Clinical pharmacology and pharmacokinetics of clonidine

Combining O2 High Flow Nasal or Non-Invasive Ventilation with Cooperative Sedation to Avoid Intubation in Early Diffuse Severe Respiratory Distress Syndrome, Especially in Immunocompromised or COVID Patients?

This overview addresses the pathophysiology of the acute respiratory distress syndrome (ARDS; conventional vs. COVID), the use of oxygen high flow (HFN) vs. noninvasive ventilation (NIV; conventional vs. helmet) and a multi-modal approach to avoid endotracheal intubation ("intubation"): low normal temperature, cooperative sedation, normalized systemic and microcirculation, anti-inflammation, reduced lung water, upright position, lowered intra-abdominal pressure. Increased ventilatory muscle activity ("respiratory drive") is observed in early ARDS, at variance with ventilatory fatigue observed in decompensated chronic obstructive pulmonary disease (COPD). This increased drive leads to impending then overt ventilatory failure. Therefore, muscle relaxation presents little rationale and should be replaced by lowering the excessive respiratory drive, increased work of breathing, continued or increased labored breathing, self-induced lung injury (SILI), i.e. preserving spontaneous breathing. As CMV is a lifesaver in the setting of failure but does not heal the lung, side-effects of intubation, controlled mechanical ventilation (CMV), paralysis and deep sedation are to be avoided. Additionally, critical care resources shortage requires practice changes. Therefore, NIV should be routine when addressing immune-compromised patients. The SARS-CoV2 pandemics extended this approach to most patients, which are immune-compromised: elderly, obese, diabetic, etc. The early COVID is a pulmonary vascular endothelial inflammatory disease requiring lower positive-end-expiratory pressure than the typical pulmonary alveolar epithelial inflammatory diffuse ARDS. This leads one to reassess a) the technique of NIV b) the sedation regimen facilitating continuous and extended NIV to avoid intubation. Autonomic, circulatory, respiratory, ventilatory physiology is hierarchized under HFN/NIV and cooperative sedation (dexmedetomidine, clonidine). A prospective randomized pilot trial, then a larger trial are required to ascertain our working hypotheses.

Alpha-2-adrenergic agonists reduce resting energy expenditure in humans during external cooling

Intravenous alpha-2-adrenergic receptor agonists reduce energy expenditure and lower the temperature when shivering begins in humans, allowing a decrease in core body temperature. Because there are few data about similar effects from oral drugs, we tested whether single oral doses of the sedative dexmedetomidine (1 µg/kg sublingual or 4 µg/kg swallowed) or the muscle relaxant tizanidine (8 mg or 16 mg), combined with surface cooling, reduce energy expenditure and core body temperature in humans. A total of 26 healthy participants completed 41 one-day laboratory studies measuring core body temperature using an ingested telemetry capsule and measuring energy expenditure using indirect calorimetry for up to 6 hours after drug ingestion. Dexmedetomidine induced a median 13% - 19% peak reduction and tizanidine induced a median 15% - 22% peak reduction in energy expenditure relative to baseline. Core body temperature decreased a median of 0.5°C - 0.6°C and 0.5°C - 0.7°C respectively. Decreases in temperature occurred after peak reductions in energy expenditure. Energy expenditure increased with a decrease in core temperature in control participants but did not occur after 4 µg/kg dexmedetomidine or 16 mg tizanidine. Plasma levels of dexmedetomidine but not tizanidine were related to mean temperature change. Decreases in heart rate, blood pressure, respiratory rate, cardiac stroke volume index, and cardiac index were associated with the change in metabolic rate after higher drug doses. We conclude that both oral dexmedetomidine and oral tizanidine reduce energy expenditure and allow decrease in core temperature in humans.

Improved understanding of the respiratory drive pathophysiology could lead to earlier spontaneous breathing in severe acute respiratory distress syndrome

Optimisation of the respiratory drive, as early as possible in the setting of severe acute respiratory distress syndrome (ARDS) and not its suppression, could be a new paradigm in the management of severe forms of ARDS. Severe ARDS is characterised by tachypnoea and hyperpnoea, a consequence of a high respiratory drive. Some patients require endotracheal intubation, controlled mechanical ventilation (CMV) and paralysis to prevent overt ventilatory failure and self-inflicted lung injury. Nevertheless, intubation, CMV and paralysis do not address per se the high respiratory drive, they only suppress it. Optimisation of the respiratory drive could be obtained by a multimodal approach that targets attenuation of fever, agitation, systemic and peripheral acidosis, inflammation, extravascular lung water and changes in carbon dioxide levels. The paradigm we present, based on pathophysiological considerations, is that as soon as these factors have been controlled, spontaneous breathing could resume because hypoxaemia is the least important input to the respiratory drive. Hypoxaemia could be handled by combining positive end-expiratory pressure (PEEP) to prevent early expiratory closure and low pressure support to minimise the work of breathing (WOB). 'Cooperative' sedation with alpha-2 agonists, supplemented with neuroleptics if required, is the pharmacological adjunct, administered immediately after intubation as the first-line sedation regimen during the multimodal approach. Given relative contraindications (hypovolaemia, auriculoventricular block, sick sinus syndrome), alpha-2 agonists can help attenuate or moderate fever, increased oxygen consumption VO2, agitation, high cardiac output, inflammation and acidosis. They may also help to preserve microcirculation, cognition and respiratory rhythm generation, thus promoting spontaneous breathing. Returning the physiology of respiratory, ventilatory, circulatory and autonomic systems to normal will support the paradigm of optimised respiratory drive favouring early spontaneous ventilation, at variance with deep sedation, extended paralysis, CMV and use of the prone position as therapeutic strategies in severe ARDS.

GLOSSARY

Glossary and Abbreviations_SDC.

