Development of physical dependence on midazolam by oral self-administration

Neuroadaptive processes in GABAergic and glutamatergic systems in benzodiazepine dependence

Knowledge of the neural mechanisms underlying the development of benzodiazepine (BZ) dependence remains incomplete. The gamma-aminobutyric acid (GABA(A)) receptor, being the main locus of BZ action, has been the main focus to date in studies performed to elucidate the neuroadaptive processes underlying BZ tolerance and withdrawal in preclinical studies. Despite this intensive effort, however, no clear consensus has been reached on the exact contribution of neuroadaptive processes at the level of the GABA(A) receptor to the development of BZ tolerance and withdrawal. It is likely that changes at the level of this receptor are inadequate in themselves as an explanation of these neuroadaptive processes and that neuroadaptations in other receptor systems are important in the development of BZ dependence. In particular, it has been hypothesised that as part of compensatory mechanisms to diazepam-induced chronic enhancement of GABAergic inhibition, excitatory mechanisms (including the glutamatergic system) become more sensitive [Behav. Pharmacol. 6 (1995) 425], conceivably contributing to BZ tolerance development and/or expression of withdrawal symptoms on cessation of treatment, including increased anxiety and seizure activity. Glutamate is a key candidate for changes in excitatory transmission mechanisms and BZ dependence, (1) since there are defined neuroanatomical relationships between glutamatergic and GABAergic neurons in the CNS and (2) because of the pivotal role of glutamatergic neurotransmission in mediating many forms of synaptic plasticity in the CNS, such as long-term potentiation and kindling events. Thus, it is highly possible that glutamatergic processes are also involved in the neuroadaptive processes in drug dependence, which can conceivably be considered as a form of synaptic plasticity. This review provides an overview of studies investigating changes in the GABAergic and glutamatergic systems in the brain associated with BZ dependence, with particular attention to the possible differential involvement of N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors in these processes.

Development of physical dependence to lorazepam in rats: the effects of repeated short treatments, dose and age

Rats were treated with lorazepam for four days (six times 2 mg kg(-1)) at the ages of 71, 118, 163 and 210 days. Increased excitation (physical dependence) in the withdrawal period was tested several times during 14 days with hexobarbital in an EEG threshold test. Lorazepam could induce physical dependence usually with a maximum (20% of the controls) on day four of withdrawal, but the age was a critical variable. A dose-response relationship with regard to lorazepam (0.5, 1, 2 mg kg(-1)) was found at 71 days but a more complicated pattern was found at 118 days of age. The rats treated with lorazepam 2 mg kg(-1) at the ages of either 71 and 118 days were given a treatment again with lorazepam 2 mg kg(-1) three months later. Compared with age-matched untreated rats, previous drug exposure influenced the pattern of increased excitation indicating a carry-over effect even after such a recovery period.

Different kinetics of tolerance to behavioral and electroencephalographic effects of chlordiazepoxide in the rat

The daily oral administration of chlordiazepoxide (40 mg/kg) over 9 weeks in rats elicited full tolerance to muscle relaxant effects within 7 weeks, as revealed by twice weekly evaluations of abdominal tone myorelaxation and decreased grip strength. No full tolerance was achieved, however, during the 9 weeks of treatment in terms of ataxia. Electroencephalographic (EEG) studies showed that this tolerance to the behavioural effects was accompanied by a progressive decrease in mean power spectra, associated with a progressive decrease in the beta band, but in this case, full tolerance was reached within 4 weeks. Once weekly evaluations of the ability of chlordiazepoxide to protect the animals against pentylenetetrazole seizures revealed a similar pattern. Treatment with flumazenil (50 mg/kg p.o.) 24 h after the last chlordiazepoxide administration induced a clear withdrawal syndrome associated with EEG changes which consisted of an increase in total power spectra associated with an increase in the delta band (in comparison with chlordiazepoxide-dependent rats not given the antagonist). These findings suggest that the different kinetics of the tolerance to anticonvulsant and EEG effects in comparison to myorelaxant effects can be attributed to a different involvement of benzodiazepine receptor subtypes.

Comparison of anticonvulsant tolerance, crosstolerance, and benzodiazepine receptor binding following chronic treatment with diazepam or midazolam

In a previous study, rats treated chronically with flurazepam were tolerant to the anticonvulsant action of some benzodiazepines (BZs), but not others (34). To determine if this differential crosstolerance was unique to flurazepam, rats were treated chronically with diazepam or midazolam, and tested for tolerance to the anticonvulsant actions of diazepam, midazolam, clonazepam, and clobazam. Regional benzodiazepine receptor binding in brain was also studied. In contrast to previous findings with flurazepam, 1 week treatment with diazepam or with midazolam did not cause tolerance. Rats treated with diazepam for 3 weeks were tolerant to diazepam, clonazepam, clobazam, and midazolam. In contrast, rats treated 3 weeks with midazolam were tolerant to diazepam and midazolam, but not clobazam or clonazepam. Neither diazepam nor midazolam treatment for 3 weeks altered BZ binding in cerebral cortex, cerebellum, or hippocampus. The effects of chronic BZ treatment depended not only on the BZ given chronically, but also on the BZ used to evaluate these effects, suggesting drug-specific interactions of different BZs with their receptors.

