Clinical pharmacology of selective alpha blockers. Hemodynamics and effects on lipid levels

High-density lipoprotein (HDL) as an indicator for alcohol use in a psychiatrically ill population

AIMS

To examine the cross sectional and longitudinal associations between the Alcohol Use Disorders Identification Test-Concise (AUDIT-C) and differences in high-density lipoprotein (HDL) in a psychiatrically ill population.

METHODS

Retrospective observational study using electronic health record data from a large healthcare system, of patients hospitalized for a mental health/substance use disorder (MH/SUD) from 1 July 2016 to 31 May 2023, who had a proximal AUDIT-C and HDL (N = 15 915) and the subset who had a repeat AUDIT-C and HDL 1 year later (N = 2915). Linear regression models examined the association between cross-sectional and longitudinal AUDIT-C scores and HDL, adjusting for demographic and clinical characteristics that affect HDL.

RESULTS

Compared with AUDIT-C score = 0, HDL was higher among patients with greater AUDIT-C severity (e.g. moderate AUDIT-C score = 8.70[7.65, 9.75] mg/dl; severe AUDIT-C score = 13.02 [12.13, 13.90] mg/dL[95% confidence interval (CI)] mg/dl). The associations between cross-sectional HDL and AUDIT-C scores were similar with and without adjusting for patient demographic and clinical characteristics. HDL levels increased for patients with mild alcohol use at baseline and moderate or severe alcohol use at follow-up (15.06[2.77, 27.69] and 19.58[2.77, 36.39] mg/dL[95%CI] increase for moderate and severe, respectively).

CONCLUSIONS

HDL levels correlate with AUDIT-C scores among patients with MH/SUD. Longitudinally, there were some (but not consistent) increases in HDL associated with increases in AUDIT-C. The increases were within range of typical year-to-year variation in HDL across the population independent of alcohol use, limiting the ability to use HDL as a longitudinal clinical indicator for alcohol use in routine care.

Drug effects on the CVS in conscious rats: separating cardiac output into heart rate and stroke volume using PKPD modelling

BACKGROUND AND PURPOSE

Previously, a systems pharmacology model was developed characterizing drug effects on the interrelationship between mean arterial pressure (MAP), cardiac output (CO) and total peripheral resistance (TPR). The present investigation aims to (i) extend the previously developed model by parsing CO into heart rate (HR) and stroke volume (SV) and (ii) evaluate if the mechanism of action (MoA) of new compounds can be elucidated using only HR and MAP measurements.

EXPERIMENTAL APPROACH

Cardiovascular effects of eight drugs with diverse MoAs (amiloride, amlodipine, atropine, enalapril, fasudil, hydrochlorothiazide, prazosin and propranolol) were characterized in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats following single administrations of a range of doses. Rats were instrumented with ascending aortic flow probes and aortic catheters/radiotransmitters for continuous recording of MAP, HR and CO throughout the experiments. Data were analysed in conjunction with independent information on the time course of the drug concentration following a mechanism-based pharmacokinetic-pharmacodynamic modelling approach.

KEY RESULTS

The extended model, which quantified changes in TPR, HR and SV with negative feedback through MAP, adequately described the cardiovascular effects of the drugs while accounting for circadian variations and handling effects.

CONCLUSIONS AND IMPLICATIONS

A systems pharmacology model characterizing the interrelationship between MAP, CO, HR, SV and TPR was obtained in hypertensive and normotensive rats. This extended model can quantify dynamic changes in the CVS and elucidate the MoA for novel compounds, with one site of action, using only HR and MAP measurements. Whether the model can be applied for compounds with a more complex MoA remains to be established.

PKPD modelling of the interrelationship between mean arterial BP, cardiac output and total peripheral resistance in conscious rats

BACKGROUND AND PURPOSE

The homeostatic control of arterial BP is well understood with changes in BP resulting from changes in cardiac output (CO) and/or total peripheral resistance (TPR). A mechanism-based and quantitative analysis of drug effects on this interrelationship could provide a basis for the prediction of drug effects on BP. Hence, we aimed to develop a mechanism-based pharmacokinetic-pharmacodynamic (PKPD) model in rats that could be used to characterize the effects of cardiovascular drugs with different mechanisms of action (MoA) on the interrelationship between BP, CO and TPR.

EXPERIMENTAL APPROACH

The cardiovascular effects of six drugs with diverse MoA, (amlodipine, fasudil, enalapril, propranolol, hydrochlorothiazide and prazosin) were characterized in spontaneously hypertensive rats. The rats were chronically instrumented with ascending aortic flow probes and/or aortic catheters/radiotransmitters for continuous recording of CO and/or BP. Data were analysed in conjunction with independent information on the time course of drug concentration using a mechanism-based PKPD modelling approach.

KEY RESULTS

By simultaneous analysis of the effects of six different compounds, the dynamics of the interrelationship between BP, CO and TPR were quantified. System-specific parameters could be distinguished from drug-specific parameters indicating that the model developed is drug-independent.

CONCLUSIONS AND IMPLICATIONS

A system-specific model characterizing the interrelationship between BP, CO and TPR was obtained, which can be used to quantify and predict the cardiovascular effects of a drug and to elucidate the MoA for novel compounds. Ultimately, the proposed PKPD model could be used to predict the effects of a particular drug on BP in humans based on preclinical data.

