Pharmacokinetic studies on atropine with special reference to age

The cephalic phase of insulin release is modulated by IL-1β

The initial cephalic phase of insulin secretion is mediated through the vagus nerve and is not due to glycemic stimulation of pancreatic β cells. Recently, IL-1β was shown to stimulate postprandial insulin secretion. Here, we describe that this incretin-like effect of IL-1β involves neuronal transmission. Furthermore, we found that cephalic phase insulin release was mediated by IL-1β originating from microglia. Moreover, IL-1β activated the vagus nerve to induce insulin secretion and regulated the activity of the hypothalamus in response to cephalic stimulation. Notably, cephalic phase insulin release was impaired in obesity, in both mice and humans, and in mice, this was due to dysregulated IL-1β signaling. Our findings attribute a regulatory role to IL-1β in the integration of nutrient-derived sensory information, subsequent neuronally mediated insulin secretion, and the dysregulation of autonomic cephalic phase responses in obesity.

TESTING THE VAGAL WITHDRAWAL HYPOTHESIS DURING LIGHT EXERCISE UNDER AUTONOMIC BLOCKADE: A HEART RATE VARIABILITY STUDY

INTRODUCTION

We performed the first analysis of heart rate variability (HRV) at rest and exercise under full autonomic blockade on the same subjects, to test the conjecture that vagal tone withdrawal occurs at exercise onset. We hypothesized that, between rest and exercise: i) no differences in total power (PTOT) under parasympathetic blockade; ii) a PTOT fall under β1-sympathetic blockade; iii) no differences in Ptot under blockade of both ANS branches.

METHODS

7 males (24±3 years) performed 5-min cycling (80W) supine, preceded by 5-min rest during control and with administration of atropine, metoprolol and atropine+metoprolol (double blockade). Heart rate and arterial blood pressure were continuously recorded. HRV and blood pressure variability were determined by power spectral analysis, and baroreflex sensitivity (BRS) by the sequence method.

RESULTS

At rest, PTOT and the powers of low (LF) and high (HF) frequency components of HRV were dramatically decreased in atropine and double blockade compared to control and metoprolol, with no effects on LF/HF ratio and on the normalised LF (LFnu) and HF (HFnu). At exercise, patterns were the same as at rest. Comparing exercise to rest, PTOT varied as hypothesized. For SAP and DAP, resting P_TOT was the same in all conditions. At exercise, in all conditions, P_TOT was lower than in control. BRS decreased under atropine and double blockade at rest, under control and metoprolol during exercise.

CONCLUSIONS

The results support the hypothesis that vagal suppression determined disappearance of HRV during exercise.

Atropine for critical care intubation in a cohort of 264 children and reduced mortality unrelated to effects on bradycardia

Background

Atropine has is currently recommended to facilitate haemodynamic stability during critical care intubation. Our objective was to determine whether atropine use at induction influences ICU mortality.

Methodology/Principal Findings

A 2-year prospective, observational study of all first non-planned intubations, September 2007–9 in PICU and Intensive Care Transport team of Hôpital Robert Debré, Paris, 4 other PICUs and 5 NICUs in the Paris Region, France. Follow-up was from intubation to ICU discharge. A propensity score was used to adjust for patient specific characteristics influencing atropine prescription. 264/333 (79%) intubations were included. The unadjusted ICU mortality was 7.2% (9/124) for those who received atropine compared to 15.7% (22/140) for those who did not (OR 0.42, 95%CI 0.19–0.95, p = 0.04). One child died during intubation (1/264, 0.4%). Two age sub-groups of neonates (≤28 days) and older children (>28 days, <8 years) were examined. This difference in mortality arose from the higher mortality in children aged over one month when atropine was not used (propensity score adjusted OR 0.22, 95%CI 0.06–0.85, p = 0.028). No effect was seen in neonates (propensity score adjusted OR 1.3, 95%CI 0.31–5.1 p = 0.74). Using the propensity score, atropine maintained the mean heart rate 45.9 bpm above that observed when no atropine was used in neonates (95%CI 34.3–57.5, p<0.001) and 43.5 bpm for older children (95%CI 25.5–61.5 bpm, p<0.001).

Conclusions/Significance

Atropine use during induction was associated with a reduction in ICU mortality in children over one month. This effect is independent of atropine’s capacity to attenuate bradycardia during intubation which occurred similarly in neonates and older children. This result needs to be confirmed in a study using randomised methodology.

