The pharmacokinetics of rectal midazolam for premedication in children

The use of midazolam in premedication

Socio-psychological factors, such as increased anxiety in developed societies and cultures, and separation anxiety, particularly in children, justify the use of premedicants. In addition, the link between a central nervous "anxiety centre" and biochemical stress responses is blocked by an efficient anxiolytic. The elimination half-life of midazolam is longer in the elderly than in the young and in the obese than in the thin, which demands longer intervals between repeated doses in old and fat patients. The hypoxic ventilatory response is depressed in most patients and the ventilatory CO2 response in patients with chronic pulmonary disorders, which justifies increased monitoring of O2 saturations. It is important for the choice of dose and for estimating the duration of recovery time to know that midazolam is at least four times as potent as diazepam.

Anesthesia and monitoring during whole body radiation in children

During whole body radiation therapy of children, treatment may be done in places not equipped with acceptable scavenging systems for anesthetic gases and where clinical observation of the patient may be impossible. In order to solve this problem, the authors have used a total intravenous (IV) anesthetic technique using midazolam, pancuronium, and fentanyl. With midazolam as the only hypnotic agent, the problem with scavenging is solved, and a computer simulation of the plasma concentration of midazolam is presented. A modified stethoscope for monitoring during radiation also has been developed. This anesthetic technique and the stethoscope have been used in seven children. The total IV anesthesia proved to be a useful method for children during whole body radiation. The modified stethoscope functioned very well and was a useful complement to the monitoring equipment.

Paradoxical reactions to rectal midazolam as premedication in children

Eighty healthy children, between the ages of 2 and 7 years, who were to undergo oral surgical procedures under general anaesthesia, were allocated randomly to 4 groups. Three groups received rectal midazolam, and the other group a placebo (saline) as premedication 30 min prior to induction of anaesthesia. Group A children received midazolam 0.25 mg/kg, Group B 0.35 mg/kg and Group C 0.45 mg/kg. No statistically significant difference was found between the treatment groups as to the effect on systolic- (p = 0.6920) and diastolic (p = 0.8701) blood pressures, respiration (p = 0.0505) and pulse (p = 0.6192) rates at either pre- or post-sedation levels. However, the results indicate that levels of anxiolysis and sedation were significantly associated with midazolam dosage (p less than 0.0001).

[Premedication with intranasal midazolam in pediatric anesthesia]

To evaluate nasally administered midazolam 0.2 mg.kg-1 for preinduction of anaesthesia in paediatric patients the authors studied ASA 1 patients scheduled for elective surgery. Forty-five children, ages 3 to 126 months, were randomized in three groups: group D (n = 16) received diazepam 0.33 mg.kg-1 orally, group P (placebo) (n = 13) 0.04 ml.kg-1 normal saline via the nasal route; in group MDZ (n = 16) the children were given intranasal midazolam 0.3 mg.kg-1. The premedication was assessed on a 5-point sedation scale, modified to include the response to mask placement and the quality of the induction of general anaesthesia. The degree of sedation, heart rate, blood pressure, respiratory rate and oxygen saturation levels were recorded on the arrival in the operating room (0 min) and 3, 6, 9, 12 and 15 min (mask placement) after drug administration. With intranasal midazolam sedation was demonstrable at 6 min and was significant at 9 and 12 min. In this group all the children were calm or drowsy. The induction of anaesthesia was equivalent in group D and MDZ but easier than in those patients receiving normal saline. Vital signs did not change during the study period in any of the three groups. Intranasal midazolam was slightly more effective than oral diazepam. In children, it produces anxiolysis and sedation with rapid onset and is an attractive alternative to other routes for preanaesthetic medication.

Rectal induction of anaesthesia in children. A comparison between ketamine-midazolam and halothane for induction and maintenance of anaesthesia

Thirty children were randomly allocated to one of three anaesthetic techniques. Rectal anaesthesia induction with a mixture of ketamine 10 mg.kg-1 BW and midazolam 0.2 mg.kg-1 BW and maintenance of anaesthesia with either intravenous ketamine or halothane were compared to induction and maintenance with halothane. Rectal induction was found reliable and useful. The frequency of side effects, the recovery time, and the time until the child could be discharged were similar in the groups maintained with halothane, whereas recovery was prolonged when intravenous ketamine was used for maintenance.

