Relationship between pharmacokinetics and pharmacodynamics of molsidomine and its metabolites in humans

Pharmacokinetics and pharmacodynamics of nitric oxide mimetic agents

Drug discovery focusing on NO mimetics has been hamstrung due to its unconventional nature. Central to these challenges is the fact that direct measurement of molecular NO in biological systems is exceedingly difficulty. Hence, drug development of NO mimetics must rely upon measurement of the NO donating specie (i.e., a prodrug) and a downstream marker of efficacy without directly measuring the molecule, NO, that is responsible for biological effect. The focus of this review is to catalog in vivo attempts to monitor the pharmacokinetics (PK) of the NO donating specie and the pharmacodynamic (PD) readout of NO bioactivity.

Effects of Aging and Oxidative Stress on Spermatozoa of Superoxide-Dismutase 1- and Catalase-Null Mice

Advanced paternal age is linked to complications in pregnancy and genetic diseases in offspring. Aging results in excess reactive oxygen species (ROS) and DNA damage in spermatozoa; this damage can be transmitted to progeny with detrimental consequences. Although there is a loss of antioxidants with aging, the impact on aging male germ cells of the complete absence of either catalase (CAT) or superoxide dismutase 1 (SOD1) has not been investigated. We used CAT-null (Cat(-/-)) and SOD1-null (Sod(-/-)) mice to determine whether loss of these antioxidants increases germ cell susceptibility to redox dysfunction with aging. Aging reduced fertility and the numbers of Sertoli and germ cells in all mice. Aged Sod(-/-) mice displayed an increased loss of fertility compared to aged wild-type mice. Treatment with the pro-oxidant SIN-10 increased ROS in spermatocytes of aged wild-type and Sod(-/-) mice, while aged Cat(-/-) mice were able to neutralize this ROS. The antioxidant peroxiredoxin 1 (PRDX1) increased with age in wild-type and Cat(-/-) mice but was consistently low in young and aged Sod(-/-) mice. DNA damage and repair markers (γ-H2AX and 53BP1) were reduced with aging and lower in young Sod(-/-) and Cat(-/-) mice. Colocalization of γ-H2AX and 53BP1 suggested active repair in young wild-type mice but reduced in young Cat(-/-) and in Sod(-/-) mice and with age. Oxidative DNA damage (8-oxodG) increased in young Sod(-/-) mice and with age in all mice. These studies show that aged Sod(-/-) mice display severe redox dysfunction, while wild-type and Cat(-/-) mice have compensatory mechanisms to partially alleviate oxidative stress and reduce age-related DNA damage in spermatozoa. Thus, SOD1 but not CAT is critical to the maintenance of germ cell quality with aging.

Cell type-dependent release of nitric oxide and/or reactive nitrogenoxide species from intracellular SIN-1: effects on cellular NAD(P)H

SIN-1 is frequently used in cell culture studies as an extracellularly operating generator of peroxynitrite. However, little is known about the nature of the reactive species produced intracellulary from SIN-1. SIN-1 can easily penetrate cells as exemplified for both L-929 mouse fibroblasts and bovine aortic endothelial cells (BAECs) by utilizing capillary zone electrophoresis. In L-929 cells, SIN-1 produced nitric oxide (*NO) as monitored by the fluorescent *NO scavenger FNOCT-1 and by means of a *NO electrode, as well as reactive nitrogenoxide species (RNOS, e.g. peroxynitrite, nitrogen dioxide, dinitrogen trioxide), as detected with the fluorescent indicator DAF-2. Laser scanning microscopy revealed that in L-929 cells SIN-1 -derived species initially oxidized the major fraction of the NAD(P)H within the cytosol and the nuclei, whereas the mitochondrial NAD(P)H level was somewhat increased. In marked contrast to this, in BAECs no evidence for *NO formation was found although the intracellular amount of SIN-1 was four-fold higher than in L-929 cells. In BAECs, the level of NAD(P)H was slightly decreased within the first 10 min after administration of SIN-1 in both the cytosol/nuclei and mitochondria. These observations reflect the capability of SIN-1 to generate intracellularly either almost exclusively RNOS as in BAECs, or RNOS and freely diffusing *NO as in L-929 cells. Nitric oxide as well as RNOS may decisively affect cellular metabolism as indicated by the alterations in the NAD(P)H level. Hence, care should be taken when applying SIN-1 as an exclusively peroxynitrite-generating compound in cell culture systems.