Muscarinic receptor antagonists: effects on pulmonary function

In healthy lungs, muscarinic receptors control smooth muscle tone, mucus secretion, vasodilation, and inflammation. In chronic obstructive pulmonary disease (COPD) and asthma, cholinergic mechanisms contribute to increased bronchoconstriction and mucus secretion that limit airflow. This chapter reviews neuronal and nonneuronal sources of acetylcholine in the lung and the expression and role of M₁, M₂, and M₃ muscarinic receptor subtypes in lung physiology. It also discusses the evidence for and against the role of parasympathetic nerves in asthma, and the current use and therapeutic potential of muscarinic receptor antagonists in COPD and asthma.

Does respiratory sinus arrhythmia serve a buffering role for diastolic pressure fluctuations?

Though many consider the magnitude of respiratory sinus arrhythmia as an index of cardiac vagal control, its physiological origins remain unclear. One influential model postulates that the systolic pressure rise within a given beat stimulates the baroreflex arc to adjust the following heart period such that diastolic pressure is "stabilized" and hence displays lesser fluctuation. Accordingly, the magnitude of diastolic pressure fluctuations with respiration should change reciprocally after augmentation or inhibition of respiratory sinus arrhythmia. To test this, we augmented and subsequently inhibited respiratory sinus arrhythmia with vagotonic and vagolytic atropine administration in 19 healthy young volunteers to assess the relation between respiratory R-R interval and diastolic pressure fluctuations. Respiratory diastolic pressure fluctuations showed parallel rather than inverse changes in relation to those in respiratory sinus arrhythmia: they increased with augmented respiratory sinus arrhythmia (138 and 190% of baseline in the frequency and time domains, both P < 0.05) and tended to decrease with inhibited respiratory sinus arrhythmia (82 and 93% of baseline in frequency and time domains, P = 0.20 and P = 0.07). Furthermore, >60% of the change in diastolic pressure fluctuations was explained by the change in respiratory sinus arrhythmia (R(2) = 0.62; P < 0.001), that is, an approximately 50-ms increase or decrease in respiratory sinus arrhythmia resulted in a parallel approximately 1-mmHg change in diastolic pressure fluctuations. Thus, in young healthy individuals during supine rest, respiratory fluctuations in R-R interval do not buffer against diastolic pressure fluctuations but actually cause diastolic pressure fluctuations. Therefore, our data provide little evidence for a predominant role of a baroreflex feedback mechanism underlying respiratory sinus arrhythmia during supine rest.

Effects of fitness and age on the response to vagotonic atropine

Previous work indicates compromised cardiac vagal control plays a prominent role in reducing arterial baroreflex gain with age, however older fit individuals display cardiovagal baroreflex responses similar to young individuals. The purpose of this study was to test the hypothesis that chronic aerobic exercise mitigates against age-related declines in cardiac parasympathetic receptor function. In forty-four young and old (fit and unfit) individuals, we used the parasympathomimetic responses to low doses of atropine to probe cardiac cholinergic receptor responses. Data were collected before and after eight doses of atropine sulfate from 0.4 to 7.2 microg/kg. Chronotropic responses were assessed from average RR intervals and heart rate variabilities were derived in time and frequency domains. All subjects exhibited bradycardia with at least one dose of atropine and peak bradycardia occurred at a similar dose in each group. However, changes in heart rate variability did not consistently track the chronotropic responses within subjects (r-square from 0.90 down to 0). As expected, basal RR interval was longer in the fit groups and was unaffected by age. However, the degree of RR interval lengthening with parasympathomimetic atropine was unaffected by physical fitness and was significantly less in all older subjects. These data indicate there are certain prepotent age-related declines in the cardiac parasympathetic system that cannot be prevented by regular physical activity.

Quantification by HPLC-MS/MS of Atropine in Human Serum and Clinical Presentation of Six Mild-to-Moderate Intoxicated Atropine-Adulterated-Cocaine Users

An unexpectedly high number of initially suspected cocaine-intoxicated patients was presented to a general hospital in Lelystad, The Netherlands. Based on the unusual toxidram rate of not fitting cocaine intoxication, the suspicion of co-presence of an anticholinergic agent was raised. A newly developed HPLC-MS/MS analytical method revealed the presence of 10% atropine in a cocaine sample retrieved and subsequently in the sera of 6 intoxicated patients.

The efficacy of a simulated intravascular test dose in sevoflurane-anesthetized children: a dose-response study

