dilated cardiomyopathy.

There is increasing evidence that chronic enhanced exogenous or endogenous catecholamine stimulation in patients with dilated cardiomyopathy may worsen hemodynamic status and prognosis. The cause of this deterioration may lie in myocellular calcium accumulation and microcirculatory disorders. In a prospective study, the calcium channel antagonist diltiazem was given to 22 patients with dilated cardiomyopathy (60 to 90 mg three times daily) in addition to conventional therapy of digitalis, diuretics and vasodilators. Twenty-five patients received the conventional therapy and served as historical controls. Eight additional patients who were not originally included in this control group received adjunctive diltiazem treatment after initially receiving conventional therapy alone. The three patient groups were similar in all hemodynamic and anamnestic features. Only patients with reduced myofibrillar volume fraction on myocardial biopsy were included in the trial, because they could be expected to show hemodynamic deterioration. The mean survival time was 29 months in the control group, whereas no patient in the diltiazem group died over a mean follow-up period of 15.4 months (p less than 0.001). Mean left ventricular ejection fraction increased from 0.34 to 0.44 (p less than 0.001) and New York Heart Association functional class improved significantly in the diltiazem group and during the diltiazem period in the crossover patients, but deteriorated in the control group. The results suggest that adjunctive diltiazem treatment in dilated cardiomyopathy has beneficial effects on mortality, hemodynamics and symptoms.

Pharmacokinetic analysis of single- or multiple-dose plasma drug concentration data with a microcomputer using multi-fraction absorption models.

A Basic program for multi-fraction absorption models was developed to link with another microcomputer program, MULTI, and was named MFA-MULTI. A main frame computer program SIMP, based on a simplex method using differential equations, was also operated using a microcomputer equipped with a FORTRAN compiler and a 8087 floating-point coprocessor. These two programs [MFA-MULTI and SIMP (M)] were applied to the analysis of plasma concentration data of several drugs with irregular absorption profiles. The results by MFA-MULTI and SIMP(M) for the single- or multiple-dose data were almost coincident with those obtained by a SIMP program. The result for nalidixic acid estimated using MFA-MULTI or PKM-MULTI was also compared. The plasma nalidixic acid concentration, with irregular absorption profiles due to characteristics of dissolution in the gastrointestinal tract, was found to be described by a two-fraction absorption model. The MFA-MULTI program was applied to the analysis of plasma cimetidine concentration data with double peaks in humans. Pharmacokinetic absorption behavior of a sustained-release preparation of theophylline after repetitive oral administration was adequately evaluated using MFA-MULTI. In addition, application of multi-fraction absorption models to population pharmacokinetics is discussed.

Effects of diltiazem on rheological properties of human blood.

The in vitro effects of diltiazem (DTZ), a coronary vasodilator, deacetyldiltiazem (D-M1), one of the metabolites of DTZ, and pentoxifylline (PTF) which is known to improve erythrocyte deformation, on the viscosity of platelet poor blood were compared. Furthermore the change in the viscosity of whole blood from patients with effort angina after intravenous administration of DTZ was examined ex vivo. The addition of DTZ into platelet poor blood at 37 degrees C caused a rapid reduction in blood viscosity and an enhancement of erythrocyte deformability within 5 min, which then diminished in a time-dependent manner. Similar effects were also found by adding D-M1. On the other hand, the effects of PTF appeared after an incubation period of more than 60 min and were enhanced in a time-dependent manner. These actions of PTF, but not those of DTZ and D-M1, paralleled the increase of erythrocyte adenosine-triphosphate content. DTZ and D-M1, but not PTF, had biphasic effects on the osmotic behavior of erythrocytes. Whole blood viscosity was reduced significantly during the period 5-30 min after intravenous administration of 10 mg of DTZ, which diminished with the elimination of plasma DTZ. In conclusion, the action mechanisms involved in the effect of DTZ and D-M1 on blood rheological properties appeared to be different from that of PTF. These effects of DTZ are clinically significant in improving the flow properties of blood in vascular diseases.

Actions of calcium ions and a calcium-influx blocker on basal and TRH- and GnRH-stimulated hormone release in patients with pituitary adenomas.

