Cost-effectiveness of oral phenytoin, intravenous phenytoin, and intravenous fosphenytoin in the emergency department  Maria I Rudis, PharmD, Daniel R Touchette, PharmD, Stuart P Swadron, MD, Amy P Chiu, PharmD, Michael Orlinsky, MD  Annals of Emergency Medicine  Volume 43, Issue 3, Pages 386-397 (March 2004) DOI: 10.1016/j.annemergmed.2003.10.011

Figure 1 Tree structure (mathematical model) used in the decision model. The tree structure was too large to demonstrate using a single figure and has been divided up into 4 sections labeled a, b, c, and d. The 3 therapies evaluated are presented after the decision node, indicated by a square, in section a. Each possible adverse event (eg, ataxia, disorientation) is presented on a tree branch after a chance node, shown as a circle on the tree. The probability of the adverse event occurring is indicated by a variable beneath the appropriate decision tree branch (eg, p_disorientation_pop for the probability of experiencing disorientation while on oral phenytoin). The complete tree is symmetrical beginning from the left of section a and moving to the right, through to sections b, c, and eventually d. The costs and outcomes were entered at the payoff node, indicated by a triangle at the end of the model in section d. An individual simulated patient can be followed through the tree by starting with the treatment choice in section a and moving through the tree (to the right). The patient will have the potential to develop adverse events based on the probabilities indicated at each chance node, which were derived from the observed adverse events in the clinical trial. At the end of the tree (in section d), the total cost for that simulated patient is calculated on the basis of the drug therapy received and adverse events experienced. The expected cost of each therapy, a weighted average of all simulated patients, was determined by multiplying through the probability of progressing down a particular branch by the payoff for that branch, to determine the weighted cost for that branch, and then adding all of these weighted branch costs together. PO, Oral; IV, intravenous. Annals of Emergency Medicine 2004 43, 386-397DOI: (10.1016/j.annemergmed.2003.10.011)

Figure 2 Base case and Labor case cost-effectiveness plane. This figure shows the results of the Monte Carlo simulation on a cost-effectiveness plane, giving an estimate of the variability in the model. Each dot represents one of the Monte Carlo runs. There is little or no overlap between the costs of therapy. However, there is considerable overlap between intravenous phenytoin and intravenous fosphenytoin in time to safe ED discharge. Annals of Emergency Medicine 2004 43, 386-397DOI: (10.1016/j.annemergmed.2003.10.011)

Figure 3 Acceptability curve for the Base scenario (cost of labor excluded). The ceiling ratio in this graph refers to the maximum cost that the institution is prepared to pay to invest to discharge a patient one hour earlier from the ED. The proportion of trials from the Monte Carlo simulation in which intravenous phenytoin is the preferred agent over oral phenytoin is plotted against the ceiling ratio. Intravenous phenytoin rapidly becomes the preferred agent as the ceiling ratio changes from $2 (where oral phenytoin is preferred >95% of the time) to $18 (where intravenous phenytoin is preferred >95% of the time). Intravenous fosphenytoin does not become a favorable therapy within this ceiling ratio range. In the Labor scenario (cost of labor included), oral phenytoin is the preferred drug in >95% of the trials to an approximate ceiling ratio of $4 per hour of ED time saved. Intravenous phenytoin is preferred >95% when the willingness to pay is $46 per hour of ED time saved. Intravenous fosphenytoin does not become a favorable therapy within this ceiling ratio. A similar pattern was observed in the Triage scenario (results not shown). For all 3 scenarios (Base, Labor, and Triage), oral phenytoin was the preferred agent if the institution was less interested in investing money to discharge patients quicker from the ED, which may be appropriate for many patients. In certain circumstances or for certain patients, it may be more desirable to pay a greater amount to discharge patients from the ED earlier. In these situations, intravenous phenytoin would likely be the preferable therapy. Annals of Emergency Medicine 2004 43, 386-397DOI: (10.1016/j.annemergmed.2003.10.011)