CLINICAL PHARMACOLOGY
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.
There are several analytical methods used to estimate
megestrol acetate plasma concentrations, including gas chromatography-mass
fragmentography (GC-MF), high pressure liquid chromatography (HPLC), and
radioimmunoassay (RIA). The GC-MF and HPLC methods are specific for megestrol acetate
and yield equivalent concentrations. The RIA method reacts to megestrol acetate
metabolites and is, therefore, non-specific and indicates higher concentrations
than the GC-MF and HPLC methods. Plasma concentrations are dependent, not only
on the method used, but also on intestinal and hepatic inactivation of the
drug, which may be affected by factors such as intestinal tract motility,
intestinal bacteria, antibiotics administered, body weight, diet, and liver
function.
The major route of drug elimination in humans is urine. When
radiolabeled 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.
Plasma steady-state pharmacokinetics of megestrol acetate
were evaluated in 10 adult, cachectic male patients with acquired
immunodeficiency syndrome (AIDS) and an involuntary weight loss greater than 10%
of baseline. Patients received single oral doses of 800 mg/day of MEGACE Oral
Suspension for 21 days. Plasma concentration data obtained on day 21 were
evaluated for up to 48 hours past the last dose.
Mean (±1SD) peak plasma concentration (Cmax) of megestrol
acetate was 753 (±539) ng/mL. Mean area under the concentration-time-curve
(AUC) was 10476 (±7788) ng × hr/mL. Median Tmax value was five hours. Seven of
10 patients gained weight in three weeks.
Additionally, 24 adult, asymptomatic HIV seropositive male
subjects were dosed once daily with 750 mg of MEGACE Oral Suspension. The
treatment was administered for 14 days. Mean Cmax and AUC values were 490
(±238) ng/mL and 6779 (±3048) ng × hr/mL respectively. The median Tmax value
was three hours. The mean Cmin value was 202 (±101) ng/mL. The mean percent of
fluctuation value was 107 (±40).
The effect of food on the bioavailability of MEGACE Oral
Suspension has not been evaluated.
Description Of Clinical Studies
The clinical efficacy of MEGACE Oral Suspension was assessed
in two clinical trials. One was a multicenter, randomized, double-blind,
placebo-controlled study comparing megestrol acetate (MA) at doses of 100 mg,
400 mg, and 800 mg per day versus placebo in AIDS patients with
anorexia/cachexia and significant weight loss. Of the 270 patients entered on
study, 195 met all inclusion/exclusion criteria, had at least two additional
post baseline weight measurements over a 12-week period, or had one post
baseline weight measurement but dropped out for therapeutic failure. The
percent of patients gaining five or more pounds at maximum weight gain in 12
study weeks was statistically significantly greater for the 800 mg (64%) and
400 mg (57%) MA-treated groups than for the placebo group (24%). Mean weight
increased from baseline to last evaluation in 12 study weeks in the 800 mg
MA-treated group by 7.8 pounds, the 400 mg MA group by 4.2 pounds, the 100 mg
MA group by 1.9 pounds, and decreased in the placebo group by 1.6 pounds. Mean
weight changes at 4, 8, and 12 weeks for patients evaluable for efficacy in the
two clinical trials are shown graphically. Changes in body composition during
the 12 study weeks as measured by bioelectrical impedance analysis showed
increases in nonwater body weight in the MA-treated groups (see Clinical
Studies table). In addition, edema developed or worsened in only 3
patients.
Greater percentages of MA-treated patients in the 800 mg
group (89%), the 400 mg group (68%), and the 100 mg group (72%), than in the
placebo group (50%), showed an improvement in appetite at last evaluation
during the 12 study weeks. A statistically significant difference was observed
between the 800 mg MA-treated group and the placebo group in the change in
caloric intake from baseline to time of maximum weight change. Patients were
asked to assess weight change, appetite, appearance, and overall perception of
well-being in a 9-question survey. At maximum weight change, only the 800 mg
MAtreated group gave responses that were statistically significantly more
favorable to all questions when compared to the placebo-treated group. A dose
response was noted in the survey with positive responses correlating with
higher dose for all questions.
