Snake, crotalidae (all North American rattlers and moccasins) Snake, coral Spider, black widow Crotalidae polyvalent immune Fab (BTG International) Antivenin (Micrurus fulvius ), monovalent (Wyeth) Antivenin Latrodectus mactans (Merck Sharp & Dohme) a Dosing b See for lead poisoning/encephalopathy Chelation regimens vary for other heavy metal poisonings package insert for dosage and administration The mechanism of action of naloxone is by competitive displacement of narcotic analgesics at central opioid receptor sites It can be used as a diagnostic test when faced with a questionable history Current dosage recommendations reflect the proven safety of naloxone in large doses and the necessity of such doses to reverse effects of synthetic opioids such as propoxyphene, pentazocine, oxycodone, and methadone If severe respiratory depression is present and the likelihood of opioid dependence is not known, the initial dose should be 0.4 mg IV Young children in whom long-term opioid exposures are not a concern may be given an initial empiric dose of to mg Repeat doses may be given every minutes until 10 mg has been administered for adolescent patients with suspected opioid overdose who fail to respond to the lower dosages Of course, concomitant airway management is vital In patients without respiratory depression, an initial dose of 0.4 to mg can be used In adolescents suspected of chronic opiate abuse, smaller initial doses (e.g., 0.05 to 0.4 mg) are warranted Again, if there is no response but a strong clinical suspicion, 2-mg doses can be repeated up to a total of 10 mg before concluding that further dosing will be of no benefit Naloxone can also be given intramuscularly (IM), sublingually, intranasally, or by endotracheal tube if no IV access is available If a patient demonstrates a response to naloxone, repeat the effective total dose every 20 to 60 minutes An alternative approach is to provide a continuous IV infusion; generally about two-thirds of the total reversal dose will need to be infused per hour initially, with subsequent adjustments as necessary This is more likely to be needed in long-acting opioid overdoses Nalmefene and naltrexone are longer-acting opioid antagonists that may have use in some clinical situations in which a longer duration of action (4 to hours for nalmefene, 24 hours for naltrexone) is beneficial, such as in reversal of procedural/postoperative opioid depression or as aids in opioid detoxification programs However, as antidotes for acute opioid overdose in the adolescent or