Pharmacokinetics of the newer benzodiazepines

The assay methods used to determine the concentrations of the newer benzodiazepines include electron-capture gas-liquid chromatography, high performance liquid chromatography with ultraviolet detection, gas chromatography-mass spectrometry, radioassay and radioreceptor assay. The method used frequently is the highly sensitive and specific electron-capture gas-liquid chromatography. Other methods are associated with limitations. The triazolo- and imidazolebenzodiazepines differ structurally from the 'classical' benzodiazepines such as diazepam, and offer distinct differences in pharmacological activity and in time-course of effect. Alprazolam and triazolam, both 1,4-triazolobenzodiazepines, have high affinities for the benzodiazepine receptor as do midazolam and loprazolam, which are 1,4-imidazolebenzodiazepines. Absorption is characteristically rapid, with peak alprazolam and triazolam concentrations occurring within 1 hour after oral administration. Sublingual administration results in peak alprazolam and triazolam concentrations that are higher and occur earlier than with the oral route. The volume of distribution of alprazolam and triazolam is approximately 1L. Alprazolam is 70% bound to plasma proteins and the extent of binding is independent of concentration. Similarly, triazolam is approximately 85% bound to plasma proteins, variability in binding being explained by variations in alpha 1-acid glycoprotein concentration. The 1,4-triazolo ring prevents the oxidative metabolism of the classical benzodiazepines which results in formation of active metabolites with long elimination half-lives. Alprazolam is extensively metabolised: 29 metabolites have been identified in the urine, and its major metabolite, alpha-hydroxyalprazolam, has pharmacological activity. alpha-Hydroxyalprazolam and 4-hydroxyalprazolam are detectable in plasma in amounts which account for less than 10% of the administered dose. Mean alprazolam elimination half-life in healthy adult subjects ranges from 9.5 to 12 hours; liver disease prolongs alprazolam elimination, but renal insufficiency does not. Triazolam also undergoes oxidation and subsequent glucuronidation. alpha-Hydroxytriazolam is the major metabolite, in addition to which 4-hydroxyalprazolam and alpha-4-hydroxytriazolam have been identified in plasma and urine. The elimination half-life of triazolam ranges between 1.8 and 5.9 hours, while that of the conjugated metabolites is short, approximately 3.8 hours. Accumulation of triazolam or its metabolites after multiple doses does not occur. Liver disease prolongs triazolam elimination from the body, but renal disease does not.(ABSTRACT TRUNCATED AT 400 WORDS)

The pharmacokinetics of midazolam in paediatric patients

A serum concentration profile study on midazolam in children was done. Fifty six children aged 3-10 years took part. The routes investigated were intravenous, intramuscular, rectal and oral at 0.15 mg.kg-1, and the oral at 0.45 mg.kg-1 and 1 mg.kg-1. Serum concentration levels for 5 h were studied using gas liquid chromatography. The volume of distribution, Vss, was 1.29 l.kg-1, the elimination half-life 1.17 h and the serum clearance 9.11 ml.kg-1.min-1. Peak serum concentrations for the intramuscular, rectal and oral routes were at 15 min, 30 min and 53 min respectively. Bioavailability was 87%, 18%, 27% respectively at a dose of 0.15 mg.kg-1. The oral route bioavailability halved to 15% at the two higher doses. Bioequivalence was present between the 0.15 mg.kg-1 intramuscular dose and the 0.45 mg.kg-1 oral dose from 45 to 120 min.

Pharmacokinetics of midazolam and alpha-hydroxy-midazolam following rectal and intravenous administration

1. In an open cross-over trial, plasma concentrations of midazolam were measured in eight healthy male volunteers following administration of 0.3 mg kg-1 body weight given by the rectal and intravenous routes. 2. Maximum plasma concentrations of 92-156 ng ml-1 (mean 118 ng ml-1) were recorded from 20 to 50 min (mean 31 min) after rectal application. The rectal bioavailability was 40-65% (mean 52%) and the terminal half-life was 114-305 min (mean 161 min). 3. A substantial first-pass hepatic effect was observed following rectal administration. 4. No systemic or local intolerance was noted. 5. In conclusion, the rectal route of administration provides a rapid and reliable absorption of midazolam.