Nitric oxide donors can increase heart rate independent of autonomic activation

Administration of nitric oxide (NO) donors in vivo is accompanied by a baroreflex-mediated increase in heart rate (HR). In vitro, however, NO donors can increase HR directly by stimulating a pathway that involves NO, cGMP, and the hyperpolarization-activated current (I(f)). The aim of this study was to assess the functional significance of this pathway in vivo by testing whether NO donors can increase HR in the anesthetized rabbit independent of the autonomic nervous system. New Zealand White rabbits were vagotomized, cardiac sympathectomized, and treated with propranolol (0.3 mg/kg iv). The NO donor molsidomine (0.2 mg/kg iv) caused a progressive increase (Delta) in HR (DeltaHR, 14 +/- 3 beats/min; P < 0.01). This effect was significantly reduced by the I(f) blocker ZD-7288 (0.2 mg/kg iv; DeltaHR, 2 +/- 3 beats/min; P = not significant). Similar results were seen with sodium nitroprusside. The positive chronotropic effect of sodium nitroprusside (50 microM) was confirmed in the isolated working rabbit heart preparation (DeltaHR, 17 +/- 3 beats/min; P < 0.01). In conclusion, NO donors exert a small, but significant, positive chronotropic effect in vivo that is independent of the autonomic nervous system. These results are also consistent with data in sinoatrial node cells that show that NO donors increase HR by stimulating I(f).

NO-cGMP pathway accentuates the decrease in heart rate caused by cardiac vagal nerve stimulation

The role of the cardiac muscarinic-receptor-coupled nitric oxide (NO) pathway in the cholinergic control of heart rate (HR) is controversial. We investigated whether adding excessive NO or its intracellular messenger cGMP could significantly modulate the HR response to vagal nerve stimulation (VNS) in the anesthetized rabbit and isolated guinea pig atria. The NO donor molsidomine (0.2 mg/kg iv) significantly enhanced the decrease in HR seen with right VNS (5 Hz, 5 V, 30 s) in vivo. A qualitatively similar effect was seen with the NO donor sodium nitroprusside (SNP; 10 and 100 microM) during VNS in vitro. This effect was still present when the baseline shift in HR caused by SNP was eliminated by using the specific hyperpolarization-activated current antagonist 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino)-pyrimidinium chloride (ZD-7288, 1 microM). The accentuated decrease in HR with SNP during VNS was mimicked by the stable analog of cyclic GMP, 8-bromoguanosine 3',5'-cyclic monophosphate (0.5 mM). This, however, was not seen with bath application of the stable analog of acetylcholine, carbamylcholine chloride (100 nM). We conclude that excessive NO enhances the magnitude of the decrease in HR caused by VNS. This effect appears to involve a presynaptic action via a cGMP-dependent pathway because it was not mimicked by bath-applied carbamylcholine chloride.

Clinical pharmacokinetics of vasodilators. Part II

Stimulating cardiac beta 1-adrenoceptors with oxyfedrine causes dilatation of coronary vessels and positive inotropic effects on the myocardium. beta 1-adrenergic agonists increase coronary blood flow in nonstenotic and stenotic vessels. The main indication for the use of the phosphodiesterase inhibitors pamrinone, mirinone, enoximone and piroximone is acute treatment of severe congestive heart failure. Theophylline is indicated for the treatment of asthma, chronic obstructive pulmonary disease, apnea in preterm infants ans sleep apnea syndrome. Severe arterial occlusive disease associated with atherosclerosis can be beneficially affected by elcosanoids. These drugs must be administered parenterally and have a half-life of only a few minutes. Sublingual or buccal preparations of nitrates are the only prompt method (within 1 or 2 min) of terminating anginal pain, except for biting nifedipine capsules. The short half-life (about 2.5 min) of nitroglycerin (glyceryl trinitrate) makes long term therapy impossible. Tolerance is a problem encountered with longer-acting nitric oxide donors. Knowledge of the pharmacokinetic properties of vasodilating drugs can prevent a too sudden and severe blood pressure decrease in patients with chronic hypertension. In considering the administration of a second dose, or another drug, the time necessary for the initially administered drug to reach maximal efficacy should be taken into account. In hypertensive emergencies urapidil, sodium nitroprusside, nitroglycerin, hydralazine and phentolamine are the drugs of choice, with the addition of beta-blockers during catecholamine crisis or dissecting aortic aneurysm. Childhood hypertension is most often treated with angiotensin-converting enzyme (ACE) inhibitors or calcium antagonists, primarily nifedipine. Because of the teratogenic risk involved with ACE inhibitors, extreme caution must be exercised when prescribing for adolescent females. The propagation of health benefits to breast-fed infants, combined with more women delaying pregnancy until their fourth decade, has entailed an increase in the need for hypertension management during lactation. Low dose hydrochlorothiazide, propranolol, nifedipine and enalapril or captopril do not pose enough of a risk of preclude breastfeeding in this group. The most frequently used antihypertensive agents during pregnancy are methyldopa, labetalol and calcium channel antagonists. Methyldopa and beta-blockers are the drugs of choice for treating mild to moderate hypertension. Prazosin and hydralazine are used to treat moderate to severe hypertension and hydralazine, urapidil or labetalol are used to treat hypertensive emergencies. The use of overly aggressive antihypertensive therapy during pregnancy should be avoided so that adequate uteroplacental blood flow is maintained. Methyldopa is the only drug accepted for use during the first trimester of pregnancy.

