Prescription Drug Information: Megestrol Acetate (Page 2 of 3)

6.3 Postmarketing Experience

Postmarketing reports associated with megestrol acetate oral suspension include thromboembolic phenomena including thrombophlebitis, deep vein thrombosis, and pulmonary embolism; and glucose intolerance.

7 DRUG INTERACTIONS

7.1 Indinavir

Due to the significant decrease in the exposure of indinavir by megestrol acetate, administration of a higher dose of indinavir should be considered when coadministering with megestrol acetate [See Clinical Pharmacology (12.3)].

7.2 Zidovudine and Rifabutin

No dosage adjustment for zidovudine and rifabutin is needed when megestrol acetate is coadministered with these drugs [See Clinical Pharmacology (12.3)].

8 USE IN SPECIFIC POPULATIONS

8.1 Pregnancy

Risk Summary

Based on animal data, megestrol acetate may cause fetal harm when administered to a pregnant woman and is contraindicated during pregnancy [see Contraindications (4)]. There are no available human data to assess for any drug-associated risks of miscarriage, birth defects, or adverse maternal or fetal outcomes. There are no adequate animal developmental toxicity data at clinically relevant doses. Pregnant rats treated with low doses of megestrol acetate resulted in a reduction in fetal weight and number of live births, and feminization of male fetuses at doses below maximum recommended clinical dosing based on body surface area (see Data). Advise a pregnant women of the potential risk to the fetus.

The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and of miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.

Data

Reproduction studies were performed in pregnant rats at oral doses ranging from 0.05 to 12.5 mg/kg/day, which are below the maximum recommended clinical dose based on body surface area. Reduction in fetal weight and number of live births were observed at 12.5 mg/kg/day (5 times lower than the maximum clinical dose) when dams were dosed on days 12 through 18 of pregnancy. Feminization of male fetuses also occurred when dams were dosed on days 13 through 20 of pregnancy at 3 mg/kg/day, approximately 22 times below the maximum clinical dose.

8.2 Lactation

Risk Summary

The Centers for Disease Control and Prevention recommend that HIV-1 infected mothers not breastfeed their infants to avoid risking postnatal transmission of HIV-1. Megestrol acetate is present in human milk. There are no data on the effects of megesterol acetate on the breastfed infant or the effects on milk production. Because of the potential for HIV transmission and adverse effects on a breastfed infant, instruct mothers not to breastfeed if they are taking megestrol acetate oral suspension.

8.3 Females and Males of Reproductive Potential

Pregnancy testing

Pregnancy testing is recommended prior to treatment with megestrol acetate oral suspension [see Dosage and Administration (2.1), Use in Specific Populations (8.1)].

Contraception

Megestrol acetate oral suspension may cause fetal harm when administered during pregnancy [see Use in Specific Populations (8.1)]. Advise females of reproductive potential to use effective contraception during treatment with megestrol acetate oral suspension.

8.4 Pediatric Use

Safety and effectiveness in pediatric patients have not been established.

8.5 Geriatric Use

Clinical studies of megestrol acetate oral suspension in the treatment of anorexia, cachexia, or an unexplained significant weight loss in patients with AIDS did not include sufficient numbers of patients aged 65 years and older to determine whether they respond differently than younger patients. Other reported clinical experience has not identified differences in responses between elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Megestrol acetate is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function.

8.6 Use in Women

Megestrol acetate has had limited use in HIV infected women.

All 10 women in the clinical trials reported breakthrough bleeding. Megestrol acetate oral suspension is a progesterone derivative, which may induce vaginal bleeding in women.

10 OVERDOSAGE

No serious unexpected side effects have resulted from studies involving megestrol acetate oral suspension administered in dosages as high as 1200 mg/day. In post-marketing experience, limited reports of overdose have been received. Signs and symptoms reported in the context of overdose included diarrhea, nausea, abdominal pain, shortness of breath, cough, unsteady gait, listlessness, and chest pain. There is no specific antidote for overdose with megestrol acetate oral suspension. In case of overdose, appropriate supportive measures should be taken. Megestrol acetate has not been tested for dialyzability; however, due to its low solubility it is postulated that dialysis would not be an effective means of treating overdose.

11 DESCRIPTION

Megestrol acetate oral suspension contains megestrol acetate, a synthetic derivative of the naturally occurring steroid hormone, progesterone. Megestrol acetate is a white, crystalline solid chemically designated as 17-Hydroxy-6-methyl pregna-4,6-diene-3,20-dione acetate. Solubility at 37° C in water is 2 mcg per mL, solubility in plasma is 24 mcg per mL. Its molecular weight is 384.52.

The chemical formula is C24 H32 O4 and the structural formula is represented as follows:

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(click image for full-size original)

Figure 1: Megestrol Acetate Chemical Structure

Megestrol acetate oral suspension is an oral suspension containing 125 mg of megestrol acetate per mL.

Megestrol acetate oral suspension contains the following inactive ingredients: alcohol (max 0.07% v/v from flavor), citric acid monohydrate, hypromellose, lemon flavor, sodium benzoate, sodium citrate dihydrate, sodium lauryl sulfate, and sucrose.

The USP dissolution test is pending.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Several investigators have reported on the appetite enhancing property of megestrol acetate and its possible use in cachexia. The precise mechanism by which megestrol acetate produces effects in anorexia and cachexia is unknown at the present time.

