Primary and secondary metabolism of pentamidine by rats

Abstract

The antiprotozoal drug pentamidine [1,5-bis(4'-amidinophenoxy)pentaneI has been previously shown to be metabolized by rat liver microsomes, and five of the seven putative primary metabolites have been identified. With the synthesis and identification of 5-(4'-amidinophenoxy)pentanoic acid and 5-(4'-amidinophenoxy)-1-pentanol as the remaining two metabolites, the primary metabolism of pentamidine in rats appears fully characterized. Use of [14C] Pentamidine [1,5-bis(4'-amidinophenoxy)pentane] has been used for decades in the prophylaxis and treatment of African trypanosomiasis and treatment of antimony-resistant leishmaniasis and Pneumocystis carinii pneumonia (11,20). The increased incidence of P. carini pneumonia associated with the AIDS epidemic has brought about an increase in the clinical use of pentamidine in North America (15). Despite several early studies of the pharmacological properties of the drug (14,16,17,22,23), little was known about the compound. With the development of sensitive and accurate highperformance liquid chromatography (HPLC) assays (1, 9, 18), more detailed studies on the distribution and pharmacokinetics of pentamidine have been conducted (2,7,8). However, these studies have been performed with the misconception that pentamidine is metabolically inert, a conclusion primarily based on the work of Launoy et al. (16,17).We have previously demonstrated that pentamidine is readily converted to seven putative metabolites by rat liver microsomes (3, 4). Five of the seven primary metabolites have been identified as hydroxylated derivatives of the parent compound (see Fig. 1). The cytochrome P-450-dependent mixed-function oxidases have been identified as the enzyme system responsible for this activity (3). In this paper, we describe the characterization of the two remaining primary metabolites of pentamidine. In addition, isolated, perfused rat livers were used to determine the secondary metabolic pathways and to determine the extent of pentamidine metabolism in a model in which both primary and secondary metabolic systems were active. MATERIALS AND METHODSCompounds. Pentamidine (Darco, Durham, N.C.). The structures of all pentamidine metabolites are shown in Fig. 1.Synthesis of 5-(4'-amidinophenoxy)pentanoic acid. A solution of 5-bromovaleric acid (Aldrich Chemical Co., Milwaukee, Wis.) (6.0 g, 0.03 mol) in absolute ethanol (150 ml) and a few drops of H2SO4 was heated under reflux for 24 h. The ethanol was removed under a vacuum to afford 6.7 g (97%) of ethyl-5-bromo-pentanoate as an oil. Sodium (0.63 g, 27.5 mmol) was dissolved in absolute ethanol (20 ml), and 4-cyanophenol (3.0 g, 25 mmol) was added. The solution was heated at reflux for 30 min before ethyl-5-bromo-pentanoate (6.67 g, 32 mmol) in absolute ethanol (10 ml) was added and the solution was heated under reflux for 60 h. The ethanol was removed under reduced pressure, and the resulting ethyl-5-(4'-cyanophenoxy)pentanoate was recrystallized from ethanol-H20 to afford 4.5 g (73%) of the desired product as a white solid.A suspen...

Pharmacokinetics and adverse reactions after a single dose of pentamidine in patients with Trypanosoma gambiense sleeping sickness.

“…Seven oxidized metabolites of pentamidine have previously been detected in experiments with isolated rat livers [13]. None of them interfered with the assay, nor did melarsoprol, phenobarbitone, betamethasone, chloroquine, doxycycline, ampicillin, sulphamethoxazole, paracetamol or acetylsalicylic acid.…”

“…Pentamidine is extensively metabolised in isolated perfused rat livers [13] and experiments with human liver microsomes indicate that cytochromes P450 CYP2D6 and CYPlAl metabolise the drug in vitro (personal communication R. R. Tidwell). The threefold variation in plasma clearance observed here may reflect differences in metabolic capacity between subjects with respect to these enzymes.…”

“…[12], in blood samples obtained at 1, 2, 4, 7, 14 and 29-34 days after pen-tamidine administration, showed that only three patients (2, 3 and 10) had uniformly detectable concentrations. The plasma phenobarbitone concentrations varied between 20 and 86 gmol l-1, except in patient 10 whose levels were in the range [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] ,umol 1-1 (the therapeutic range for treatment of convulsive disorders is 40-135 gmol l-l). A majority of the subjects were also given a single intramuscular injection of betamethasone (Diprostene®, ScheringPlough, Levallois-Perret, France).…”

Synthesis, DNA Interactions and Anticancer Evaluation of Novel Diamidine Derivatives of 3,4-Ethylenedioxythiophene

“…The development of pentamidine as a therapeutic drug is limited due to its known toxic side effects as a consequence of parent drug metabolism. 18 Unfortunately, metabolic breakup of the parent molecule may be a problem encountered with many of direct pentamidine analogues, especially those containing an ether bond in the bridge between the cationic moieties. 12 It is well established that varying the central linker, substitutive group or substituent position can create a significant difference in the space configuration and distribution of electron density within the molecule, and thus influence the DNA-binding mode.…”

“…12 It is well established that varying the central linker, substitutive group or substituent position can create a significant difference in the space configuration and distribution of electron density within the molecule, and thus influence the DNA-binding mode. 19,20 This stimulate us to design, synthesize and test the new pentamidine analogues with a robust 3,4-ethylenedioxythiophene (EDOT) linker instead of an unstable alkyl chain 18 or unstable benzo[c]thiophene ring. 21 Diarylamidine derivatives of EDOT previously synthesized in our laboratory (Figure 1) have shown significant antitumor activity.…”