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British Journal of Clinical Pharmacology Oct 19801 The rate of absorption of oral paracetamol depends on the rate of gastric emptying and is usually rapid and complete. The mean systemic availability is about 75%. 2... (Review)
Review
1 The rate of absorption of oral paracetamol depends on the rate of gastric emptying and is usually rapid and complete. The mean systemic availability is about 75%. 2 Paracetamol is extensively metabolized and the plasma half-life is 1.5-2.5 hours. About 55% and 30% of a therapeutic dose is excreted in the urine as glucuronide and sulphate conjugates, respectively, whereas mercapturic acid and cysteine conjugates (representing conversion to a potentially toxic intermediate metabolite) each account for some 4% of the dose. Paracetamol metabolism is age- and dose-dependent. 3 With hepatotoxic doses, paracetamol metabolism is impaired and the half-life prolonged. Sulphate conjugation is saturated and the proportion excreted as mercapturic acid and cysteine conjugates is increased. 4 The renal clearance of paracetamol depends on urine flow rate by not pH. The renal clearances of the glucuronide and sulphate conjugates often exceed the glomerular filtration rate and are independent of urine flow and pH. 5 Phenacetin absorption depends on formulation. It is extensively metabolized to paracetamol and minor metabolites are probably responsible for toxicity.
Topics: Acetaminophen; Administration, Oral; Adult; Animals; Biotransformation; Humans; Intestinal Absorption; Kinetics; Metabolic Clearance Rate; Phenacetin; Tissue Distribution
PubMed: 7002186
DOI: 10.1111/j.1365-2125.1980.tb01812.x -
IUCrData Jul 2023The title compound, CHNO, crystallizes with ' = 2 in space group 2 with the two independent mol-ecules having almost the same conformation, differing mostly at the end...
The title compound, CHNO, crystallizes with ' = 2 in space group 2 with the two independent mol-ecules having almost the same conformation, differing mostly at the end of the butanamide chain. A local inversion center near 1/8, 3/4, relates the two mol-ecules, as is common for structures in this space group with ' = 2. The mol-ecule crystallizes as the keto tautomer, and the β-diketone moieties are twisted out of planarity, with O-C⋯C-O pseudo torsion angles of -74.4 (5) and -83.9 (5)°. The N-H group of each independent mol-ecule donates an inter-molecular hydrogen bond to an amide carbonyl oxygen atom by positive or negative translations along the axis, thus forming anti-parallel chains propagating in the [010] direction.
PubMed: 37937129
DOI: 10.1107/S2414314623005655 -
IUCrData Apr 2023The title compound, CHNO, crystallizes with a disordered nitro group in twinned crystals. Both the meth-oxy group and the acetamide groups are nearly coplanar with the...
The title compound, CHNO, crystallizes with a disordered nitro group in twinned crystals. Both the meth-oxy group and the acetamide groups are nearly coplanar with the phenyl ring, and the C-N-C-O torsion angle [0.2 (4)°] is also insignificantly different from zero. Overall, the 12-atom meth-oxy-phenyl-acetamide group is nearly planar, with an r.m.s. deviation of 0.042 Å. The nitro group is twisted out of this plane by about 30°, disordered into two orientations with opposite senses of twist. In the crystal, the N-H group donates a hydrogen bond to a nitro oxygen atom, generating chains propagating in the [101] direction. The amide carbonyl oxygen atom is not involved in the hydrogen bonding.
PubMed: 37151207
DOI: 10.1107/S2414314623002985 -
Heliyon Jun 2022Direct evidence of Triphala-drug interactions has not been provided to date.
CONTEXT
Direct evidence of Triphala-drug interactions has not been provided to date.
OBJECTIVE
This study was aimed to determine the effects of Triphala on cytochrome P450 (CYP) isoforms and P-glycoprotein (P-gp) and to investigate pharmacokinetic interactions of Triphala with CYP-probes in rats.
MATERIALS AND METHODS
Effects of Triphala on the activities of CYP isoforms and P-gp were examined using human liver microsomes (HLMs) and Caco-2 cells, respectively. Pharmacokinetic interactions between Triphala and CYP-probes (i.e., phenacetin and midazolam) were further examined in rats.
