12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action
Sertraline potentiates serotonergic activity in the central nervous system through inhibition of neuronal reuptake of serotonin (5-HT).
Studies at clinically relevant doses have demonstrated that sertraline blocks the uptake of serotonin into human platelets. In vitro studies in animals also suggest that sertraline is a potent and selective inhibitor of neuronal serotonin reuptake and has only very weak effects on norepinephrine and dopamine neuronal reuptake. In vitro studies have shown that sertraline has no significant affinity for adrenergic (alpha1, alpha2, beta), cholinergic, GABA, dopaminergic, histaminergic, serotonergic (5HT1A, 5HT1B, 5HT2), or benzodiazepine receptors. The chronic administration of sertraline was found in animals to down regulate brain norepinephrine receptors. Sertraline does not inhibit monoamine oxidase.
In healthy subjects, the acute cognitive and psychomotor effects of alcohol were not potentiated by ZOLOFT.
The effect of sertraline on the QTc interval was evaluated in a randomized, double-blind, placebo- and positive-controlled three-period crossover thorough QTc study in 54 healthy adult subjects. At 2-fold the maximum recommended daily dose (~3-fold the steady-state exposure for sertraline and N-desmethylsertraline), the largest mean ΔΔQTc was 10 ms with upper bound of two-sided 90% confidence interval of 12 ms. The length of the QTc interval was also positively correlated with serum concentrations of sertraline and N- desmethylsertraline concentrations. These concentration-based analyses, however, indicated a lesser effect on QTc at maximally observed concentration than in the primary analysis [See Warnings and Precautions (5), Adverse Reactions (6), Drug Interactions (7), Overdosage (10)].
Following oral once-daily ZOLOFT dosing over the range of 50 to 200 mg for 14 days, mean peak plasma concentrations (Cmax) of sertraline occurred between 4.5 to 8.4 hours post-dosing. The average terminal elimination half-life of plasma sertraline is about 26 hours. Consistent with the terminal elimination half-life, there is an approximately two-fold accumulation up to steady-state concentrations, which are achieved after one week of once-daily dosing. Linear dose-proportional pharmacokinetics were demonstrated in a single dose study in which the Cmax and area under the plasma concentration time curve (AUC) of sertraline were proportional to dose over a range of 50 to 200 mg. The single dose bioavailability of ZOLOFT tablets is approximately equal to an equivalent dose of ZOLOFT oral solution. Administration with food causes a small increase in Cmax and AUC.
Sertraline undergoes extensive first pass metabolism. The principal initial pathway of metabolism for sertraline is N-demethylation. N-desmethylsertraline has a plasma terminal elimination half-life of 62 to 104 hours. Both in vitro biochemical and in vivo pharmacological testing have shown N-desmethylsertraline to be substantially less active than sertraline. Both sertraline and N-desmethylsertraline undergo oxidative deamination and subsequent reduction, hydroxylation, and glucuronide conjugation. In a study of radiolabeled sertraline involving two healthy male subjects, sertraline accounted for less than 5% of the plasma radioactivity. About 40–45% of the administered radioactivity was recovered in urine in 9 days. Unchanged sertraline was not detectable in the urine. For the same period, about 40–45% of the administered radioactivity was accounted for in feces, including 12–14% unchanged sertraline.
Desmethylsertraline exhibits time-related, dose dependent increases in AUC (0–24-hour), Cmax and Cmin, with about a 5- to 9-fold increase in these pharmacokinetic parameters between day 1 and day 14.
In vitro protein binding studies performed with radiolabeled 3H-sertraline showed that sertraline is highly bound to serum proteins (98%) in the range of 20 to 500 ng/mL. However, at up to 300 and 200 ng/mL concentrations, respectively, sertraline and N-desmethylsertraline did not alter the plasma protein binding of two other highly protein bound drugs, warfarin and propranolol.
Studies in Specific Populations
Sertraline pharmacokinetics were evaluated in a group of 61 pediatric patients (29 aged 6–12 years, 32 aged 13–17 years) including both males (N=28) and females (N=33). Relative to the adults, pediatric patients aged 6–12 years and 13–17 years showed about 22% lower AUC (0–24 hr) and Cmax values when plasma concentration was adjusted for weight. The half-life was similar to that in adults, and no gender-associated differences were observed [See Dosage and Administration (2.1), Use in Specific Populations (8.4)].
Sertraline plasma clearance in a group of 16 (8 male, 8 female) elderly patients treated with 100 mg/day of ZOLOFT for 14 days was approximately 40% lower than in a similarly studied group of younger (25 to 32 year old) individuals. Steady-state, therefore, was achieved after 2 to 3 weeks in older patients. The same study showed a decreased clearance of desmethylsertraline in older males, but not in older females [See Use in Specific Populations (8.5)].
In patients with chronic mild liver impairment (N=10: 8 patients with Child-Pugh scores of 5–6; and 2 patients with Child-Pugh scores of 7–8) who received 50 mg of ZOLOFT per day for 21 days, sertraline clearance was reduced, resulting in approximately 3-fold greater exposure compared to age-matched volunteers with normal hepatic function (N=10). The exposure to desmethylsertraline was approximately 2-fold greater in patients with mild hepatic impairment compared to age-matched volunteers with normal hepatic function. There were no significant differences in plasma protein binding observed between the two groups. The effects of ZOLOFT in patients with moderate and severe hepatic impairment have not been studied [See Dosage and Administration (2.4), Use in Specific Populations (8.6)].
