Ephedrine pharmacokinetics

Amphetamine is a racemic mixture of phenylisopropylamine (Figure 9-4) that is important chiefly because of its use and misuse as a central nervous system stimulant (see Chapter 32). Pharmacokinetically, it is similar to ephedrine however, amphetamine even more... 

Berlin 1, Warot D, Aymard G, Acquaviva E, Legrand M, Labarthe B, Peyron 1, Diquet B, Lechat P. Pharmacodynamics and pharmacokinetics of single nasal (5 mg and 10 mg) and oral (50 mg) doses of ephedrine in healthy subjects. Eur J Clin Pharmacol 2001 57(6-7) 447-55. 

Studies have shown that resultant effects are similar, regardless of whether pure synthetic ephedrine or naturally occurring ephedra is ingested (24,25). There are,however, significant enantioselective differences between the enantomers in both pharmacokinetic and pharmacodynamic effects. All of the ephedra alkaloids have important effects on the cardiovascular and respiratory systems, but not to the same degree. 

The pharmacokinetic and toxicokinetic behavior of any isomer cannot be used to predict that of any other ephedrine isomer. The (+) isomer of meth-amphetamine, for example, is a potent CNS stimulant, but the (-)-isomer is merely a decongestant. There is a tendency in the literature to lump together all ephedrine alkaloids and use the term class effect to assume that all the different drugs in that class exert the same effects on the same biological targets. In fact, some of the drugs in the class will be similar in some regards and different in others. 

The rate at which any of the enantiomers is eliminated depends upon the urinary pH. At high pHs, excretion time is prolonged. At low pH ranges, excretion is accelerated. In controlled laboratory studies, where volunteer subjects were given either bicarbonate or ammonium chloride, the higher the urine pH, the more slowly the ephedrine and pseudoephedrine were excreted. Conversely, when the urine pH is low, excretion is accelerated (71). The importance of these observations is hard to assess, because without the addition of bicarbonate, urine pH values in the general population rarely approach 8.0. A study of pseudoephedrine pharmacokinetics in 33 volunteers who were not treated with drugs to alter urine pH found that these parameters could not be... 

Vanakoski J, Stromberg C, Seppala T (1993) Effects of a sauna on the pharmacokinetics of midazolam and ephedrine in healthy young women. Eur J Clin Pharmacol 45 377-381... 

Kaddoumi, A. Kubota, A. Nakashima, M.N. Takahashi, M. Nakashima, K. High performance liquid chromatography with UV detection for the simultaneous determination of sympathomimetic amines using 4-(4,5-diphenyl-lH-imidazole-2-yl)benzoyl chloride as a label, Biomed.Chromatogr., 2001, 15, 379-388. [human rat plasma derivatization LOD 50-100 nM ephedrine norephedrine 2-phenylethylamine fenfluramine phentermine cyclohexylamine fluoxetine is internal standard pharmacokinetics]... 

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