Comparative bioavailability of two sildenafil tablet formulations after single-dose administration in healthy Thai male volunteers.

OBJECTIVE: To compare the rate and extent of absorption of two sildenafil tablet formulations (Tonafil®, T.O. Chemicals (1979) Ltd., Thailand as a test formulation and Viagra®, Pfizer Pty Limited., Australia as a reference formulation) in healthy Thai male volunteers after single-dose administration under fasting condition. METHODS: A randomized crossover study with a washout period of 2 weeks was conducted in 20 healthy Thai male volunteers. The volunteers received either 100 mg of the reference or test formulation. Blood samples were collected at 0, 0.16, 0.33, 0.67, 1, 1.5, 2, 2.5, 4, 6, 9 and 12 h after drug administration. The plasma sildenafil concentrations were determined using a validated high performance liquid chromatography method. The pharmacokinetic parameters of sildenafil were calculated from the observed plasma concentration-time profiles by using a non-compartmental model. RESULTS AND CONCLUSIONS: The geometric means, C(max), of the reference and the test formulations were 696.42 and 734.06 ng/ml. The mean values of the AUC(0-t) and AUC(0-inf) of the test formulation were 2,073.03 and 2,237.37 ng × h/ml, while those of the reference formulation were 1,950.26 and 2,078.06 ng × h/ml. The geometric mean ratios (%) and 90% confidence intervals (CI) of the test and reference products for the log transformed C(max), AUC(0-t) and AUC(0-inf) of sildenafil were 105.40% (95.0 - 116.95%), 106.30% (99.74 - 113.28%) and 107.67% (100.83 - 116.48%). These values were within 80 to 125% of the US-FDA and the Thai-FDA criteria and therefore it can be concluded that the test formulation was bioequivalent to the reference formulation both in terms of rate and extent of absorption after single-dose administration under fasting condition.

Paracrine control of mesenteric perivascular axo-axonal interaction.

Immunohistochemical study of rat mesenteric arteries showed dense innervation of adrenergic nerves, calcitonin gene-related peptide (CGRP)-containing nerves (CGRPergic nerves), nitric oxide-containing nerves (nitrergic nerves). Double-immunostaining revealed that most CGRPergic or nitrergic nerves were in close contact with adrenergic nerves. CGRPergic and transient receptor potential vanilloid-1 (TRPV1)-immunopositive nerves appeared in the same neurone. In rat perfused mesenteric vascular beds without endothelium and with active tone, perfusion of nicotine, or bolus injection of capsaicin and acetylcholine and periarterial nerve stimulation (PNS) lowered pH levels of out flowed perfusate concomitant with vasodilation. Cold-storage denervation of preparations abolished pH lowering induced by nicotine and PNS. Guanethidine inhibited PNS- and nicotine-, but not acetylcholine- and capsaicin-, induced pH lowering. Pharmacological analysis showed that protons were released not only from adrenergic nerves but also from CGRPergic nerves. A study using a fluorescent pH indicator demonstrated that nicotine, acetylcholine and capsaicin applied outside small mesenteric artery lowered perivascular pH levels, which were not observed in Ca(2+) free medium. Exogenously injected hydrochloric acid in denuded preparations induced pH lowering and vasodilation, which was inhibited by denervation, TRPV1 antagonists and capsaicin without affecting pH lowering. These results suggest that excitement of adrenergic nerves releases protons to activate TRPV1 in CGRPergic nerves and thereby induce vasodilation. It is also suggested that CGRPergic nerves release protons with exocytosis to facilitate neurotransmission via a positive feedback mechanism.

Comparative bioavailability of two risperidone orodispersible tablet products after single dose administration.

OBJECTIVES: To compare the bioavailability of two risperidone orodispersible tablet products, Risperidone 1 mg Mouth dissolving tablet, Ranbaxy (Malaysia) Sdn. Bhd., Malaysia, as a test product and Risperdal 1 mg Quicklet, Janssen Ortho LLC, Gurabo, Puerto Rico, as a reference product, in healthy male volunteers under fasting condition. MATERIALS AND METHODS: A randomized, 2-treatment, 2-period, 2-sequence, single dose, crossover with a washout period of 2 weeks, was conducted in 24 healthy Thai male volunteers. Blood samples were collected at 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 10, 12, 24, 36, 48, 72 and 96 h following drug administration. Plasma concentrations of risperidone and 9-hydroxyrisperidone were determined using a validated LC-MS-MS method. The pharmacokinetic parameters of risperidone and 9-hydroxyrisperidone were determined using a non-compartmental model. RESULTS: The geometric means ratios (%) and 90% confidence interval (CI) of the test and reference products for the log-transformed pharmacokinetic parameters, Cmax, AUC0-t and AUC0-inf of risperidone were 104.49 % (92.79% - 117.66%), 100.96 % (92.15% - 110.61 %) and 97.99 % (90.72% - 105.85%). The 90% CI of geometric means ratios of the test and reference products for the log-transformed pharmacokinetic parameters, Cmax, AUC0-t and AUC0-inf of 9-hydroxyrisperidone were 97.00%, 96.97% and 97.49%. CONCLUSIONS: The 90% CI for the geometric means ratios (test/reference) of the log-trasformed Cmax, AUC0-t and AUC0-inf of risperidone and its major active metabolite were within the bioequivalence acceptance criteria of 80% - 125% of the US-FDA.

Bioequivalence study of two meloxicam tablet formulations after single-dose administration in healthy Thai male volunteers.

OBJECTIVES: To compare the bioavailability of two meloxicam tablet formulations (MEL-OD, Zydus Cadila Healthcare Limited, India, as a test formulation and Mobic, Boehringer Ingelheim International GmbH, Germany, as a reference formulation) in healthy Thai male volunteers under fasting condition. MATERIALS AND METHODS: A randomized, 2-treatment, 2-period, 2-sequence, single dose, crossover with a washout period of 2 weeks, was conducted in 26 healthy Thai male volunteers. Blood samples were collected 0, 1, 2, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 10, 12, 24, 36, 48, 72 and 96 h post dose. Plasma concentrations of meloxicam were determined using a validated HPLC method. The pharmacokinetic parameters of meloxicam were determined using a non-compartmental model. RESULTS: The mean Cmax was 1,027.32 +/- 251.91 and 1,151.89 +/- 282.58 ng/ml while the mean AUC0-t was 34,024.31 +/- 11,811.68 and 35,137.66 +/- 11,970.47 ng x h/ml for the test and reference formulation, respectively. In addition, the mean AUC0-infinity for test formulation was 37,241.44 +/- 14,888.85 ng x h/ml and for the reference formulation was 39,541.04 +/- 16,624.64 ng x h/ml. The median tmax for the test and reference formulation was 4.50 (range 2.00 - 12.00) and 4.50 (range 3.00 - 10.00), respectively. The geometric means (90% confidence intervals) of the ratio for the log-transformed pharmacokinetic parameters, Cmax, AUC0-t and AUC0-inf were 0.8919 (82.58 - 96.32%), 0.9697 (89.46 - 105.10%) and 0.9525 (87.68 - 103.47%), respectively. CONCLUSIONS: It can be concluded that two meloxicam tablet formulations are bioequivalent both in term of rate and extent of absorption after single-dose administration under fasting condition.