A randomized single-dose, two-period crossover bioequivalence study of two fixed-dose Paracetamol/Orphenadrine combination preparations in healthy volunteers under fasted condition.

BACKGROUND: Paracetamol/Orphenadrine is a fixed dose combination containing 35 mg orphenadrine and 450 mg paracetamol. It has analgesic and muscle relaxant properties and is widely available as generics. This study is conducted to investigate the relative bioavailability and bioequivalence between one fixed dose paracetamol/orphenadrine combination test preparation and one fixed dose paracetamol/orphenadrine combination reference preparation in healthy volunteers under fasted condition for marketing authorization in Malaysia. METHOD: This is a single-center, single-dose, open-label, randomized, 2-treatment, 2-sequence and 2-period crossover study with a washout period of 7 days. Paracetamol/Orphenadrine tablets were administered after a 10-h fast. Blood samples for pharmacokinetic analysis were collected at scheduled time intervals prior to and up to 72 h after dosing. Blood samples were centrifuged, and separated plasma were kept frozen (- 15 °C to - 25 °C) until analysis. Plasma concentrations of orphenadrine and paracetamol were quantified using liquid-chromatography-tandem mass spectrometer using diphenhydramine as internal standard. The pharmacokinetic parameters AUC0-∞, AUC0-t and Cmax were determined using plasma concentration time profile for both preparations. Bioequivalence was assessed according to the ASEAN guideline acceptance criteria for bioequivalence which is the 90% confidence intervals of AUC0-∞, AUC0-t and Cmax ratio must be within the range of 80.00-125.00%. RESULTS: There were 28 healthy subjects enrolled, and 27 subjects completed this trial. There were no significant differences observed between the AUC0-∞, AUC0-t and Cmax of both test and reference preparations in fasted condition. The 90% confidence intervals for the ratio of AUC0-t (100.92-111.27%), AUC0-∞ (96.94-108.08%) and Cmax (100.11-112.50%) for orphenadrine (n = 25); and AUC0-t (94.29-101.83%), AUC0-∞ (94.77-101.68%) and Cmax (87.12-101.20%) for paracetamol (n = 27) for test preparation over reference preparation were all within acceptable bioequivalence range of 80.00-125.00%. CONCLUSION: The test preparation is bioequivalent to the reference preparation and can be used interchangeably. TRIAL REGISTRATION: NMRR- 17-1266-36,001; registered and approved on 12 September 2017.

Pharmacokinetic, metabolism and withdrawal time of orphenadrine in camels (Camelus dromedarius) after intravenous administration.

The pharmacokinetics of orphenadrine (ORPH) following a single intravenous (i.v.) dose was investigated in six camels (Camelus dormedarius). Orphenadrine was extracted from the plasma using a simple sensitive liquid-liquid extraction method and determined by gas chromatography/mass spectrometry (GC/MS). Following i.v. administration plasma concentrations of ORPH decline bi-exponentially with distribution half-life (t(1/2)(alpha)) of 0.50+/-0.07h, elimination half-life (t(1/2)(beta)) of 3.57+/-0.55h, area under the time concentration curve (AUC) of 1.03+/-0.10g/hl(-1). The volume of distribution at steady state (Vd(ss)) 1.92+/-0.22lkg(-1), volume of the central compartment of the two compartment pharmacokinetic model (V(c)) 0.87+/-0.09lkg(-1), and total body clearance (Cl(T)) of 0.60+/-0.09l/hkg(-1). Three orphenadrine metabolites were identified in urine samples of camels. The first metabolite N-desmethyl-orphenadrine resulted from N-dealkylation of ORPH with molecular ion m/z 255. The second N,N-didesmethyl-orphenadrine, resulted from N-didesmethylation with molecular ion m/z 241. The third metabolite, hydroxyl-orphenadrine, resulted from the hydroxylation of ORPH with molecular ion m/z 285. ORPH and its metabolites in camel were extensively eliminated in conjugated form. ORPH remains detectable in camel urine for three days after i.v. administration of a single dose of 350mg orphenadrine aspartate.

Pharmacokinetic study of orphenadrine using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).

