Pramipexole dihydrochloride tablets contain Pramipexole, a nonergot dopamine agonist. The chemical name of Pramipexole dihydrochloride is (S)-2-amino-4,5,6,7-tetrahydro-6-(propylamino)benzothiazole dihydrochloride monohydrate.
The structural formula is:
C10H21C12N3OS M.W. 302.25
Pramipexole dihydrochloride is a white to off-white crystalline powder substance. Melting occurs in the range of 296°C to 301°C, with decomposition. Pramipexole dihydrochloride is more than 20% soluble in water, about 8% in methanol, about 0.5% in ethanol, and practically insoluble in dichloromethane.
Pramipexole dihydrochloride tablets, for oral administration, contain 0.75 mg of Pramipexole dihydrochloride monohydrate. Inactive ingredients consist of colloidal silicon dioxide, magnesium stearate, mannitol, microcrystalline cellulose, povidone, sodium starch glycolate, and sodium stearyl fumarate.
Pramipexole - Clinical Pharmacology
Mechanism of Action
Pramipexole is a nonergot dopamine agonist with high relative in vitro specificity and full intrinsic activity at the D2 subfamily of dopamine receptors, binding with higher affinity to D3 than to D2 or D4 receptor subtypes.
Parkinson’s Disease
The precise mechanism of action of Pramipexole as a treatment for Parkinson's disease is unknown, although it is believed to be related to its ability to stimulate dopamine receptors in the striatum. This conclusion is supported by electrophysiologic studies in animals that have demonstrated that Pramipexole influences striatal neuronal firing rates via activation of dopamine receptors in the striatum and the substantia nigra, the site of neurons that send projections to the striatum. The relevance of D3 receptor binding in Parkinson’s disease is unknown.
Pharmacokinetics
Pramipexole displays linear pharmacokinetics over the clinical dosage range. Its terminal half-life is about 8 hours in young healthy volunteers and about 12 hours in elderly volunteers (see CLINICAL PHARMACOLOGY, Pharmacokinetics in Special Populations). Steady-state concentrations are achieved within 2 days of dosing.
Absorption
Pramipexole is rapidly absorbed, reaching peak concentrations in approximately 2 hours. The absolute bioavailability of Pramipexole is greater than 90%, indicating that it is well absorbed and undergoes little presystemic metabolism. Food does not affect the extent of Pramipexole absorption, although the time of maximum plasma concentration (Tmax) is increased by about 1 hour when the drug is taken with a meal.
Distribution
Pramipexole is extensively distributed, having a volume of distribution of about 500 L (coefficient of variation [CV] = 20%). It is about 15% bound to plasma proteins. Pramipexole distributes into red blood cells as indicated by an erythrocyte-to-plasma ratio of approximately 2.
Metabolism and Elimination
The terminal half-life of Pramipexole is about 8 hours in healthy volunteers and 12 hours in elderly volunteers.
Urinary excretion is the major route of Pramipexole elimination, with 90% of a Pramipexole dose recovered in urine, almost all as unchanged drug. Nonrenal routes may contribute to a small extent to Pramipexole elimination, although no metabolites have been identified in plasma or urine. The renal clearance of Pramipexole is approximately 400 mL/min (CV = 25%), approximately three times higher than the glomerular filtration rate. Thus, Pramipexole is secreted by the renal tubules, probably by the organic cation transport system.
Pharmacokinetics in Special Populations
Because therapy with Pramipexole dihydrochloride tablets is initiated at a low dose and gradually titrated upward according to clinical tolerability to obtain the optimum therapeutic effect, adjustment of the initial dose based on gender, weight, or age is not necessary. However, renal insufficiency, which can cause a large decrease in the ability to eliminate Pramipexole, may necessitate dosage adjustment (see CLINICAL PHARMACOLOGY, Renal Insufficiency).
Gender
Pramipexole clearance is about 30% lower in women than in men, but most of this difference can be accounted for by differences in body weight. There is no difference in half-life between males and females.
Age
Pramipexole clearance decreases with age as the half-life and clearance are about 40% longer and 30% lower, respectively, in elderly (aged 65 years or older) compared with young healthy volunteers (aged less than 40 years). This difference is most likely due to the well-known reduction in renal function with age, since Pramipexole clearance is correlated with renal function, as measured by creatinine clearance (see CLINICAL PHARMACOLOGY, RenalInsufficiency).
