CLINICAL PHARMACOLOGY
Pharmacology
The analgesic ingredient, oxycodone, is a semi-synthetic narcotic with multiple actions qualitatively
similar to those of morphine; the most prominent of these involves the central nervous system and
organs composed of smooth muscle.
Oxycodone, as the hydrochloride salt, is a pure agonist opioid whose principal therapeutic action is
analgesia and has been in clinical use since 1917. Like all pure opioid agonists, there is no ceiling
effect to analgesia, such as is seen with partial agonists or non-opioid analgesics. Based upon a singledose,
relative-potency study conducted in humans with cancer pain, 10 to 15 mg of oxycodone given
intramuscularly produced an analgesic effect similar to 10 mg of morphine given intramuscularly. Both
drugs have a 3 to 4 hour duration of action. Oxycodone retains approximately one half of its analgesic
activity when administered orally.
Effects On Central Nervous System
The precise mechanism of the analgesic action is unknown.
However, specific CNS opioid receptors for endogenous compounds with opioid-like activity have
been identified throughout the brain and spinal cord and play a role in the analgesic effects of this drug.
A significant feature of opioid-induced analgesia is that it occurs without loss of consciousness. The
relief of pain by morphine-like opioids is relatively selective, in that other sensory modalities, (e.g.,
touch, vibrations, vision, hearing, etc.) are not obtunded.
Oxycodone produces respiratory depression by direct action on brain stem respiratory centers. The
respiratory depression involves both a reduction in the responsiveness of the brain stem respiratory
centers to increases in carbon dioxide tension and to electrical stimulation.
Oxycodone depresses the cough reflex by direct effect on the cough center in the medulla. Antitussive
effects may occur with doses lower than those usually required for analgesia. Oxycodone causes
miosis, even in total darkness. Pinpoint pupils are a sign of opioid overdose but are not pathognomonic
(e.g., pontine lesions of hemorrhagic or ischemic origins may produce similar findings). Marked
mydriasis rather than miosis may be seen due to hypoxia in overdose situations.
Effects On Gastrointestinal Tract And Other Smooth Muscle
Oxycodone, like other opioid analgesics,
produces some degree of nausea and vomiting which is caused by direct stimulation of the
chemoreceptor trigger zone (CTZ) located in the medulla. The frequency and severity of emesis
gradually diminishes with time.
Oxycodone may cause a decrease in the secretion of hydrochloric acid in the stomach that reduces
motility while increasing the tone of the antrum, stomach, and duodenum. Digestion of food in the small
intestine is delayed and propulsive contractions are decreased. Propulsive peristaltic waves in the colon
are decreased, while tone may be increased to the point of spasm resulting in constipation. Other
opioid-induced effects may include a reduction in biliary and pancreatic secretions, spasm of sphincter
of Oddi, and transient elevations in serum amylase.
Effects On Cardiovascular System
Oxycodone, in therapeutic doses, produces peripheral vasodilatation
(arteriolar and venous), decreased peripheral resistance, and inhibits baroreceptor reflexes.
Manifestations of histamine release and/or peripheral vasodilatation may include pruritus, flushing, red
eyes, sweating, and/or orthostatic hypotension.
Caution should be used in hypovolemic patients, such as those suffering acute myocardial infarction,
because oxycodone may cause or further aggravate their hypotension. Caution should also be used in
patients with cor pulmonale who received therapeutic doses of opioids.
Pharmacodynamics
The relationship between the plasma level of oxycodone and the analgesic response will depend on the
patient’s age, state of health, medical condition and extent of previous opioid treatment.
The minimum effective plasma concentration of oxycodone to achieve analgesia will vary widely
among patients, especially among patients who have been previously treated with potent agonist opioids.
Thus, patients need to be treated with individualized titration of dosage to the desired effect. The
minimum effective analgesic concentration of oxycodone for any individual patient may increase with
repeated dosing due to an increase in pain and/or development of tolerance.
Pharmacokinetics
The activity of ROXICODONE® (oxycodone hydrochloride) tablets is primarily due to the parent drug
oxycodone. ROXICODONE® tablets are designed to provide immediate release of oxycodone.
Table 1 Pharmacokinetic Parameters (Mean ± SD)
Dose\Parameters |
AUC
(ngxhr/mL) |
Cmax
(ng/mL) |
Tmax
(hr) |
Cmin
(ng/mL) |
Cavg
(ng/mL) |
Half-
Life
(hr) |
Single Dose Pharmacokinetics |
|
|
|
|
|
|
ROXICODONE® 5 mg tabs x 3 |
133.2 ± 33 |
22.3 ± 8.2 |
1.8 ± 1.8 |
n/a |
n/a |
3.73 ± 0.9 |
ROXICODONE® 15 mg tab |
128.2 ± 35.1 |
22.2 ± 7.6 |
1.4 ± 0.7 |
n/a |
n/a |
3.55 ± 1.0 |
ROXICODONE® Liquid Concentrate 15
mg oral solution |
130.6 ± 34.7 |
21.1 ± 6.1 |
1.9 ± 1.5 |
n/a |
n/a |
3.71 ± 0.8 |
ROXICODONE® 30 mg tab |
268.2 ± 60.7 |
39.3 ± 14.0 |
2.6 ± 3.0 |
n/a |
n/a |
3.85 ± 1.3 |
Food-Effect, Single Dose |
|
|
|
|
|
|
ROXICODONE® 10 mg/10 mL oral sol’n
(fasted) |
105 ± 6.2 |
19.0 ± 3.7 |
1.25 ± 0.5 |
n/a |
n/a |
2.9 ± 0.4 |
ROXICODONE® 10 mg/10 mL oral sol’n
(fed) |
133 ± 25.2 |
17.7 ± 3.0 |
2.54 ± 1.2 |
n/a |
n/a |
3.3 ± 0.5 |
Multiple-Dose Studies |
AUC
(72-84) |
|
|
|
|
|
ROXICODONE® 5 mg tabs q6h x 14
doses |
113.3 ± 24.0 |
15.7 ± 3.2 |
1.3 ± 0.3 |
7.4 ± 1.8 |
9.4 ± 2.0 |
n/a |
ROXICODONE® 3.33 mg (3.33 mL) oral
sol’n.