We investigated the influence of calcium ions on the secretion of anterior pituitary hormones basally and in response to exogenous hypothalamic releasing factors in 6 men with pituitary tumors. To this end, concentrations of LH, FSH, TSH, growth hormone and prolactin were measured in blood collected at 10-min intervals basally and during a continuous infusion of combined TRH (2 micrograms/min) and GnRH (1 microgram/min). Study sessions were randomized to iv saline, calcium, or diltiazem infusions or oral diltiazem administration. Our results indicate that in contrast to responses in normal men, iv calcium injections do not suppress circulating prolactin concentrations in patients with prolactin-secreting pituitary tumors. Moreover, neither oral diltiazem administration for one week nor acute iv diltiazem infusion suppressed the hyperprolactinemia of tumor patients. However, there were significant effects of drug and calcium treatments on serum concentrations of FSH, GH and testosterone, but not LH or TSH. Moreover, during GnRH-TRH stimulation, there were significant differences in LH, TSH, and testosterone responses in tumor patients compared to normal men. In summary, iv calcium infusion was associated with invariant basal release of anterior pituitary tumoral hormones in patients with pituitary adenomas. However, there were significant differences in the GnRH/TRH-stimulated release of certain anterior pituitary hormones in tumor patients compared to normal men in response to iv calcium and the calcium-channel antagonist, diltiazem.

Assay of diltiazem and deacetyldiltiazem by capillary gas chromatography.

A highly sensitive gas chromatographic method for the analysis of diltiazem and deacetyldiltiazem in plasma or serum is reported. After silylation with bis (trimethylsilyl) trifluoroacetamide, separation was obtained on a cross-linked fused-silica column and detection was by electron-capture. The minimum measurable concentrations were 3 and 1 ng/ml for diltiazem and deacetyldiltiazem, respectively. Intra- and inter-day coefficients of variation were less or equal to 6.0 and 8.0%, respectively, for both compounds. The method was used to study the kinetics of a single oral dose of 60 mg of diltiazem hydrochloride in a patient with renal failure.

Effects of diltiazem, dipyridamole, and their combination on hemostasis.

Calcium channel blockers and antiplatelet agents, alone and in combination, have been reported to induce bleeding in patients undergoing surgery. Since diltiazem and dipyridamole influence platelet function in vitro and in vivo, their influence on hemostasis was examined in five normal men given diltiazem, 90 mg by mouth, followed by 60 mg every 6 hr for 48 hr, or dipyridamole, 75 mg by mouth every 8 hr for 48 hr. At 24 hr, the alternate drug was added to the regimen to assess effects of the combination on hemostasis. Platelet aggregation, serum thromboxane B2 and 6-keto-PGF1 alpha concentrations (stable metabolites of thromboxane A2 and prostacyclin), bleeding time, prothrombin time, partial thromboplastin time, and serum diltiazem concentrations were measured. Diltiazem and dipyridamole alone and in combination had no significant effect on bleeding time, prothrombin time, or partial thromboplastin time. Platelet aggregation induced by threshold concentrations of adenosine diphosphate, epinephrine, and calcium ionophore A 23187 were inhibited by diltiazem and dipyridamole alone and in combination. The only change in prostaglandin concentrations was a slight increase in serum 6-keto-PGF1 alpha after diltiazem. Despite influences on platelet function, neither diltiazem nor dipyridamole alone or in combination induced clinically relevant changes in hemostasis.

Improved gas chromatographic determination of diltiazem and deacetyldiltiazem in human plasma.

This study describes an improved, simple, and specific gas chromatographic method for the determination of diltiazem (I) and deacetyldiltiazem (II) in human plasma using loxapine (III) as an internal standard. After extraction at pH 7.5 with anhydrous ether-ethyl acetate (1:1), II was silylated with N-methyl-N-(trimethylsilyl)trifluoroacetamide. The gas chromatograph, equipped with an electron-capture detector, allowed measurements as low as 2 ng/mL for I and 3 ng/mL for II. Recoveries of III, I, and II were 95, 85, and 79%, respectively. There were no interferences with endogenous substances in plasma or with common cardiovascular drugs. This method was used to measure plasma concentrations of two patients who received 20 mg iv of I. The areas under the curve for these two patients were 275 and 273 ng.h/mL, respectively. The apparent volumes of distribution were 493.6 and 288.6 L, and the elimination half-lives were 4.70 and 2.73 h. No deacetyldiltiazem could be detected in the blood after the single-dose diltiazem administration.