Parkinson's Disease Patients
A cross-study comparison of data suggests that the clearance of Pramipexole may be reduced by about 30% in Parkinson's disease patients compared with healthy elderly volunteers. The reason for this difference appears to be reduced renal function in Parkinson's disease patients, which may be related to their poorer general health. The pharmacokinetics of Pramipexole were comparable between early and advanced Parkinson's disease patients.
Pediatric
The pharmacokinetics of Pramipexole in the pediatric population have not been evaluated.
Hepatic Insufficiency
The influence of hepatic insufficiency on Pramipexole pharmacokinetics has not been evaluated. Because approximately 90% of the recovered dose is excreted in the urine as unchanged drug, hepatic impairment would not be expected to have a significant effect on Pramipexole elimination.
Renal Insufficiency
The clearance of Pramipexole was about 75% lower in patients with severe renal impairment (creatinine clearance approximately 20 mL/min) and about 60% lower in patients with moderate impairment (creatinine clearance approximately 40 mL/min) compared with healthy volunteers. Also, it took longer to achieve steady state. A lower starting and/or maintenance dose may be appropriate in these patients (see PRECAUTIONS and DOSAGE AND ADMINISTRATION). In patients with varying degrees of renal impairment, Pramipexole clearance correlates well with creatinine clearance. Therefore, creatinine clearance can be used as a predictor of the extent of decrease in Pramipexole clearance. Pramipexole clearance is extremely low in dialysis patients, as a negligible amount of Pramipexole is removed by dialysis. Caution should be exercised when administering Pramipexole to patients with renal disease.
CLINICAL STUDIES
Parkinson's Disease
The effectiveness of Pramipexole dihydrochloride tablets in the treatment of Parkinson's disease was evaluated in a multinational drug development program consisting of seven randomized, controlled trials. Three were conducted in patients with early Parkinson's disease who were not receiving concomitant levodopa, and four were conducted in patients with advanced Parkinson's disease who were receiving concomitant levodopa. Among these seven studies, three studies provide the most persuasive evidence of Pramipexole's effectiveness in the management of patients with Parkinson's disease who were and were not receiving concomitant levodopa. Two of these three trials enrolled patients with early Parkinson's disease (not receiving levodopa), and one enrolled patients with advanced Parkinson's disease who were receiving maximally tolerated doses of levodopa.
In all studies, the Unified Parkinson's Disease Rating Scale (UPDRS), or one or more of its subparts, served as the primary outcome assessment measure. The UPDRS is a four-part multi-item rating scale intended to evaluate mentation (part I), Activities of Daily Living (ADL) (part II), motor performance (part III), and complications of therapy (part IV).
Part II of the UPDRS contains 13 questions relating to ADL, which are scored from 0 (normal) to 4 (maximal severity) for a maximum (worst) score of 52. Part III of the UPDRS contains 27 questions (for 14 items) and is scored as described for part II. It is designed to assess the severity of the cardinal motor findings in patients with Parkinson's disease (e.g., tremor, rigidity, bradykinesia, postural instability, etc.), scored for different body regions, and has a maximum (worst) score of 108.
Studies in Patients With Early Parkinson's Disease
Patients (N = 599) in the two studies of early Parkinson's disease had a mean disease duration of 2 years, limited or no prior exposure to levodopa (generally none in the preceding 6 months), and were not experiencing the "on-off" phenomenon and dyskinesia characteristic of later stages of the disease.
One of the two early Parkinson's disease studies (N = 335) was a double-blind, placebo-controlled, parallel trial consisting of a 7 week dose-escalation period and a 6 month maintenance period. Patients could be on selegiline, anticholinergics, or both, but could not be on levodopa products or amantadine. Patients were randomized to Pramipexole dihydrochloride tablets or placebo. Patients treated with Pramipexole dihydrochloride tablets had a starting daily dose of 0.375 mg and were titrated to a maximally tolerated dose, but no higher than 4.5 mg/day in three divided doses. At the end of the 6 month maintenance period, the mean improvement from baseline on the UPDRS part II (ADL) total score was 1.9 in the group receiving Pramipexole dihydrochloride tablets and -0.4 in the placebo group, a difference that was statistically significant. The mean improvement from baseline on the UPDRS part III total score was 5.0 in the group receiving Pramipexole dihydrochloride tablets and -0.8 in the placebo group, a difference that was also statistically significant. A statistically significant difference between groups in favor of Pramipexole dihydrochloride tablets was seen beginning at week 2 of the UPDRS part II (maximum dose 0.75 mg/day) and at week 3 of the UPDRS part III (maximum dose 1.5 mg/day).
