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

Determination of Rate and Extent of Scopolamine Release from Transderm Scōp® Transdermal Drug Delivery Systems in Healthy Human Adults

To estimate strength of a scopolamine transdermal delivery system (TDS) in vivo, using residual drug vs. pharmacokinetic analyses with the goal of scientifically supporting a single and robust method for use across the dosage form and ultimately facilitate the development of more consistent and clinically meaningful labeling. A two-arm, open-label, crossover pharmacokinetic study was completed in 26 volunteers. Serum samples were collected and residual scopolamine was extracted from worn TDS. Delivery extent and rate were estimated by (1) numeric deconvolution and (2) steady-state serum concentration determined from graphical and non-compartmental analyses. In residual drug analyses, mean ± SD scopolamine release rate was 0.015 ± 0.002 mg/h (11% RSD), vs. 0.016 ± 0.006 mg/h (35% RSD) from numeric deconvolution, 0.015 ± 0.005 mg/h (34% RSD) from graphical analysis, and 0.015 ± 0.007 mg/h (44% RSD) from non-compartmental analysis. In residual drug analyses, total drug released was 1.09 ± 0.11 mg (10% RSD), vs. 1.12 ± 0.40 mg (35% RSD) from numeric deconvolution, 1.07 ± 0.35 mg (33% RSD) from graphical analysis, and 1.07 ± 0.45 (42% RSD) from non-compartmental analysis. Extent and rate of scopolamine release were comparable by both approaches, but pharmacokinetic analysis demonstrated greater inter-subject variability.

Tropane Alkaloids: Chemistry, Pharmacology, Biosynthesis and Production

Tropane alkaloids (TA) are valuable secondary plant metabolites which are mostly found in high concentrations in the Solanaceae and Erythroxylaceae families. The TAs, which are characterized by their unique bicyclic tropane ring system, can be divided into three major groups: hyoscyamine and scopolamine, cocaine and calystegines. Although all TAs have the same basic structure, they differ immensely in their biological, chemical and pharmacological properties. Scopolamine, also known as hyoscine, has the largest legitimate market as a pharmacological agent due to its treatment of nausea, vomiting, motion sickness, as well as smooth muscle spasms while cocaine is the 2nd most frequently consumed illicit drug globally. This review provides a comprehensive overview of TAs, highlighting their structural diversity, use in pharmaceutical therapy from both historical and modern perspectives, natural biosynthesis in planta and emerging production possibilities using tissue culture and microbial biosynthesis of these compounds.

Three Cases of Substitution Errors Leading to Hyoscine Hydrobromide Overdose

We report three patients with anticholinergic poisoning caused by the substitution of hyoscine hydrobromide for hyoscine butylbromide in preparations compounded by two different pharmacists. The patients took the preparations for gastrointes tinal discomfort and presented with altered mental status tachycardia, facial flushing, dilated pupils, and dry skin shortly after the ingestion. In one patient the intoxication was initially not recognized and he was treated as suffering from an acute cerebrovascular accident. Two patients experienced long-lasting effects such as decreased ability to concentrate, memory dis turbances, tremor, and photo- and phonophobia. It was obviously impossible to elucidate the exact nature of the relationship between the intoxication and these long-lasting complaints. Information from the Belgian poison control center revealed that cases of substitution error with hyoscine hydrobromide are not unique The Belgian authorities issued a warning to all pharmacists.

Transdermal scopolamine for prevention of motion sickness : clinical pharmacokinetics and therapeutic applications