Is the Sympathetic System Detrimental in the Setting of Septic Shock, with Antihypertensive Agents as a Counterintuitive Approach? A Clinical Proposition

Mortality in the setting of septic shock varies between 20% and 100%. Refractory septic shock leads to early circulatory failure and carries the worst prognosis. The pathophysiology is poorly understood despite studies of the microcirculatory defects and the immuno-paralysis. The acute circulatory distress is treated with volume expansion, administration of vasopressors (usually noradrenaline: NA), and inotropes. Ventilation and anti-infectious strategy shall not be discussed here. When circulation is considered, the literature is segregated between interventions directed to the systemic circulation vs. interventions directed to the micro-circulation. Our thesis is that, after stabilization of the acute cardioventilatory distress, the prolonged sympathetic hyperactivity is detrimental in the setting of septic shock. Our hypothesis is that the sympathetic hyperactivity observed in septic shock being normalized towards baseline activity will improve the microcirculation by recoupling the capillaries and the systemic circulation. Therefore, counterintuitively, antihypertensive agents such as beta-blockers or alpha-2 adrenergic agonists (clonidine, dexmedetomidine) are useful. They would reduce the noradrenaline requirements. Adjuncts (vitamins, steroids, NO donors/inhibitors, etc.) proposed to normalize the sepsis-evoked vasodilation are not reviewed. This itemized approach (systemic vs. microcirculation) requires physiological and epidemiological studies to look for reduced mortality.

Clinical Practice: Should we Radically Alter our Sedation of Critical Care Patients, Especially Given the COVID-19 Pandemics?

The high number of patients infected with the SARS-CoV-2 virus requiring care for ARDS puts sedation in the critical care unit (CCU) to the edge. Depth of sedation has evolved over the last 40 years (no-sedation, deep sedation, daily emergence, minimal sedation, etc.). Most guidelines now recommend determining the depth of sedation and minimizing the use of benzodiazepines and opioids. The broader use of alpha-2 adrenergic agonists ('alpha-2 agonists') led to sedation regimens beginning at admission to the CCU that contrast with hypnotics+opioids ("conventional" sedation), with major consequences for cognition, ventilation and circulatory performance. The same doses of alpha-2 agonists used for 'cooperative' sedation (ataraxia, analgognosia) elicit no respiratory depression but modify the autonomic nervous system (cardiac parasympathetic activation, attenuation of excessive cardiac and vasomotor sympathetic activity). Alpha-2 agonists should be selected only in patients who benefit from their effects ('personalized' indications, as opposed to a 'one size fits all' approach). Then, titration to effect is required, especially in the setting of systemic hypotension and/or hypovolemia. Since no general guidelines exist for the use of alpha-2 agonists for CCU sedation, our clinical experience is summarized for the benefit of physicians in clinical situations in which a recommendation might never exist (refractory delirium tremens; unstable, hypovolemic, hypotensive patients, etc.). Because the physiology of alpha-2 receptors and the pharmacology of alpha-2 agonists lead to personalized indications, some details are offered. Since interactions between conventional sedatives and alpha-2 agonists have received little attention, these interactions are addressed. Within the existing guidelines for CCU sedation, this article could facilitate the use of alpha-2 agonists as effective and safe sedation while awaiting large, multicentre trials and more evidence-based medicine.

Pharmacologic Treatment of Opioid Use Disorder: a Review of Pharmacotherapy, Adjuncts, and Toxicity

Opioid use disorder continues to be a significant source of morbidity and mortality in the USA and the world. Pharmacologic treatment with methadone and buprenorphine has been shown to be effective at retaining people in treatment programs, decreasing illicit opioid use, decreasing rates of hepatitis B, and reducing all cause and overdose mortality. Unfortunately, barriers exist in accessing these lifesaving medications: users wishing to start buprenorphine therapy require a waivered provider to prescribe the medication, while some states have no methadone clinics. As such, users looking to wean themselves from opioids or treat their opioid dependence will turn to alternative agents. These agents include using prescription medications, like clonidine or gabapentin, off-label, or over the counter drugs, like loperamide, in supratherapeutic doses. This review provides information on the pharmacology and the toxic effects of pharmacologic agents that are used to treat opioid use disorder. The xenobiotics reviewed in depth include buprenorphine, clonidine, kratom, loperamide, and methadone, with additional information provided on lofexidine, akuamma seeds, kava, and gabapentin.

Hypertension in Pediatrics

Hypertension occurring during childhood and adolescence is being recognized more frequently today than in the past. Hypertension in the pediatric population differs from that in adults with respect to incidence, etiology, clinical presentation, and drug treatment. This article reviews both the pathophysiology and drug treatment of hypertension in pediatric patients. A plan for drug management is presented.

The effects of clonidine premedication and scalp infiltration of lidocaine on hemodynamic responses to laryngoscopy and skull pin head-holder insertion during skull base procedures

This study was designed to determine if oral clonidine or lidocaine, injected into the scalp before head-holder (H-H) insertion, would attenuate the hemodynamic effects associated with intubation and H-H placement. Thirty-four patients undergoing skull base procedures were randomized to four groups. Group 1 received clonidine 5 mcg/kg po before surgery with 10 to 15 ml of 1% lidocaine infiltrated at pin insertion sites; Group 2 received clonidine with saline infiltration; Group 3 received a placebo preoperatively and had lidocaine infiltrated at pin sites; and Group 4 received a placebo with saline infiltrated. All patients had a standard anesthetic titrated to a 10 to 14 Hz EEG endpoint during laryngoscopy and H-H placement. Mean arterial pressure (MAP) was similar between groups during intubation, but heart rate (HR) increased in patients who did not receive clonidine. H-H application increased HR and MAP in Group 4. HR also increased after H-H placement in patients who received oral clonidine, while patients receiving scalp lidocaine or both clonidine and scalp lidocaine had little change in either value. Clonidine attenuated HR increases after laryngoscopy but not after H-H placement. Lidocaine injected at the pin sites reduced HR, and MAP increased after H-H insertion. The combination of oral clonidine and scalp lidocaine blunted hemodynamic responses to both intubation and H-H placement.