The second early Parkinson's disease study (N = 264) was a double-blind, placebo-controlled, parallel trial consisting of a 6 week dose-escalation period and a 4 week maintenance period. Patients could be on selegiline, anticholinergics, amantadine, or any combination of these, but could not be on levodopa products. Patients were randomized to 1 of 4 fixed doses of Pramipexole dihydrochloride tablets (1.5 mg, 3 mg, 4.5 mg, or 6 mg per day) or placebo. At the end of the 4 week maintenance period, the mean improvement from baseline on the UPDRS part II total score was 1.8 in the patients treated with Pramipexole dihydrochloride tablets, regardless of assigned dose group, and 0.3 in placebo-treated patients. The mean improvement from baseline on the UPDRS part III total score was 4.2 in patients treated with Pramipexole dihydrochloride tablets and 0.6 in placebo-treated patients. No dose-response relationship was demonstrated. The between-treatment differences on both parts of the UPDRS were statistically significant in favor of Pramipexole dihydrochloride tablets for all doses.
No differences in effectiveness based on age or gender were detected. There were too few non-Caucasian patients to evaluate the effect of race. Patients receiving selegiline or anticholinergics had responses similar to patients not receiving these drugs.
Studies in Patients With Advanced Parkinson's Disease
In the advanced Parkinson's disease study, the primary assessments were the UPDRS and daily diaries that quantified amounts of "on" and "off" time.
Patients in the advanced Parkinson's disease study (N = 360) had a mean disease duration of 9 years, had been exposed to levodopa for long periods of time (mean 8 years), used concomitant levodopa during the trial, and had "on-off" periods.
The advanced Parkinson's disease study was a double-blind, placebo-controlled, parallel trial consisting of a 7 week dose-escalation period and a 6 month maintenance period. Patients were all treated with concomitant levodopa products and could additionally be on concomitant selegiline, anticholinergics, amantadine, or any combination. Patients treated with Pramipexole dihydrochloride tablets had a starting dose of 0.375 mg/day and were titrated to a maximally tolerated dose, but no higher than 4.5 mg/day in three divided doses. At selected times during the 6 month maintenance period, patients were asked to record the amount of "off," "on," or "on with dyskinesia" time per day for several sequential days. At the end of the 6 month maintenance period, the mean improvement from baseline on the UPDRS part II total score was 2.7 in the group treated with Pramipexole dihydrochloride tablets and 0.5 in the placebo group, a difference that was statistically significant. The mean improvement from baseline on the UPDRS part III total score was 5.6 in the group treated with Pramipexole dihydrochloride tablets and 2.8 in the placebo group, a difference that was statistically significant. A statistically significant difference between groups in favor of Pramipexole dihydrochloride tablets was seen at week 3 of the UPDRS part II (maximum dose 1.5 mg/day) and at week 2 of the UPDRS part III (maximum dose 0.75 mg/day). Dosage reduction of levodopa was allowed during this study if dyskinesia (or hallucinations) developed; levodopa dosage reduction occurred in 76% of patients treated with Pramipexole dihydrochloride tablets versus 54% of placebo patients. On average, the levodopa dose was reduced 27%.
The mean number of "off" hours per day during baseline was 6 hours for both treatment groups. Throughout the trial, patients treated with Pramipexole dihydrochloride tablets had a mean of 4 "off" hours per day, while placebo-treated patients continued to experience 6 "off" hours per day.
No differences in effectiveness based on age or gender were detected. There were too few non-Caucasian patients to evaluate the effect of race.
Indications and Usage for Pramipexole
Parkinson's Disease
Pramipexole dihydrochloride tablets are indicated for the treatment of the signs and symptoms of idiopathic Parkinson's disease.
