Methadone-Opiod analgesic

                                                                            METHADONE

Methadone, sold under the brand names Dolophine among others, is an opioid used to treat pain and as maintenance therapy or to help with detoxification in people with opioid dependence.^[3] Detoxification can either occur relatively rapidly in less than a month or gradually over as long as six months

MEDICAL USE

·         Sedation

·         Diarrhea^] or constipation

·         Flushing

·         Perspiration

·         Heat intolerance

·         Dizziness or fainting

·         Weakness

·         Chronic fatigue, sleepiness and exhaustion

·         Sleep problems such as drowsine

OVER DOSE

Most people who have overdosed on methadone may show some of the following symptoms:

·         Miosis (constricted pupils)

·         Hypoventilation (breathing that is too slow/shallow

·         Drowsiness^[] Sleepiness, disorientation, sedation, unresponsiveness

·         Skin that is cool, clammy, and pale

·         Limp muscles,^] trouble staying awake, nausea.

·         Unconsciousness and 

MEACHINSM OF ACTION

Levomethadone is a full µ-opioid agonist Dextromethadone does not affect opioid receptors but binds to the glutamatergic NMDA (N-methyl-D-aspartate) receptor, and thus acts as a receptor antagonist against glutamate. Methadone has been shown to reduce neuropathic pain in rat models, primarily through NMDA antagonism. Glutamate is the primary excitatory neurotransmitter in the CNS. NMDA receptors have a very important role in modulating long term excitation and memory formation. NMDA antagonists such as dextromethorphan (DXM), ketamine (a dissociative anaesthetic, also M.O.A+.), tiletamine (a veterinary anaesthetic) and ibogaine (from the African tree Tabernanthe iboga, also M.O.A+.) are being studied for their role in decreasing the development of tolerance to opioids and as possible for eliminating addiction/tolerance/withdrawal, possibly by disrupting memory circuitry. Acting as an NMDA antagonist may be one mechanism by which methadone decreases craving for opioids and tolerance, and has been proposed as a possible mechanism for its distinguished efficacy regarding the treatment of neuropathic pain. The dextrorotary form (d-methadone) acts as an NMDA antagonist and is devoid of opioid activity:

SIDE EFFECT OF METHADONE

·         Black, tarry stools

·         bleeding gums

·         blood in the urine or stools

·         blurred vision

·         bulging soft spot on the head of an infant

·         change in the ability to see colors, especially blue or yellow

·         changes in skin color

·         chest discomfort or pain

·         confusion

·         convulsions

Reference: Tripathi KD," Essentials of Medical Pharmacology", 7th edition,page no- 474,476.