Atomoxetine is useful in children with ADHD. The mechanism of action is by:
A. Atomoxetine is the first non-stimulant drug to be approved for ADHD. It has a tricyclic like structure; it is classified as a phenylpropanolamine derivative. It acts through selective inhibition of the presynaptic norepinephrine transporter. It has a half-life of approximately 5 hours and is metabolized through the CYP2D6 pathway. Drugs such as fluoxetine, paroxetine or bupropion are CYP2D6 inhibitors and may raise atomoxetine levels. Atomoxetine is used for patients who fi nd stimulants too activating or who experience other intolerable side-effects. Atomoxetine has been associated with cases of severe liver injury in a few patients. It must be avoided in patients taking MAOI.
Reference:
A 30-year-old known heroin user is brought to A&E after an overdose of heroin, with a GCS of 3, a respiratory rate of four breaths per minute, and pinpoint pupils. On administration of naloxone he develops running nose, diarrhoea and profuse sweating, and multiple joint aches.
The most likely explanation is:
D. Naloxone is an opioid antagonist. It can precipitate acute withdrawal when administered to patients who are actively taking opioid drugs. Symptoms of acute opioid withdrawal include a strong urge to seek the drug, feeling of temperature change, pain, and abdominal distress. Patient may also have confusion, drowsiness, vomiting, and diarrhoea. When opioid antagonists that act for a long duration, such as naltrexone, are prescribed to encourage abstinence and maintain remission in opioid users it is absolutely essential that the use of street drugs has been completely stopped for at least a period of 5 to 7 days. If not, acute withdrawal symptoms will be precipitated. Naloxone produces opioid antagonism that lasts less than 1 hour, whereas naltrexone-induced withdrawal can persist for more than 24 hours.
A 30-year-old known heroin user develops opioid intoxication which reverses on administration of naloxone. He takes a self-discharge against medical advice. He was brought back within a few hours of this self-discharge with signs suggestive of opioid intoxication, but without any history of additional opioid intake.
The most likely explanation is
C. Naloxone produces opioid antagonism that lasts less than 1 hour, as its plasma half-life is between 1 and 2 hours. In opioid overdose, naloxone is administered intravenously and repeated at 2- to 3-minute intervals until the desired response is achieved. In order to maintain recovery in significant overdoses, it is often necessary to continue naloxone by infusion or repeated administration. As this has not happened in the patient described in this question, signs of intoxication have returned.
Naloxone can be life-saving in cases of opioid toxicity. The commonest route of administration of naloxone for this purpose is:
E. Naloxone is commonly administered via intravenous injections in the UK. It can also be administered intramuscularly or via subcutaneous injections.
Lofexidine is useful in managing symptoms of opiate withdrawal. The mechanism of action of lofexidine is by:
A. Lofexidine is an analogue of clonidine, and licensed only in the UK for use in opiate detoxification. It is an α2 adrenoceptor agonist, similar to clonidine but it causes significantly less hypotension. Action of lofexidine peaks at 3 hours and its elimination half-life is 12–15 hours. It is administered in divided doses to achieve the desired peak effect coincidental with the peak of withdrawal effects. It is used for 1 to 3 weeks in opiate detoxification, with or without substituting a tapering dose of prescribed opiates. α2 agonism leads to increased auto-receptor activity and resultant reduction in sympathetic stimulation, which mediates the withdrawal symptoms when administration of opioids is suddenly stopped.
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