Abrupt and gradual change from clonidine to beta blockers in hypertension

Elective change of antihypertensive therapy from clonidine to beta-blockers was studied in 18 hypertensive inpatients on diuretic treatment. An abrupt cessation of clonidine (0.3 mg t.i.d.) and start of treatment 12 hours later with atenolol (50 mg b.i.d.) resulted, within 24-36 hours, in severe rise of blood pressure and intolerable symptoms of clonidine withdrawal in all 4 patients studied. Plasma noradrenaline levels were elevated 18-24 hours after the last dose of clonidine. Halving the previous daily clonidine dose (0.15 mg t.i.d.) and discontinuing it after three days on concomitant treatment with atenolol or timolol in increasing doses proved successful and caused only few side-effects in 14 hypertensive inpatients.

The effectiveness of clonidine as an antihypertensive in a two-dose regimen

The therapeutic efficacy of clonidine as an antihypertensive in a b.i.d. schedule 150--300 micrograms daily was evaluated. The blood pressure reduction in patients with essential hypertension was satisfactory on this regimen and the steady-state plasma concentrations were within the BP-lowering concentration range at the end of a dosage interval.

Clonidine disposition in children; a population analysis

BACKGROUND

There are few data describing clonidine population pharmacokinetics in children (0-15 years) despite common use. Current pediatric data, described in terms of elimination half-life or C(max) and T(max), poorly explain variability in drug responses among individuals representative of those in whom the drug will be used clinically.

METHODS

Published data from four studies investigating clonidine PK after intravenous (i.v.), rectal and epidural administration (n = 42) were combined with an open-label study undertaken to examine the pharmacokinetics of i.v. clonidine 1-2 microg x kg(-1) bolus in children after cardiac surgery (n = 41). A population pharmacokinetic analysis of clonidine time-concentration profiles (380 observations) was undertaken using nonlinear mixed effects modeling. Estimates were standardized to a 70-kg adult using allometric size models.

RESULTS

Children had a mean age of 4 (sd 3.6 years, range 1 week-14 years) years and weight 17.8 (sd 12.6, range 2.8-60) kg. A two compartment disposition model with first-order elimination was superior to a one compartment model. Population parameter estimates (between subject variability) were clearance (CL) 14.6 (CV 35.1%) l x h(-1 )70 kg(-1), central volume of distribution (V1) 62.5 (71.1%) l 70 kg(-1), intercompartment clearance (Q) 157 (77.3%) l x h(-1) 70 kg(-1) and peripheral volume of distribution (V2) 119 (22.9%) l 70 kg(-1). Clearance at birth was 3.8 l x h(-1) 70 kg(-1) and matured with a half-time of 25.7 weeks to reach 82% adult rate by 1 year of age. The volumes of distribution, but not clearance, were increased after cardiac surgery (V1 123%, V2 126%). There was a lag time of 2.3 (CV 73.2%) min before absorption began in the rectum. The absorption half-life from the epidural space was slower than that from the rectum (0.98 CV 24.5% h vs 0.26 CV 32.3% h). The relative bioavailability of epidural and rectal clonidine was unity (F = 1).

CONCLUSIONS

Clearance in neonates is approximately one-third that described in adults, consistent with immature elimination pathways. Maintenance dosing, which is a function of clearance, should be reduced in neonates and infants when using a target concentration approach.

Does preoperative oral clonidine inhibit salivary secretion during general anesthesia?

Clonidine is known to inhibit salivary secretions and cause dryness of the mouth. We evaluated the effect of preoperative oral clonidine on salivary secretions before and during general anesthesia. Twenty-eight adult patients, equally divided into four groups, received the following premedication 2 hr prior to induction of anesthesia. Group 1 patients received oral ranitidine 5 mg.kg(-1) alone. Groups 2 and 3 patients received oral clonidine 1 microg.kg(-1) and 3 microg.kg(-1) respectively with oral ranitidine 5 mg.kg(-1). Group 4 patients received no premedication and served as control. The volume of salivary secretions was determined by calculating the change in weight of four cotton wool cylinders placed in the oral space 10 min before and 30, 60 and 120 min after induction of anesthesia. Salivary volume was significantly less in the clonidine treatment groups before induction of anesthesia. After induction of anesthesia, there were no significant differences in salivary secretions among the four groups. No severe hypotension or bradycardia was seen in any patient of four groups. Preoperative oral ranitidine 5 mg.kg(-1) had no effect on salivary secretion. In conclusion, clonidine did not decrease salivary secretions further over the already decreased level during general anesthesia.

Central and peripheral evaluation of rupatadine, a new antihistamine/platelet-activating factor antagonist, at different doses in healthy volunteers

AIMS

To assess peripheral anti-H1 and central nervous system (CNS) activity of single increasing doses of rupatidine fumarate (RU), a new antihistamine/platelet-activating factor antagonist compound, in comparison with hydroxyzine and placebo.

METHODS

Eighteen healthy young subjects of both sexes took part in a crossover, randomised, double-blind, placebo-controlled study. Treatments tested were: RU 10, 20, 40 and 80 mg and hydroxyzine 25 mg, as a positive standard. Before and several times after drug intake, peripheral anti-H1 activity was appraised by the skin reactivity to intradermal injection of histamine. CNS effects were also obtained by objective tests of psychomotor performance and subjective mood scales.

RESULTS

All active treatments showed a significant reduction of the wheal and flare reaction in relation to placebo, RU displaying a potent dose-dependent inhibition pattern. The global nonparametric Friedman test to changes from placebo in 15 objective variables from psychomotor performance showed a significant impairment of similar magnitude after hydroxyzine 25 mg (p = 0.01) and RU 80 mg (p = 0.02), but this was slower in development and recovery after the latter. After RU 40 mg, a smaller impairment was also obtained (p = 0.04). Activity (p = 0.01) and drowsiness (p = 0.02) scales showed significant changes, the subjects feeling less active and more drowsy after all active treatments.

CONCLUSION

RU presents a potent dose-dependent peripheral anti-H1 activity, displaying psychomotor impairment activity only at the highest dose (80 mg), while therapeutically relevant lower doses (10 and 20 mg) were similar to placebo.

