Parlodel (Bromocriptine Mesylate) - Description and Clinical Pharmacology

DESCRIPTION

Parlodel^® (bromocriptine mesylate) is an ergot derivative with potent dopamine receptor agonist activity. Each Parlodel^® (bromocriptine mesylate) SnapTabs^® tablet for oral administration contains 2½ mg and each capsule contains 5 mg bromocriptine (as the mesylate). Bromocriptine mesylate is chemically designated as Ergotaman‑3′,6′,18‑trione, 2‑bromo‑12′‑hydroxy‑2′‑ (1‑methylethyl)‑5′‑(2‑methylpropyl)‑, (5′α)‑monomethanesulfonate (salt).

The structural formula is:

CLINICAL PHARMACOLOGY

Parlodel^® (bromocriptine mesylate) is a dopamine receptor agonist, which activates post-synaptic dopamine receptors. The dopaminergic neurons in the tuberoinfundibular process modulate the secretion of prolactin from the anterior pituitary by secreting a prolactin inhibitory factor (thought to be dopamine); in the corpus striatum the dopaminergic neurons are involved in the control of motor function. Clinically, Parlodel significantly reduces plasma levels of prolactin in patients with physiologically elevated prolactin as well as in patients with hyperprolactinemia. The inhibition of physiological lactation as well as galactorrhea in pathological hyperprolactinemic states is obtained at dose levels that do not affect secretion of other tropic hormones from the anterior pituitary. Experiments have demonstrated that bromocriptine induces long-lasting stereotyped behavior in rodents and turning behavior in rats having unilateral lesions in the substantia nigra. These actions, characteristic of those produced by dopamine, are inhibited by dopamine antagonists and suggest a direct action of bromocriptine on striatal dopamine receptors.

Bromocriptine mesylate is a nonhormonal, nonestrogenic agent that inhibits the secretion of prolactin in humans, with little or no effect on other pituitary hormones, except in patients with acromegaly, where it lowers elevated blood levels of growth hormone in the majority of patients.

Bromocriptine mesylate produces its therapeutic effect in the treatment of Parkinson's disease, a clinical condition characterized by a progressive deficiency in dopamine synthesis in the substantia nigra, by directly stimulating the dopamine receptors in the corpus striatum. In contrast, levodopa exerts its therapeutic effect only after conversion to dopamine by the neurons of the substantia nigra, which are known to be numerically diminished in this patient population.

Pharmacokinetics

Absorption

Following single dose administration of Parlodel tablets, 2 x 2.5 mg to 5 healthy volunteers under fasted conditions, the mean peak plasma levels of bromocriptine, time to reach peak plasma concentrations and elimination half-life were 465 pg/mL ± 226, 2.5 hrs ± 2 and 4.85 hr, respectively.¹ Linear relationship was found between single doses of Parlodel and C_max and AUC in the dose range of 1 to 7.5 mg.² The pharmacokinetics of bromocriptine metabolites have not been reported.

Food did not significantly affect the systemic exposure of bromocriptine following administration of Parlodel tablets, 2.5 mg.³ It is recommended that Parlodel be taken with food because of the high percentage of subjects who vomit upon receiving bromocriptine under fasting conditions.

Following Parlodel 5 mg administered twice daily for 14 days, the bromocriptine C_max and AUC at steady state were 628 ± 375 pg/mL and 2377 ± 1186 pg*hr/mL, respectively.⁴

Distribution

In vitro experiments showed that bromocriptine was 90%-96% bound to serum albumin.

Metabolism

Bromocriptine undergoes extensive first-pass biotransformation, reflected by complex metabolite profiles and by almost complete absence of parent drug in urine and feces.