A transdermal therapeutic system for scopolamine (TTS-S) was developed to counter the adverse effects and short duration of action that has restricted the usefulness of scopolamine when administered orally or parenterally. The plaster contains a reservoir of 1.5 mg of scopolamine programmed to deliver 0.5 mg over a 3-day period. A priming dose (140 microg) is incorporated into the adhesive layer to saturate certain binding sites within the skin and to accelerate the achievement of steady-state blood levels. The remainder is released at a constant rate of approximately 5 microg/hour. The protective plasma concentration of scopolamine is estimated to be 50 pg/mL. TTS-S attains that concentration after 6 hours; a steady state of about 100 pg/mL is achieved 8-12 hours after application. Yet 20-30% of subjects failed to attain the estimated protective concentration, and plasma concentrations measured in subjects who failed to respond to TTS-S were lower than in responders. These findings may explain some of the treatment failures. Overall, the product appears to be the approximate functional equivalent of a 72-hour slow intravenous infusion. A combination of transdermal and oral scopolamine (0.3 or 0.6 mg) was effective and well tolerated in producing desired plasma concentrations 1-hour post-treatment. TTS-S has proved to be significantly superior to placebo in reducing the incidence and severity of motion sickness by 60-80%. It was more effective than oral meclizine or cinnarizine, similar to oral scopolamine 0.6 mg or promethazine plus ephedrine, and the same as or superior to dimenhydrinate. The addition of ephedrine or the use of two patches did not improve its efficacy, but rather increased the rate of adverse effects. TTS-S was most effective against motion sickness 8-12 hours after application. Despite previous evidence to the contrary, a recent bioavailability study demonstrated similar intraindividual absorption and sustained clinical efficacy with long-term use of the drug. The adverse effects produced by TTS-S, although less frequent, are qualitatively typical of those reported for the oral and parenteral formulations of this agent. Dry mouth occurs in about 50-60% of subjects, drowsiness in up to 20%, and allergic contact dermatitis in 10%. Transient impairment of ocular accommodation has also been observed, in some cases possibly the result of finger-to-eye contamination. Low-dose pyridostigmine was found effective in preventing cycloplegia but not mydriasis. Adverse CNS effects, including toxic psychosis (mainly in elderly and paediatric patients), have been reported only occasionally, as have difficulty in urinating, headache, rashes and erythema. Adverse effects were not correlated with plasma scopolamine concentrations. TTS-S produced only about half the incidence of drowsiness caused by oral dimenhydrinate or cinnarizine, and a level of adverse effects similar to that found with oral meclizine. Performance is not affected by short-term use. Prolonged or repeated application may cause some impairment of memory storage for new information. However, sea studies revealed significantly less reports of a decrement in performance or drowsiness due to prevention of sea sickness. The recommended dosage is a single TTS-S patch applied to the postauricular area at least 6-8 hours before the anti-motion sickness effect is required. For faster protection, the patch may be applied 1 hour before the journey in combination with oral scopolamine (0.3 or 0.6 mg). After 72 hours, the patch should be removed and a new one applied behind the opposite ear. Its place in therapy is mainly on long journeys (6-12 hours or longer), to avoid repeated oral doses, or when oral therapy is ineffective or intolerable.