A recent study demonstrated that changes in both heart rate (HR; positive if > or = 10bpm increase) and T-wave amplitude (positive if > or = 25% increase) reliably detect accidental intravascular injection when a full test dose containing epinephrine 0.5 microg/kg is injected intravascularly. We designed this study to prospectively determine whether a smaller dose of epinephrine would produce reliable HR and T-wave changes in sevoflurane-anesthetized children. We studied 80 ASA physical status I infants and children (6-72 mo) undergoing elective surgeries during 1.0 minimum alveolar anesthetic concentration sevoflurane and 67% nitrous oxide in oxygen. After the administration of i.v. atropine 0.01 mg/kg, the patients were randomly assigned to receive either i.v. saline (n = 20), an i.v. test dose (0.1 mL/kg) consisting of 1% lidocaine with 1:200,000 epinephrine (epinephrine 0.5 microg/kg group, n = 20), an i.v. test dose (0.05 mL/kg) (epinephrine 0.25 microg/kg group, n = 20), or an i.v. test dose (0.025 mL/kg) (epinephrine 0.125 microg/kg group, n = 20) via a peripheral vein to simulate the intravascular injection of the test dose. HR and systolic blood pressure were recorded every 20 and 30 s, respectively, and T-wave amplitude of lead II was continuously recorded for subsequent analysis. After the i.v. injection of the test dose, all children in the epinephrine 0.5 and 0.25 microg/kg groups developed positive responses based on the peak T-wave amplitude, whereas all children in the epinephrine 0.5 microg/kg group and 17 children (85%) in the epinephrine 0.25 microg/kg group elicited a positive response according to the peak HR criterion. No false-positive responses were observed with saline injections. Children in the epinephrine 0.125 microg/kg group showed clinically unacceptable efficacy based on either criterion. We conclude that the efficacies of detecting an intravascular injection of the test dose based on the hemodynamic and T-wave criteria are reduced with smaller doses of epinephrine and that HR and T-wave changes are still useful indicators in most patients if epinephrine 0.25 microg/kg is accidentally injected intravascularly.

IMPLICATIONS

To determine whether an epidurally administered local anesthetic has been unintentionally injected into a blood vessel, a small dose of epinephrine is often added to a local anesthetic. We found that an increase in T-wave amplitude > or = 25% in lead II and a heart rate increase > or = 10 bpm are useful indicators for detecting the accidental intravascular injection of a small dose of epinephrine in sevoflurane-anesthetized children.

Cardiovascular pharmacology of aging

Despite the relative paucity of drug trials in the old and especially the very old (> 85 years), some general principles of pharmacology in the aging patient can be taken from available data and clinical experience. The pharmacokinetic changes most consistently seen with aging occur in the volume of distribution, clearance, and half-life of a drug. Renal drug clearance is consistently diminished with aging. Hepatic metabolism is more variably affected, and in contrast to renal clearance, no reliable formula exists to estimate hepatic drug clearance. Pharmacodynamic changes, although present, are less well studied or described in the elderly. Drug interactions and adverse drug reactions increase with increasing numbers of medications prescribed and represent a complex interplay of age, underlying disease, and number and types of medications. The clinical caveats that apply to drug prescription in the very old include reduced starting doses with slow incremental increases; elimination of unnecessary medications; and anticipating and monitoring for drug interactions and ADRs, especially when prescribing warfarin, digoxin, and amiodarone. Future studies that look at the aging patient in the presence of effects of age, physiology, gender, comorbid illness, and multiple drug therapies may help evolve a new set of paradigms for geriatric drug prescribing.

Pharmacokinetics of HI-6 and atropine in anaesthetized pigs after administration by a new autoinjector

A newly developed autoinjector (Astra Tech, Sweden) containing 500 mg HI-6 and 2 mg atropine sulphate was tested in anaesthetized normal pigs. The pharmacokinetics and pharmacodynamics of the drugs after administration by the autoinjector were compared with those after conventional needle and syringe delivery intramuscularly and intravenously. Cardiopulmonary parameters were monitored and serum concentrations of oxime, atropine, and acetylcholinesterase were determined in blood samples taken at intervals over a 6 h period postinjection. After injection in anaesthetized pigs, both HI-6 and atropine were absorbed rapidly and completely from the injection site. Therapeutic serum concentrations of HI-6, arbitrarily taken as 4 micrograms mL-1, were reached within 1 min of intravenous and autoinjector administration, and within 5 min of intramuscular injection. The concentrations remained above this level for 3-4 h. There were no significant changes in acetylcholinesterase activity, mean arterial blood pressure, or respiration frequency after injection of HI-6 and atropine sulphate. The heart rates increased significantly after administration of the two drugs (cardioacceleration defined as > or = 5% increase in heart rate), regardless of the technique employed. Our results show that HI-6 and atropine sulphate can be given intramuscularly by the new autoinjector with the same effectiveness and speed as when given intravenously. Irrespective of the injection technique, no overt signs of toxicity were observed at the drug concentrations used.

Pharmacokinetics of glycopyrrolate in children

STUDY OBJECTIVE

To investigate the pharmacokinetics of glycopyrrolate in children.

DESIGN

Open study with three parallel groups.

SETTING

Pediatric surgery department at a university hospital.

PATIENTS

26 healthy ASA physical status I children undergoing minor surgery.