In vitro studies using human liver microsomes showed that bromocriptine has a high affinity for CYP3A and hydroxylations at the proline ring of the cyclopeptide moiety constituted a main metabolic pathway.⁵ Inhibitors and/or potent substrates for CYP3A4 might therefore inhibit the clearance of bromocriptine and lead to increased levels. (see PRECAUTIONS, drug interactions section). The participation of other major CYP enzymes such as 2D6, 2C8, and 2C19 on the metabolism of bromocriptine has not been evaluated. Bromocriptine is also an inhibitor of CYP3A4 with a calculated IC50 value of 1.69 μM.⁶ Given the low therapeutic concentrations of bromocriptine in patients (Cmax=0.82 nM), a significant alteration of the metabolism of a second drug whose clearance is mediated by CYP3A4 should not be expected. The potential effect of bromocriptine and its metabolites to act as inducers of CYP enzymes has not been reported.

Excretion

About 82% and 5.6 % of the radioactive dose orally administered was recovered in feces and urine, respectively. Bromolysergic acid and bromoisolysergic acid accounted for half of the radioactivity in urine.⁵

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¹ Nelson, M. et. al. (1990). Pharmacokinetic evaluation of erythromycin and caffeine administered with bromocriptine. Clin Pharmacol Ther; 47(6):694-7.
² Schran, H.F., Bhuta, S.I., Schwartz, et al. (1980). The pharmacokinetics of bromocriptine in man. In: Golstein, M. Calne, D.B.,et. Al (eds). Ergot compound and brain function: Neuroendocrine and neuropsychiatric aspects, pp. 125-139, New York, Rave Press.
³ Kopitar, Z., Vrhovac, B., Povsic, L., Plavsic, F., Francetic, I., Urbancic, J. (1991). The effect of food and metoclopramide on the pharmacokinetics and side effects of bromocriptine. Eur J Drug Metab Pharmacokinet; 16(3):177-81
⁴ Flogstad, A.K., Halse, J., Grass, P., Abisch, E., Djoseland, O., Kutz, K., Bodd, E., and Jervell, J., (1994). A comparison of octreotide, bromocriptine, or a combination of both drugs in acromegaly. Journal of Clinical Endocrinology & Metabolism; Vol 79, 461-465
⁵ Peyronneau MA, Delaforge M, Riviere R et al. 1994. High affinity of ergopeptides for CYP P450 3A. Importance of their peptide moiety for P450 recognition and hydroxylation of bromocriptine. Eur J Biochem 223:947-56.
⁶ Wynalda, M.A., Wienkers, L.C. (1997). Assessment of potential interactions between dopamine receptor agonists and various human cytochrome P450 enzymes using a simple in vitro inhibition screen. Drug Metab Dispos; 25:1211-14.

Specific Populations

Effect of Renal Impairment

The effect of renal function on the pharmacokinetics of bromocriptine has not been evaluated.

Since parent drug and metabolites are almost completely excreted via metabolism, and only 6% eliminated via the kidney, renal impairment may not have a significant impact on the PK of bromocriptine and its metabolites (see PRECAUTIONS, general).

Effect of Hepatic Impairment

The effect of liver impairment on the PK of Parlodel and its metabolites has not been evaluated. Since Parlodel is mainly eliminated by metabolism, liver impairment may increase the plasma levels of bromocriptine, therefore, caution may be necessary (see PRECAUTIONS, general).

The effect of age, race, and gender on the pharmacokinetics of bromocriptine and its metabolites has not been evaluated.

Clinical Studies

In about 75% of cases of amenorrhea and galactorrhea, Parlodel therapy suppresses the galactorrhea completely, or almost completely, and reinitiates normal ovulatory menstrual cycles.

Menses are usually reinitiated prior to complete suppression of galactorrhea; the time for this on average is 6-8 weeks. However, some patients respond within a few days, and others may take up to 8 months.

Galactorrhea may take longer to control depending on the degree of stimulation of the mammary tissue prior to therapy. At least a 75% reduction in secretion is usually observed after 8-12 weeks. Some patients may fail to respond even after 12 months of therapy.

In many acromegalic patients, Parlodel produces a prompt and sustained reduction in circulating levels of serum growth hormone.