Duloxetine

Formulation

The table below describes the formulation of duloxetine hydrochloride and the controls morphine sulfate and gabapentin for the experiments shown on this page.

Experiment(s)	Compound	Dose(s) mg/kg	Correction factor	Dose volume mL/kg	Route	Vehicle	Suspension / Solution
Pharmacokinetics	Duloxetine	60	1.12	2	PO	Water	Suspension
Irwin, Rotarod	Duloxetine	10, 30, 60, 100	1.12	5	PO	Water	Solution
Plantar incision,	Duloxetine	3, 10, 30, 60	1.12	1	PO	Water	Solution
L5/L6 SNL	Duloxetine	3, 10, 30, 60		1	PO	Water	Solution
Plantar incision	Morphine	6	1.33	1	SC	Saline	Solution
L5/L6 SNL	Gabapentin	60	1.00	1	PO	Saline	Solution

L5/L6 SNL = L5/L6 spinal nerve ligation; PO = per os; SC = subcutaneous

Results

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Method: Pharmacokinetics

Duloxetine concentrations were measured in serially collected plasma samples and terminally collected brain samples (shown on two graphs) from males and females treated with 60 mg/kg duloxetine (PO) in a vehicle of water. There were 2-4 rats/group for plasma and 3-4 rats/group for brain.

Method: Pharmacokinetics

A table shows pharmacokinetics parameters calculated for duloxetine using non-compartmental analysis in male and female rats treated with duloxetine (60 mg/kg, PO, vehicle of water). The means for the 2 groups (males and females treated with 60 mg/kg duloxetine, respectively) are as follows. The highest concentration (Cmax) was 3.84 and 4.74 µM; the time at the maximum concentration (Tmax) was 5 and 2.5 hours; the half-life (T1/2) was not calculated for males and 10.45 hours for females; area under the curve for time 0 to 8 hours was 1396 and 1520 minutes*µM; area under the curve for time 0 to infinity was 1396 and 2177 minutes*µM; the brain-to-plasma ratio at 2 hours was 1.4 and 1.47; the brain-to-plasma ratio at 8 hours was 0.66 and 0.94

Method: Modified Irwin functional observational battery

Two reviewers observed and scored 39 behaviors in a modified Irwin test. For each animal, the scores for behavioral observations from each reviewer are summed then averaged for male and female rats (shown on two graphs). Responses are shown at the following time points: baseline (before treatment) and at 1, 2, 4, and 6 hours after treatment with vehicle (water, delivered PO) or duloxetine (10, 30, 60, or 100 mg/kg, delivered PO). There were 4 rats per group. Kruskal-Wallis tests were performed at each timepoint for each sex, followed by Dunn’s tests when a significant effect was observed. Dunn’s tests found an increase in the number of observations relative to vehicle in males at 1 hour post-treatment with 100 mg/kg duloxetine (p<0.05), at 2 hours post-treatment with 100 mg/kg duloxetine (p<0.05), at 4 hours post-treatment with 60 mg/kg duloxetine (p<0.05) and 100 mg/kg duloxetine (p<0.01), and at 6 hours post-treatment with 30 mg/kg duloxetine (p<0.05) and 100 mg/kg duloxetine (p<0.01). Dunn’s tests found an increase in the number of observations relative to vehicle in females at 1, 2, 4, and 6 hours post-treatment with 100 mg/kg duloxetine (p<0.05, 0.001, 0.01, 0.01, respectively). Data were analyzed using GraphPad Prism version 10.0.2

Method: Modified Irwin functional observational battery

A heat map depicts the severity of the behaviors observed by two reviewers in a modified Irwin test at baseline and at 1, 2, 4, and 6 hours following the administration of vehicle (water, delivered PO) or duloxetine (10, 30, 60, or 100 mg/kg, delivered PO). There were 8 rats per group (4 male and 4 female). Severity score was calculated as the sum of scores given by the two reviewers for all animals at that dose and timepoint divided by the maximum possible score, transformed into a percentage. In summary, duloxetine administration produced effects including decreased body position, decreased locomotor activity, and sedation in a dose- and time-dependent manner

Method: Modified Irwin functional observational battery

Two graphs show the body temperature of male or female rats during the modified Irwin test. Responses are shown at the following timepoints: baseline (before treatment) and at 1 and 6 hours after treatment with vehicle (water, delivered PO) or duloxetine (10, 30, 60, or 100 mg/kg, delivered PO). There were 4 rats per group. Dunnett’s tests performed after finding a significant effect of time in a two-way repeated measures ANOVA for female rats showed a significant decrease in body temperature after 6 hours relative to baseline (p<0.01). Data were analyzed using GraphPad Prism version 10.0.2

Method: Rat Rotarod

Two graphs show the latency for male or female rats to fall off a rotarod apparatus. Responses are shown at the following time points: baseline (before treatment) and at 1, 2, 4, and 6 hours after treatment with vehicle (water, delivered PO) or duloxetine (10, 30, 60, or 100 mg/kg, delivered PO). There were 10 rats per group. Neither males nor females had a significant interaction of time x treatment in a two-way repeated measures ANOVA.