Benzodiazepine withdrawal reaction in two children following discontinuation of sedation with midazolam

OBJECTIVE

To report the occurrence of recurrent benzodiazepine withdrawal reactions in two very young children following discontinuation of sedation with midazolam.

CASE SUMMARY

A 15-month-old boy with apneic episodes was sedated with midazolam for 12 days with constant infusion. Half a day after discontinuation of the midazolam the boy became restless, tachycardic, and hyperpyrexic. When midazolam was readministered, all symptoms disappeared. Four days later midazolam was again discontinued and within 12 hours the same signs and symptoms reappeared. Midazolam infusion was restarted, and the signs and symptoms disappeared for the second time. After thoracotomy, a 14-day-old boy received intravenous midazolam for sedation for 29 days. Within 12 hours after discontinuation of midazolam he became restless, developed a bulging stomach secondary to aerophagia, and was vomiting. Midazolam therapy was reinstituted and continued for another 2 months by constant infusion. Thereafter, the boy was successfully weaned from artificial ventilation in 5 days under sedation with midazolam. About 12 hours after discontinuation of midazolam the boy became restless, tachycardic, again developed a bulging stomach because of aerophagia, and vomited. When the child was sedated with clorazepate by continuous infusion, the signs and symptoms disappeared.

DISCUSSION

Case reports describing benzodiazepine withdrawal reaction upon discontinuation of midazolam were reviewed and compared. The symptoms observed in the children we present resemble those mentioned in the three children and two adults reported previously. Unique in the very young children in this article is the occurrence of gastrointestinal symptoms, which most likely are the result of air being swallowed secondary to severe agitation.

CONCLUSIONS

Midazolam withdrawal reactions in adults and children, particularly in an intensive care unit, can be significant. Considerable caution must be taken with relatively long-term administration and abrupt discontinuation of midazolam.

Midazolam withdrawal and discriminative motor control: effects of FG 7142 and Ro 15-1788

Rats chronically drank either water or midazolam solution (0.1 mg/ml) in daily, 3-h schedule-induced polydipsia sessions and were evaluated in daily motor control sessions after polydipsia when midazolam metabolite levels had fallen to zero (withdrawal). Under midazolam polydipsia, animals orally self-administered between 21 and 38 mg/kg daily. The effect of acute drug administration [midazolam (0.75-3 mg/kg, SC), FG 7142 (1-8 mg/kg, IP), Ro 15-1788 (10-20 mg/kg, IP)] on motor control performance was similar after either chronic water or midazolam polydipsia. Thus chronic, oral midazolam self-administration did not lead to tolerance to the motor impairment produced by SC midazolam, nor did the daily discontinuation lead to impaired motor performance, nor had these performances, which occurred after daily elevated midazolam metabolite levels had reached zero (withdrawal), become sensitized to the effects of either the benzodiazepine inverse agonist FG 7142 or the agonist Ro 15-1788.

Diazepam and discriminative motor control: acute, chronic and withdrawal effects

Rats were trained to hold a force transducer operated with a paw so that it remained between upper and lower limits of a force band for a continuous 1.5-sec period to deliver each food pellet. Acute doses of diazepam impaired measures of this performance. Separate groups received chronic diazepam injections (6 mg/kg, IP) either presession (Before Group) or postsession (After Group), or presession vehicle (Vehicle Group). The After and Vehicle Groups demonstrated that neither chronic postsession diazepam, nor time alone, altered motor performance. The performance of the Before Group was affected by the daily diazepam, and although tolerance to the impairment developed, it was incomplete. Late in the chronic-administration phase (after 75 days) a toxic effect of the suspending agent became evident in all groups as a decrease in work rate, although the other performance indices were not affected. The withdrawal of diazepam from the Before Group led to improved performance which returned to the original baseline level.

Precipitation of benzodiazepine withdrawal following sudden discontinuation of midazolam

Midazolam hydrochloride is an ultra-short acting benzodiazepine recently approved by the Food and Drug Administration for anesthesia induction and preoperative sedation. Frequently, midazolam is also used as an injection or infusion for the treatment of agitation in ventilator-dependent patients. A 53-year-old man underwent a gastrojejunostomy and was later intubated following the development of pseudomonal pneumonia. Midazolam was initiated in an effort to resolve his agitation and the patient continued to receive frequent bolus injections, averaging 22 mg/d over 21 days. Approximately eight hours after midazolam was abruptly discontinued, the patient became increasingly anxious and developed somatic complaints felt to be consistent with benzodiazepine withdrawal syndrome. Symptoms rapidly abated upon the reintroduction of midazolam and the drug was ultimately tapered over a period of four days and discontinued without further incident. Implications derived from the association of long-term midazolam therapy with benzodiazepine withdrawal syndrome are discussed.