We developed and validated a simple, rapid, and accurate HPLC-MS/MS method with simple protein precipitation for the determination of orphenadrine. Injection-to-injection running time was 3 min with a retention time of orphenadrine of 1.1 min. The linear assay range was 1-200 ng/mL (r2 > 0.99). The intra- and inter-assay imprecisions were CV 0.6-4.2% and CV 1.6-6.1%, respectively. The accuracy, extraction recovery, specificity and stability were satisfactory. Using the measured plasma concentrations of orphenadrine in 24 healthy subjects, pharmacokinetic profiles of orphenadrine were evaluated (AUC(0-72,) 1565+/-731 ng h/mL, Cmax 82.8+/-26.2 ng/mL, Tmax 3.0+/-0.9 h, elimination half-life 25.8+/-10.3 h).

Upregulation of cytochromes P450 2B in rat liver by orphenadrine.

1 The alkylamine drug orphenadrine (ORPH) is an inducer and inhibitor of the microsomal cytochrome P450 (CYP) system in mammals. This study evaluated the selectivity of CYP induction by ORPH in rat liver. 2 Immunoblot analysis indicated that ORPH was a selective inducer of the phenobarbitone (PB)-inducible CYP2B in rat liver. CYP2B protein was increased to approximately 14-fold of levels in untreated rat liver. By comparison PB increased CYP2B expression 40-fold. Corresponding increases in the activity of CYP2B-dependent androstenedione 16beta-hydroxylation were measured in microsomes from ORPH and PB-induced rats. 3 Northern analysis indicated that CYP2B1/2 mRNA was increased in ORPH-induced rat liver. Consistent with this finding, ORPH was found to activate a PB-responsive enhancer module in constitutive androstane receptor (CAR)-transfected Hep G2 cells. 4 Other alkylamines like troleandomycin impair CYP turnover. We tested whether ORPH induction of CYP2B may include a post-translational component. In PB-pretreated animals ORPH administration delayed the loss of CYP2B after PB withdrawal, but no evidence for altered turnover was found. 5 These studies establish ORPH as a selective inducer of CYP2B in rat liver. Induction appears to be mediated pretranslationally by CAR activation of CYP2B gene transcription. Post-translational stabilisation by an ORPH metabolite does not elicit induction. Induction of CYP2B may influence pharmacokinetic interactions involving ORPH.

Ex vivo percutaneous absorption of ketamine, bupivacaine, diclofenac, gabapentin, orphenadrine, and pentoxifylline: comparison of versatile cream vs. reference cream.

This ex vivo human percutaneous absorption study evaluated a set of six model drugs (ketamine hydrochloride, bupivacaine hydrochloride, diclofenac sodium, gabapentin, orphenadrine citrate, pentoxifylline) from two popular formulations for topically applied compounding preparations. The compounded preparations used in this study were Versatile cream and a reference cream. Each formulation was applied to human trunk skin mounted on Franz Diffusion Cells, 50 mg/chamber (or 28.2 mg/cm2). Serial dermal receiver solutions were collected for 48 hours. Analysis of the resultant data supports the concept that the Versatile base formulation provides improved characteristics relative to the reference base. This is of key importance where the patient does not show clinical improvement when a conventional topical delivery vehicle is used in the formulation. From the results, it is reasonable to anticipate that, relative to the reference formulation, the Versatile formulation provides enhanced transdermal delivery of some analgesic medications.

Evaluation of enantioselective binding of antihistamines to human serum albumin by ACE.

The drug binding to plasma and tissue proteins is a fundamental factor in determining the overall pharmacological activity of a drug. HSA, together with alpha(1)-acid glycoprotein, are the most important plasma proteins, which act as drug carriers, with implications on the pharmacokinetic of drugs. Among plasma proteins, HSA possesses the highest enantioselectivity. In this paper, a new methodology for the study of enantiodifferentiation of chiral drugs with HSA is developed and applied to evaluate the possible enantioselective binding of four antihistamines: brompheniramine, chlorpheniramine, hydroxyzine and orphenadrine to HSA. This study includes the determination of affinity constants of drug enantiomers to HSA and the evaluation of the binding sites of antihistamines on the HSA molecule. The developed methodology includes the ultrafiltration of samples containing HSA and racemic antihistaminic drugs and the analysis of the free or bound drug fraction using the affinity EKC-partial filling technique and HSA as chiral selector. The results shown in this paper represent the first evidence of the enantioselective binding of antihistamines to HSA, the major plasmatic protein.