The second trial was a multicenter, randomized,
double-blind, placebo-controlled study comparing megestrol acetate 800 mg/day
versus placebo in AIDS patients with anorexia/cachexia and significant weight
loss. Of the 100 patients entered on study, 65 met all inclusion/exclusion
criteria, had at least two additional post baseline weight measurements over a
12-week period or had one post baseline weight measurement but dropped out for
therapeutic failure. Patients in the 800 mg MA-treated group had a
statistically significantly larger increase in mean maximum weight change than
patients in the placebo group. From baseline to study week 12, mean weight
increased by 11.2 pounds in the MA-treated group and decreased 2.1 pounds in
the placebo group. Changes in body composition as measured by bioelectrical
impedance analysis showed increases in non-water weight in the MA-treated group
(see Clinical Studies table). No edema was reported in the MA-treated
group. A greater percentage of MA-treated patients (67%) than placebo-treated
patients (38%) showed an improvement in appetite at last evaluation during the
12 study weeks; this difference was statistically significant. There were no
statistically significant differences between treatment groups in mean caloric
change or in daily caloric intake at time to maximum weight change. In the same
9-question survey referenced in the first trial, patientsâ⬙ assessments of
weight change, appetite, appearance, and overall perception of well-being showed
increases in mean scores in MA-treated patients as compared to the placebo
group.
In both trials, patients tolerated the drug well and no
statistically significant differences were seen between the treatment groups
with regard to laboratory abnormalities, new opportunistic infections, lymphocyte
counts, T4 counts, T8 counts, or skin reactivity tests (see ADVERSE
REACTIONS).
MEGACE (megestrol acetate, USP) Oral Suspension Clinical
Efficacy Trials
|
Trial 1
Study Accrual Dates
11/88 to 12/90 |
Trial 2
Study Accrual Dates
5/89 to 4/91 |
Megestrol Acetate, mg/day |
0 |
100 |
400 |
800 |
0 |
800 |
Entered Patients |
38 |
82 |
75 |
75 |
48 |
52 |
Evaluable Patients |
28 |
61 |
53 |
53 |
29 |
36 |
Mean Change in Weight (lb.) |
Baseline to 12 Weeks |
0.0 |
2.9 |
9.3 |
10.7 |
-2.1 |
11.2 |
% Patients > 5-Pound Gain at Last Evaluation in 12 Weeks |
21 |
44 |
57 |
64 |
28 |
47 |
Mean Changes in Body Composition* |
Fat Body Mass (lb.) |
0.0 |
2.2 |
2.9 |
5.5 |
1.5 |
5.7 |
Lean Body Mass (lb.) |
-1.7 |
-0.3 |
1.5 |
2.5 |
-1.6 |
-0.6 |
Water (liters) |
-1.3 |
-0.3 |
0.0 |
0.0 |
-0.1 |
-0.1 |
% Patients With Improved Appetite |
At Time of Maximum Wt. Change |
At Last Evaluation in 12 |
50 |
72 |
72 |
93 |
48 |
69 |
Weeks |
50 |
72 |
68 |
89 |
38 |
67 |
Mean Change in Daily Caloric Intake: |
Baseline to Time of Maximum |
Weight Change |
-107 |
326 |
308 |
646 |
30 |
464 |
* Based on bioelectrical impedance analysis determinations
at last evaluation in 12 weeks |
Presented below are the results of mean weight changes for
patients evaluable for efficacy in Trials 1 and 2.
Animal Toxicology
Long-term treatment with MEGACE may increase the risk of
respiratory infections. A trend toward increased frequency of respiratory
infections, decreased lymphocyte counts, and increased neutrophil counts was
observed in a 2-year chronic toxicity/carcinogenicity study of megestrol
acetate conducted in rats.