The effectiveness of Pramipexole dihydrochloride tablets was demonstrated in randomized, controlled trials in patients with early Parkinson's disease who were not receiving concomitant levodopa therapy as well as in patients with advanced disease on concomitant levodopa (see CLINICAL STUDIES).
Contraindications
Pramipexole dihydrochloride tablets are contraindicated in patients who have demonstrated hypersensitivity to the drug or its ingredients.
Warnings
Falling Asleep During Activities of Daily Living
Patients treated with Pramipexole dihydrochloride tablets have reported falling asleep while engaged in activities of daily living, including the operation of motor vehicles which sometimes resulted in accidents. Although many of these patients reported somnolence while on Pramipexole dihydrochloride tablets, some perceived that they had no warning signs such as excessive drowsiness, and believed that they were alert immediately prior to the event. Some of these events had been reported as late as one year after the initiation of treatment.
Somnolence is a common occurrence in patients receiving Pramipexole dihydrochloride tablets at doses above 1.5 mg/day (0.5 mg TID) for Parkinson’s disease. Many clinical experts believe that falling asleep while engaged in activities of daily living always occurs in a setting of preexisting somnolence, although patients may not give such a history. For this reason, prescribers should continually reassess patients for drowsiness or sleepiness, especially since some of the events occur well after the start of treatment. Prescribers should also be aware that patients may not acknowledge drowsiness or sleepiness until directly questioned about drowsiness or sleepiness during specific activities.
Before initiating treatment with Pramipexole dihydrochloride tablets, patients should be advised of the potential to develop drowsiness and specifically asked about factors that may increase the risk with Pramipexole dihydrochloride tablets such as concomitant sedating medications, the presence of sleep disorders, and concomitant medications that increase Pramipexole plasma levels (e.g., cimetidine - see PRECAUTIONS, Drug Interactions). If a patient develops significant daytime sleepiness or episodes of falling asleep during activities that require active participation (e.g., conversations, eating, etc.), Pramipexole dihydrochloride tablets should ordinarily be discontinued. If a decision is made to continue Pramipexole dihydrochloride tablets, patients should be advised to not drive and to avoid other potentially dangerous activities. While dose reduction clearly reduces the degree of somnolence, there is insufficient information to establish that dose reduction will eliminate episodes of falling asleep while engaged in activities of daily living.
Symptomatic Hypotension
Dopamine agonists, in clinical studies and clinical experience, appear to impair the systemic regulation of blood pressure, with resulting orthostatic hypotension, especially during dose escalation. Parkinson's disease patients, in addition, appear to have an impaired capacity to respond to an orthostatic challenge. For these reasons, Parkinson's disease patients being treated with dopaminergic agonists ordinarily require careful monitoring for signs and symptoms of orthostatic hypotension, especially during dose escalation, and should be informed of this risk (see PRECAUTIONS, Information for Patients).
In clinical trials of Pramipexole, however, and despite clear orthostatic effects in normal volunteers, the reported incidence of clinically significant orthostatic hypotension was not greater among those assigned to Pramipexole dihydrochloride tablets than among those assigned to placebo. This result, especially with the higher doses used in Parkinson’s disease, is clearly unexpected in light of the previous experience with the risks of dopamine agonist therapy.
While this finding could reflect a unique property of Pramipexole, it might also be explained by the conditions of the study and the nature of the population enrolled in the clinical trials. Patients were very carefully titrated, and patients with active cardiovascular disease or significant orthostatic hypotension at baseline were excluded.
Hallucinations
In the three double-blind, placebo-controlled trials in early Parkinson's disease, hallucinations were observed in 9% (35 of 388) of patients receiving Pramipexole dihydrochloride tablets, compared with 2.6% (6 of 235) of patients receiving placebo. In the four double-blind, placebo-controlled trials in advanced Parkinson's disease, where patients received Pramipexole dihydrochloride tablets and concomitant levodopa, hallucinations were observed in 16.5% (43 of 260) of patients receiving Pramipexole dihydrochloride tablets compared with 3.8% (10 of 264) of patients receiving placebo. Hallucinations were of sufficient severity to cause discontinuation of treatment in 3.1% of the early Parkinson's disease patients and 2.7% of the advanced Parkinson's disease patients compared with about 0.4% of placebo patients in both populations.