Pharmacokinetics and pharmacodynamics in clinical use of scopolamine

The alkaloid L-(-)-scopolamine [L-(-)-hyoscine] competitively inhibits muscarinic receptors for acetylcholine and acts as a nonselective muscarinic antagonist, producing both peripheral antimuscarinic properties and central sedative, antiemetic, and amnestic effects. The parasympatholytic scopolamine, structurally very similar to atropine (racemate of hyoscyamine), is used in conditions requiring decreased parasympathetic activity, primarily for its effect on the eye, gastrointestinal tract, heart, and salivary and bronchial secretion glands, and in special circumstances for a CNS action. Therefore, scopolamine is most suitable for premedication before anesthesia and for antiemetic effects. This alkaloid is the most effective single agent to prevent motion sickness. Scopolamine was the first drug to be made commercially available in a transdermal therapeutic system (TTS-patch) delivering alkaloid. Recently, pharmacokinetic data on scopolamine in different biozlogic matrices were obtained most efficiently using liquid chromatographic-tandem mass spectrometric (LC-MS/MS) or gas chromatography online coupled to mass spectrometry. Pharmacokinetic parameters are dependent on the dosage form (oral dose, tablets; parenteral application; IV infusion; SC and IM injection). Scopolamine has a limited bioavailability if orally administered. The maximum drug concentration occurs approximately 0.5 hours after oral administration. Because only 2.6% of nonmetabolized L-(-)-scopolamine is excreted in urine, a first-pass metabolism is suggested to occur after oral administration of scopolamine. Because of its short half-life in plasma and dose-dependent adverse effects (in particular hallucinations and the less serious reactions, eg, vertigo, dry mouth, drowsiness), the clinical use of scopolamine administered orally or parenterally is limited. To minimize the relatively high incidence of side effects, the transdermal dosage form has been developed. The commercially available TTS-patch contains a 1.5-mg drug reservoir and a priming dose (140 microg) to reach the steady-state concentration of scopolamine quickly. The patch releases 0.5 mg alkaloid over a period of 3 days (releasing rate 5 microg/h). Following the transdermal application of scopolamine, the plasma concentrations of the drug indicate major interindividual variations. Peak plasma concentrations (Cmax) of approximately 100 pg/mL (range 11-240 pg/mL) of the alkaloid are reached after about 8 hours and achieve steady state. During a period of 72 hours the plaster releases scopolamine, so constantly high plasma levels (concentration range 56-245 pg/mL) are obtained, followed by a plateau of urinary scopolamine excretion. Although scopolamine has been used in clinical practice for many years, data concerning its metabolism and the renal excretion in man are limited. After incubation with beta-glucuronidase and sulfatase, the recovery of scopolamine in human urine increased from 3% to approximately 30% of the drug dose (intravenously administered). According to these results from enzymatic hydrolysis of scopolamine metabolites, the glucuronide conjugation of scopolamine could be the relevant pathway in healthy volunteers. However, scopolamine metabolism in man has not been verified stringently. An elucidation of the chemical structures of the metabolites extracted from human urine is still lacking. Scopolamine has been shown to undergo an oxidative demethylation during incubation with CYP3A (cytochrome P-450 subfamily). To inhibit the CYP3A located in the intestinal mucosa, components of grapefruit juice are very suitable. When scopolamine was administered together with 150 mL grapefruit juice, the alkaloid concentrations continued to increase, resulting in an evident prolongation of tmax (59.5 +/- 25.0 minutes; P < 0.001). The AUC0-24h values of scopolamine were higher during the grapefruit juice period. They reached approximately 142% of the values associated with the control group (P < 0.005). Consequently, the related absolute bioavailabilities (range 6% to 37%) were significantly higher than the corresponding values of the drug orally administered together with water (range 3% to 27%). The effect of the alkaloid on quantitative electroencephalogram (qEEG) and cognitive performance correlated with pharmacokinetics was shown in studies with healthy volunteers. From pharmacokinetic-pharmacodynamic modeling techniques, a direct correlation between serum concentrations of scopolamine and changes in total power in alpha-frequency band (EEG) in healthy volunteers was provided. The alkaloid readily crosses the placenta. Therefore, scopolamine should be administered to pregnant women only under observation. The drug is compatible with nursing and is considered to be nonteratogenic. In conclusion, scopolamine is used for premedication in anesthesia and for the prevention of nausea and vomiting associated with motion sickness. Pharmacokinetics and pharmacodynamics of scopolamine depend on the dosage form. Effects on different cognitive functions have been extensively documented.

Real-time high-resolution MRI for the assessment of gastric motility: pre- and postpharmacological stimuli

PURPOSE

To determine the practicality of MRI using a new real-time sequence for the assessment of gastric motion, and quantify the effects of motility-modifying substances.

MATERIALS AND METHODS

Six healthy volunteers ingested 400 mL of a high-calorie liquid nutrient. Two-dimensional real-time TrueFISP sequences were acquired for up to 30 minutes following the ingestion. The acquisition plane was chosen parallel to the axis of the gastric antrum. The examination was performed on three separate days with and without i.v. administration of 10 mg metoclopramide or 20 mg scopolamine. A motility index was calculated for each real-time data set.

RESULTS

Delineation of the gastric lumen proved easy and robust. The intravenous application of motility-modifying agents resulted in significant changes in the motility index. The administration of metoclopramide resulted in an average increase of the index by a factor of 1.5, whereas the application of scopolamine led to a decrease of the index by a factor of 3.0.

CONCLUSION

TrueFISP MRI performed well in depicting the gastric lumen and assessing gastric motility. Furthermore, we were able to evaluate and quantify the effect of motility-modifying agents. The noninvasive nature of MRI makes this imaging modality an attractive alternative to conventional invasive diagnostic tools for gastric motility disorders and monitoring of therapy.