Infusions with molsidomine and isosorbide-5-mononitrate in congestive heart failure: mechanisms underlying attenuation of effects

The use of nitrates for treatment of heart failure is encumbered by tolerance, caused by whatever mechanism, which has been reported only in a few instances with sydnonimines. Accordingly, we compared molsidomine (6 mg/h) and isosorbide-5-mononitrate (3.75 mg/h) with respect to maximal hemodynamic effects, rapidity and extent of attenuation, and underlying mechanisms by means of constant infusions over 24 h each in 15 patients with chronic congestive heart failure (NYHA II-III) with a placebo-controlled, double-blind, randomized, crossover protocol. Hemodynamic measurements and determinations of neurohormones were performed at baseline and at 2, 8, and 24 h after the beginning of infusions. With molsidomine, reductions of diastolic pulmonary artery pressure by 29% (p < 0.001), by 24% (p < 0.01), and by 24% (p < 0.01) versus placebo were found at 2, 8, and 24 h, which amounted to 19% (p < 0.01), 10% (NS), and 14% (NS) with the nitrate. Cardiac output was meaningfully affected only with molsidomine (+5%, NS, at 2 h; +9%, p < 0.05, at 8 h; and +15%, p < 0.05, at 24 h), as was systemic vascular resistance (-13%, p < 0.05; -9%, NS; and -18%, p < 0.01) at the corresponding times. Increases in renin activity amounted to 130% (p < 0.001), 117% (p < 0.001), and 112% (p < 0.001) with molsidomine, and to 14, 16%, and 0 (each NS) with the nitrate at the corresponding times. Hematocrit was reduced by 5% (p < 0.001), 7% (p < 0.001), and 12% (p < 0.01) with molsidomine and by 5% (NS), 5% (p < 0.05), and 5% (NS) with the nitrate. We conclude that neurohumoral counterregulation or fluid shift, which is even more pronounced with molsidomine despite longer-lasting effects, has no essential role in nitrate-tolerance development. With molsidomine, such a role cannot be ruled out, although alternatively, a fluid shift from arterial to the low-pressure arm of circulation during the later course of infusion would be even more likely.

Lack of cross-tolerance to short-term linsidomine in forearm resistance vessels and dorsal hand veins in subjects with nitroglycerin tolerance

BACKGROUND

Therapy with nitroglycerin is widely used in the treatment of angina pectoris, but development of tolerance is a major problem. Nitrovasodilators other than nitroglycerin may be less prone to induce vascular tolerance. This investigation was designed to test whether the alternative nitric oxide donor linsidomine maintains its vasodilator effects in the presence of nitroglycerin tolerance.

METHODS

We tested the vascular effects of nitroglycerin and linsidomine (SIN-1) in forearm resistance arteries (venous occlusion plethysmography) and hand veins (venous compliance technique) using a randomized, double-blind placebo-controlled regimen in 33 healthy subjects (age range, 22 to 38 years; mean age, 26 years) before and after 7 days of assignment to either 1 week of nitroglycerin administration (0.83 mg/hr) for induction of tolerance or placebo administration.

RESULTS

Vascular responses of both vascular beds to nitroglycerin (in veins: mean difference, 42.3%; confidence interval [CI], 3% to 81.7%; p < 0.05; in arteries: mean difference, 65.0%; CI, 38.9% to 91.1%; p < 0.01) but not to linsidomine (in veins: mean difference, -13.8%; CI, -53.5 to 25.8%; not significant; in arteries: -19.7%; CI, -33.7% to -5.6%; not significant) were attenuated in the nitroglycerin patch group, whereas the placebo group showed no differences to either nitroglycerin (in arteries: mean difference, -7.5%; CI, -44.6% to 29.6%; in veins: -10.6%; CI, -58.2% to 36.9%) or linsidomine (in arteries: 4.5%; CI, -12.8% to 21.7%; in veins: -13.1%; CI, -4.5% to 29.8%).

