The effects of gabapentin in human experimental pain models.

Background The antidepressant drugs imipramine and venlafaxine relieve clinical neuropathic pain and have been shown to increase pain thresholds in healthy volunteers during repetitive electrical sural nerve stimulation causing temporal pain summation, whereas pain during the cold pressor test is unaltered by these drugs. If this pattern of effect in experimental pain models reflects potential efficacy in clinical neuropathic pain, the pain summation model may potentially be used to identify new drugs for such pain conditions. Gabapentinoids are evidence-based treatments of clinical neuropathic pain and could contribute with additional knowledge of the usefulness of the pain summation model. The aim of this study To test the analgesic effect of the gabapentinoid gabapentin in a sural nerve stimulation pain model including temporal pain summation and the cold pressor test. Method 18 healthy volunteers completed a randomized, double-blind, cross-over trial with medication of 600 mg gabapentin orally dosed 3 times over 24 h against placebo. Pain tests were performed before and 24 h after medication including pain detection and tolerance to single sural nerve stimulation and pain summation threshold to repetitive stimulation (3 Hz). Peak pain intensity and discomfort were rated during a cold pressor test. Results Compared to placebo, gabapentin had a highly significant effect on the threshold of pain summation to repetitive electrical sural nerve stimulation (P = 0.009). Gabapentin significantly increased the pain tolerance threshold to single electrical sural nerve stimulation (P = 0.04), whereas the pain detection threshold to single electrical sural nerve stimulation tended to be increased (P = 0.06). No significant differences were found on pain ratings during the cold pressor test. Conclusion Gabapentin had a selective hypoalgesic effect in a human experimental pain model of temporal pain summation and the results lend further support to the usefulness of the pain summation model to identify drugs for neuropathic pain.

Specific effect of levetiracetam in experimental human pain models.

BACKGROUND: Levetiracetam is a new antiepileptic drug. There is only limited experience with levetiracetam in clinical neuropathic pain. AIM: To test the analgesic effect of levetiracetam in a human experimental pain model in order to obtain preclinical evidence for its potential effect in neuropathic pain. METHODS: Sixteen healthy volunteers completed a randomized, double-blind, cross-over trial with a single oral dose of 1500 mg levetiracetam against placebo. Pain tests included pain detection and tolerance to single electrical stimulation and temporal pain summation threshold to repetitive electrical stimulation (3 Hz) of the sural nerve. RESULTS: Levetiracetam significantly increased the pain tolerance thresholds (p=0.04), and the pain detection thresholds tended to be increased (p=0.06), whereas levetiracetam had no effect on temporal pain summation thresholds (p=0.30). CONCLUSION: Levetiracetam has an analgesic effect in the electrical sural nerve stimulation pain model, but it did not increase temporal pain summation threshold. Levetiracetam may still be effective in clinical neuropathic pain.

Dose-dependent pharmacokinetics of delavirdine in combination with amprenavir in healthy volunteers.

OBJECTIVES: To investigate different dose combinations of amprenavir and delavirdine in order to assess an optimal dose suitable for clinical use. METHODS: This was a prospective, open-label, controlled, three-period, multiple-dose study with nine healthy volunteers. The volunteers received three different dose combinations of amprenavir and delavirdine twice a day for 10 days with a subsequent 12 h pharmacokinetic evaluation. Combination 1: amprenavir 600 mg and delavirdine 600 mg; combination 2: amprenavir 600 mg and delavirdine 800 mg; combination 3: amprenavir 450 mg and delavirdine 1000 mg. The combinations were taken at least 2 weeks apart. RESULTS: Differences in median delavirdine Cmax, C12 and AUC0-12 were seen when comparing the three combinations (3 > 2>1) (P<0.04). A considerable and clinically important higher median C12 was seen with combination 3 when compared to combination 1 (835 to 3944 ng/mL) (P=0.0039). Only small differences in the amprenavir pharmacokinetic parameters were seen between the three dose combinations, with a median C12 of 412, 434 and 536 ng/mL, respectively. CONCLUSIONS: In this study, an increase of 472% in median delavirdine C12 was seen with a delavirdine dose increase of only 67% (600 to 1000 mg). Saturation of the CYP3A4 enzymes and/or possibly also P-glycoprotein could be involved. Combination 3 was considered most suitable for clinical use, but because of the large inter-individual variation in steady-state concentrations, the use of the combination should be supported by therapeutic drug monitoring and restricted to certain patients.

Pharmacokinetic interaction between amprenavir and delavirdine after multiple-dose administration in healthy volunteers.

AIMS: To evaluate the safety and the pharmacokinetic interaction between amprenavir and delavirdine after multiple dose administration in healthy volunteers. METHODS: This was a prospective, open-label, randomized, controlled, two-sequence, two-period multiple dose study with 18 healthy subjects. Volunteers were randomly assigned to amprenavir, 600 mg twice a day, or delavirdine, 600 mg twice a day, for 10 days, followed by both drugs for another 10 days with pharmacokinetic evaluation on day 10 and day 20. Adverse events were recorded throughout the study. RESULTS: Amprenavir decreased all the delavirdine pharmacokinetic parameters apart from tmax. Delavirdine C12h dropped from 7,916 to 933 ng ml-1 (median decrease 5,930 ng ml-1, 95% CI 3,013, 8,955 ng ml-1). A decrease in amprenavir t(1/2) was also seen leading to almost identical median amprenavir C24h values. No serious clinical adverse events were observed during the study. The most frequently reported effects were gastrointestinal symptoms, headache, fatigue and rash. CONCLUSIONS: Amprenavir is an effective inducer of delavirdine metabolism, probably through its effect on hepatic CYP3A4. This could have consequences in other drug-drug interaction situations. Delavirdine is an inhibitor of amprenavir metabolism. The regimen of amprenavir 600 mg and delavirdine 600 mg twice a day is not recommended when an antiretroviral effect from delavirdine is required.

Effect of long-term hormone replacement therapy on plasma homocysteine in postmenopausal women: a randomized controlled study.

OBJECTIVE: The purpose of this study was to investigate the long-term effect of hormone replacement therapy on total homocysteine and to study whether there was any difference in effect between opposed and unopposed hormone replacement therapy or whether the methylenetetrahydrofolate reductase C677T polymorphism was associated with the effect of hormone replacement therapy on total homocysteine. STUDY DESIGN: Two hundred nine healthy postmenopausal women were randomized to hormone replacement therapy (n = 103) or no substitution (n = 106) 5 to 7 years earlier. RESULTS: Women who received hormone replacement therapy had significantly lower total homocysteine concentrations than women in the control group; median total homocysteine values were 8.6 micromol/L and 9.7 micromol/L, respectively, in a per-protocol analysis (P =.02). The effect was comparable in all methylenetetrahydrofolate reductase genotypes, and no difference between unopposed and opposed hormone replacement therapy could be demonstrated. Similar results were obtained when an intention-to-treat analysis was performed. CONCLUSION: Long-term hormone replacement therapy results in lower total homocysteine concentrations in all methylenetetrahydrofolate reductase genotypes without demonstrable difference in effect between unopposed and opposed hormone replacement therapy.