On the urinary disposition of phenformin and 4-hydroxy-phenformin and their rapid simultaneous measurement

Study of phenformin metabolism in rat liver microsomes by HPLC, CE and on-line HPLC-electrospray ionization mass spectrometry

Methods for the analysis of phenformin and its metabolite by high-performance liquid chromatography (HPLC), capillary electrophoresis (CE) and high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESIMS) are developed. The effects of pH, buffer concentration and proportion of organic modifier on the retention of the compounds in HPLC have been studied. The optimum condition was used for the separation and identification of phenformin and its metabolite in microsomal metabolism by HPLC-ESIMS. A simple CE method is also described for the separation of these compounds. Optimum incubation conditions and cofactor requirements for the formation of 4-hydroxyphenformin by microsomal preparations of rat liver were determined. A linear response in the formation of product was found with increasing concentrations of protein and up to 15 min incubation. High concentrations of phenformin inhibited its metabolite formation, and K(m) was 4 microM.

Effect of iron deficiency anaemia and its treatment on the absorption and elimination of phenformin

1. The extent of phenformin absorption and its rate of urinary excretion have been assessed in adult patients with iron deficiency anaemia, a condition which compromises gastrointestinal function. 2. Phenformin (100 mg) was administered orally to patients before treatment, three days after the start of a course of iron treatment (oral 300 mg b.d. or total intravenous iron) and at the end of 28 days, when haemoglobin was over 10 gm%. 3. No significant difference was found between mean total amounts of phenformin and 4-hydroxyphenformin excreted in urine, before treatment or after 3 or 28 days replacement therapy. It is concluded that phenformin absorption is not affected by iron deficiency. 4. In addition, iron deficiency had no significant effect on phenformin elimination half-life.

Psychotropic effects of adrenergic beta-blockers on agonistic behavior between resident and intruder mice

The present study was conducted to investigate the effect of adrenergic beta-blockers on agonistic behavior in male mice, using quantitative ethological methods. Agonistic behavior was evoked using a resident-intruder paradigm. The following drugs were administered orally at four dose levels (vehicle, 5, 10 and 20 mg/kg) to either resident or intruder mice: dl-propranolol, practolol, d-propranolol, and l-propranolol. When the resident was treated with either dl-propranolol or l-propranolol, aggressive episodes (offensive sideways posture, attack bite, tail rattle) were suppressed significantly in a dose-dependent manner, whereas practolol and d-propranolol were ineffective. All treatments except the high dose of l-propranolol failed to affect the resident's solitary behavior (locomotion). When the intruder was treated with beta-blockers, agonistic behavior was not altered. Since practolol does not cross the blood-brain barrier, the differential suppression of agonistic behavior is due to the central action of beta-blockers. d-Propranolol does cross the blood-brain barrier but is devoid of beta-receptor blocking property; hence l-propranolol suppression of agonistic behavior implies inactivation of brain adrenergic beta-receptors. The findings seem to indicate that beta-blockers such as dl-propranolol and l-propranolol have a psychotropic action.

The effects of diabetes mellitus, exercise, and single doses of biguanides upon lactate metabolism in man

The polymorphism of phenformin oxidation has been investigated in 103 non-insulin-dependent (Type II) diabetics. The frequency distribution was clearly bimodal and 14 poor metabolisers were identified. The frequency of the recessive allele (0.369) was not significantly different from that found previously in non-diabetics. Six of the extensive metabolisers of phenformin were matched for age, sex and oxidizer phenotype with non-diabetic controls. All subjects underwent a standard 3-min exercise test, using a bicycle ergometer, after which plasma lactate concentration was monitored for 90 min. There was no significant difference between groups in lactate accumulation or elimination. Ten extensive metabolisers, ten poor metabolisers and seven non-diabetics (matched for age, sex and phenotype with seven of the diabetic extensive metabolisers) were challenged with a fasting oral dose of phenformin (50 mg), after which plasma lactate, and blood pyruvate and glucose concentrations were monitored for 4 h. A further ten diabetics (five extensive and five poor metabolisers of phenformin) received a single dose of metformin (1 g) following an identical protocol. No significant changes were observed in any group.

The genetic control of phenformin 4-hydroxylation

Previously published results of phenformin 4-hydroxylation in 195 unrelated white British volunteers and 87 family members of 27 randomly selected probands have been subjected to genetic analysis. The results clearly show that about 9% of this population has a genetically determined defect in carrying out this oxidation reaction. The character for the defect is inherited in a Mendelian autosomal recessive fashion. The polymorphism shows a substantial degree of dominance.