Clinical pharmacokinetics of drugs used to treat urge incontinence

Urge incontinence (also known as overactive bladder) is a common form of urinary incontinence, occurring alone or as a component of mixed urinary incontinence, frequently together with stress incontinence. Because of the pathophysiology of urge incontinence, anticholinergic/antispasmodic agents form the cornerstone of therapy. Unfortunately, the pharmacological activity of these agents is not limited to the urinary tract, leading to systemic adverse effects that often promote nonadherence. Although the pharmacokinetics of flavoxate, propantheline, scopolamine, imipramine/desipramine, trospium chloride and propiverine are also reviewed here, only for oxybutynin and tolterodine are there adequate efficacy/tolerability data to support their use in urge incontinence. Oxybutynin is poorly absorbed orally (2-11% for the immediate-release tablet formulation). Controlled-release oral formulations significantly prolong the time to peak plasma concentration and reduce the degree of fluctuation around the average concentration. Significant absorption occurs after intravesical (bladder) and transdermal administration, although concentrations of the active N-desethyl metabolite are lower after transdermal compared with oral administration, possibly improving tolerability. Food has been found to significantly affect the absorption of one of the controlled-release formulations of oxybutynin, enhancing the rate of drug release. Oxybutynin is extensively metabolised, principally via N-demethylation mediated by the cytochrome P450 (CYP) 3A isozyme. The pharmacokinetics of tolterodine are dependent in large part on the pharmacogenomics of the CYP2D6 and 3A4 isozymes. In an unselected population, oral bioavailability of tolterodine ranges from 10% to 74% (mean 33%) whereas in CYP2D6 extensive metabolisers and poor metabolisers mean bioavailabilities are 26% and 91%, respectively. Tolterodine is metabolised via CYP2D6 to the active metabolite 5-hydroxymethyl-tolterodine and via CYP3A to N-dealkylated metabolites. Urinary excretion of parent compound plays a minor role in drug disposition. Drug effect is based upon the unbound concentration of the so-called 'active moiety' (sum of tolterodine + 5-hydroxymethyl-tolterodine). Terminal disposition half-lives of tolterodine and 5-hydroxymethyl-tolterodine (in CYP2D6 extensive metabolisers) are 2-3 and 3-4 hours, respectively. Coadministration of antacid essentially converts the extended-release formulation into an immediate-release formulation. Knowledge of the pharmacokinetics of these agents may improve the treatment of urge incontinence by allowing the identification of individuals at high risk for toxicity with 'usual' dosages. In addition, the use of alternative formulations (controlled-release oral, transdermal) may also facilitate adherence, not only by reducing the frequency of drug administration but also by enhancing tolerability by altering the proportions of parent compound and active metabolite in the blood.

Respiratory tract secretions in the dying patient: a retrospective study

Respiratory tract secretions (RTS), the sound created by poorly-cleared mucous in the hypopharynx or bronchial tree, can be alarming for dying patients, relatives and staff. Increased knowledge into the etiology of RTS and its response to treatment is needed to improve future management. We studied retrospectively the data from 202 patients who died on a 30-bed specialist palliative care unit during a one-year period. These patients were observed every four hours during the dying phase. RTS was treated with hyoscine hydrobromide. Ninety-nine patients (49%) developed RTS. The median time from onset of RTS till death was 16 hours. Fifty-nine patients could have their treatment response assessed. Of these, 30.5% responded within four hours, 33.9% after four hours, and 35.5% died with RTS. Increasing the dose for nonresponders had no significant effect. Significant risk factors for developing RTS were found to be prolonged dying phase, primary lung cancer and male gender.

A signal transduction pharmacodynamic model of the kinetics of the parasympathomimetic activity of low-dose scopolamine and atropine in rats

We used a novel pharmacokinetic-pharmacodynamic (PK-PD) approach that had been applied for signal transduction kinetics to investigate the kinetics of the parasympathomimetic effect of scopolamine and atropine in rats. The parasympathetic tone was assessed by continuous measurement of the power of the high frequency band (HF) of electrocardiogram (ECG) R-R intervals obtained by power spectral analysis (PSA) of heart rate variability (HRV). To overcome the inherent noise of the HRV-HF data and to quantitatively identify temporal changes in the autonomic tone, a new approach of stepwise regression of the cumulative HF data was applied. The elevation of the parasympathetic tone occurred after a significant lag time (>70 min) following scopolamine administrations [0.25 and 0.5 mg/kg intravenous (iv) bolus or infusion over 100 min], followed by a gradual return to the baseline levels. A similar lag time in parasympathetic stimulation was observed following iv bolus administration of atropine (0.1 mg/kg). The plasma drug concentration versus time data were linked to the response versus time data using a signal transduction pharmacodynamic model that was fitted simultaneously to all four experimental data sets. This PK-PD model resolved the significant discrepancy between the concentration versus time and the response versus time patterns and successfully described the kinetics of the parasympathetic stimulation obtained for different drugs and different rates of administration. This work paves the way for further PK-PD preclinical investigations in this field.