Model: Plantar Incision Model in Rat (Brennan Model)
Endpoint: Rat Hind Paw Mechanical Allodynia Behavior (von Frey Filaments) Method

Two graphs show ipsilateral hind paw mechanical allodynia behavior assessed with von Frey filaments in male or female rats that have undergone plantar incision surgery. Responses are shown at the following time points: baseline (before surgery), prior to treatment at 1 day after surgery, and at 1, 2, 4, and 6 hours after treatment at 1 day after surgery. The treatments are vehicle (saline, delivered PO), duloxetine (3, 10, 30, or 60 mg/kg, delivered PO), or the positive control morphine (6 mg/kg, delivered SC). There were 10 rats per group. A significant interaction of time x treatment was found in a two-way repeated measures ANOVA. Dunnett’s tests found significant differences from vehicle in males at 1 hour post-treatment with 3, 10, 30, and 60 mg/kg duloxetine (p<0.05, 0.01, 0.001, 0.0001, respectively) and morphine (p<0.0001); at 2 hours post-treatment with 3, 10, 30, and 60 mg/kg duloxetine (p<0.05, 0.01, 0.01, 0.0001, respectively) and morphine (p<0.0001); at 4 hours post-treatment with 3, 10, 30, and 60 mg/kg duloxetine (p<0.05, 0.05, 0.05, 0.001, respectively) and morphine (p<0.0001); and at 6 hours post-treatment with 3, 30, and 60 mg/kg duloxetine (p<0.05, 0.05, 0.01, respectively) and morphine (p<0.05). Dunnett’s tests found significant differences from vehicle in females at 1 hour post-treatment with 60 mg/kg duloxetine (p<0.0001) and morphine (p<0.0001); at 2 hours post-treatment with 60 mg/kg duloxetine (p<0.01) and morphine (p<0.001); and at 4 hours post-treatment with 60 mg/kg duloxetine (p<0.001) and morphine (p<0.05).

Model: Plantar Incision Model in Rat (Brennan Model)
Endpoint: Guarding Behavior

Two graphs show ipsilateral hind paw guarding behavior evaluated in male or female rats that have undergone plantar incision surgery. Responses are shown at the following time points: baseline (before surgery), prior to treatment at 1 day after surgery, and at 1, 2, 4, and 6 hours after treatment at 1 day after surgery. The treatments are vehicle (saline, delivered PO), duloxetine (3, 10, 30, or 60 mg/kg, delivered PO), or the positive control morphine (6 mg/kg, delivered SC). There were 10 rats per group. A significant interaction of time x treatment was found in a two-way repeated measures ANOVA. Dunnett’s tests found significant differences from vehicle in males at 1 hour post-treatment with 30 mg/kg duloxetine (p<0.05), 60 mg/kg duloxetine (p<0.01), and morphine (p<0.0001); at 2 hours post-treatment with 30 mg/kg duloxetine (p<0.05), 60 mg/kg duloxetine (p<0.01), and morphine (p<0.0001); and at 4 hours post-treatment with morphine (p<0.05). Dunnett’s tests found significant differences from vehicle in females at 1 hour post-treatment with 10, 30, and 60 mg/kg duloxetine (p<0.05, 0.01, 0.0001, respectively) and morphine (p<0.0001); at 2 hours post-treatment with 10, 30, and 60 mg/kg duloxetine (p<0.05, 0.001, 0.0001, respectively) and morphine (p<0.0001); at 4 hours post-treatment with 10, 30, and 60 mg/kg duloxetine (p<0.05, 0.05, 0.0001, respectively) and morphine (p<0.0001); and at 6 hours post-treatment with 60 mg/kg duloxetine (p<0.0001).

Model: L5/L6 Spinal Nerve Ligation Model
Endpoint: Rat Hind Paw Mechanical Allodynia Behavior (von Frey Filaments) Method

Model: L5/L6 Spinal Nerve Ligation Model
Endpoint: Rat Hind Paw Cold Allodynia (Acetone Evaporation) Test

Two graphs show ipsilateral hind paw cold allodynia behavior assessed with 5 trials of the acetone evaporation test in male or female rats that have undergone L5/L6 spinal nerve ligation surgery. Responses are shown at the following time points: baseline (before surgery), prior to treatment at 3 weeks after surgery, and at 1 and 2 hours after treatment at 3 weeks after surgery. The treatments are vehicle (water, delivered PO), duloxetine (3, 10, 30, or 60 mg/kg, delivered PO), or the positive control gabapentin (60 mg/kg, delivered PO). There were 8 rats per group for males, except n=9 for vehicle. There were 9 rats per group for females, except n=8 for 3, 10, and 30 mg/kg duloxetine. A significant interaction of time x treatment was found in a two-way repeated measures ANOVA. Dunnett’s tests found significant decreases in acetone responses relative to vehicle in males at 1 hour post-treatment with 30 mg/kg duloxetine (p<0.01), 60 mg/kg duloxetine (p<0.001), and gabapentin (p<0.0001) and at 2 hours post-treatment with 60 mg/kg duloxetine (p<0.01) and gabapentin (p<0.05). Dunnett’s tests found significant decreases in acetone responses relative to vehicle in females at 1 hour post-treatment with 30 mg/kg duloxetine (p<0.05), 60 mg/kg duloxetine (p<0.01), and gabapentin (p<0.05) and at 2 hours post-treatment with 60 mg/kg duloxetine (p<0.001) and gabapentin (p<0.01)

This work was conducted by PsychoGenics Inc. (Paramus, NJ) in collaboration with PSPP, NINDS, NIH under contract # 75N95019D00026. Prescribing information for clinically used controls can be found at labels.fda.gov.

Duloxetine

Formulation

Results

Pharmacokinetics: Concentration in Plasma and Brain

Pharmacokinetics: Calculated Parameters

Irwin: Total Observations

Irwin: Behavioral Severity Scores

Irwin: Body Temperature

Rotarod

Plantar Incision: von Frey

Plantar Incision: Guarding Behavior

L5/L6 Spinal Nerve Ligation: von Frey

L5/L6 Spinal Nerve Ligation: Acetone