CONCLUSION

These results suggest that short-term administration of sydnonimines can overcome the loss of vascular relaxation associated with long-term nitroglycerin therapy.

Clinical pharmacokinetics of molsidomine

Molsidomine is a prodrug for the formation of nitric oxide (NO). Its pharmacokinetics are characterised by rapid absorption and hydrolysis, taking a short time to achieve maximal systemic concentrations of both the parent compound and its active metabolite, SIN-1. The time to peak plasma drug concentration (tmax) is 1 to 2 hours. The bioavailability of the parent compound after oral administration in tablet form is 44 to 59%, but further metabolism to release NO and form polar metabolites is rapid; the half-life (t-1/2) of SIN-1 is 1 to 2 hours. Urinary excretion accounts for more than 90% of the part of the administered dose of molsidomine which is not excreted unchanged. Protein binding of the parent compound is very low (3 to 11%) and its volume of distribution (Vd) corresponds to the range of bodyweight. Single-dose studies (1, 2 and 4 mg) have revealed linear pharmacokinetics, and multiple dose studies in healthy individuals (2 mg 3 times daily for 7 days) and coronary artery disease (CAD) patients (4 mg 4 times daily for 4 weeks) do not show any accumulation of the drug. A study in young and elderly individuals indicated that the first-pass effect is decreased and t-1/2 prolonged with age, resulting in an increased area under the concentration-time curve (AUC) of molsidomine and SIN-1. In patients with liver disease and congestive heart failure similar changes were observed, but much less so in patients with CAD. Clearance was also impaired in patients with liver disease, but the pharmacokinetics of molsidomine were not markedly altered by impaired renal function. In general, due to a large therapeutic dose range, dosage adjustments are not required on the basis of clinical experience. In certain patients a lower starting dose may be recommended, such as in those with impaired liver or kidney function, in congestive heart failure or in the presence of concomitant treatment with other vasoactive compounds. A linear dose-effect relationship is observed with counterclockwise hysteresis, i.e. a greater effect associated with the decrease of plasma concentrations than during their increase, which may be at least partly due to the metabolic delay in the formation of NO from SIN-1. Accordingly, the duration of action of molsidomine is longer than would be expected on the basis of the elimination half-life. The pharmacokinetics of molsidomine support the recommended dosages for use in angina pectoris.

Haemodynamic evaluation of two regimens of molsidomine in patients with chronic congestive heart failure

We investigated the extent and duration of the haemodynamic effects of two regimens of molsidomine, i.e. two tablets of a standard regimen consisting of 4 mg given 6 h apart and one tablet of 16 mg in sustained-release form once daily in 13 patients with chronic congestive heart failure using a placebo-controlled, randomized, double-blind and crossover protocol over a period of 12 h. Both regimens significantly affected systolic, mean and diastolic pulmonary arterial pressure (reductions of up to 15%), right atrial pressure (reductions of up to 35%) and total pulmonary resistance (reductions of up to 18%). The lower dose achieved its maximum action after about 1 h and remained effective for 2 h, whereas the higher dose in sustained-release form showed maximal efficacy at 2 h and remained active even at 12 h. In contrast, only minor changes in arterial blood pressure, systemic vascular resistance and cardiac output were observed on both regimens, almost exclusively at 2 h. Heart rate was not affected by either of the regimens tested. Neither regimen led to any untoward adverse effects. Thus, molsidomine is a potent vasodilating agent which, apart from its effects on preload, also acts on pulmonary arterial and right atrial pressures, leaving systemic circulation largely unaffected on the regimens tested. Administered on its own, it is therefore suitable for treatment of congestive heart failure.

Pharmacokinetic profile of a novel slow release preparation of molsidomine

A novel slow release preparation containing 24 mg molsidomine has been investigated in 6 healthy subjects. Individual concentration/time-profiles after the tablet showed two separate concentration peaks at 2.2 h and 15.0 h. The relative bioavailability of the slow release preparation in comparison to an aqueous solution of molsidomine was 0.67. The in vivo dissolution profile revealed either a progressive decrease in dissolution velocity caused by altered physico-chemical conditions in the ileum and the colon or a progressive reduction in the absorption constant. In all subjects deconvolution revealed a punctual increase in absorption about 15 h post-dose, coinciding with the second peak of the concentration/time-profile. Therapeutic plasma levels of molsidomine (greater than 5 ng.ml-1) were not maintained over 24 h by this slow release formulation.