Age appears to increase the risk of hallucinations attributable to Pramipexole. In the early Parkinson's disease patients, the risk of hallucinations was 1.9 times greater than placebo in patients younger than 65 years and 6.8 times greater than placebo in patients older than 65 years. In the advanced Parkinson's disease patients, the risk of hallucinations was 3.5 times greater than placebo in patients younger than 65 years and 5.2 times greater than placebo in patients older than 65 years.
Precautions
Rhabdomyolysis
A single case of rhabdomyolysis occurred in a 49-year-old male with advanced Parkinson's disease treated with Pramipexole dihydrochloride tablets. The patient was hospitalized with an elevated CPK (10,631 IU/L). The symptoms resolved with discontinuation of the medication.
Renal
Since Pramipexole is eliminated through the kidneys, caution should be exercised when prescribing Pramipexole dihydrochloride tablets to patients with renal insufficiency (see DOSAGE AND ADMINISTRATION).
Dyskinesia
Pramipexole dihydrochloride tablets may potentiate the dopaminergic side effects of levodopa and may cause or exacerbate preexisting dyskinesia. Decreasing the dose of levodopa may ameliorate this side effect.
Retinal Pathology in Albino Rats
Pathologic changes (degeneration and loss of photoreceptor cells) were observed in the retina of albino rats in the 2 year carcinogenicity study. While retinal degeneration was not diagnosed in pigmented rats treated for 2 years, a thinning in the outer nuclear layer of the retina was slightly greater in rats given drug compared with controls. Evaluation of the retinas of albino mice, monkeys, and minipigs did not reveal similar changes. The potential significance of this effect in humans has not been established, but cannot be disregarded because disruption of a mechanism that is universally present in vertebrates (i.e., disk shedding) may be involved (see ANIMAL TOXICOLOGY).
Events Reported With Dopaminergic Therapy
Although the events enumerated below may not have been reported in association with the use of Pramipexole in its development program, they are associated with the use of other dopaminergic drugs. The expected incidence of these events, however, is so low that even if Pramipexole caused these events at rates similar to those attributable to other dopaminergic therapies, it would be unlikely that even a single case would have occurred in a cohort of the size exposed to Pramipexole in studies to date.
Withdrawal-Emergent Hyperpyrexia and Confusion
Although not reported with Pramipexole in the clinical development program, a symptom complex resembling the neuroleptic malignant syndrome (characterized by elevated temperature, muscular rigidity, altered consciousness, and autonomic instability), with no other obvious etiology, has been reported in association with rapid dose reduction, withdrawal of, or changes in antiparkinsonian therapy.
Fibrotic Complications
Although not reported with Pramipexole in the clinical development program, cases of retroperitoneal fibrosis, pulmonary infiltrates, pleural effusion, and pleural thickening, pericarditis, and cardiac valvulopathy have been reported in some patients treated with ergot-derived dopaminergic agents. While these complications may resolve when the drug is discontinued, complete resolution does not always occur.
Although these adverse events are believed to be related to the ergoline structure of these compounds, whether other, nonergot derived dopamine agonists can cause them is unknown.
A small number of reports have been received of possible fibrotic complications, including peritoneal fibrosis, pleural fibrosis, and pulmonary fibrosis, in the post-marketing experience for Pramipexole dihydrochloride tablets. While the evidence is not sufficient to establish a causal relationship between Pramipexole dihydrochloride tablets and these fibrotic complications, a contribution of Pramipexole dihydrochloride tablets cannot be completely ruled out in rare cases.
Melanoma
Epidemiological studies have shown that patients with Parkinson’s disease have a higher risk (2 to approximately 6 fold higher) of developing melanoma than the general population. Whether the increased risk observed was due to Parkinson’s disease or other factors, such as drugs used to treat Parkinson’s disease, is unclear.
For the reasons stated above, patients and providers are advised to monitor for melanomas frequently and on a regular basis when using Pramipexole dihydrochloride tablets for any indication. Ideally, periodic skin examinations should be performed by appropriately qualified individuals (e.g., dermatologists).
Information for Patients (Also see Patient Package Insert)
Patients should be instructed to take Pramipexole dihydrochloride tablets only as prescribed.