INTERVENTIONS

Patients were assigned to 1 of 3 groups: under 1 year of age (Group 1, n = 8), between 1 and 3 years of age (Group 2, n = 7), and over 3 years of age (Group 3, n = 11). Glycopyrrolate 5 micrograms/kg was given as a single intravenous (i.v.) injection before induction of general anesthesia. Blood samples (for determination of drug concentrations in plasma) were collected via venous cannula inserted into the contralateral antecubital vein.

MEASUREMENTS AND MAIN RESULTS

ECG was observed continuously, blood pressure was measured with an automatic noninvasive device, and blood samples were taken just before and at 2, 4, 6, 10, 15, 30, 60, 120, 180, 240, 360, and 480 minutes after injection of glycopyrrolate. Glycopyrrolate concentrations in plasma were determined with a radioreceptor assay. The only significant difference in the pharmacokinetic parameters was the shortened elimination half-life in patients between 1 and 3 years of age. Glycopyrrolate 5 micrograms/kg i.v. did not cause any significant alterations in heart rate.

CONCLUSIONS

There were no significant changes in the distribution volume or clearance of glycopyrrolate in children of different ages. The shortened elimination half-life in children between 1 and 3 years of age is of minor clinical importance.

Pharmacokinetics and related pharmacodynamics of anticholinergic drugs

The pharmacokinetics and some pharmacodynamic properties of atropine, glycopyrrolate and scopolamine are reviewed. With the development of new analytical methods for drug determination, it is now possible to measure relatively low concentrations of these drugs in biological fluids and, consequently, some new kinetic data have been collected. Following intravenous administration, a fast disappearance from the circulation is observed and due to a high total clearance value their elimination phase half-lives vary from 1 to 4 h. All these agents are nonselective muscarinic receptor antagonists, but their actions on various organ systems with cholinergic innervation show considerable diversity. The cardiovascular effects are of short duration; other peripheral muscarinic effects and CNS effects can last up to 8 h or even longer. Differing from atropine and scopolamine, glycopyrrolate as a quaternary amine penetrates the biological membranes (blood-CNS, placental barriers) slowly and incompletely, making it the drug of choice for elderly patients with coexisting diseases and for obstetric use. Similarly, its oral absorption is slow and erratic, and hence it cannot be used as an oral premedicant. Atropine, scopolamine and glycopyrrolate have a definitely faster absorption rate, when injected into the deltoid muscle compared with administration into the gluteal or vastus lateralis muscles. There appear to be significant differences in the metabolism and renal excretion of these agents. Scopolamine is apparently excreted into the urine mainly as inactive metabolites, nearly half of the atropine dose administered is recovered in the urine as the parent drug or as active metabolites and about 80% of glycopyrrolate is excreted as unchanged drug or active metabolites.(ABSTRACT TRUNCATED AT 250 WORDS)

Postoperative retention of urine: a prospective urodynamic study

OBJECTIVE

To investigate the cause of post-operative retention of urine in elderly men.

DESIGN

Prospective study.

SETTING

Northern General Hospital, Sheffield.

PATIENTS

32 consecutive men (median age 73, range 55-85) referred to the urology department who were unable to pass urine either within 48 hours after operation and required catheterisation (23) or after removal of a catheter inserted at the initial operation (nine).

INTERVENTION

Intermittent self catheterisation.

MAIN OUTCOME MEASURES

Urological investigation by medium fill and voiding cystometry within four weeks after operation, and minimum follow up three months thereafter.

RESULTS

6 patients resumed normal voiding before urodynamic assessment, three proceeded straight to prostatectomy, and one was unfit for self catheterisation. Of 22 men who underwent urodynamic investigation, only five had bladder outflow obstruction, who subsequently had successful prostatectomy; 15 showed either a low pressure-low flow system (seven) or complete detrusor failure (eight) and two showed pelvic parasympathetic nerve damage. With intermittent self catheterisation spontaneous voiding returned in all but one man within a median of 8 weeks (range 6-32 weeks). Recovery of bladder function took significantly longer in men with detrusor failure than in those with an underactive bladder (median 10 weeks (range 6-32 weeks) v median 8 weeks (range 6-8 weeks); p = 0.05). Three months later all patients had re-established their own normal voiding pattern with minimal residual urine on ultrasonography and satisfactory flow rates.

CONCLUSIONS

Postoperative urinary retention in elderly men is not an indication for prostatectomy; a normal pattern of micturition can be re-established by intermittent self catheterisation in most men.

