As previously mentioned, acetaminophen and pentazocine contains two pain-relieving medicines: pentazocine and acetaminophen. Pentazocine works by binding to opioid receptors and mimicking the action of naturally occurring chemicals that block pain. It usually starts to relieve pain 15 to 30 minutes after it is taken, and can continue to control pain for 3 hours or longer.
The main effects of pentazocine occur when it binds to opioid receptors in the central nervous system (the brain and spinal cord). However, the drug can produce effects anywhere opioid receptors are found in the body.
There are several types of opioid receptors located throughout the body. Acetaminophen and pentazocine is classified as an opioid agonist-antagonist, which means it binds to and activates certain opioid receptors (called kappa receptors), but also partially blocks certain other opioid receptors (called mu receptors). Because it can block mu opioid receptors, acetaminophen and pentazocine may block the action of opioid medications that bind to mu receptors, such as morphine, and cause withdrawal symptoms if taken with these other opioids.
Compared to full agonists, such as morphine, partial agonists-antagonists like acetaminophen and pentazocine usually have a limited effective dosing range. This means there is a maximum dose above which the drug will have no further effects. This can help make acetaminophen and pentazocine a less-desirable drug for abuse and can make it less dangerous than full agonist drugs, particularly in the case of an overdose. However, because it contains acetaminophen, acetaminophen and pentazocine can be quite dangerous in the case of an overdose.
It is not entirely understood how acetaminophen works to relieve pain. What is known is that the drug blocks the body's production of prostaglandins (naturally occurring chemicals that cause inflammation and fever). However, it only blocks prostaglandin production in the central nervous system, not throughout the body.
Adding acetaminophen to pentazocine may help improve the pain-relieving effects of both medications. It may also limit the abuse potential of pentazocine, as the maximum dose of acetaminophen and pentazocine is limited by the amount of acetaminophen taken. It is important to carefully monitor your acetaminophen intake, including acetaminophen from other sources, while taking acetaminophen and pentazocine in order to avoid acetaminophen toxicity (see Tylenol Poisoning).
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