Patients should be alerted to the potential sedating effects associated with Pramipexole dihydrochloride tablets, including somnolence and the possibility of falling asleep while engaged in activities of daily living. Since somnolence is a frequent adverse event with potentially serious consequences, patients should neither drive a car nor engage in other potentially dangerous activities until they have gained sufficient experience with Pramipexole dihydrochloride tablets to gauge whether or not it affects their mental and/or motor performance adversely. Patients should be advised that if increased somnolence or new episodes of falling asleep during activities of daily living (e.g., watching television, passenger in a car, etc.) are experienced at any time during treatment, they should not drive or participate in potentially dangerous activities until they have contacted their physician. Because of possible additive effects, caution should be advised when patients are taking other sedating medications or alcohol in combination with Pramipexole dihydrochloride tablets and when taking concomitant medications that increase plasma levels of Pramipexole (e.g., cimetidine).
Patients should be informed that hallucinations can occur and that the elderly are at a higher risk than younger patients with Parkinson's disease.
There have been reports of patients experiencing intense urges to gamble, increased sexual urges, and other intense urges and the inability to control these urges while taking one or more of the medications that increase central dopaminergic tone, that are generally used for the treatment of Parkinson’s disease, including Pramipexole dihydrochloride. Although it is not proven that the medications caused these events, these urges were reported to have stopped in some cases when the dose was reduced or the medication was stopped. Prescribers should ask patients about the development of new or increased gambling urges, sexual urges or other urges while being treated with Pramipexole dihydrochloride. Patients should inform their physician if they experience new or increased gambling urges, increased sexual urges or other intense urges while taking Pramipexole dihydrochloride. Physicians should consider dose reduction or stopping the medication if a patient develops such urges while taking Pramipexole dihydrochloride.
Patients may develop postural (orthostatic) hypotension, with or without symptoms such as dizziness, nausea, fainting or blackouts, and sometimes, sweating. Hypotension may occur more frequently during initial therapy. Accordingly, patients should be cautioned against rising rapidly after sitting or lying down, especially if they have been doing so for prolonged periods and especially at the initiation of treatment with Pramipexole dihydrochloride tablets.
Because the teratogenic potential of Pramipexole has not been completely established in laboratory animals, and because experience in humans is limited, patients should be advised to notify their physicians if they become pregnant or intend to become pregnant during therapy (see PRECAUTIONS, Pregnancy).
Because of the possibility that Pramipexole may be excreted in breast milk, patients should be advised to notify their physicians if they intend to breast-feed or are breast-feeding an infant.
If patients develop nausea, they should be advised that taking Pramipexole dihydrochloride tablets with food may reduce the occurrence of nausea.
Laboratory Tests
During the development of Pramipexole dihydrochloride tablets, no systematic abnormalities on routine laboratory testing were noted. Therefore, no specific guidance is offered regarding routine monitoring; the practitioner retains responsibility for determining how best to monitor the patient in his or her care.
Drug Interactions
Carbidopa/levodopa: Carbidopa/levodopa did not influence the pharmacokinetics of Pramipexole in healthy volunteers (N = 10). Pramipexole did not alter the extent of absorption (AUC) or the elimination of carbidopa/levodopa, although it caused an increase in levodopa Cmax by about 40% and a decrease in Tmax from 2.5 to 0.5 hours.
Selegiline: In healthy volunteers (N = 11), selegiline did not influence the pharmacokinetics of Pramipexole.
Amantadine: Population pharmacokinetic analyses suggest that amantadine may slightly decrease the oral clearance of Pramipexole.
Cimetidine: Cimetidine, a known inhibitor of renal tubular secretion of organic bases via the cationic transport system, caused a 50% increase in Pramipexole AUC and a 40% increase in half-life (N = 12).
Probenecid: Probenecid, a known inhibitor of renal tubular secretion of organic acids via the anionic transporter, did not noticeably influence Pramipexole pharmacokinetics (N = 12).
Other drugs eliminated via renal secretion: Population pharmacokinetic analysis suggests that coadministration of drugs that are secreted by the cationic transport system (e.g., cimetidine, ranitidine, diltiazem, triamterene, verapamil, quinidine, and quinine) decreases the oral clearance of Pramipexole by about 20%, while those secreted by the anionic transport system (e.g., cephalosporins, penicillins, indomethacin, hydrochlorothiazide, and chlorpropamide) are likely to have little effect on the oral clearance of Pramipexole.