Pharmacokinetics of scopolamine during caesarean section: relationship between serum concentration and effect

The pharmacokinetics (radioreceptor assay, RRA) and some of the clinical effects of the anticholinergic agent, scopolamine, were studied in 16 parturients during caesarean section. Following a single 0.005 mg/kg intramuscular injection (deltoid muscle), a very fast rate of absorption was found with mean peak serum concentrations occurring after only 10 min (n = 6). Due to severe bradycardia, 0.5 mg of atropine i.v. had to be given in addition to the i.m. scopolamine treatment to one parturient. The RRA measured the total concentration produced by the two anticholinergic agents in both serum and urine. There was a fundamental difference in the diffusion of scopolamine through the placenta and the blood-lumbar (CSF-barrier (n = 15). There was significant drug penetration in the foeto-placental unit, indicating an efficient drug transfer to the child, but there were measurable levels of the drug in the lumbar CSF in only three cases. The apparent elimination phase half-life of scopolamine in serum was only around 1 h. The urinary excretion of scopolamine and/or its antimuscarinic metabolites lasted only for 6 h (2.63 +/- 1.14% of the dose). The onset of the clinical effects of scopolamine appeared to be delayed, but long-lasting in contrast to the rapid absorption and quick disappearance from the serum. Both the heart rate changes, sedative and antisialogogue effects and serum concentrations did not show any correlation. There appears to be a surprisingly great difference between the pharmacokinetic parameters and the clinical effects of scopolamine.

Intramuscular atropine in elderly people: pharmacokinetic studies using the radioreceptor assay and some pharmacodynamic responses

The pharmacokinetics (radioreceptor assay, RRA) and some clinical effects of atropine were studied in 7 elderly gynaecological surgery patients. The RRA measures only the pharmacologically active isomer of atropine, 1-hyoscyamine. Following a single 0.01 mg/kg intramuscular (M. deltoideus) injection, a very fast rate of absorption was found with mean peak serum concentration occurring after only 13 min. The reason for this could be either a preferential tissue uptake of the 1-form or the injection site or both. The elimination half-life was 2.27 hr. Only 23.1% of the given drug was excreted in urine in 24 hr as a pharmacologically active form. The clinical effects (heart rate rise, subjective sedation and antisialogogue effect) were seen after only 30 min. This somewhat faster appearance of clinical effects than in previous studies can be due to the injection site. The sedative effect of the drug is clear and long lasting in elderly people.

Glycopyrrolate: pharmacokinetics and some pharmacodynamic findings

In the present study, a sensitive and reproducible radioreceptor assay (RRA) was used to evaluate the basic pharmacokinetic properties of glycopyrrolate, a quaternary amine with peripheral antimuscarinic activity. Based on the plasma levels after a single intravenous injection, 6 micrograms/kg (n = 6), the distribution phase half-life (2.22 +/- 1.26 s.d. min) and the elimination phase half-life (0.83 +/- 0.29 h) of glycopyrrolate were short due to the low distribution volume during the elimination phase (0.64 +/- 0.29 l/kg) and to the respectively high total plasma clearance value (0.54 +/- 0.14 l/kg/h). An intramuscular injection, 8 micrograms/kg (n = 6), was followed by a fast and predictable systemic drug absorption and clinical effects (heart rate increase, dry mouth). In this group the time to maximum plasma concentration (tmax) was 27.48 +/- 6.12 min and the maximum plasma concentration (Cmax) was 3.47 +/- 1.48 micrograms/l. After oral drug intake, 4 mg (n = 6), an apparently low and variable gastrointestinal absorption was found (tmax = 300.0 +/- 197.2 min, Cmax = 0.76 +/- 0.35 microgram/l), thus indicating that the oral route of drug administration is of no value as a routine premedication. The correlation between the plasma concentration of glycopyrrolate and the drug effects appears to be variable. Because of its sensitivity, the RRA method proved to be quite useful in evaluating the kinetics of glycopyrrolate and its relationship to various clinical effects.

Difference in scopolamine sensitivity during ageing in rats: dichotomy between behavioural repertoire and learning performances

The effects of different doses of scopolamine in adult and aged rats were compared in two behavioural experiments. The first experiment involved visual reversal learning, while the second experiment investigated individual and social behavioural patterns. Results showed that the same dose of scopolamine was more effective in impairing the reverse discrimination in aged than in adult rats. In contrast, low doses which were effective in modifying behavioural patterns in adults, were inactive in aged rats. This difference in scopolamine sensitivity (supersensitivity versus hyposensitivity), observed between the two types of behaviour, is discussed in relation to age-related functional receptor adaptation, selective changes in muscarinic receptors in the different brain areas and dopaminergic- cholinergic interactions.

