Dural permeability to narcotics: in vitro determination and application to extradural administration

The permeability of cranial and lumbar dura to various substances including a number of narcotic analgesics was measured in vitro. Preliminary data On human postmortem material is reported. Permeability had a linear relation to the inverse of the square root of molecular weight. This is the expected relationship for a diffusion process dependent upon molecular weight. The differential mass selectivity coefficients for lumbar and cranial dura were calculated; they were similar at 0.8 and 0.9. This was greater than for diffusion in simple liquids, but much less than that for biological lipid membranes. This suggests that the low rates of diffusion are a property of the thickness of the dura rather than any inherent impermeability. A simple model for the dural transfer of drugs is described, and applied to narcotics. Its purposes were to suggest: the factors involved in the dural transfer of drugs; the physicochemical properties of drugs relevant to their dural transfer; worthwhile measurements in future studies. The model indicates that drug molecular weight and rate of absorption are important determinants of the efficiency of dural transfer. Low molecular weight and slow absorption produce high dural transfers. When applied to narcotics, these factors could produce a difference of up to an order of magnitude in the amount transferred directly across the dura.

Some patients don't need analgesics after surgery

Postoperative analgesic requirements of 410 patients undergoing elective orthopaedic limb surgery were studied. Premedication and anaesthetic were standardized with no narcotic. Twenty-three patients required no analgesic at all during their hospital stay. The importance of acknowledging the existence of this group of patients is discussed. The distribution of time to first analgesic requirement for the other patients was obtained. The importance of knowing the distribution for particular operative procedures and the effect of analgesic interventions such as premedication is discussed.

Some Patients Don't Need Analgesics after Surgery

Postoperative analgesic requirements of 410 patients undergoing elective orthopaedic limb surgery were studied. Premedication and anaesthetic were standardized with no narcotic. Twenty-three patients required no analgesic at all during their hospital stay. The importance of acknowledging the existence of this group of patients is discussed. The distribution of time to first analgesic requirement for the other patients was obtained. The importance of knowing the distribution for particular operative procedures and the effect of analgesic interventions such as premedication is discussed.

Sublingual buprenorphine used postoperatively: ten hour plasma drug concentration analysis

1 A 10 h study of plasma drug concentrations of the opiate buprenorphine after use was designed because a previous 3 h study had shown that peak plasma drug concentrations in some patients had not occurred by 3 h after the sublingual dose. 2 Fifteen postoperative patients were studied: at 3 h after a 0.3 mg intravenous dose five patients received a sublingual preparation of 0.4 mg of buprenorphine, five 0.8 mg of buprenorphine and five placebo. Plasma drug concentrations of buprenorphine were measured by specific radioimmuno-assay. 3 Plasma drug concentrations after sublingual buprenorphine were significantly higher than those in the placebo group by 1 h. They remained significantly higher over the succeeding nine hours. The mean time to peak plasma drug concentration was about 200 min in both the 0.4 mg and 0.8 mg groups (range 90-360 min). The plasma drug concentrations in the 0.8 mg group were approximately twice those in the 0.4 mg group; the ratio of the relative systemic availabilities was similarly 1.8:1. The absolute systemic availability was estimated at about 55% for both groups. Uptake of buprenorphine from the sublingual site was essentially complete by 5 h after the dose was given. 4 The implications for the timing of sublingual doses in clinical use are discussed.

A controlled comparison of the effects of extradural diamorphine and bupivacaine on plasma glucose and plasma cortisol in postoperative patients

The effects of an extradural narcotic, diamorphine, and of an extradural local anesthetic, bupivacaine, on postoperative responses of plasma glucose and cortisol levels following surgery were investigated in 20 fit women undergoing major gynecologic operations. The operations were conducted with morphine premedication and extradural local anesthetic with nitrous oxide, oxygen, and halothane. After surgery the patients were given either further extradural local anesthetic or 5 mg of extradural diamorphine. After surgery plasma glucose and plasma cortisol concentrations decreased in patients given extradural diamorphine, but increased in those given extradural local anesthetic. The differences between the groups were statistically highly significant (p less than 0.05) for both glucose and cortisol. The effects on metabolic responses to surgery produced by a small (5 mg) dose of diamorphine injected into the extradural space suggest a local action of the narcotic at the level of the spinal cord. Only very large intravenous doses of narcotics have previously been shown to suppress these responses.