CYP interactions: Inhibitors of cytochrome P450 enzymes would not be expected to affect Pramipexole elimination because Pramipexole is not appreciably metabolized by these enzymes in vivo or in vitro. Pramipexole does not inhibit CYP enzymes CYP1A2, CYP2C9, CYP2C19, CYP2E1, and CYP3A4. Inhibition of CYP2D6 was observed with an apparent Ki of 30 µM, indicating that Pramipexole will not inhibit CYP enzymes at plasma concentrations observed following the clinical dose of 4.5 mg/day (1.5 mg TID).
Dopamine antagonists: Since Pramipexole is a dopamine agonist, it is possible that dopamine antagonists, such as the neuroleptics (phenothiazines, butyrophenones, thioxanthenes) or metoclopramide, may diminish the effectiveness of Pramipexole dihydrochloride tablets.
Drug/Laboratory Test Interactions
There are no known interactions between Pramipexole dihydrochloride tablets and laboratory tests.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Two-year carcinogenicity studies with Pramipexole have been conducted in mice and rats. Pramipexole was administered in the diet to Chbb:NMRI mice at doses of 0.3, 2, and 10 mg/kg/day [0.3, 2.2, and 11 times the Maximum Recommended Human Dose (MRHD) (MRHD of 1.5 mg TID on a mg/m2 basis)]. Pramipexole was administered in the diet to Wistar rats at 0.3, 2, and 8 mg/kg/day (plasma AUCs were 0.3, 2.5, and 12.5 times the AUC in humans at the MRHD). No significant increases in tumors occurred in either species.
Pramipexole was not mutagenic or clastogenic in a battery of assays, including the in vitro Ames assay, V79 gene mutation assay for HGPRT mutants, chromosomal aberration assay in Chinese hamster ovary cells, and in vivo mouse micronucleus assay.
In rat fertility studies, Pramipexole at a dose of 2.5 mg/kg/day (5 times the MRHD on a mg/m2 basis), prolonged estrus cycles and inhibited implantation. These effects were associated with reductions in serum levels of prolactin, a hormone necessary for implantation and maintenance of early pregnancy in rats.
Pregnancy
Teratogenic Effects
Pregnancy category C
When Pramipexole was given to female rats throughout pregnancy, implantation was inhibited at a dose of 2.5 mg/kg/day (5 times the MRHD on a mg/m2 basis). Administration of 1.5 mg/kg/day of Pramipexole to pregnant rats during the period of organogenesis (gestation days 7 through 16) resulted in a high incidence of total resorption of embryos. The plasma AUC in rats at this dose was 4 times the AUC in humans at the MRHD. These findings are thought to be due to the prolactin-lowering effect of Pramipexole, since prolactin is necessary for implantation and maintenance of early pregnancy in rats (but not rabbits or humans). Because of pregnancy disruption and early embryonic loss in these studies, the teratogenic potential of Pramipexole could not be adequately evaluated. There was no evidence of adverse effects on embryo-fetal development following administration of up to 10 mg/kg/day to pregnant rabbits during organogenesis (plasma AUC was 71 times that in humans at the MRHD). Postnatal growth was inhibited in the offspring of rats treated with 0.5 mg/kg/day (approximately equivalent to the MRHD on a mg/m2 basis) or greater during the latter part of pregnancy and throughout lactation.
There are no studies of Pramipexole in human pregnancy. Because animal reproduction studies are not always predictive of human response, Pramipexole should be used during pregnancy only if the potential benefit outweighs the potential risk to the fetus.
Nursing Mothers
A single-dose, radio-labeled study showed that drug-related materials were excreted into the breast milk of lactating rats. Concentrations of radioactivity in milk were three to six times higher than concentrations in plasma at equivalent time points.
Other studies have shown that Pramipexole treatment resulted in an inhibition of prolactin secretion in humans and rats.
It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants from Pramipexole, a decision should be made as to whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.
Pediatric Use
The safety and efficacy of Pramipexole dihydrochloride tablets in pediatric patients has not been established.
Geriatric Use
Pramipexole total oral clearance was approximately 30% lower in subjects older than 65 years compared with younger subjects, because of a decline in Pramipexole renal clearance due to an age-related reduction in renal function. This resulted in an increase in elimination half-life from approximately 8.5 hours to 12 hours. In clinical studies with Parkinson’s disease patients, 38.7% of patients were older than 65 years. There were no apparent differences in efficacy or safety between older and younger patients, except that the relative risk of hallucination associated with the use of Pramipexole dihydrochloride tablets was increased in the elderly.