A study comparing hyoscine hydrobromide and glycopyrrolate in the treatment of death rattle

This study looked at the efficacy of drug treatment in managing death rattle in a 30-bedded specialist palliative care unit. The study was conducted in two phases. In the first, patients received hyoscine hydrobromide as the antimuscarinic; glycopyrrolate was used in the second phase. The patients in the two phases were well matched for diagnosis, age, sex and duration of death rattle. A noise score scale of 0-3 was used, which was separately validated using a verbal rating scale and noise-meter readings. Noise scores were taken at the start; 30 min after an antimuscarinic drug was administered; an hour after the initial injection if a repeat dose was given at 30 min; and 4-hourly thereafter. Drug charts of all patients with death rattle were analysed to ascertain the amount of each drug given and the cost. The incidence of death rattle was 44% in phase I, and 36% in phase II. The percentage of patients with reduced noise scores 30 min after one injection of hyoscine was significantly greater than after one dose of glycopyrrolate (56% vs 27%, P = 0.002). The need for a second injection after 30 min was less using hyoscine (33% vs 50%, P = 0.03). There was no statistically significant difference in improvement at 1 h, or at the last recorded score before death. A comparison of the cost of drug treatment using hyoscine or glycopyrrolate was made, and the potential reduction in cost per patient in the glycopyrrolate group was largely offset by increased expenditure on other drugs, especially diamorphine, midazolam and levomepromazine. The results of this study suggest that: (1) glycopyrrolate 0.2 mg is less effective at reducing death rattle than hyoscine hydrobromide 0.4 mg when assessed at 30 min, (2) the use of glycopyrrolate may lead to an increased need for other sedative or anti-emetic medication such as diamorphine, midazolam or levomepromazine, and (3) the cost benefit of using glycopyrrolate over hyoscine hydrobromide is a small part of the total drug budget, and may be less than anticipated due to the increased need of these other drugs.

Pharmacokinetic-pharmacodynamic modeling of the electroencephalogram effects of scopolamine in healthy volunteers

Scopolamine is a muscarinic receptor antagonist commonly used as a pharmacological model substance based on the "cholinergic hypothesis" of memory loss in senile dementia of the Alzheimer type. The objective of the study was to relate pharmacodynamic electroencephalogram (EEG) changes and scopolamine serum concentration using pharmacokinetic-pharmacodynamic (PK-PD) modeling techniques. This was a randomized, three-way crossover, open-label study involving 10 healthy nonsmoking young male volunteers who received either scopolamine 0.5 mg as an intravenous (i.v.) infusion over 15 minutes or an intramuscular (i.m.) injection or a placebo. The pharmacodynamic EEG measure consists of the total power in delta, theta, alpha, and beta bands over frontal, central, and occipital brain areas. The values of the pharmacokinetic parameters of scopolamine after i.v. infusion were clearance (CL) 205 +/- 36.6 L/h, volume of distribution (Vd) 363 +/- 66.7 L, distribution half-life (t1/2 alpha) 2.9 +/- 0.67 min, and terminal half-life (t1/2 beta) 105.4 +/- 9.94 min (mean +/- SEM). Mean peak serum concentrations (Cmax) were 4.66 and 0.96 ng/ml after i.v. and i.m. administration, respectively (p < 0.05). The area under the serum concentration versus time curve (AUC) after i.m. administration (81.27 +/- 11.21 ng/ml/min) was significantly lower compared to the value after i.v. infusion (157.28 +/- 30.86 ng/ml/min) (mean +/- SEM, p < 0.05). Absolute bioavailability of scopolamine after i.m. injection was 57% +/- 0.08% (mean +/- SEM). After both i.v. and i.m. administration, scopolamine induced a decrease in EEG alpha power (7.50-11.25 Hz) over frontal, central, and occipital brain areas compared to placebo (p < 0.05). The individual concentration-EEG effect relationships determined after i.v. infusion of scopolamine were successfully characterized by a sigmoidal Emax model. The averaged values of the pharmacodynamic parameters were E0 = 0.58 microV2, Emax = 0.29 microV2, EC50 = 0.60 ng/ml, and gamma = 1.17. No time delay between serum concentrations and changes in alpha power was observed, indicating a rapid equilibration between serum and effect site. The results provide the first demonstration of a direct correlation between serum concentrations of scopolamine and changes in total power in alpha frequency band in healthy volunteers using PK-PD modeling techniques. As regards the effect on the EEG, 0.5 mg of scopolamine administered i.v. appears to be a suitable dose.