Single-dose comparison of buprenorphine 0.3 and 0.6 mg i.v. given after operation: clinical effects and plasma concentration

The plasma concentrations and clinical effects of a single i.v. dose of buprenorphine 0.3 or 0.6 mg were studied in patients recovering from surgery. Analgesic and hormonal effects were greater with the greater dose without a parallel increase in respiratory depression. A comparison with previous work suggests that increased efficacy results either from the use of the larger dose or equivalently if the first required postoperative dose of 0.3 mg has been preceded by a similar loading dose.

An oral buprenorphine and paracetamol combination compared with paracetamol alone: a single dose double-blind postoperative study

1 An oral combination of buprenorphine and paracetamol was compared with paracetamol alone in a single dose, double-blind postoperative study. One hundred and twenty patients undergoing elective minor orthopaedic operations were allocated to four groups of 30 patients. The four treatments were 1,1.5 or 2 mg of buprenorphine with paracetamol 1,000 mg or paracetamol 1,000 mg alone. 2 There were no significant differences between the groups in analgesia measured by the observer over the 6 h period of direct observations. The oral opiate produced a significant increase in duration of analgesia beyond the 6 h study period. A significant increase in side-effects was seen only at the highest buprenorphine dose compared with paracetamol. 3 The problems of trial design for analgesic combinations are considered. Drug mixtures create additional complexities which decrease the certainty of the conclusion that no real benefits result from such mixtures.

Sublingual buprenorphine used postoperatively: clinical observations and preliminary pharmacokinetic analysis

1 Buprenorphine is a long-acting opiate analgesic. This study was designed to investigate the pharmacokinetics of this drug when given by the sublingual route to ten postoperative patients. Plasma levels of buprenorphine were measured by a specific radioimmunoassay. 2 Plasma levels of the drug following sublingual administration of 0.4 mg showed an apparent delay in absorption and then rose slowly to reach low but significant levels by 3 h. There was considerable variation in the time at which peak levels were achieved. The average systemic availability of the drug by this route was estimated to be 30% by 3 h. 3 Analgesic efficacy and duration of sublingual buprenorphine were assessed using demand analgesia. The analgesia was of about 9 h duration, similar to that achieved by parenteral administration of 0.3 mg of the drug to an equivalent group of patients. The sublingual dose caused a significant fall in the postoperatively elevated group of patients. The sublingual dose caused a significant fall in the postoperatively elevated plasma glucose, and prevented any further rise in plasma cortisol. 4 Reasons for the efficacy of the sublingual route are discussed and it is suggested that this route may be particularly appropriate for highly lipophilic drugs like buprenorphine.

Sex and surgical stress

The endocrine and metabolic response to anaesthesia and surgery was studied in 12 men and eight women undergoing elective total hip replacement using buprenorphine as the intra- and postoperative analgesic. Plasma glucose, cortisol and prolactin were measured, and the results obtained for men and women compared. Statistically significant difference between men and women were found for prolactin during and after operation, and also for cortisol postoperatively. Men, but not women, demonstrated a significant fall in plasma cortisol following a dose of buprenorphine after operation. These results are discussed in relation to known procedures for ablating the stress response and to the neuroendocrine effects of opiate agonists and partial agonists.

Buprenorphine kinetics

Buprenorphine kinetics was determined in surgical patients using radioimmunoassay. Buprenorphine was measured in the plasma of 24 patients who had received 0.3 mg buprenorphine intraoperatively. After 3 hr 10 of these patients then received a further 0.3 mg buprenorphine intravenously for postoperative pain relief, and 11 patients were given 0.3 mg intramuscularly; again, plasma levels were measured for 3 hr. The data fitted closely to a triexponential decay curve. There was a very fast initial phase, with a half-life (t1/2) of 2 min. The terminal t1/2 was slow, approximately 3 hr. Comparison of the kinetics of the same patient, awake and anesthetized, showed that the clearance was significantly lower in the anesthetized state. A notable feature of the drug given intramuscularly is rapid systemic availability, so that peaks are obtained in 2 to 5 min, and in 10 min the resulting levels are the same as for the intravenous and intramuscular routes.

Clinical effects of buprenorphine during and after operation

The analgesic, respiratory and hormonal effects of two doses of buprenorphine were studied during and after operation in 20 patients undergoing total hip replacement. The drug provided analgesia of long duration. The analesic and hormonal effects of the drug were greater after i.m. than after i.v. administration. The postoperative analgesic requirement of women was less than that of men. The pharmacodynamic differences shown between the sexes and between the two routes of administration are discussed in relation to the pharmacokinetics of the drug.