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Biomedical subjects

A Shafer

Publications and source records attributed to A Shafer.

23 records · Page 2Linked to original sources
PubMed1986

Pharmacokinetics and pharmacodynamics of alfentanil infusions during general anesthesia.

The pharmacokinetic and pharmacodynamic properties of alfentanil were studied in 64 surgical patients. Alfentanil was administered as a loading infusion (25-130 micrograms/kg) followed by a maintenance infusion (0.25-1.3 micrograms X kg-1 X min-1) as part of a nitrous oxide-narcotic-muscle relaxant technique. Although alfentanil doses of at least 50 micrograms/kg (in combination with thiopental, 2 mg/kg) were required to prevent hemodynamic changes during intubation, apnea or chest wall rigidity frequently occurred with alfentanil loading infusions exceeding 75 micrograms/kg. The alfentanil clearance rate was significantly lower in patients with liver dysfunction (2.3 +/- 1.3 vs 4.2 +/- 2.0 ml X kg-1 X min-1, mean +/- SD). In addition, the patients who required opioid antagonists to reverse postoperative respiratory depression had lower clearance rates (1.5 +/- 0.7 vs 4.1 +/- 1.9 ml X kg-1 X min-1) and longer elimination half-life values (406 +/- 304 vs 87 +/- 53 min). For maintenance of hemodynamic stability during superficial and intraabdominal operations, alfentanil serum concentration-response curves revealed ED95 values exceeding 300 ng/ml and 400 ng/ml, respectively. Our study also demonstrated a wide range of clinical responses to fixed doses of alfentanil. At equivalent doses, some patients required supplemental anesthetics, whereas others required an opioid antagonist. Careful titration of the alfentanil maintenance infusion is recommended to minimize the possibility of postoperative respiratory depression.

Adult↗
PubMed1985

Comparative pharmacology of the ketamine isomers. Studies in volunteers.

The clinical and electroencephalographic (EEG) effects of the individual ketamine isomers were compared with the racemic mixture in five volunteers who received each drug on a separate occasion. Racemic ketamine 275 +/- 25 mg, s(+) ketamine 140 +/- 21 mg or R(-) ketamine 429 +/- 37 mg produced an anaesthetic state lasting 6 +/- 2 min (mean +/- SD). However, the EEG evaluation of the R(-) isomer revealed less overall slowing, and an absence of the large slow wave complexes produced by the S(+) isomer and the racemic mixture. The pharmacokinetic profiles for the individual isomers of ketamine did not differ significantly from the racemic mixture. Even though the apparent anaesthetic state produced in these healthy volunteers did not differ qualitatively between the three drug groups, recovery times (assessed using a standardized battery of psychometric tests) were consistently shorter following the individual isomers compared with the racemic mixture. The serum ketamine concentrations associated with regaining consciousness and orientation were consistent with an S(+):R(-) isomer potency ratio of 4:1. In terms of their ability to impair psychomotor function, the S(+):R(-) potency ratio varied from 3:1 to 5:1. After comparable degrees of CNS depression, we conclude that the more potent S(+) isomer of ketamine was associated with a more rapid recovery of psychomotor skills than the currently used racemic mixture.

Adult↗
PubMedDate not supplied

Cue reactivity in cocaine-dependent subjects: effects of cue type and cue modality.

Thirty cocaine-dependent subjects were enrolled into a cue-laboratory study to determine the specificity and sensitivity of this paradigm as a craving measure. Subjects experienced three cue types (i.e., cocaine, arousing, and neutral stimuli) in three cue modalities (i.e., audio, visual, and manual). Cue types were administered in different experimental sessions with a period of 2 to 3 days between sessions. Our results showed that subjective and physiological craving for cocaine was relatively specific for the cocaine cue as compared with either the arousing or the neutral cue. The relative sensitivities of the cue modalities in decreasing order was manual, audio, and visual. We suggest that a modified conditioned-cue paradigm could be a useful tool in the repeated assessment of craving during a clinical study.

Adult↗