RESULTS
Triphala extract inhibited the activities of CYP isoforms in the order of CYP1A2>3A4>2C9>2D6 with the IC values of 23.6 ± 9.2, 28.1 ± 9.8, 30.41 ± 16.7 and 93.9 ± 27.5 μg/mL, respectively in HLMs. It exhibited a non-competitive inhibition of CYP1A2 and 2C9 with the values of 23.6 and 30.4 μg/mL, respectively, while its inhibition on CYP3A4 was competitive manner with the i values of 64.9 μg/mL. The inhibitory effects of Triphala on CYP1A2 and 3A4 were not time-dependent. Moreover, Triphala did not affect the P-gp activity in Caco-2 cells. Triphala, after its oral co-administration at 500 mg/kg, increased the bioavailabilities of phenacetin and midazolam by about 61.2% and 40.7%, respectively, in rats.
DISCUSSION AND CONCLUSIONS
Increases observed in the bioavailabilities of phenacetin and midazolam after oral co-administration of Triphala in rats provided a direct line of evidence to show Triphala-drug interactions inhibition of CYP1A and CYP3A activities, respectively. These results, together with the lack of time-dependency of CYP 1A2 and 3A4 inhibition , suggested that the inhibitory effect of Triphala is primarily reversible.
PubMed: 35785236
DOI: 10.1016/j.heliyon.2022.e09764 -
Canadian Medical Association Journal Jan 1965Four patients who had ingested large amounts of phenacetin-salicylate medications were studied during a 12-month period. Renal failure had progressed slowly over a...
Four patients who had ingested large amounts of phenacetin-salicylate medications were studied during a 12-month period. Renal failure had progressed slowly over a number of years. All patients took the drug because of psychogenic headache. Considerable skill was required to elicit the history of drug habituation. The major features of the nephropathy were multiple episodes of metabolic acidosis, minimal proteinuria, pyuria but no bacteriuria, and polyuria and polydipsia early in the course of drug ingestion. Papillary necrosis was not a prominent clinical feature of this series. Discontinuation of drug ingestion by one patient was associated with recovery of a considerable degree of renal function. Preliminary experimental evidence obtained in the dog suggests that salicylate impaired the efficiency of the counter-current multiplier by decreasing sodium transport in the ascending limb of Henle, and decreased the permeability to water of the distal convoluted and collecting tubule; phenacetin had no such effect.
Topics: Acidosis; Animals; Aspirin; Bacteriuria; Biological Transport; Caffeine; Codeine; Dogs; Drug Therapy; Headache; Humans; Kidney Diseases; Kidney Papillary Necrosis; Kidney Tubules; Metabolism; Neoplasm Recurrence, Local; Neoplasms; Phenacetin; Polyuria; Proteinuria; Pyuria; Salicylates; Sodium; Toxicology
PubMed: 14228236
DOI: No ID Found -
Environmental Health Perspectives Mar 1983Phenacetin can be metabolized to reactive metabolites by a variety of mechanisms. (1) Phenacetin can be N-hydroxylated, and the resulting N-hydroxyphenacetin can be... (Review)
Review
Phenacetin can be metabolized to reactive metabolites by a variety of mechanisms. (1) Phenacetin can be N-hydroxylated, and the resulting N-hydroxyphenacetin can be sulfated or glucuronidated. Whereas phenacetin N-O sulfate immediately rearranges to form a reactive metabolite which may covalently bind to protein, phenacetin N-O glucuronide slowly rearranges to form reactive metabolites. Incubation of the purified phenacetin N-O glucuronide under a variety of conditions suggests that N-acetyl-p-benzoquinone imine is a reactive metabolite. This metabolite covalently binds to protein, reacts with glutathione to form an acetaminophen-glutathione conjugate, is reduced by ascorbate to acetaminophen or is partially hydrolyzed to acetamide. (2) Phenacetin can be O-deethylated to acetaminophen, and acetaminophen can be converted directly to a reactive metabolite which may be also N-acetyl-p-benzoquinone imine. (3) Phenacetin can be sequentially N-hydroxylated and O-deethylated to N-hydroxyacetaminophen which spontaneously dehydrates to N-acetyl-p-benzoquinone imine. (4) Phenacetin can be 3, 4-epoxidated to form an alkylating and an arylating metabolite. In the presence of glutathione, a S-ethylglutathione conjugate and an acetaminophen-glutathione conjugate are formed. In the absence of glutathione, the alkylating metabolite may bind to protein and the arylating metabolite is completely hydrolyzed to acetamide and another arylating metabolite which may bind to protein. The structures of the alkylating and arylating metabolites are unknown. Control experiments have shown that in pathway (1) the phenolic oxygen of the acetaminophenglutathione conjugate is derived from water, whereas in pathways (2) and (3) the phenolic oxygen of this metabolite is derived from phenacetin. In pathway (4) the phenolic oxygen was 50% derived from molecular oxygen and 50% from phenacetin. Administration of [p-(18)0]phenacetin to hamsters revealed only a 10% loss of (18)0 in the acetaminophen mercapturic acid (the further metabolic product of the glutathione conjugate) which suggests that, in the hamster, pathways (2) and/or (3) are the primary mechanism of conversion of phenacetin to reactive metabolites in vivo.