Postoperative urinary retention in general surgical patients

A prospective study has been performed to measure the incidence of postoperative urinary retention in 280 general surgical patients. Eighteen patients (6 per cent) were catheterized after a range of operations under general anaesthesia. There was no statistical difference in the retention rate between men and women. Increasing age did not predispose to retention of urine. Of 72 patients who had either herniorrhaphy, haemorrhoidectomy or testicular operations, only 1 was catheterized, whereas 16 (23 per cent) of 70 patients undergoing laparotomy were catheterized. Most of these laparotomy patients had upper abdominal procedures carried out. Those having lower abdominal operations were usually catheterized pre-operatively and were excluded from the study. There was a significantly higher incidence of retention among patients who had long anaesthetics (greater than 60 min). There was also a significantly higher incidence of retention among those who were ventilated, relaxed and reversed by atropine and neostigmine. Of those 193 patients who had opiate analgesia, 15 (8 per cent) developed retention of urine, compared with 3 (3 per cent) of the 87 patients who had non-opiate analgesia. There was a significantly higher retention rate among the patients who had opiate analgesia by intravenous infusion compared with those who had opiates by intramuscular bolus injection; 7 patients had painful and 11 had painless retention. This study suggests that postoperative retention of urine is a result more commonly of diminished awareness of bladder sensation, than of factors such as anxiety or local pain.

Heart rate response to atropine in humans anaesthetized with five different techniques

Atropine, 0.01 mg.kg-1, was given intravenously before the start of surgery to 169 patients who were anaesthetized with one of five different techniques; halothane, enflurane, cervical epidural, lumbar epidural or narcotic anaesthesia in addition to nitrous oxide and oxygen. Atropine produced a significant increase in heart rate (HR) within 1 min in all patients studied; the HR increases in patients anaesthetized with halothane (37 +/- 11 beats.min-1, n = 37) or narcotic (34 +/- 12 beats.min-1, n = 30) were significantly greater than in those anaesthetized with enflurane (25 +/- 10 beats.min-1, n = 35; P less than 0.01) or epidural anaesthesia. Because of the presence of an acute cardiac sympathectomy, the patients who received cervical epidural anaesthesia were expected to have different responses to the atropine. However, there was no significant difference in the HR increases between the patient groups with cervical (19 +/- 12 beats.min-1, n = 32) and lumbar (22 +/- 8 beats.min-1, n = 35) epidural anaesthesia. Atropine also produced a small but significant increase in arterial pressure in all five groups of patients. These results suggest that the cardiac responses to atropine may differ depending on the individual anaesthetic agent used, and are likely dependent upon the agent's effect on autonomic nervous system activity.

Pharmacokinetic implications for the clinical use of atropine, scopolamine and glycopyrrolate

Several specific and sensitive new methods for determining atropine and its metabolites in biological fluids have increased the possibility to characterise the pharmacokinetic properties of this antimuscarinic agent. Following i.v. injection, atropine disappears very quickly from the circulation, resembling its fast onset of action. Age, but not sex, appears to have a clear effect on its kinetics, explaining at least partly the higher sensitivity of very young and very old patients to this anticholinergic agent. Following i.m. or oral atropine administration, typical anticholinergic effects coincide quite well with the absorption rate of the drug, indicating that the premedication should be given about 1 and 2 h before induction of anaesthesia. A sufficient absorption after rectal administration offers an alternative treatment, especially in children. Differing from its placental transfer, atropine has a delayed and incomplete lumbar cerebrospinal fluid penetration, indicating a fundamental difference between these two biological membranes. Oropharyngeally administered atropine has a very variable absorption, but inhaled or intratracheally given drug has produced interesting new results, e.g. pulmonary atropine administration appears to have clinical significance in special situations, such as cardiac arrest and organophosphate poisoning (military personnel). Depending on the method used, different data on the metabolism and excretion for atropine have been reported and therefore further studies are needed in this respect. The pharmacokinetics of scopolamine and glycopyrrolate and their relation to clinical response are poorly understood.

Age-related scopolamine effects on social and individual behaviour in rats

The modulation of spontaneous (social and individual) behaviour as a function of the age of the rat (1, 3, 6, 12, 18 and 24 months) and of scopolamine dose (0.1, 0.2, 0.3 and 0.5 mg/kg) was studied. Observations were conducted during the dark phase of the reverse light/dark schedule using a reintroduction procedure. Results showed a marked effect of scopolamine on most of the behavioural patterns considered. Environmental interaction was enhanced whilst agonistic and social active interactions (social grooming) and play fighting were reduced by the drug. A slight hyposensitivity in the youngest rats and a marked hyposensitivity to the drug in the oldest ones were observed. The relationship to biochemical data and human sensitivity on the one hand and to learning and memory tasks and cholinergic specificity on the other hand, are discussed.