Impact of age, race, and obesity on hypertensive mechanisms and therapy

Despite the demonstrated efficacy of traditional antihypertensive therapy in reducing blood pressure, hypertension continues to be a major cause of cardiovascular disease morbidity and mortality. Stepped-care therapy is a nonphysiologic approach that, due to potential metabolic derangements and stimulation of undesirable reflex responses, may not substantially reduce the cardiovascular and renal complications associated with hypertension or improve long-term survival in many hypertensive patients. Because of fundamental hemodynamic differences related to the age, race, and weight of hypertensive patients, drug treatment often elicits varying responses. Certain classes of drugs are not only more effective but also more appropriate from a physiologic standpoint in specific types of patients. Therapy selection based in part on hemodynamic mechanisms and demographic patterns is a more rational approach to patient management and may contribute to a better overall outcome than has been observed with conventional treatment.

Inhibition of sympathetic nerve activity by acute administration of the tricyclic antidepressant desipramine

In rats anesthetized with pentobarbital/chloral hydrate, the i.v. injection of desipramine (0.3 mg/kg) caused a rapid fall in mean arterial blood pressure accompanied by a reduction in efferent renal nerve integrated activity. A similar reduction in electrical activity was seen in the preganglionic splanchnic nerve. Pretreatment of the rats with yohimbine (0.3 mg/kg) increased renal nerve activity by 20%, and the decrease in blood pressure and renal nerve activity elicited by a subsequent dose of desipramine was blocked. I.v. injection of prazosin (0.05 mg/kg) caused a reduction in systemic blood pressure. The hypotensive effect of a subsequent dose of desipramine was largely blocked, whereas the fall in renal nerve activity was attenuated, but still present. The data are consistent with an action of desipramine to reduce central sympathetic tone by increasing the release of endogenous noradrenaline which acts on alpha 2-adrenoceptors at CNS sites controlling sympathetic activity. An additional involvement of central alpha 1-adrenoceptors cannot be ruled out.

Alpha-1 blockers. A new generation of antihypertensive agents

Alpha-1 blockers have certain disadvantages over conventional and antihypertensive therapies in their haemodynamic profile and metabolic effects. This paper reviews the development of alpha-blockade, the therapeutic efficacy of prazosin, the prototype alpha-1 blocker, and the rationale for the once-daily antihypertensive compounds, terazosin and doxazosin. These drugs offer a useful alternative to first- or second-line therapy in suitable hypertensive patients, particularly with their potentially beneficial effects on serum lipids.

Clinical pharmacokinetics in heart failure. An updated review

Pharmacokinetics is the study of the effect that the body has on drug absorption, distribution, metabolism and excretion. The pharmacokinetics of a specific drug are assessed by the volume of distribution, bioavailability, clearance and elimination half-life. Elimination half-life is directly related to the volume of distribution and inversely related to clearance. Any 1 or more of these parameters may be altered by physiological changes such as ageing, or disease states such as congestive heart failure. Congestive heart failure is associated with hypoperfusion to various organs including the sites of drug clearance, i.e. the liver and kidneys. It also leads to organ congestion as seen in the liver and gut. The main changes in drug pharmacokinetics seen in congestive heart failure are a reduction in the volume of distribution and impairment of clearance. The change in elimination half-life consequently depends on whether both clearance and the apparent volume of distribution change, and the extent of that change. Pharmacokinetic changes are not always predictable in congestive heart failure, but it seems that the net effect of reduction in the volume of distribution and impairment of clearance is that plasma concentrations of drugs are usually higher in patients with congestive heart failure than in healthy subjects. The changes in pharmacokinetics assume importance only in the case of drugs with a narrow therapeutic ratio (e.g. digoxin) and some of the antiarrhythmics such as lignocaine (lidocaine), procainamide and disopyramide. This necessitates reduction in both the loading and maintenance doses. Prolongation of the elimination half-life leads to delay in reaching steady-state, and therefore dose increments must be made more gradually. Plasma concentration measurements of the drugs concerned are a good guide to therapy and help to avoid toxicity. Pharmacokinetic changes are of less importance in the case of drugs with immediate clinical response, e.g. diuretics and intravenous vasodilators such as nitrates and phosphodiesterase inhibitors. The dose in the latter group can be titrated to the desired effect. Not all adverse reactions to drugs that may occur in heart failure are the result of alterations in pharmacokinetics; rather, some may be due to important drug interactions. An interaction may occur directly e.g. reduction of renal clearance of digoxin by captopril and quinidine; or indirectly, e.g. through diuretic-induced hypokalaemia, which exacerbate arrhythmias associated with digoxin and antiarrhythmics such as quinidine and procainamide.

Physiologic and hemodynamic considerations in blood pressure control while maintaining organ perfusion

Essential hypertension remains a significant contributor to mortality, despite treatments effective in decreasing blood pressure. A major reason mortality remains high may be that the conventional stepped-care approach does not always reduce blood pressure in a physiologic manner, which may result in metabolic derangements and elicitation of undesirable reflex mechanisms. Use of the stepped-care approach does not take into account fundamental hemodynamic differences associated with a hypertensive patient's age, race and weight. A nonphysiologic approach in the use of antihypertensive agents may be associated with progression of left ventricular hypertrophy, metabolic derangements, arrhythmias, sudden death, and increased atherosclerotic and nephrosclerotic complications. Considerations of the alterations in cardiovascular structure that can occur in light of the activity of the renin-angiotensin system, the sympathetic nervous system and transcellular calcium flux are discussed as to how they affect long-term survival.