Clonidine toxicity revisited

The incidence of clonidine overdose is increasing, yet there is a paucity of new information regarding treatment options for clonidine toxicity. Reported treatment approaches vary widely, demonstrating the lack of science on which current treatment is based. Available research needs to be reassessed. Neurotransmitters, receptors, endogenous opioids, and baseline sympathetic tone determine the clinical response to clonidine as well as the potential response to drug therapy following clonidine overdose. This article reviews aspects of clonidine toxicity that need to be further investigated. Multicenter research trials will be required to evaluate new treatment options.

Imidazoline antihypertensive drugs: a critical review on their mechanism of action

It was long thought that the prototypical centrally acting antihypertensive drug clonidine lowers sympathetic tone by activating alpha(2)-adrenoceptors in the brain stem. Supported by the development of two new centrally acting drugs, rilmenidine and moxonidine, the imidazoline hypothesis evolved recently. It assumes the existence of a new group of receptors, the imidazoline receptors, and attributes the sympathoinhibition to activation of I(1) imidazoline receptors in the medulla oblongata. This review analyzes the mechanism of action of clonidine-like drugs, with special attention given to the imidazoline hypothesis. Two conclusions are drawn. The first is that the arguments against the imidazoline hypothesis outweigh the observations that support it and that the sympathoinhibitory effects of clonidine-like drugs are best explained by activation of alpha(2)-adrenoceptors. The second conclusion is that this class of drugs lowers sympathetic tone not only by a primary action in cardiovascular regulatory centres in the medulla oblongata. Peripheral presynaptic inhibition of transmitter release from postganglionic sympathetic neurons contributes to the overall sympathoinhibition.

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.

Clonidine poisoning in Jefferson County, Alabama

STUDY OBJECTIVE

To describe the epidemiology of clonidine-related hospitalization in children, to evaluate the efficacy of naloxone, and to review the clinical effects of clonidine toxicity.

METHODS

This was a retrospective analysis in an urban teaching pediatric emergency department with an annual census of 55,000 involving 80 children younger than 6 years who were admitted for clonidine ingestion during a 6-year period.

RESULTS

Clonidine commonly belonged to the patient's grand-mother (54%). Black children were twice as likely to be hospitalized for clonidine ingestion than white children compared with children hospitalized for any injury. Average time to onset of symptoms was 35 minutes. Decreased level of consciousness was the most common presenting symptom (96%). Mean ED vital signs were systolic blood pressure, 102 mm Hg; pulse, 98; respirations, 25 (six patients intubated); and temperature, 36.6 degrees C, Naloxone was administered to 49% of patients, 84% of whom demonstrated no response.

CONCLUSION

Clonidine ingestion is endemic in our area. Serious clinical effects mandate that all children with clonidine ingestion be triaged to a health care facility. Naloxone as an antidote for clonidine remains controversial.

Low-dose intravenous clonidine in children: plasma concentrations and haemodynamic response

The beneficial perioperative effects of the alpha-2 agonist clonidine have recently been verified in paediatric patients, and the pharmacokinetics have been found to be similar to what has been reported in adults. In a previous study we found that 2.5 micrograms/kg of clonidine causes a significant reduction in blood pressure. The aim of the present study was to evaluate if even lower doses of clonidine are associated with dose dependent or plasma-dependent haemodynamic changes. In a prospective, single, blind, controlled clinical trial, 24 paediatric patients (age range: 13-78 months) were randomised into three groups: control, intravenous clonidine 0.625 microgram/kg and intravenous clonidine 1.25 micrograms/kg respectively. Non-invasive blood pressure and heart rate were recorded at 3-min intervals for 30 min. Plasma concentrations of clonidine were analysed at 15 and 30 min post-injection. A decrease in MABP compared to baseline values was observed in all groups. A significantly greater reduction in blood pressure was seen in all groups receiving clonidine compared to control. In conclusion, low doses of clonidine (0.625 and 1.25 micrograms/kg) were found capable of causing a blood pressure reduction compared to control. We could not establish a plasma concentration dependent blood pressure effect. The observed blood pressure reductions caused by clonidine were of moderate magnitude. No effect on heart rate was observed, a finding which most likely is explained by the inclusion of atropine in the premedication.

Postoperative analgesia using a low-dose, oral-transdermal clonidine combination: lack of clinical efficacy

STUDY OBJECTIVE

To determine if a lower than previously reported oral-transdermal clonidine regimen could reduce postoperative morphine requirements without producing systemic side effects.

DESIGN

Double-blind, randomized, placebo-controlled study.

SETTING

University-affiliated hospital.

PATIENTS

29 healthy, ASA physical status I and II females undergoing elective abdominal hysterectomy.

INTERVENTIONS

Patients received preoperative oral clonidine 4 to 5 mu/kg and a 7 cm2 transdermal clonidine patch (0.2 mg/24 hours) or a placebo tablet and patch.

MEASUREMENTS AND MAIN RESULTS

Postoperative patient-controlled analgesia pumps provided morphine during the 48-hour study period. Morphine use, hemodynamic changes, and nonhemodynamic side effects were recorded. Additionally, visual analog pain scales (VAPS) and plasma concentrations of morphine and clonidine were measured. We found that low-dose clonidine had no potentiating effect on morphine analgesia. Postoperative morphine use, VAPS, and morphine plasma levels were similar between the control and clonidine-treated groups. Nevertheless, patients in the clonidine group experienced a significantly greater incidence of intraoperative and postoperative hypotension and bradycardia than did the control group. No differences were noted in the incidence of nonhemodynamic side effects.

CONCLUSIONS

The low-dose oral-transdermal clonidine regimen evaluated failed to reduce postoperative morphine requirements, although patients who received clonidine were still at risk for developing hypotension.

Concentration-related pharmacodynamic effects of thioridazine and its metabolites in humans

OBJECTIVE

To measure cardiac and other effects of thioridazine and relate these to the plasma concentration of the parent drug and its principal metabolites.