Placental and blood-CSF transfer of orally administered diazepam in the same person

Both placental and blood-lumbar CSF transfer of diazepam (5 mg orally) and its two metabolites, N-desmethyldiazepam and unconjugated oxazepam, was measured (by GLC) in 15 patients undergoing Caesarean section under spinal analgesia. Differing from our earlier studies with atropine (Virtanen et al. 1982; Kanto et al. 1981 & 1987), a reasonably fast penetration of diazepam and its two metabolites through the two biological membranes was found. Diazepam, N-desmethyldiazepam and to a lesser extent unconjugated oxazepam accumulated on the foetal side of the placenta, apparently due to a higher degree of plasma protein binding in the foetus. No accumulation was found in CSF, probably due to the lack of binding proteins in this tissue compartment. Concerning atropine, lumbar CSF with an incomplete drug penetration was found to be a "deeper" compartment than amniotic fluid, but in the present study with diazepam there was no clear difference between these two tissue compartments.

Elimination of and heart rate response to atropine in the elderly are independent of sex

Sex-related changes in the pharmacokinetics and pharmacodynamics (heart rate) of atropine were studied in female (n = 9) and male (n = 9) elderly patients after a single 0.02 mg/kg i.v. injection of the drug at the beginning of a combination anaesthesia. No significant differences were found between the sexes, which indicates that there are no sex-related alterations in the response to this anticholinergic agent.

Placental and blood-CSF transfer of intramuscularly administered atropine in the same person

Both placental and blood-CSF transfer of atropine (0.01 mg/kg intramuscularly) was measured (by RIA) in 11 parturients undergoing Caesarean section under spinal analgesia. In the foeto-placental unit a significant penetration into amniotic fluid was found, whereas in CSF there was a measurable level of the drug (greater than 1.5 ng/ml) in only one mother. Our results show that there is a fundamental difference in the penetrability of tertiary ammonium alkaloids like atropine through these two biological membranes. However, our results concern penetration into human lumbar CSF and do not necessarily reflect potential penetration into the ventricular CSF, choroid plexus or brain ventricular ependyma.

Pharmacokinetics and clinical effects of scopolamine in caesarean section patients

A new method (ELISA) was used to evaluate the pharmacokinetics of scopolamine following intravenous (0.005 mg/kg), intramuscular (0.01 mg/kg), and oropharyngeal (0.035 mg/kg) administration of the drug to pregnant patients anaesthetized for caesarean section. After intravenous (N = 4) the drug fast disappeared from the circulation with a half-life of about 5 min., and the serum levels generally were measurable up to 3 hours, mean elimination half-life was 1.85 hours. A fast absorption was found after intramuscular injection, tmax = 10 min. (N = 4), and the drug had a clinically significant oropharyngeal absorption as well, tmax was around 1 hour (N = 6). The intramuscular and oropharyngeal, but not the intravenous, administrations produced a marked postoperative sedative and amnesic effects. All three administration ways caused a significant antisecretory action.

Effect of induced hypotension on serum concentrations of atropine after intramuscular administration

The serum concentrations of atropine after a single intramuscular injection of 0.01 mg/kg were determined by radioimmunoassay in nine general surgical patients during and after a combination anaesthesia and compared with those of 13 neurosurgical patients operated on during induced hypotensive anaesthesia (sodium nitroprusside plus trimetaphan). Surprisingly, comparable serum levels were found in both patient groups. We conclude that this kind of induced hypotension cannot be used as a model of drug absorption in such clinical situations as cardiac failure, haemorrhage or anaphylactic drug reactions.

The influence of body weight on plasma concentration of atropine after rectal administration in children

To avoid an unpleasant injection, the rectal administration of drugs to children is often to be preferred. Very little has been published on plasma concentrations of atropine given rectally. To determine whether body weight has any influence on the plasma concentrations of atropine, 18 children weighing 7.5-55.0 kg were given 0.02 mg atropine sulphate per kg rectally, and the plasma levels of atropine were determined. The mean peak plasma concentration of atropine was 1.17 ng/ml and it was reached after 33 min. In the group of smaller children (b.w. less than 15 kg) the peak plasma concentration was (0.83 ng/ml) lower than that observed in older children (1.26-1.36 ng/ml), but this difference was not statistically significant. Plasma concentrations in the group of smaller children declined significantly faster than in the other weight groups.

Comparison of pharmacokinetic and pharmacodynamic parameters following oral or intramuscular atropine in children. Atropine overdose in two small children