Topics: Acetaminophen; Animals; Benzoquinones; Biotransformation; Cricetinae; Epoxy Compounds; Glucuronates; Glutathione; Hydroxylation; Imines; Microsomes, Liver; Phenacetin; Protein Binding; Rats; Sulfates
PubMed: 6339229
DOI: 10.1289/ehp.834971 -
Drug Metabolism and Pharmacokinetics 2012In this review, novel aspects of the role of esterases, which contribute to the metabolism of 10% of therapeutic drugs, are described. Esterases hydrolyze the compounds... (Review)
Review
In this review, novel aspects of the role of esterases, which contribute to the metabolism of 10% of therapeutic drugs, are described. Esterases hydrolyze the compounds that contain ester, amide, and thioester bonds, which cause prodrug activation or detoxification. Among esterases, carboxylesterases are well known to be involved in the hydrolysis of a variety of drugs. Additionally, other esterases have recently received attention for their pharmacological and toxicological roles. Arylacetamide deacetylase (AADAC) is involved in the hydrolysis of flutamide, phenacetin, and rifamycins. AADAC is associated with adverse drug reactions because the hydrolytic metabolites of flutamide and phenacetin appear to be associated with hepatotoxicity and nephrotoxicity/hematotoxicity, respectively. Paraoxonase and butyrylcholinesterase hydrolyze pirocarpine/simvastatin and succinylcholine/bambuterol, respectively. Although the esterases that hydrolyze the acyl-glucuronides of drugs have largely been unknown, we recently found that α/β hydrolase domain containing 10 (ABHD10) is responsible for the hydrolysis of mycophenolic acid acyl-glucuronide in human liver. Because acyl-glucuronides are associated with toxicity, ABHD10 might function as a detoxification enzyme. Thus, various esterases, which include enzymes that have not been known to hydrolyze drugs, are involved in drug metabolism with different substrate specificity. Further esterase studies should be conducted to promote our understanding in clinical pharmacotherapy and drug development.
Topics: Animals; Esterases; Humans; Hydrolysis; Inactivation, Metabolic; Pharmacokinetics; Prodrugs
PubMed: 22813719
DOI: 10.2133/dmpk.dmpk-12-rv-042 -
The Indian Medical Gazette Jan 1890
PubMed: 29000569
DOI: No ID Found -
Molecules (Basel, Switzerland) Jul 2021The thermodynamic properties of phenacetin in solid state and in saturated conditions in neat and binary solvents were characterized based on differential scanning...
The thermodynamic properties of phenacetin in solid state and in saturated conditions in neat and binary solvents were characterized based on differential scanning calorimetry and spectroscopic solubility measurements. The temperature-related heat capacity values measured for both the solid and melt states were provided and used for precise determination of the values for ideal solubility, fusion thermodynamic functions, and activity coefficients in the studied solutions. Factors affecting the accuracy of these values were discussed in terms of various models of specific heat capacity difference for phenacetin in crystal and super-cooled liquid states. It was concluded that different properties have varying sensitivity in relation to the accuracy of heat capacity values. The values of temperature-related excess solubility in aqueous binary mixtures were interpreted using the Jouyban-Acree solubility equation for aqueous binary mixtures of methanol, DMSO, DMF, 1,4-dioxane, and acetonitrile. All binary solvent systems studied exhibited strong positive non-ideal deviations from an algebraic rule of mixing. Additionally, an interesting co-solvency phenomenon was observed with phenacetin solubility in aqueous mixtures with acetonitrile or 1,4-dioxane. The remaining three solvents acted as strong co-solvents.
Topics: Phenacetin; Physical Phenomena; Solubility; Solvents; Temperature; Thermodynamics; Water
PubMed: 34279418
DOI: 10.3390/molecules26134078