Spectral analysis of heart rate variability as a quantitative measure of parasympatholytic effect--integrated pharmacokinetics and pharmacodynamics of three anticholinergic drugs

The time course and concentration-effect relationship of parasympatholytic effects of three anticholinergic drugs were investigated using spectral analysis of heart rate (HR) variability. Single intravenous (i.v.) doses of atropine (10 microg/kg), glycopyrrolate (5 microg/kg), scopolamine (5 microg/kg), and placebo were given to eight healthy volunteers in a double-blind, randomized cross-over study. Electrocardiogram (ECG) was recorded at baseline and 2.5, 5, 10, 20, and 30 minutes, and 1, 1.5, 2, 3, 4, 5, and 6 hours after drug administration, while the subjects breathed at a fixed 0.25 Hz frequency. The powers of two frequency bands (low frequency [LF] = 0.07-0.15 Hz and high frequency [HF] = 0.15-0.40 Hz) were calculated using stationary time series of R-R intervals (RRI) free from ectopic beats. To perform pharmacokinetic-pharmacodynamic (PK-PD) modeling, venous plasma drug concentrations were measured. Atropine and glycopyrrolate, and, to a lesser extent, scopolamine induced decreases in HF power and increases in LF/HF ratio of HR variability, indicating parasympatholytic activity and corresponding changes in sympathovagal balance. Maximal average decreases in HF power were 99%, 94%, and 82%, respectively, but in two scopolamine subjects, a parasympathomimetic effect was dominant. Interindividual variability was least for the Hayano index of HF power (square root (RRI HF-power)/RRI*100), and profound and consistent decreases were seen after atropine and glycopyrrolate. Pharmacokinetics were best fitted to a two-compartment open model, and effect compartment link modeling using the Hayano index was performed with the atropine and glycopyrrolate data. The best description of the PK-PD relationship for both drugs was achieved using the sigmoidal Emax model. Mean (+/-SD) EC50, sigmoidicity factor (gamma), and equilibration rate constant (k(e0)) estimates were 1.35 (+/-0.27) ng/mL, 6.07 (+/-1.98) and 11.0 (+/-5.28) l/h for atropine and 1.35 (+/-0.49) ng/mL, 4.34 (+/-1.55) and 2.26 (+/-0.81) l/h for glycopyrrolate. Spectral analysis of HR variability appears to be a powerful tool in monitoring parasympatholytic drug activity. A sigmoidal Emax model with an extremely steep concentration-response relationship was revealed for atropine and glycopyrrolate. The effects of scopolamine were more incongruous.

Pharmacokinetics and pharmacodynamics of scopolamine after subcutaneous administration

The effects of subcutaneously administered scopolamine on quantitative electroencephalogram (qEEG) and cognitive performance were evaluated and correlated with pharmacokinetic parameters in a randomized, double-blind placebo-controlled crossover study of 10 healthy male volunteers. Changes in qEEG and cognition were determined for 8 hours after drug administration. Scopolamine produced dose- and time-dependent impairments of attention and memory and a time-dependent increase in delta power (1.25-4.50 Hz) and a decrease in fast alpha power (9.75-12.50 Hz) on qEEG compared with placebo. Maximum serum concentrations of scopolamine occurred 10 to 30 minutes after drug administration. Mean peak serum concentrations (free base) were 3.27, 8.99, and 18.81 ng/mL after administration of 0.4, 0.6 mg, and 0.8 mg scopolamine, respectively. Elimination half-life was approximately 220 minutes. The findings indicate temporary changes in qEEG and psychometric tests, and support the possible use of such a testing model for impaired cognitive functions such as age-related memory disturbances.

Pharmacokinetics and clinical effects of intramuscular scopolamine plus morphine. A comparison of two injection sites

BACKGROUND

Intramuscular scopolamine plus morphine premedication is traditionally used when prominent sedative or antisialogogue effect is needed. Knowledge of the pharmacokinetics of scopolamine is limited due to low plasma concentrations found after therapeutic doses. This investigation compares the pharmacokinetics and the clinical responses of this drug combination injected into two commonly used injection sites.