METHODS

A double-blind, randomized-order crossover study involving nine healthy male subjects compared the effects of single doses of thioridazine (10 mg and 50 mg) with placebo. Plasma concentrations of thioridazine and its ring sulfoxide, side-chain sulfoxide, and side-chain sulfone metabolites were measured, together with effects on the ECG, blood pressure, salivary flow, and a batch of psychomotor tests for 72 hours after administration.

RESULTS

Thioridazine, 50 mg, reduced standing systolic blood pressure (mean peak changes from baseline [95% CI] -32 mm Hg [-55, 10 mm Hg]; p < 0.01 versus placebo) and diastolic blood pressure (-14 mm Hg [-26, -2 mm Hg]; p < 0.05), increased standing heart rate (7 beats/min [-1, 16 beats/min]; p < 0.05), impaired psychomotor function, and prolonged the JT (20 ms1/2 [7, 34 ms1/2]; p < 0.05), QTa (22 ms1/2 [8, 36 ms1/2]; p < 0.05), and QTc (22 ms1/2 [11, 33 ms1/2]; p < 0.01) intervals, but had no effect on QT dispersion (-12 ms1/2 [-31, 6 ms1/2]). Thioridazine, 1.0 mg, also significantly increased QTc, but the effect was less marked (9 ms1/2 [-1, 19 ms1/2]; p < 0.05). Plasma thioridazine and metabolite concentrations did not correlate significantly with these effects. Maximum effects on QTc occurred after peak concentrations of thioridazine but before peak concentrations of the ring sulfoxide and side-chain sulfone metabolites.

CONCLUSIONS

These data suggest that thioridazine has dose-related effects on ventricular repolarization and that the parent drug causes an important proportion of these effects, although its metabolites may also contribute.

Stereoselective cardiotoxic effects of terodiline

OBJECTIVE

To study the cardiovascular and electrocardiographic (ECG) effects of the R(+)- and S(-)- enantiomers of terodiline. The racemic drug was previously used to treat detrusor instability but was withdrawn after it caused serious ventricular arrhythmias associated with prolongation of the QT interval.

METHODS

A double-blind, placebo-controlled, randomized crossover study was performed that involved nine healthy volunteers who were given single oral doses of racemic terodiline hydrochloride (200 mg), R(+)-terodiline hydrochloride (100 mg), S(-)-terodiline tartrate (100 mg), or placebo. Plasma concentrations of each enantiomer and cardiovascular and ECG effects, including QT intervals and QT dispersion, were measured over 14 days after each treatment.

RESULTS

Both racemic and R(+)-terodiline significantly increased QT interval, corrected QT interval (QTc), and QRS duration (all p < 0.05), without affecting QT dispersion. S(-)-Terodiline tartrate (100 mg) did not affect QTc. Peak effects occurred 8 hours after dosing when increases in QTc from baseline (95% confidence intervals) were -3 (-20, 13) for placebo, 23 (8, 37) for racemic terodiline, 19 (6, 33) for R(+)-terodiline, and 0 (-10, 9) ms1/2 for S(-)-terodiline. Although differences were observed between the pharmacokinetics of the two enantiomers, these were not sufficient to account for the differences in ECG effects, and elimination half-lives were similar. Elimination of terodiline enantiomers was not significantly delayed in two genotypic poor metabolizers of debrisoquin (CYP2D6).

CONCLUSIONS

QT prolongation associated with racemic terodiline is caused exclusively by the R(+)-enantiomer, which therefore appears to be responsible for the ventricular arrhythmias caused by the drug.

Oral clonidine premedication enhances the quality of postoperative analgesia by intrathecal morphine

Since clonidine potentiates the analgesia by morphine, the current study was performed to investigate whether oral clonidine premedication would enhance the postoperative analgesia by intrathecal morphine. Twenty-six patients, aged 37-60 yr, schedule for abdominal total hysterectomy under spinal anesthesia, were studied. Patients were randomly allocated to one of two groups; the clonidine group (n = 13) received oral clonidine approximately 5 micrograms/kg, and the control group (n = 13) received no clonidine. All patients received hyperbaric tetracaine 12 mg dissolved in 10% dextrose and morphine 0.2 mg for spinal anesthesia. We measured duration of analgesia (time to the first request for supplemental analgesics) and motor block. We also recorded the total number of injections of supplemental analgesics, and intensity of postoperative visual analog pain scores, nausea, and pruritus for 48 h after intrathecal administration. Duration of analgesia in the clonidine group was longer than the control group (2017 +/- 263 vs 1190 +/- 199 min, mean +/- SEM; P < 0.05). Although there was no difference in the total number of injections of supplemental analgesics (1.1 +/- 0.4 and 2.2 +/- 0.3 in the clonidine and control groups, respectively), the number of patients not requiring supplemental analgesics during the entire study period was larger in the clonidine group than the control group (six patients versus one patient; P < 0.05). There were no differences at any observation point between groups in visual analog pain scores, or the incidence of nausea and pruritus. Oral clonidine preanesthetic medication enhances the postoperative analgesia of intrathecal morphine plus tetracaine without increasing the intensity of side effects from morphine.

Preoperative alpha2-adrenergic receptor agonists prevent the deterioration of renal function after cardiac surgery: results of a randomized, controlled trial

OBJECTIVE

To evaluate the influence of the alpha2-adrenergic receptor agonist clonidine on creatinine clearance as a measure of renal function.

DESIGN

Prospective, double-blind, randomized, placebo-controlled clinical trial.

SETTING

University hospital.

PATIENTS

Patients undergoing coronary artery bypass graft surgery (n = 48) with normal risk.

INTERVENTIONS

Administration of clonidine (4 micrograms/kg iv)) or placebo 1 hr before induction of anesthesia.