Comparison of haemodynamic effects of nifedipine and molsidomine in patients with coronary artery disease

The haemodynamic effects of oral nifedipine 20 mg and molsidomine 4 mg were compared in 24 patients with coronary artery disease. Molsidomine unlike nifedipine caused a significant fall in mean pulmonary artery pressure and left ventricular end-diastolic pressure. Both drugs caused a significant and comparable reduction in systolic and diastolic blood pressure. Although only nifedipine significantly reduced systemic vascular resistance the difference between the drugs was not significant. The heart rate was significantly increased by nifedipine but not by molsidomine. The ejection phase indices were all increased by molsidomine and the increment in the mean normalized systolic ejection rate was significantly greater than that due to nifedipine. The left ventricular end-systolic volume index decreased significantly after molsidomine but not nifedipine. Neither drug significantly affected left ventricular end diastolic volume index, stroke volume index, maximal rate of rise of left ventricular pressure or left ventricular stroke work index.

[Molsidomine in the treatment of coronary insufficiency]

Molsidomine, a predominantly venous vasodilator, has been coronary disease. The basic mechanism of its anti-anginal effect is a reduction in myocardial oxygen consumption due to a fall in left ventricular end-diastolic pressure resulting from the vasodilator action of the drug. To this may be added direct dilatation of the main coronary vessels on the surface of the heart, which may account for part in its therapeutic effects in unstable and vasospastic angina. The effectiveness of molsidomine has been evaluated by controlled drug versus placebo or drug versus reference anti-anginal drug studies in 3 types of angina pectoris: exertion, unstable and vasospastic. The usefulness of the drug has also been established in acute and chronic left ventricular failure of ischaemic origin. Because of its high bioavailability when administered orally, molsidomine shows little inter-individual variations in its pharmacodynamic effects. Unlike nitrates, it can be administered for long period without gradual loss of activity with time. Finally, on several experimental models molsidomine has been shown to exert an antiplatelet effect, but the therapeutic implications of this finding have yet to be evaluated.

Exercise tolerance in coronary patients: randomized trial of two-week treatment with molsidomine versus placebo

Using a randomized, double-blind, crossover protocol, we compared the effects of oral molsidomine (Corvaton, 6 mg/day) and placebo, administered alternately for two 14-day periods, on the exercise tolerance of 25 outpatients with coronary heart disease. Resting heart rate and oxygen consumption increased by 6.8% (p less than 0.005) and 12.6% (p less than 0.01), while peripheral systolic blood pressure was reduced by 5.1% (p less than 0.05). At submaximal workloads, systolic and diastolic blood pressures were reduced by 5.6% (p less than 0.001) and 6.1% (p less than 0.001), the pressure-rate product was reduced by 8.5% (p less than 0.05), and ST segment depression was reduced by 40.0% (p less than 0.005). At maximal exercise level, mechanical power increased by 32.4% (p less than 0.001) and oxygen consumption by 15.5% (p less than 0.005), while ST segment depression was reduced by 30.6% (p less than 0.001). No alteration was found in postexercise lung function tests. It is concluded that molsidomine reduces myocardial ischemia at both submaximal and maximal work levels and increases exercise tolerance significantly. These effects could be related to reduced myocardial oxygen requirements, reflected in a lower pressure-rate product at submaximal exercise and perhaps enhanced by a lower preload, which, moreover, would favor coronary flow in subendocardial layers. The drug has no adverse bronchopulmonary effects.

Mean time and first-pass metabolism

The theoretical principles are outlined for estimating the fraction of a drug undergoing first-pass metabolism using only the plasma levels found after a single oral dose. Data for 3 drugs are used to illustrate the method. It involves analysis of the parent drug and the metabolite formed during the first passage through the gut wall and liver and evaluation of their total mean times. The mean time characteristics of molsidomine, nortriptyline and propranolol are considered and they confirm the theoretically deduced dependency of the mean time of the parent drug and the metabolite. Whether the results are more precise than those obtained from comparison of areas after oral and intravenous administration is discussed. From the data presented it is clear that the mean time method depends on the scatter inherent in the data. In order to estimate the true first-pass effect, greater scatter requires an increased number of data pairs, i.e. subjects. If intravenous data are not available, however, the method described provides a rough but worthwhile estimate of the first pass effect.