12.3 Pharmacokinetics

Absorption and Distribution

Mean plasma concentrations of megestrol acetate after administration of 625 mg (125 mg/mL) of megestrol acetate oral suspension are equivalent under fed conditions to 800 mg (40 mg/mL) of megestrol acetate oral suspension in healthy volunteers.

In order to characterize the dose proportionality of megestrol acetate oral suspension, pharmacokinetic studies across a range of doses were conducted when administered under fasting and fed conditions. Pharmacokinetics of megestrol acetate was linear in the dosing range between 150 mg and 675 mg after megestrol acetate oral suspension administration regardless of meal condition. The mean peak plasma concentration (Cmax ) and the mean area under the concentration time-curve (AUC) after a high fat meal were increased by 48% and 36%, respectively, compared to those under the fasting condition after 625 mg megestrol acetate oral suspension administration. This food effect is less than that seen for the original formulation, megestrol acetate 800 mg/20 mL, where a high fat meal significantly increased AUC and Cmax of megestrol acetate to 2-fold and 7-fold, respectively, compared to those under the fasting condition. There was no difference in safety following administration in the fed state, therefore megestrol acetate oral suspension could be taken without regard to meals.

Plasma steady state pharmacokinetics of megestrol acetate was evaluated in 10 adult, cachectic male adult patients with acquired immunodeficiency syndrome (AIDS) and an involuntary weight loss greater than 10% of baseline who received single oral doses of 800 mg/day of megestrol acetate oral suspension for 21 days. The Mean (±1SD) Cmax of megestrol acetate was 753 (±539) ng/mL. The mean AUC was 10476 (±7788) ng x hr/mL. Median Tmax value was five hours.

In another study, 24 asymptomatic HIV seropositive male adult subjects were dosed once daily with 750 mg of megestrol acetate oral suspension for 14 days. Mean Cmax and AUC values were 490 (±238) ng/mL and 6779 (±3048) hr x ng/mL, respectively. The median Tmax value was three hours. The mean Cmin value was 202 (±101) ng/mL. The mean % of fluctuation value was 107 (±40).

Metabolism and Excretion

The major route of drug elimination in humans is urine. When radio-labeled megestrol acetate was administered to humans in doses of 4 to 90 mg, the urinary excretion within 10 days ranged from 56.5% to 78.4% (mean 66.4%) and fecal excretion ranged from 7.7% to 30.3% (mean 19.8%). The total recovered radioactivity varied between 83.1% and 94.7% (mean 86.2%).

Megestrol acetate metabolites which were identified in urine constituted 5% to 8% of the dose administered. Respiratory excretion as labeled carbon dioxide and fat storage may have accounted for at least part of the radioactivity not found in urine and feces.

The mean elimination half-life of megestrol ranged from 20 to 50 hours in healthy subjects.

Specific Populations

The pharmacokinetics of megestrol acetate has not been studied in specific population, for example, pediatric, renal impairment, and hepatic impairment.

Drug Interactions

The effects of indinavir, zidovudine or rifabutin on the pharmacokinetics of megestrol acetate were not studied.

Zidovudine

Pharmacokinetic studies show that there are no significant alterations in exposure of zidovudine when megestrol acetate is administered with this drug.

Rifabutin

Pharmacokinetic studies show that there are no significant alterations in exposure of rifabutin when megestrol acetate is administered with this drug.

Indinavir

A pharmacokinetic study in healthy male subjects demonstrated that coadministration of megestrol acetate (675 mg for 14 days) and indinavir (single dose 800 mg) results in a significant decrease in the pharmacokinetic parameters (~32% for Cmax and ~21% for AUC) of indinavir.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Data on carcinogenesis were obtained from studies conducted in dogs, monkeys and rats treated with megestrol acetate at doses below the recommended clinical dose based on body surface area. No males were used in the dog and mon­key studies. In female beagles, megestrol acetate (0.01, 0.1 or 0.25 mg/kg/day) administered for up to 7 years induced both benign and malignant tumors of the breast at doses greater than or equal to 0.01 mg/kg/day, approximately 75 to 187 times below the maximum clinical dose. In female monkeys, no tumors were found following 10 years of treatment with 0.01, 0.1 or 0.5 mg/kg/day megestrol acetate, up to 65 times below the maximum clinical dose. Pituitary tumors were observed in female rats treated for 2 years with 3.9 or 10 mg/kg/day of megestrol acetate, approximately 6 to 17 times below the maximum clinical dose. The relationship of these tumors in rats and dogs to humans is unknown but should be considered in assess­ing the risk-to-benefit ratio when prescribing megestrol acetate oral suspension and in surveillance of patients on therapy.

Megestrol acetate induced unscheduled DNA synthesis in primary cultures of human hepatocytes, but not in rat hepatocytes. Megestrol administered to mice increased the frequency of sister chromatid exchange and chromosomal aberrations in bone marrow cells after single intraperitonial doses of 16.25 and 32.50 mg/kg.

Impaired reproductive capability was observed in male offspring born to female rats treated during gestation days 13 through 20 with oral doses greater than or equal to 3 mg/kg/day megestrol, approximately 22 times below the maximum clinical dose. Female dogs treated daily with megestrol oral capsules for 7 years experienced a complete cessation of estrus activity and ovulation at doses of 0.1, or 0.25 mg/kg/day, approximately 187 and 75 times below the maximum clinical dose, respectively.

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