MEASUREMENTS AND MAIN RESULTS

Induction and maintenance of anesthesia (etomidate, midazolam, and fentanyl) and cardiopulmonary bypass technique (nonpulsatile, normothermic, intermittent cold blood cardioplegia) were standardized in all patients. The night before surgery and the first and third night after surgery, creatinine clearance was calculated from a 12-hr urine collection period. Venous blood samples for determination of plasma antidiuretic hormone (ADH) concentrations were taken the evening before surgery, immediately before induction of anesthesia and the evening after surgery (n = 16). Arterial catecholamine plasma concentrations were determined (high-performance liquid chromatography) before induction, 15 mins after induction of anesthesia, immediately after sternotomy, before initiation of cardiopulmonary bypass, as well as 5, 15, and 30 mins after initiation of cardiopulmonary bypass (n = 16). The total amount of anesthetics, infusions, transfusions, diuresis, and blood loss was not different between the groups. Creatinine clearance decreased over the first postoperative night from 98 +/- 18 (preoperatively) to 68 +/- 19 mL/min (p < .05) in placebo-treated patients. Creatinine clearance remained unchanged in clonidine-treated patients (90 +/- 19 [preoperatively] to 92 +/- 17 mL/min). There was a significant difference in creatinine clearance between the groups during the first postoperative night (p < .05; Mann-Whitney U test). In the third postoperative night, mean creatinine clearance of both groups was not different (75 +/- 31 vs. 86 +/- 28 mL/min). ADH concentrations were not different between the groups at any time, while plasma catecholamine concentrations were always significantly lower in clonidine-treated patients.

CONCLUSIONS

Preoperative treatment with clonidine (4 microgram/kilogram) prevents the deterioration of renal function after cardiac surgery. This effect might be due to clonidine-induced reduction in the sympathetic nervous system response to coronary artery bypass graft surgery.

Oral clonidine reduces thiamylal requirement for induction of anesthesia in adult patients

Although preanesthetic clonidine, an α-2 agonist, is known to reduce anesthetic requirements, the effect of preanesthetic oral clonidine medication per se on the requirement of thiamylal in adult humans has not yet been examined. One hundred and sixty-one adult patients (14-78 years of age) were randomly assigned to groups that received oral clonidine (5μg·kg(-1) (n=51), 2.5μg·kg(-1) (n=55), or none (n=55)) in addition to 20mg oral famotidine 90min before anesthesia induction. Thiamylal was injected at the rate of 25mg every 15 s until the eyelash reflex disappeared, while blood pressure and heart rate were recorded at 30-s intervals from the start of the induction. Thiamylal requirements were significantly less in both clonidine groups (2.95±0.09 and 3.14±0.10 mg·kg(-1) (mean±SE) for patients receiving 5μg·kg(-1) and 2.5μg·kg(-1) clonidine, respectively) than in the control group (3.81±0.11 mg·kg(-1),P<0.05); however, no difference was found between the two clonidine groups. Although mean blood pressure and heart rate during the study period were significantly lower in both clonidine groups than in the control group, no profound hypotension or marked bradycardia were noted in the clonidine groups.

Contrasting effects of clonidine and diazepam on tests of working memory and planning

The alpha 2 adrenoceptor has recently been implicated in working memory (WM), a function dependent on the integrity of the prefrontal cortex. Using a double-blind, placebo-controlled design, the present investigation examines the effects of two doses (1.5 micrograms/kg and 2.5 micrograms/kg) of the mixed alpha 1/alpha 2 adrenoceptor agonist clonidine (CLO) on performance of various computerised tests of WM and planning in healthy, young volunteers. These are compared to the effects produced by two doses (5 mg and 10 mg) of diazepam (DZP) on largely the same set of neuropsychological tests in a comparable set of subjects. Administration of CLO resulted in impulsivity of responding in a planning task, as well as differential dose-dependent effects on two analogous tests of spatial and visual WM. The nature of these effects were suggestive of mnemonic, rather than executive, dysfunction. Conversely, DZP produced specific deficits on tests of spatial WM and planning very similar to those seen following lesions to the frontal lobes. Therefore, these two sedative drugs produce doubly dissociable, dose-dependent effects on different aspects of cognitive function.

Clinical pharmacology of drugs acting on imidazoline and adrenergic receptors. Studies with clonidine, moxonidine, rilmenidine, and atenolol

Centrally acting antihypertensive drugs are recognized to be safe and effective treatment for high blood pressure. Centrally mediated side effects, such as sedation, are commonly dose- and treatment-limiting events. Imidazoline-preferring receptors, while functionally similar to alpha 2 adrenoceptors, are distinguishable not only on the basis of in vitro radioligand binding but also in vivo in terms of side effects. Drugs with an imidazoline structure lower blood pressure but are less likely to impair psychomotor function. A placebo-controlled study compared moxonidine 0.1 mg with clonidine 0.1 mg orally in nine normal subjects. Both active drugs lowered blood pressure compared to placebo (clonidine more than moxonidine). However, psychomotor function and self-scored sedation and dry mouth were significantly affected only by clonidine. In a long-term (4 weeks) double-blind cross-over study in essential hypertension, rilmenidine was well tolerated and had similar effects to those of atenolol on erect and supine blood pressure. Rilmenidine had no effect on a wide range of autonomic and psychomotor tests or on responses to mental or physical stress. Atenolol, by contrast, had the predicted effects of a beta adrenoceptor antagonist on heart rate during exercise and the Valsalva maneuver. Imidazoline-preferring drugs offer a new and realistic approach to antihypertensive therapy with blood pressure reduction not limited by marked sedation within the therapeutic dose range.