METHODS

Twelve ASA class 1 patients scheduled for minor surgery under spinal anaesthesia received scopolamine 6 micrograms/kg plus morphine 200 micrograms/kg injected in either deltoid (group D, n = 6) or gluteal (group G, n = 6) muscle.

RESULTS

The peak plasma concentrations of scopolamine after deltoid or gluteal injection (2.2 vs 1.6 micrograms/l) and the time they were reached (17 vs 19 min) were comparable. The absorption of morphine was similar in both groups (Tmax 16 min), but the peak plasma concentrations were higher after deltoid injection (71 vs 49 micrograms/l). The individual variation in the elimination half-lives of both scopolamine and morphine was smaller after deltoid injection (T1/2 scopolamine 1.9 +/- 0.7 vs 2.1 +/- 1.1 h, morphine 1.3 +/- 0.7 vs 2.3 +/- 1.5 h). Moderate slowing (25%) of heart rate was found in both groups. A heavy sedation and antisialogogue effect (VAS) was found in both groups with faster occurrence of maximal effect in group D (60 vs 120-180 min).

CONCLUSION

More predictable pharmacokinetics and clinical effects of intramuscular scopolamine plus morphine premedication can be achieved after an injection into deltoid muscle.

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)

Risk-benefit assessment of anaesthetic agents in the puerperium

A critical evaluation of anaesthetic agents in the puerperium is difficult because systematic, relevant studies are still lacking. Current knowledge of the effects of different agents used in labour and caesarean section indicates that significant residual effects on the mother and newborn are limited. In the early puerperium, based on physiological and/or hormonal changes, the mother could be more sensitive to inhalational anaesthetic agents and local analgesics. To date there is no evidence that any anaesthetic agent is excreted in breast milk in clinically significant amounts when given as a single dose. The only exception is perhaps in the case of very premature neonates whose mothers have had multidrug therapy before labour. Even then the importance of breast milk should be carefully assessed against possible adverse drug effect. However, repeated administration of long-acting benzodiazepines and continuous epidural administration of pethidine (meperidine) can have adverse effects on the neonate. The essential conclusion of this review is that breast-feeding is best. The different anaesthetic agents are excreted in the milk in amounts so low that detrimental effects on the neonate should not be expected.

Pharmacokinetics of glycopyrronium in parturients

A sensitive radioreceptor assay was used to determine the pharmacokinetics of glycopyrronium 6 micrograms/kg after intramuscular (deltoid muscle) administration in eight Caesarean section patients. A fast absorption rate was found with a mean maximum plasma concentration (Cmax) of 6.3 (SD 1.5) ng/ml, a mean time to Cmax (Tmax) of 10.0 (3.8) minutes and the elimination half-life (t1) of 33.4 (1.92). The respective AUC0-8 h value was 5.61 (1.27) hours ng/ml. This dose produced a significant increase in the maternal heart rate after 10 minutes (p less than 0.05) and an antisialogogue effect after 30 minutes (p less than 0.05) of the drug injection. Almost half of drug (48.3%) was excreted into the urine within 3 hours. There were no measurable levels of glycopyrronium in the lumbar cerebrospinal fluid (CSF) after 60 minutes of drug injection. The concentrations of glycopyrronium in the umbilical venous (0.28 (0.25) ng/ml) and in the umbilical arterial (0.18 (0.11) ng/ml) plasma after 86 minutes of drug injection were low and clinically insignificant, as was the case in the amniotic fluid (0.15 (0.08) ng/ml).

Systemic absorption of ocular scopolamine in patients

The systemic absorption of scopolamine 0.25% eyedrops given unilaterally was quantitated in eight patients following therapeutic drug application. Another set of eight patients received placebo drops to study the effect of scopolamine on heart rate, blood pressure and salivation. Scopolamine was rapidly and efficiently absorbed after its ocular administration. The peak plasma scopolamine concentration of 550 +/- 60 pg/ml was reached within 15 minutes in all but two patients. Ocular scopolamine did not affect patients blood pressure or heart rate when compared to patients in the placebo group. Thirty minutes after administration of scopolamine the salivary secretion was slightly but insignificantly reduced.