A1,
A2,
B,
C1,
C2,
D,
E,
F,
G-H,
I-K,
L,
M,
N,
O,
P1,
P2,
Q-R,
S,
T,
U-V,
W-Z
Talacen Pharmacology, Pharmacokinetics, Studies, Metabolism - Pentazocine and Acetaminophen
Talacen Pharmacology, Pharmacokinetics, Studies, Metabolism - Pentazocine and Acetaminophen
CLINICAL PHARMACOLOGY
TALACEN is an analgesic possessing antipyretic actions.
Pentazocine is an analgesic with agonist/antagonist action which when administered
orally is approximately equivalent on a mg for mg basis in analgesic effect
to codeine.
Acetaminophen is an analgesic and antipyretic.
Onset of significant analgesia with pentazocine usually occurs between 15 and
30 minutes after oral administration, and duration of action is usually three
hours or longer. Onset and duration of action and the degree of pain relief
are related both to dose and the severity of pretreatment pain. Pentazocine
weakly antagonizes the analgesic effects of morphine, meperidine, and phenazocine;
in addition, it produces incomplete reversal of cardiovascular, respiratory,
and behavioral depression induced by morphine and meperidine. Pentazocine has
about 1/50 the antagonistic activity of nalorphine. It also has sedative activity.
Pentazocine is well absorbed from the gastrointestinal tract. Plasma levels
closely correspond to the onset, duration, and intensity of analgesia. The time
to mean peak concentration in 24 normal volunteers was 1.7 hours (range 0.5
to 4 hours) after oral administration and the mean plasma elimination half-life
was 3.6 hours (range 1.5 to 10 hours).
The action of pentazocine is terminated for the most part by biotransformation
in the liver with some free pentazocine excreted in the urine. The products
of the oxidation of the terminal methyl groups and glucuronide conjugates are
excreted by the kidney. Elimination of approximately 60% of the total dose occurs
within 24 hours. Pentazocine passes the placental barrier.
Onset of significant analgesic and antipyretic activity of acetaminophen when
administered orally occurs within 30 minutes and is maximal at approximately
2 1 / 2 hours. The pharmacological mode of action of acetaminophen
is unknown at this time.
Acetaminophen is rapidly and almost completely absorbed from the gastrointestinal
tract. In 24 normal volunteers the time to mean peak plasma concentration was
1 hour (range 0.25 to 3 hours) after oral administration and the mean plasma
elimination half-life was 2.8 hours (range 2 to 4 hours).
The effect of pentazocine on acetaminophen plasma protein binding or vice versa
has not been established. For acetaminophen there is little or no plasma protein
binding at normal therapeutic doses. When toxic doses of acetaminophen are ingested
and drug plasma levels exceed 90 mcg/mL, plasma binding may vary from 8% to
43%.
Acetaminophen is conjugated in the liver with glucuronic acid and to a lesser
extent with sulfuric acid. Approximately 80% of acetaminophen is excreted in
the urine after conjugation and about 3% is excreted unchanged. The drug is
also conjugated to a lesser extent with cysteine and additionally metabolized
by hydroxylation.
If TALACEN is taken every 4 hours over an extended period of time, accumulation
of pentazocine and to a lesser extent, acetaminophen, may occur.
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