Antagonism of the effects of clonidine by the alpha 2-adrenoceptor antagonist, fluparoxan

1. The effects of fluparoxan, an alpha 2-adrenoceptor antagonist, on the pharmacodynamic changes induced by clonidine were investigated in this placebo-controlled, double-blind, two-period, cross-over study in 16 healthy male volunteers (aged 19 to 44 years). 2. Subjects received either fluparoxan or placebo, twice-daily for 5 1/2 days (11 doses). One hour after the first and last dose of each treatment period, clonidine (200 micrograms) was infused intravenously over 5 min. 3. Indices of clonidine-mediated pharmacodynamic responses (growth hormone secretion, bradycardia, hypotension, xerostomia and sedation) were taken before and after clonidine infusion. Growth hormone secretion was assessed by quantifying serum growth hormone concentrations; sedation was assessed by both visual analogue scales (VAS) and by a visual psychomotor response meter, measuring critical flicker fusion (CFF). 4. The majority of subjects reported minor adverse events such as lethargy, headache and dry mouth following clonidine infusion. All adverse events were likely to be related to clonidine, as they occurred consistently between treatment groups. Fluparoxan has, however, in previous studies been reported to cause headache and light-headedness. 5. Prior to the clonidine infusion, fluparoxan caused small but statistically significant increases in systolic blood pressure (4 mm Hg) and salivary flow (approximately 30%) after both single and repeated doses. A small increase in heart rate (2 beats min-1) was seen after a single dose which was also statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the cholinomimetic SDZ ENS-163 on scopolamine-induced cognitive impairment in humans

Scopolamine-induced cognitive impairment was used in healthy men to evaluate the central nervous system activity of the new cholinomimetic SDZ ENS-163. Eighteen subjects were treated in a crossover design with oral placebo/intravenous saline, 50 mg of oral SDZ ENS-163/intravenous saline, oral placebo/0.4 mg of intravenous scopolamine, and 50 mg of oral SDZ ENS-163/0.4 mg of intravenous scopolamine. The administration of placebo with scopolamine caused significant cognitive impairment, as assessed by the Computerized Neuropsychological Test Battery (CNTB), and also decreased salivation and heart rate. In contrast, SDZ ENS-163 with saline had no effect on CNTB scores, increased salivation, and increased heart rate. Despite the observed cholinomimetic effects of SDZ ENS-163 when administered with saline, the changes in CNTB scores, heart rate, and salivation were indistinguishable between placebo/scopolamine and SDZ ENS-163/scopolamine. Thus, 50 mg of oral SDZ ENS-163 has cholinomimetic activity in normal men, but this dose is insufficient to reverse the muscarinic effects of 0.4 mg of intravenous scopolamine.

Comparative pharmacokinetics of oral versus sublingual clonidine

STUDY OBJECTIVE

To compare the pharmacokinetic and pharmacodynamic profile of orally versus sublingually administered clonidine.

DESIGN

Randomized, crossover, nonblinded, open-label study.

SETTING

University tertiary-care center.

PATIENTS

10 healthy male and female volunteers aged 20 to 42 years.

INTERVENTIONS

A heparinized catheter was placed intravenously for blood-sampling purposes. An automatic sphygmomanometer was placed on the volunteers' left upper arm to obtain systolic and diastolic blood pressure, and a pulse oximeter was placed on the right index finger to measure heart rate (HR).

MEASUREMENTS AND MAIN RESULTS

Serial blood samples were collected throughout the 24-hour study period to determine clonidine concentrations. The effect of clonidine on blood pressure (BP) and HR also was measured. The half-life, area under the curve, maximum concentration, and time to reach maximum concentration were similar for both the sublingual and oral routes. BP and HR changes were similar for both sublingual and oral clonidine.

CONCLUSION

Both routes of administration resulted in similar pharmacokinetic and pharmacodynamic profiles. Attempts to shorten clonidine's latency with sublingual administration were unsuccessful. Our study shows that a single dose of clonidine 0.3 mg has the same pharmacokinetic and dynamic profile when administered orally or sublingually. Therefore, the sublingual route can be predictably used in fasting patients, those having difficulty swallowing, or those who are unable to absorb drugs through the gastrointestinal tract; the sublingual dose is the same as the oral dose.

Advances in pharmacotherapy: treatment of hypertensive crisis

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

Pattern of inhibition of parasympathetic activity in response to incremental bolus doses of atropine in carotid sinus hypersensitivity

Patients with established reproducible cardioinhibitory carotid sinus hypersensitivity were studied to define the dose of atropine required to abolish the heart rate slowing in response to carotid sinus massage, the heart rate response to the Valsalva manoeuvre and salivary gland flow. Bolus doses of intravenous atropine were given to a cumulative dose of 700 mcg. Cardioinhibition was abolished in all patients with a total dose of 700 mcg. The heart rate ratio during the Valsalva manoeuvre did not vary significantly. The decline in salivary gland flow was evident earliest, at a dose of 75 mcg. In clinical studies, 700 mcg of atropine will abolish the diagnostic cardioinhibitory response to carotid sinus message in patients with the syndrome. This may not prevent syncope, as could occur in the key frequent vasodepressor form of carotid sinus hypersensitivity syndrome.

Clonidine-induced changes in the spectral distribution of heart rate variability correlate with performance on a test of sustained attention

Conventional measures of cardiovascular activity correlate poorly with psychological variables and therefore provide imperfect physiological indices of arousal. We have investigated the effects of clonidine upon the spectral distribution of heart rate variability and upon performance on a test of sustained attention. Our findings suggest that activity of the central noradrenergic system influences the distribution of heart rate variability in the ~ 0.1 Hz range. Furthermore, the finding of a strong correlation between the effects of clonidine upon each of these variables supports the use of spectral analysis of heart rate variability in the study of arousal.

Long-term (5 year) experience with transdermal clonidine in the treatment of mild to moderate hypertension

The long-term safety and efficacy of transdermal clonidine (C-TTS) was evaluated in 102 patients with mild to moderate hypertension over a mean treatment period of 4.9 +/- 1.4 years. C-TTS size 1 was used by 29.4%, C-TTS size 2 by 35.3%; in 35.3% of the patients a diuretic agent was given in addition. The baseline blood pressure of 168/100 mmHg was reduced to 150/85 mmHg at the end of titration and remained stable during long-term treatment. After 5 years seated blood pressure was 147/83 mmHg. Systemic side-effects, e.g. 4.9% dry mouth, were reported mainly during the first month. Transient local side-effects occurred mainly between weeks 4-26, thereafter the incidence clearly diminished and did not cause any withdrawal due to skin reactions from 1 year up to 6.5 years. Overall the long-term transdermal clonidine treatment was highly accepted by the patients, was effective and was well tolerated.