q4h x 21 doses |
99.0 ± 24.8 |
12.9 ± 3.1 |
1.0 ± 0.3 |
7.2 ± 2.3 |
9.7 ± 2.6 |
n/a |
Absorption
About 60% to 87% of an oral dose of oxycodone reaches the systemic circulation in
comparison to a parenteral dose. This high oral bioavailability (compared to other oral opioids) is due
to lower presystemic and/or first-pass metabolism of oxycodone. The relative oral bioavailability of
ROXICODONE® 15 mg and 30 mg tablets, compared to the 5 mg ROXICODONE® tablets, is 96% and
101% respectively. ROXICODONE® 15 mg tablets and 30 mg tablets are bioequivalent to the 5 mg
ROXICODONE® tablet (see Table 1 for pharmacokinetic parameters). Dose proportionality of
oxycodone has been established using the ROXICODONE® 5 mg tablets at doses of 5 mg, 15 mg (three
5 mg tablets) and 30 mg (six 5 mg tablets) based on extent of absorption (AUC) (see Figure 1). It takes
approximately 18 to 24 hours to reach steady-state plasma concentrations of oxycodone with
ROXICODONE® .
Food Effect
A single-dose food effect study was conducted in normal volunteers using the 5 mg/5 mL
solution. The concurrent intake of a high fat meal was shown to enhance the extent (27% increase in
AUC), but not the rate of oxycodone absorption from the oral solution (see Table 1). In addition, food
caused a delay in Tmax (1.25 to 2.54 hour). Similar effects of food are expected with the 15 mg and 30
mg tablets.
Distribution
Following intravenous administration, the volume of distribution (Vss) for oxycodone was
2.6 L/kg. Plasma protein binding of oxycodone at 37°C and a pH of 7.4 was about 45%. Oxycodone has
been found in breast milk (see PRECAUTIONS-Nursing Mothers).
Metabolism
Oxycodone hydrochloride is extensively metabolized to noroxycodone, oxymorphone, and
their glucuronides. The major circulating metabolite is noroxycodone with an AUC ratio of 0.6 relative
to that of oxycodone. Oxymorphone is present in the plasma only in low concentrations. The analgesic
activity profile of other metabolites is not known at present.
The formation of oxymorphone, but not noroxycodone, is mediated by CYP2D6 and as such its
formation can, in theory, be affected by other drugs (see DRUG INTERACTIONS).
Elimination
Oxycodone and its metabolites are excreted primarily via the kidney. The amounts
measured in the urine have been reported as follows: free oxycodone up to 19%; conjugated oxycodone
up to 50%; free oxymorphone 0%; conjugated oxymorphone ≤ 14%; both free and conjugated
noroxycodone have been found in the urine but not quantified. The total plasma clearance was 0.8 L/min
for adults. Apparent elimination half-life of oxycodone following the administration of
ROXICODONE® was 3.5 to 4 hours.
Special Populations
Geriatric
Population pharmacokinetic studies conducted with ROXICODONE® , indicated that the
plasma concentrations of oxycodone did not appear to be increased in patients over the age of 65.
Gender
Population pharmacokinetic analyses performed in the clinical study support the lack of gender
effect on the pharmacokinetics of oxycodone from ROXICODONE® .
Race
Population pharmacokinetic analyses support the lack of race effect on oxycodone
pharmacokinetics after administration of ROXICODONE® , but these data should be interpreted
conservatively, since the majority of patients enrolled into the studies were Caucasians (94%).
Renal Insufficiency
In a clinical trial supporting the development of ROXICODONE® , too few patients
with decreased renal function were evaluated to study these potential differences. In previous studies,
patients with renal impairment (defined as a creatinine clearance < 60 mL/min) had concentrations of
oxycodone in the plasma that were higher than in subjects with normal renal function. Based on
information available on the metabolism and excretion of oxycodone, dose initiation in patients with
renal impairment should follow a conservative approach. Dosages should be adjusted according to the
clinical situation.
Hepatic Failure
In a clinical trial supporting the development of ROXICODONE® , too few patients
with decreased hepatic function were evaluated to study these potential differences. However, since
oxycodone is extensively metabolized, its clearance may decrease in hepatic failure patients. Dose
initiation in patients with hepatic impairment should follow a conservative approach. Dosages should be
adjusted according to the clinical situation.