A. Marzo

Metabolism and disposition of intravenously administered acetyl-L-carnitine in healthy volunteers

SummaryThe pharmacokinetics of acetyl-L-carnitine hydrochloride were investigated in 6 healthy volunteers of both sexes after i.v. injection of 500 mg of the drug, expressed as inner salt.Plasma concentrations and urinary excretion of acetyl-L-carnitine (A), L-carnitine (B) and total acid soluble L-carnitine fraction were evaluated over a period lasting from 24 h before to 48 h after the administration. Plasma concentrations of A increased quickly after administration and then declined reaching base values within 12 h.Conversely, plasma concentrations of B rose more slowly, reaching a peak in 30–60 min, and then declined to base values within 24 h. Most of the injected dose of acetyl-L-carnitine was recovered in the urine during the first 24 h after administration as B and A.Mean renal clearance of both A and B during the first 12 h after injection was higher than the base values, suggesting the presence of a saturable tubular reabsorption process which may counterbalance major changes occurring in plasma concentrations of L-carnitine pattern.

High-performance liquid chromatography and capillary electrophoresis of l- and d-carnitine by precolumn diastereomeric derivatization

A new method for the simultaneous assay of D- and L-enantiomers of carnitine is described. The method is based on precolumn derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate [(+)FLEC] producing a diastereomeric derivative which can be detected both by UV absorbance and fluorescence detection. Also acyl esters of carnitine can be processed with this method, after alkaline hydrolysis. The D-enantiomer of carnitine and acylcarnitine can be detected at a concentration as low as 0.2% in the raw material and in pharmaceuticals. Assays can be carried out using an autoinjector either by HPLC or capillary electrophoresis (CE) because the derivative proved to be very stable. Its application is proposed for the routine assay of the enantiomeric excess of L-carnitine and their acyl esters in pharmaceutical products.

Determination of aliphatic amines by gas and high-performance liquid chromatography

Abstract Aliphatic amines, such as mono-, di- and trimethylamine (MMA, DMA, TMA) and trimethylamine N-oxide (TMAO), are produced by bacterial degradation of trimethylalkylammonium compounds, such as choline, acetylcholine, carnitine and γ-betaines. This degradation can be environmental, intestinal or faecal1.2. This paper describes an analytical investigation by gas chromatography (GC) with flame ionization detection (FID) or thermionic specific detection (TSD) and by high-performance liquid chromatography (HPLC) with conductimetric, refractive index (RI) and electrochemical detection (ED) for the simultaneous determination of the above amines, mainly applied to biological samples such as urine, and an assay procedure adopted consisting in chemical reduction of TMAO to TMA, followed by evaluation of the latter by GC in order to determine the TMAO.

Chromatographic and non-chromatographic assay of L-carnitine family components.

L-Carnitine and its acyl esters constitute an endogenous pool of the L-carnitine family, involved in the uptake of free fatty acids in the mitochondria by transfer across their membrane of the acyl moieties to fuel the beta-oxidation and the release of the acetyl group from the mitochondria to the cytosol. Therefore acyl-L-carnitine and acyl-L-carnitine transferase are involved in a homeostatic equilibrium with the cells. As most of these substances need to be monitored in foods, chemical and pharmaceutical processes and biological fluids, an overview of the main methods for assaying them is provided here, with specific reference to the intrinsic performance of each analytical procedure and with suggestions on the correct storage and manipulation of analytical samples.

L-CARNITINE AND CARNITINE ESTER TRANSPORT IN THE RAT SMALL INTESTINE

L-carnitine and its esters (acetyl-L-carnitine and propionyl-L-carnitine) at pharmacological doses (1, 5 and 10 mM) are absorbed by the rat jejunum by simple diffusion. Partition coefficients of carnitine esters determined in lipophilic media (diethyl ether/water and olive oil/water) are greater than that of L-carnitine. It would therefore seem that esters diffuse more easily through the lipid component of the intestinal barrier. The transport of acetyl- and propionyl-L-carnitine at pharmacological doses seems to be linearly and positively correlated with K+ transport but not with Na+ transport.

Application of high-performance liquid chromatography to the analysis of propionyl-L-carnitine by a stereospecific enzyme assay.

Propionyl-L-carnitine was converted by chemical hydrolysis (0.3 M potassium hydroxide, pH 12.8, room temperature) into L-carnitine, which competes with crotonoylbetaine formation and can be quantitatively evaluated by an enzyme assay. Under the conditions selected, hydrolysis of propionyl-L-carnitine to L-carnitine was completed in a few minutes with less than 0.5% of crotonoylbetaine being formed. The method described is enantioselective and possesses the analytical requirements for assaying propionyl-L-carnitine during chemical synthesis procedures and in pharmaceutical formulations.

Some pharmacokinetic considerations about homeostatic equilibrium of endogenous substances

SummaryEndogenous substances in the body are controlled through simple, very effective mechanisms, that preserve an optimum homeostatic equilibrium of baseline concentration and restore it when impaired. When planning a pharmacokinetic investigation of an endogenous substance exogenously administered, it is imperative to carefully ascertain the above mechanisms as well as the baseline value and their possible variations associated with daily rhythm, food, age, sex, menstrual cycle.Often the control mechanisms operate through non-linear processes, therefore a non-compartmental analysis or a tailored model may be more appropriate than the compartmental models used in standard pharmacokinetic analysis.Some specific examples of endogenous substances are discussed here on the basis of the data from the literature and personal experience.

Pharmacokinetics of oral acetyl-L-carnitine in renal impairment

SummaryAcetyl-L-carnitine 1.5 g and 3.0 g was administered as three divided doses on each of two occasions to 24 people with varying renal failure (creatinine clearance 127 – 8 ml·min−1). Plasma and urinary concentrations of total-L-carnitine, free (non-esterified) carnitine, short-chain esters and acetyl-L-carnitine were measured.The baseline (pre-study) concentrations of all four substances were related to renal function. Patients whose creatinine clearance was below about 30–40 ml·min−1 were had the highest concentrations.Renal elimination of all four substances was related to dose and to renal function. There was evidence for dose-related elimination, with greater elimination of the larger dose.

High-performance liquid chromatographic evaluation of Med 15 and its metabolites Med 5 and tolmetin in rat plasma.

A simple and reliable high-performance liquid chromatographic method is described for the quantitative analysis of the new non-steroidal anti-inflammatory agent Med 15 and its metabolites Med 5 and tolmetin in rat plasma. After selective extraction the three analytes and an internal standard (p-phenyl-phenol) were separated on a reversed-phase Ultrasphere 5 micron column using potassium dihydrogenphosphate (0.05 M)-acetonitrile (52:48) (pH 4.7) as the mobile phase. The analytes were detected at 313 nm; the sensitivity of the method proved to be 0.05 microgram/ml for all three compounds. The method has been applied to investigate Med 15 pharmacokinetics in rats.

NaF and two other esterase inhibitors unaffect acetyl salicylic acid enzyme hydrolysis

Prevention of chemical or enzyme hydrolysis of drugs such as esters, amides and carbamates during analytical manipulation is a mandatory need in pharmacokinetics (Stella 1990). This hydrolysis occurs through the action of non-specific esterases which are present in blood, plasma and tissues, and it is common to add NaF or other esterase inhibitors to plasma during extraction procedures (Mays et a1 1984). We have investigated the enzyme hydrolysis of acetyl salicylic acid as a model for evaluating the inhibitory effect of sodium fluoride (NaF), diisopropyl-fluorophosphate (DFP) and 1,5 bis(4-ally1 dimethyl ammonium phenyl)-pentan-3-one dibromide (ADAPP).