Effects of clonidine on the calcium content and morphology of rat salivary glands

These effects were examined with and without pretreatment of animals with reserpine and the adrenergic antagonists prazosin (alpha 1), yohimbine (alpha 2) and propranolol (beta). The effects of clonidine on glandular concentrations of norepinephrine and dopamine also were examined. These effects were compared with those of xylazine, a presynaptic alpha 2-adrenergic agonist. A single, high dose of clonidine followed by an overnight fast caused marked increases in calcium content and acinar secretory granules in the submandibular and sublingual glands, similar to those caused by reserpine. However, the calcium content of the parotid gland was not altered by clonidine, although there seemed to be a modest increase in acinar secretory granules. The clonidine-induced increase in submandibular calcium content could not be attributed to any adrenergic receptor activity since it was not blocked by either alpha- or beta-adrenergic antagonists. Unlike reserpine, clonidine did not affect catecholamine concentrations in the parotid and submandibular glands. Pretreatment with reserpine did not significantly alter the clonidine-induced increase in submandibular calcium content. It is likely that the greater accumulation of acinar secretory granules is related to the increased calcium stores of the glands in clonidine- and/or reserpine-treated rats. The large differences in calcium content among the three glands might be attributable, in part, to differences in the calcium-binding capacity of their secretory granules. Possible mechanisms for the clonidine effects on salivary-gland calcium include disturbances in membrane-associated pools or gating mechanisms for calcium, which need further study.

Up-regulation of beta-adrenoceptors on circulating mononuclear cells after reduction of central sympathetic outflow by clonidine in normal subjects

Short term regulation of beta-adrenoceptors in peripheral blood mononuclear cells after sympathetic activation has been previously documented in normal individuals but changes after a central reduction in sympathetic activity are not known. We have studied beta-adrenoceptor number and affinity on peripheral blood mononuclear cells in normal subjects, before and after intravenous clonidine, an alpha 2-adrenoceptor agonist which lowers blood pressure predominantly by reducing central nervous system sympathetic outflow. After clonidine there was a decrease in plasma levels of noradrenaline and adrenaline, and an increase in growth hormone. There was up-regulation of beta-adrenergic receptors on peripheral blood mononuclear cells 30 and 60 min after clonidine which was related to the fall in blood pressure, noradrenaline and adrenaline levels and to the increase in growth hormone levels. The affinity of the receptors was decreased. Return to baseline values was observed after 2 h. Intracellular production of cAMP after isoproterenol stimulation demonstrated that the up-regulation was not functional. Our studies indicate short term up-regulation of beta-adrenoceptors in peripheral blood mononuclear cells after clonidine. These observations after a reduction in sympathetic activity may be of importance if they mirror the pattern of redistribution of adrenoceptors, which are present in a wide range of tissues.

Cerebrospinal fluid kinetics of epidural clonidine in man

Ten patients with deafferentation pain after spinal cord injury were given 150 micrograms clonidine epidurally. CSF and plasma samples were collected over the following 24 h, and drug concentrations were measured by radio-immunoassay. The results of only 6 patients are included in the pharmacokinetic analysis because the catheters were not in the epidural space in the remaining 4 patients. These analyses revealed a mean maximum CSF concentration of 228 ng/ml whereas the mean plasma concentration at all time points was less than 0.7 ng/ml. The elimination half-life of epidural clonidine was 66 +/- 2 min, while the absorption half-life was 31 +/- 7 min, Tmax was 60 +/- 7 min and Cmax was 228 +/- 56 ng/ml. The ratio of the area under the curve (AUC) for CSF and plasma was 52. One patient's catheter was intrathecal and 3 were not in the epidural space. The measured plasma concentrations were similar after all injections. As 4 of 6 patients with epidural catheters obtained pain relief and all 3 patients with spasms obtained relief from epidural clonidine, these data suggest that clonidine has a place in the treatment of patients with spinal cord injury.

The effect of pirenzepine on gastric emptying and salivary flow rate: constraints on the use of saliva paracetamol concentrations for the determination of paracetamol pharmacokinetics

1. The effects of pirenzepine on gastric emptying, salivary flow and saliva paracetamol concentrations were investigated in healthy volunteers. 2. Pirenzepine significantly reduced the area under the saliva flow-time curves (7.29 +/- 3.30 g min-1 h without pirenzepine; 4.19 +/- 2.59 g min-1 h with pirenzepine, P less than 0.01). Pirenzepine had no significant effect on plasma paracetamol Cmax (17.5 +/- 7.8 micrograms ml-1 without pirenzepine; 12.6 +/- 7.7 micrograms ml-1 with pirenzepine), plasma tmax (0.2 h (0.2-0.8 h) without pirenzepine; (0.2 h 0.2-0.8 h) with pirenzepine) and plasma AUC(0.6 h) (32.3 +/- 7.2 micrograms ml-1 h without pirenzepine; 30.3 +/- 6.5 micrograms ml-1 h with pirenzepine). 3. Mean ratios of saliva:plasma paracetamol AUC (1.06 +/- 0.24 without pirenzepine; 1.84 +/- 0.48 with pirenzepine, P less than 0.001) and saliva:plasma paracetamol Cmax (1.7 +/- 1.0 without pirenzepine; 6.5 +/- 2.7 with pirenzepine, P less than 0.01) were significantly increased by pirenzepine pretreatment, but there was a poor correlation between the percentage change in the area under the saliva flow-time curve and the percentage change in saliva paracetamol AUC (r = 0.47, P = 0.21). 4. The findings suggest that a) pirenzepine is a more selective antagonist of the muscarinic receptors in salivary glands than those in gastric smooth muscle and b) caution is required when using saliva paracetamol concentrations to determine the pharmacokinetics of the drug in the presence of other agents which may influence salivary flow rate.