ADVERSE EVENTS
Parkinson’s Disease
During the premarketing development of Pramipexole, patients with either early or advanced Parkinson's disease were enrolled in clinical trials. Apart from the severity and duration of their disease, the two populations differed in their use of concomitant levodopa therapy. Patients with early disease did not receive concomitant levodopa therapy during treatment with Pramipexole; those with advanced Parkinson's disease all received concomitant levodopa treatment. Because these two populations may have differential risks for various adverse events, this section will, in general, present adverse-event data for these two populations separately.
Because the controlled trials performed during premarketing development all used a titration design, with a resultant confounding of time and dose, it was impossible to adequately evaluate the effects of dose on the incidence of adverse events.
Early Parkinson's Disease
In the three double-blind, placebo-controlled trials of patients with early Parkinson's disease, the most commonly observed adverse events (> 5%) that were numerically more frequent in the group treated with Pramipexole dihydrochloride tablets were nausea, dizziness, somnolence, insomnia, constipation, asthenia, and hallucinations.
Approximately 12% of 388 patients with early Parkinson's disease and treated with Pramipexole dihydrochloride tablets who participated in the double-blind, placebo-controlled trials discontinued treatment due to adverse events compared with 11% of 235 patients who received placebo. The adverse events most commonly causing discontinuation of treatment were related to the nervous system (hallucinations [3.1% on Pramipexole dihydrochloride tablets vs 0.4% on placebo]; dizziness [2.1% on Pramipexole dihydrochloride tablets vs 1% on placebo]; somnolence [1.6% on Pramipexole dihydrochloride tablets vs 0% on placebo]; extrapyramidal syndrome [1.6% on Pramipexole dihydrochloride tablets vs 6.4% on placebo]; headache and confusion [1.3% and 1.0%, respectively, on Pramipexole dihydrochloride tablets vs 0% on placebo]); and gastrointestinal system (nausea [2.1% on Pramipexole dihydrochloride tablets vs 0.4% on placebo]).
Adverse-event incidence in controlled clinical studies in early Parkinson's disease
Table 1 lists treatment-emergent adverse events that occurred in the double-blind, placebo-controlled studies in early Parkinson's disease that were reported by ≥ 1% of patients treated with Pramipexole dihydrochloride tablets and were numerically more frequent than in the placebo group. In these studies, patients did not receive concomitant levodopa. Adverse events were usually mild or moderate in intensity.
The prescriber should be aware that these figures cannot be used to predict the incidence of adverse events in the course of usual medical practice where patient characteristics and other factors differ from those that prevailed in the clinical studies. Similarly, the cited frequencies cannot be compared with figures obtained from other clinical investigations involving different treatments, uses, and investigators. However, the cited figures do provide the prescribing physician with some basis for estimating the relative contribution of drug and nondrug factors to the adverse-event incidence rate in the population studied.
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| Body System/Adverse Event | Pramipexole Dihydrochloride Tablets | Placebo |
| N = 388 | N = 235 | |
| Body as a Whole | ||
| Asthenia | 14 | 12 |
| General edema | 5 | 3 |
| Malaise | 2 | 1 |
| Reaction unevaluable | 2 | 1 |
| Fever | 1 | 0 |
| Digestive System | ||
| Nausea | 28 | 18 |
| Constipation | 14 | 6 |
| Anorexia | 4 | 2 |
| Dysphagia | 2 | 0 |
| Metabolic & Nutritional System | ||
| Peripheral edema | 5 | 4 |
| Decreased weight | 2 | 0 |
| Nervous System | ||
| Dizziness | 25 | 24 |
| Somnolence | 22 | 9 |
| Insomnia | 17 | 12 |
| Hallucinations | 9 | 3 |
| Confusion | 4 | 1 |
| Amnesia | 4 | 2 |
| Hypesthesia | 3 | 1 |
| Dystonia | 2 | 1 |
| Akathisia | 2 | 0 |
| Thinking abnormalities | 2 | 0 |
| Decreased libido | 1 | 0 |
| Myoclonus | ||
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