Sertraline is extensively metabolized and excretion of unchanged drug in urine is a minor route of elimination. In volunteers with mild to moderate (CLcr=30–60 mL/min), moderate to severe (CLcr=10–29 mL/min) or severe (receiving hemodialysis) renal impairment (N=10 each group), the pharmacokinetics and protein binding of 200 mg sertraline per day maintained for 21 days were not altered compared to age-matched volunteers (N=12) with no renal impairment. Thus sertraline multiple dose pharmacokinetics appear to be unaffected by renal impairment [See Use in Specific Populations (8.7)].
Drug Interaction Studies
In a controlled study of a single dose (2 mg) of pimozide, 200 mg ZOLOFT (once daily) co-administration to steady state was associated with a mean increase in pimozide AUC and Cmax of about 40%, but was not associated with any changes in ECG. The highest recommended pimozide dose (10 mg) has not been evaluated in combination with ZOLOFT. The effect on QTc interval and PK parameters at doses higher than 2 mg of pimozide are not known [See Drug Interactions (7.1)].
Drugs Metabolized by CYP2D6
Many antidepressant drugs (e.g., SSRIs, including ZOLOFT, and most tricyclic antidepressant drugs) inhibit the biochemical activity of the drug metabolizing isozyme CYP2D6 (debrisoquin hydroxylase), and, thus, may increase the plasma concentrations of co-administered drugs that are metabolized by CYP2D6. The drugs for which this potential interaction is of greatest concern are those metabolized primarily by CYP2D6 and that have a narrow therapeutic index (e.g., tricyclic antidepressant drugs and the Type 1C antiarrhythmics propafenone and flecainide). The extent to which this interaction is an important clinical problem depends on the extent of the inhibition of CYP2D6 by the antidepressant and the therapeutic index of the co-administered drug. There is variability among the drugs effective in the treatment of MDD in the extent of clinically important 2D6 inhibition, and in fact ZOLOFT at lower doses has a less prominent inhibitory effect on 2D6 than some others in the class. Nevertheless, even ZOLOFT has the potential for clinically important 2D6 inhibition [See Drug Interactions (7.1)].
Clinical trial data suggested that ZOLOFT may increase phenytoin concentrations [See Drug Interactions (7.1)].
In a study assessing disposition of ZOLOFT (100 mg) on the second of 8 days of cimetidine administration (800 mg daily), there were increases in ZOLOFT mean AUC (50%), Cmax (24%) and half-life (26%) compared to the placebo group [See Drug Interactions (7.2)].
In a study comparing the disposition of intravenously administered diazepam before and after 21 days of dosing with either ZOLOFT (50 to 200 mg/day escalating dose) or placebo, there was a 32% decrease relative to baseline in diazepam clearance for the ZOLOFT group compared to a 19% decrease relative to baseline for the placebo group (p<0.03). There was a 23% increase in Tmax for desmethyldiazepam in the ZOLOFT group compared to a 20% decrease in the placebo group (p<0.03) [See Drug Interactions (7.2)].
In a placebo-controlled trial in normal volunteers, the administration of two doses of ZOLOFT did not significantly alter steady-state lithium levels or the renal clearance of lithium [See Drug Interactions (7.2)].
In a placebo-controlled trial in normal volunteers, administration of ZOLOFT for 22 days (including 200 mg/day for the final 13 days) caused a statistically significant 16% decrease from baseline in the clearance of tolbutamide following an intravenous 1000 mg dose. ZOLOFT administration did not noticeably change either the plasma protein binding or the apparent volume of distribution of tolbutamide, suggesting that the decreased clearance was due to a change in the metabolism of the drug [See Drug Interactions (7.2)].
ZOLOFT (100 mg) when administered to 10 healthy male subjects had no effect on the beta-adrenergic blocking ability of atenolol [See Drug Interactions (7.2)].
In a placebo-controlled trial in normal volunteers, administration of ZOLOFT for 17 days (including 200 mg/day for the last 10 days) did not change serum digoxin levels or digoxin renal clearance [See Drug Interactions (7.2)].
Drugs Metabolized by CYP3A4
In three separate in vivo interaction studies, ZOLOFT was co-administered with CYP3A4 substrates, terfenadine, carbamazepine, or cisapride under steady-state conditions. The results of these studies indicated that ZOLOFT did not increase plasma concentrations of terfenadine, carbamazepine, or cisapride. These data indicate that ZOLOFT's extent of inhibition of CYP3A4 activity is not likely to be of clinical significance. Results of the interaction study with cisapride indicate that ZOLOFT 200 mg (once daily) induces the metabolism of cisapride (cisapride AUC and Cmax were reduced by about 35%) [See Drug Interactions (7.2)].
Microsomal Enzyme Induction
Preclinical studies have shown ZOLOFT to induce hepatic microsomal enzymes. In clinical studies, ZOLOFT was shown to induce hepatic enzymes minimally as determined by a small (5%) but statistically significant decrease in antipyrine half-life following administration of 200 mg of ZOLOFT per day for 21 days. This small change in antipyrine half-life reflects a clinically insignificant change in hepatic metabolism.