Pharmacology: Mechanism of Action: The active ingredient of Obsenil HCl is basically a tricyclic antidepressant which has been extensively documented as a highly effective agent for the treatment of obsessive compulsive disorders and phobic states. The efficacy of Obsenil in obsessive compulsive disorders has been linked to its somewhat selective inhibitory action on the serotonin (5-hydroxytryptamine) re-uptake mechanism.
Pharmacokinetics: Obsenil HCl is well absorbed on oral administration producing peak plasma concentrations of 56-154 mg/mL (mean 92 mg/mL), 2-6 hrs (mean 4.7 hrs) after a single oral dose of 50 mg. After multiple daily dose of Obsenil 150 mg, steady-state plasma concentrations range from 94-399 mg/mL (mean 218 mg/mL) for Obsenil and from 134-532 mg/mL (mean 274 mg/mL) for its major and active metabolite, desmethylclomipramine. The drug is well distributed in the body appearing in significant concentrations in the cerebrospinal fluid, brain and breast milk. Obsenil HCl bound to the plasma proteins, mostly albumin to the extent of 97%.
Take Obsenil only as directed by your doctor to benefit your condition as much as possible. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered.
Obsenil should come with a Medication Guide. Read and follow these instructions carefully. Ask your doctor or pharmacist if you have any questions.
It is best to take Obsenil with food.
The dose of Obsenil will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of Obsenil. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
If you miss a dose of Obsenil, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Ask your healthcare professional how you should dispose of any medicine you do not use.
Follow all directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results. Do not take this medicine in larger or smaller amounts or for longer than recommended.
Take Obsenil with food to reduce stomach upset.
It may take up to 4 weeks before your symptoms improve. Keep using the medication as directed and tell your doctor if your symptoms do not improve after 4 weeks of treatment.
If you need surgery, tell the surgeon ahead of time that you are using Obsenil. You may need to stop using the medicine for a short time.
Do not stop using Obsenil suddenly, or you could have unpleasant withdrawal symptoms. Ask your doctor how to avoid withdrawal symptoms when you stop using Obsenil.
Store at room temperature away from moisture and heat.
Obsenil (CMI) is presumed to influence obsessive and compulsive behaviors through its effects on serotonergic neuronal transmission. The actual neurochemical mechanism is unknown, but CMI's capacity to inhibit the reuptake of serotonin (5-HT) is thought to be important.
CMI from Obsenil capsules is as bioavailable as CMI from a solution. The bioavailability of CMI from capsules is not significantly affected by food.
In a dose proportionality study involving multiple CMI doses, steady-state plasma concentrations (Css) and area-under-plasma-concentration-time curves (AUC) of CMI and CMI's major active metabolite, desmethylclomipramine (DMI), were not proportional to dose over the ranges evaluated, i.e., between 25 to 100 mg/day and between 25 to 150 mg/day, although Css and AUC are approximately linearly related to dose between 100 to 150 mg/day. The relationship between dose and CMI/DMI concentrations at higher daily doses has not been systematically assessed, but if there is significant dose dependency at doses above 150 mg/day, there is the potential for dramatically higher Css and AUC even for patients dosed within the recommended range. This may pose a potential risk to some patients.
After a single 50 mg oral dose, maximum plasma concentrations of CMI occur within 2 to 6 hours (mean, 4.7 hr) and range from 56 ng/mL to 154 ng/mL (mean, 92 ng/mL). After multiple daily doses of 150 mg of Obsenil, steady-state maximum plasma concentrations range from 94 ng/mL to 339 ng/mL (mean, 218 ng/mL) for CMI and from 134 ng/mL to 532 ng/mL (mean, 274 ng/mL) for DMI. Additional information from a rising dose study of doses up to 250 mg suggests that DMI may exhibit nonlinear pharmacokinetics over the usual dosing range. At a dose of Obsenil 200 mg, subjects who had a single blood sample taken approximately 9 to 22 hours, (median 16 hours), after the dose had plasma concentrations of up to 605 ng/mL for CMI, 781 ng/mL for DMI, and 1386 ng/mL for both.
CMI distributes into cerebrospinal fluid (CSF) and brain and into breast milk. DMI also distributes into CSF, with a mean CSF/plasma ratio of 2.6. The protein binding of CMI is approximately 97%, principally to albumin, and is independent of CMI concentration. The interaction between CMI and other highly protein-bound drugs has not been fully evaluated, but may be important.
CMI is extensively biotransformed to DMI and other metabolites and their glucuronide conjugates. DMI is pharmacologically active, but its effects on OCD behaviors are unknown. These metabolites are excreted in urine and feces, following biliary elimination. After a 25 mg radiolabeled dose of CMI in two subjects, 60% and 51%, respectively, of the dose were recovered in the urine and 32% and 24%, respectively, in feces. In the same study, the combined urinary recoveries of CMI and DMI were only about 0.8% to 1.3% of the dose administered. CMI does not induce drug-metabolizing enzymes, as measured by antipyrine half-life.
Evidence that the C and AUC for CMI and DMI may increase disproportionately with increasing oral doses suggests that the metabolism of CMI and DMI may be capacity limited. This fact must be considered in assessing the estimates of the pharmacokinetic parameters presented below, as these were obtained in individuals exposed to doses of 150 mg. If the pharmacokinetics of CMI and DMI are nonlinear at doses above 150 mg, their elimination half-lives may be considerably lengthened at doses near the upper end of the recommended dosing range (i.e., 200 mg/day to 250 mg/day). Consequently, CMI and DMI may accumulate, and this accumulation may increase the incidence of any dose- or plasma-concentration-dependent adverse reactions, in particular seizures.
After a 150 mg dose, the half-life of CMI ranges from 19 hours to 37 hours (mean, 32 hr) and that of DMI ranges from 54 hours to 77 hours (mean, 69 hr). Steady-state levels after multiple dosing are typically reached within 7 to 14 days for CMI. Plasma concentrations of the metabolite exceed the parent drug on multiple dosing. After multiple dosing with 150 mg/day, the accumulation factor for CMI is approximately 2.5 and for DMI is 4.6. Importantly, it may take two weeks or longer to achieve this extent of accumulation at constant dosing because of the relatively long elimination half-lives of CMI and DMI. The effects of hepatic and renal impairment on the disposition of Obsenil have not been determined.
Co-administration of haloperidol with CMI increases plasma concentrations of CMI. Coadministration of CMI with phenobarbital increases plasma concentrations of phenobarbital. Younger subjects (18 to 40 years of age) tolerated CMI better and had significantly lower steady-state plasma concentrations, compared with subjects over 65 years of age. Children under 15 years of age had significantly lower plasma concentration/dose ratios, compared with adults. Plasma concentrations of CMI were significantly lower in smokers than in nonsmokers.
Phospholipidosis and testicular changes, commonly associated with tricyclic compounds, have been observed with Obsenil. In chronic rat studies, changes related to Obsenil consisted of systemic phospholipidosis, alterations in the testes (atrophy, mineralization) and secondary changes in other tissues. In addition cardiac thrombosis and dermatitis/keratitis were observed in rats treated for 2 years at doses which were 24 and 10 times the maximum recommended human daily dose (MRHD), respectively, on a mg/kg basis, and 4 and 1.5 times the MRHD, respectively, on a mg/m² basis.
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Information checked by Dr. Sachin Kumar, MD Pharmacology