OPIOIDS - III
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Drug | Agent | Fentanyl | Sufentanil | Alfentanil | Remifentanil |
| Class | Phenylpiperidine | Phenylpiperidine | Phenylpiperidine | Phenylpiperidine ester | |
| Structure
| (Related to pethidine) | (thienyl analogue fent) |
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| Formulation
| Fent HCl 100mcg/2ml Transdermal 25, 50, 75, 100mcg/hr lollipop 5-20mcg/kg | Iv | Iv | Crystalline powder Glycine (NOT neuraxial) | |
| Isomers |
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P/kin | pKa | 8.4 | 8.0 | 6.5 | 7.3 |
| % unionised @ pH 7.4 | 8% (ion trapping) | 20% | 90% → fast onset | 60% (no ion trapping) | |
| Lipid solubility | 800 x morphine → ↑potency, faster onset | 1500 x morphine | 150 x morphine |
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| po absorption |
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| Bioavailability | Low (hepaticmetab, lung uptake 75%) | Lung uptake 60% | Lung uptake 10% |
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| PPB (%) | 80% | 93% (a1acid glyco) | 92% (a1 acid glyco) | 66-93% | |
| Vdss (L/kg) | 4.6 | 1.7 (high PPB) | 0.5 – 1 (low lipid sol, high PPB) | 0.6 | |
| CL(ml/kg/min) | 17 | 13 | 7 | 60 | |
| Metabolism | Desmethylation, alkylation (inactive) | HHER (high lipid sol) Inactive metab | N dealkylation, conjug | Non-specific tissue and plasma esterases (metabolite potency 1/1000) | |
| Excretion |
| Bile:urine 1:1 | renal (metabolites) |
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| t½α (min) |
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| t½β (hr) | 3-4hr (larger Vd) | 2-3hr | 1-1.5hr | 15-20min | |
| CSHT 4hr ivi | 260min (saturate lung) | 30min ( | 60min | 4min (independent of infusion duration) | |
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Admin | Potency | 100 x morphine | 1000 x morphine 10 x fentanyl (↑affinity) | 30 x morphine 1/5 – 1/10 x fentanyl | 100 x morphine 1 x fentanyl |
| Dose | 1-2mcg/kg iv analgesia <10mcg/kg> 50-100mcg/kg iv cardiac 50-100mcg epi | 0.1-0.4mcg/kg analgesia better kinetic profile for infusions than alfentanil | 15mcg/kg analgesia for laryngoscopy, retrobulbar block, transient noxious stim 150-300mcg/kg induction | 1mcg/kg over 1min or 0.5-1mcg/kg over 10min → induction | |
| Hepatic failure | No change (?why not) | No change | increased | 0 | |
| Renal failure |
| ↑ | 0 | 0 | |
| Target level |
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| Onset | Faster than morphine |
| Rapid (90% unionised) |
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| Effect site equilibration | 6.8min | 6.2min | 1.4min | 1.1min | |
| Duration | <10mcg/kg> 50-100mcg/kg iv 6hr |
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| Offset | Redistribution to fat and skel muscle | Rapid redistribution | Rapid elimination (small Vd) > redistribution | Rapid elimination | |
| Other |
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Category: Pharmacology Notes
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