Consult a Certified Poison Control Center for up-to-date guidance and advice (1-800-222-1222 or www.poison.org). In case of an overdose, provide supportive care, including close medical supervision and monitoring. Treatment should consist of those general measures employed in the management of overdosage with any drug. Consider the possibility of multiple drug overdose. Ensure an adequate airway, oxygenation, and ventilation. Monitor cardiac rhythm and vital signs. Provide supportive and symptomatic measures.
Venlafaxine hydrochloride extended-release capsule, USP is an extended-release capsule for once-a-day oral administration that contains venlafaxine hydrochloride, a serotonin and norepinephrine reuptake inhibitor (SNRI).
Venlafaxine is designated (R/S)-1-[2-(dimethylamino)-1-(4-methoxyphenyl)ethyl] cyclohexanol hydrochloride or (±)-1-[α- [(dimethylamino)methyl]-p-methoxybenzyl] cyclohexanol hydrochloride and has the molecular formula of C 17 H 27 NO 2 HCl. Its molecular weight is 313.86. The structural formula is shown as follows:
Drug release is controlled by diffusion through the coating membrane on the spheroids and is not pH-dependent. Venlafaxine hydrochloride extended-release capsules, USP intended for oral administration contains 37.5 mg, 75 mg and 150 mg of venlafaxine. In addition, each capsule contains the following inactive ingredients: colloidal silicon dioxide, cetostearyl alcohol, gelatin, hypromellose, microcrystalline cellulose, polyacrylate dispersion, sodium lauryl sulfate, talc and titanium dioxide. Additionally each 37.5 mg capsule shell contains black iron oxide and each 75 mg and 150 mg capsule shell contains red iron oxide. The capsule is printed with black pharmaceutical ink which contains black iron oxide as coloring agent.
The product complies with USP dissolution test 7.
The exact mechanism of the antidepressant action of venlafaxine in humans is unknown, but is thought to be related to the potentiation of serotonin and norepinephrine in the central nervous system, through inhibition of their reuptake. Non- clinical studies have demonstrated that venlafaxine and its active metabolite, ODV, are potent and selective inhibitors of neuronal serotonin and norepinephrine reuptake and weak inhibitors of dopamine reuptake.
Venlafaxine and ODV have no significant affinity for muscarinic-cholinergic, H1-histaminergic, or α1 adrenergic receptors in vitro. Pharmacologic activity at these receptors is hypothesized to be associated with the various anticholinergic, sedative, and cardiovascular effects seen with other psychotropic drugs. Venlafaxine and ODV do not possess monoamine oxidase (MAO) inhibitory activity.
The effect of venlafaxine on the QT interval was evaluated in a randomized, double-blind, placebo-and positive-controlled three-period crossover thorough QT study in 54 healthy adult subjects. No significant QT prolongation effect of venlafaxine 450 mg was detected.
Steady-state concentrations of venlafaxine and ODV in plasma are attained within 3 days of oral multiple- dose therapy. Venlafaxine and ODV exhibited linear kinetics over the dose range of 75 to 450 mg per day. Mean±SD steady-state plasma clearance of venlafaxine and ODV is 1.3±0.6 and 0.4±0.2 L/h/kg, respectively; apparent elimination half-life is 5±2 and 11±2 hours, respectively; and apparent (steady state) volume of distribution is 7.5±3.7 and 5.7±1.8 L/kg, respectively. Venlafaxine and ODV are minimally bound at therapeutic concentrations to plasma proteins (27% and 30%, respectively).
Absorption and Distribution
Venlafaxine is well absorbed and extensively metabolized in the liver. ODV is the major active metabolite. On the basis of mass balance studies, at least 92% of a single oral dose of venlafaxine is absorbed. The absolute bioavailability of venlafaxine is approximately 45%.
Administration of venlafaxine hydrochloride extended-release capsules (150 mg once daily) generally resulted in lower Cmax and later Tmax values than for venlafaxine hydrochloride tablets administered twice daily (Table 16). When equal daily doses of venlafaxine were administered as either an immediate-release tablet or the extended-release capsule, the exposure to both venlafaxine and ODV was similar for the two treatments, and the fluctuation in plasma concentrations was slightly lower with the venlafaxine hydrochloride extended-release capsules. Therefore, venlafaxine hydrochloride extended-release capsules provide a slower rate of absorption, but the same extent of absorption compared with the immediate-release tablet.
|C max (ng/mL)||T max (h)||C max (ng/mL)||T max (h)|
|Venlafaxine Hydrochloride Extended-Release Capsules (150 mg once daily)||150||5.5||260||9|
|Venlafaxine Hydrochloride Tablets (75 mg twice daily)||225||2||290||3|
Food did not affect the bioavailability of venlafaxine or its active metabolite, ODV. Time of administration (AM versus PM) did not affect the pharmacokinetics of venlafaxine and ODV from the 75 mg venlafaxine hydrochloride extended-release capsules.
Venlafaxine is not highly bound to plasma proteins; therefore, administration of venlafaxine hydrochloride extended-release capsules to a patient taking another drug that is highly protein-bound should not cause increased free concentrations of the other drug.
Metabolism and Elimination
Following absorption, venlafaxine undergoes extensive presystemic metabolism in the liver, primarily to ODV, but also to N-desmethylvenlafaxine, N,O-didesmethylvenlafaxine, and other minor metabolites. In vitro studies indicate that the formation of ODV is catalyzed by CYP2D6; this has been confirmed in a clinical study showing that patients with low CYP2D6 levels (poor metabolizers) had increased levels of venlafaxine and reduced levels of ODV compared to people with normal CYP2D6 levels (extensive metabolizers) [ see Use in Specific Populations ( 8.7) ].
Approximately 87% of a venlafaxine dose is recovered in the urine within 48 hours as unchanged venlafaxine (5%), unconjugated ODV (29%), conjugated ODV (26%), or other minor inactive metabolites (27%). Renal elimination of venlafaxine and its metabolites is thus the primary route of excretion.
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