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Biomedical subjects

H Buerkle

Publications and source records attributed to H Buerkle.

38 records · Page 3Linked to original sources
PubMed1996

Comparison of the spinal actions of the mu-opioid remifentanil with alfentanil and morphine in the rat.

BACKGROUND: mu-Opioids administered spinally produce a potent, dose-dependent analgesic response in preclinical and clinical investigations. Side-effect profile of these compounds may be altered as a function of pharmacokinetics. The effects of intrathecal and intraperitoneal remifentanil, an esterase-metabolized mu opioid, alfentanil, and morphine were compared. METHODS: Intrathecal and intraperitoneal remifentanil, alfentanil, and morphine were examined in rats tested for hind-paw thermal withdrawal latency. The antinociceptive response was assessed and in parallel a scoring of four different parameters summarized as a supraspinal index to assess supraspinal side-effect profiles after the several drugs were delivered by the different routes. RESULTS: All opioids produced a dose-dependent analgesic response after intrathecal administration. The ordering of potency (intrathecal ED50 in micrograms) was remifentanil (0.7) > morphine (12.0) > alfentanil (16.3) > GR90291, principal remifentanil metabolite (> 810 micrograms). Time until onset of analgesia after intrathecal or intraperitoneal delivery was morphine > remifentanil = alfentanil. When matched for analgesic effect, the relative duration of action was morphine >> alfentanil > remifentanil. The supraspinal index showed a dose-dependent increase for all agents. All intraperitoneal drugs showed dose-dependent increases in antinociception with potency (intraperitoneal ED50 in micrograms) of remifentanil (4.3) > alfentanil (24.4) > morphine (262). Calculation of intrathecal or intraperitoneal ratios for supraspinal side effects/analgesia (supraspinal index ED50/analgesia ED50) revealed remifentanil to be greatest when intrathecally administered: remifentanil (4 intrathecal: 1.4 intraperitoneal); alfentanil (0.7 intrathecal: 1.5 intraperitoneal); and morphine (1 intrathecal: 5.6 intraperitoneal). CONCLUSIONS: These observations indicate that remifentanil has a powerful spinal opioid action. Consistent with its lipid-solubility, it has an early onset like alfentanil but displays a shorter duration of action after bolus delivery. Despite lipid solubility, remifentanil has a significant spinal therapeutic ratio. These observations likely reflect the rapid inactivation of systemically redistributed agent by plasma esterases.

Alfentanil↗
PubMed1996

Continuous intrathecal administration of shortlasting mu opioids remifentanil and alfentanil in the rat.

BACKGROUND: Lipid soluble mu opioids given intrathecally produce a potent, dose-dependent analgesic response, which because of rapid clearance, is of short duration. Such agents delivered by continuous infusion can result in systemic accumulation and significant extraspinally mediated side effects. The effects of intrathecal infusions of two lipid-soluble mu opioids were investigated: remifentanil, an esterase metabolized agent with an inactive metabolite, and alfentanil. METHODS: Rats with chronic lumbar intrathecal catheters received intrathecal infusions (in flow rates of 1.0 microliters/min and 0.1 microliters/min) of remifentanil or alfentanil and were tested for hind paw thermal withdrawal latency, supraspinal side effects (sedation, block of pinna, and corneal responses) and motor impairment. Remifentanil was delivered either in a glycine formulation (R(g)) or in a saline vehicle (R(s)). Separate studies with the glycine vehicle also were undertaken. RESULTS: At an infusion rate of 0.1 microliters/min, remifentanil and alfentanil produced naloxone-reversible, dose-dependent analgesia and supraspinal side effects with the intrathecal ED(50) (micrograms/min; 95% confidence interval) for analgesia: R(s) = 1.5 (1.2-1.8), R(g) = 1.2 (0.7-2.3); alfentanil = 1.5 (1.4-1.6) and for supraspinal side effects: R(s) = 1.7 (1.4-1.9); R(g) = 1.9 (1.6-2.4); alfentanil = 1.5 (1.4-1.7). There was no difference in potency or time until onset for analgesia at either delivery rate (12-20 min), whereas for supraspinal side effects, 1.0 microliters/min resulted in a faster onset for R(g). Recovery of normal thresholds after equianalgesic doses was faster in R(s) than alfentanil and for the supraspinal index faster in R(s) and R(g) groups. R(g), but not R(s), or alfentanil, produced a dose-dependent motor impairment after 90 min of intrathecal infusion at a flow rate of 0.1 microliters/min. Both glycine in R(g) and glycine (matching glycine dose) alone showed parallel time courses for motor impairment and similar intrathecal ED(50) (6.6 vs. 6.4 micrograms/min over 90 min) for this nonnaloxone reversible effect. Intrathecal bolus administration of the same total dose of glycine showed no significant motor effects. CONCLUSIONS: Remifentanil has a rapid onset like alfentanil but shows a faster recovery of action after intrathecal infusion. Despite its rapid clearance, remifentanil induces supraspinal side effects at analgesic effective doses. Moreover, in the current formulation, with glycine, a reversible motor impairment can occur after intrathecal delivery.

Alfentanil↗