Pharmacokinetic and pharmacodynamic parameters of atropine 0.03 mg/kg p.o. or 0.02 mg/kg i.m. were compared in a double-blind study in 20 children with a mean age of 5.1 years undergoing otolaryngological surgery, mostly adenotomy. Outside the study protocol, two small children accidentally received an overdose of atropine 0.3 mg/kg p.o. In addition to atropine, all children received triclofos 70 mg/kg p.o. Following p.o. administration of atropine, the mean maximum serum concentration of 6.7 nmol/l occurred at 2 h. The corresponding result after i.m. administration was 5.7 nmol/l at 0.5 h. Serum concentrations of atropine were 3.5 and 1.3 nmol/l 8 h after p.o. and i.m. administration, respectively. At 70 min the anti-sialogogue effect was clinically satisfactory after both modes of administration. The heart rate increased statistically significantly only after i.m. administration. The mean maximum rise in the rectal temperature before the start of anaesthesia occurred at 1 h and was 0.5 degrees C in the p.o. group and 0.7 degrees C in the i.m. group. The flush phenomenon, mostly on the face and sometimes also on the chest, occurred in both groups, being more intense in the i.m. group than in the p.o. group. The children who developed flush had a statistically significantly higher rise in rectal temperature than the children without flush. There was a positive but weak correlation between the serum concentration of atropine and the heart rate, whereas the correlation between the serum concentration after i.m. atropine and the rectal temperature was weakly negative. On the basis of the present study, there were no decisive differences between the effects and side-effects of the two modes of administration of atropine.(ABSTRACT TRUNCATED AT 250 WORDS)

Integrated pharmacokinetics and pharmacodynamics of atropine in healthy humans. I: Pharmacokinetics

The pharmacokinetics of atropine in three healthy male volunteers after intravenous administration of 1.35 and 2.15 mg of the drug was determined. Pharmacodynamic effects of atropine were measured simultaneously. All the data were fitted to a novel integrated kinetic-dynamic model. Plasma concentrations of atropine and the amounts of atropine and its primary metabolite, tropine, excreted in the urine were measured by a sensitive gas chromatographic-mass spectrometric assay. The kinetics of elimination of atropine was first order. There was evidence that the kinetics of distribution of the drug was dose dependent. Two phases with apparent half-lives of 1 and 140 min were distinguishable in accordance with a linear two-compartment disposition model for atropine. The urinary excretion of unchanged drug was 57% of the dose. The steady-state volume of distribution was 210 L, implying extensive tissue binding and/or partitioning. Renal plasma clearance was 660 mL/min, suggesting significant tubular secretion. The renal clearance of atropine depended on urine flow. Urinary excretion of tropine amounted to 29% of the dose. The kinetics of the metabolite was first order.

Failure of IV atropine to abolish nasal irritation caused by chlormethiazole infusion in elderly patients undergoing spinal anaesthesia

The efficacy of intravenous atropine in abolishing the nasal irritation of chlormethiazole was assessed. Forty elderly patients undergoing transurethral resection of prostate under spinal anaesthesia were studied. One ml of either atropine sulphate (0.6 mg) or normal saline was administered intravenously in a double-blind fashion 10 minutes prior to infusion of 0.8% chlormethiazole edisylate. A loading infusion of 5 ml X min-1 of the chlormethiazole solution was followed by a variable rate of infusion in order to maintain a predetermined state of sedation--i.e. where the patient lapsed into sleep but was easily awakened to obey commands. Sneezing was the commonest side-effect occurring in 45% and 70% of patients in atropine and saline groups respectively. This was not effectively abolished by IV atropine in incremental doses of 0.6 mg up to 1.8 mg. Because of the sneezing and restlessness, four patients in the atropine group required general anaesthesia to improve operating conditions. These side-effects of chlormethiazole may limit its use as a sedative for surgery in this elderly age group.

Comparison of radioreceptor assay and radioimmunoassay for atropine: pharmacokinetic application

A membrane suspension prepared from rat brain was able to bind the potent muscarinic antagonist quinuclidinyl benzilate (QNB). The KD for binding was 0.48 nM and Bmax was 1.42 pmol/mg protein. Atropine competitively inhibited the binding of tritiated QNB to muscarinic receptors. This new radioreceptor assay (RRA) for atropine has been compared with a radioimmunoassay (RIA) for atropine. The RRA measures only the active component of atropine, 1-hyoscyamine and in this respect it differs from the RIA. As little atropine as 1.25 ng/ml (4.33 nmol/l) in a 25 microliters serum sample could be reliably assayed by the RRA. Using both assay techniques the pharmacokinetics of atropine was studied after a single 0.02 mg/kg i.v. dose given to 8 anaesthetized patients. The half-life calculated by the RRA was 3.7 +/- 2.3 h (m +/- SD) and by the RIA 4.3 +/- 1.7 h. Both the volume of distribution and the total clearance were higher according to the RRA than the RIA: 3.9 +/- 1.5 vs 1.7 +/- 0.71/kg and 15.4 +/- 10.3 vs 5.9 +/- 3.6 ml/min/kg, respectively. The AUC measured by the RRA and RIA was 29.8 +/- 18.9 and 103.9 +/- 110.7 micrograms X h/l, respectively. The differences in the pharmacokinetics according to the 2 methods are presumably due to preferential tissue uptake of the l-form.