Many of the advantages of the MAOIs are seen with selective serotonin reuptake inhibitors, which have become the drugs of choice in the treatment of panic disorder.
Even though few large-scale, placebo-controlled studies are available (Oehrberg and coworkers; Den Boer and Westenberg 1988 and 1990; Black and others) SSRIs have essentially become a first-line treatment for panic disorder as reflected in uncontrolled trials (Gorman and others; Schneier and others) and clinical practice.
When compared to TCAs, SSRIs cause fewer anticholinergic effects and fewer cardiac effects, such as orthostatic hypotension, palpitations and dizziness. As mentioned previously, these latter two side effects can mimic a panic attack and frighten the patient. SSRIs cause less sedation and weight gain as compared with TCAs. When compared to MAOIs, SSRIs do not have the dietary constrictions and also cause less orthostatic hypotension. SSRIs do not have the abuse potential of the benzodiazepines.
The initial approach to the treatment of panic with SSRIs is listed in Table 3. As with TCAs and MAOIs, the primary treatment guideline is to start slowly (begin with a low dose such as 5 mg of fluoxetine [Prozac], 25 mg sertraline [Zoloft]) so as to avoid activation, but build up gradually to high doses to achieve a more complete blockade of the panic attacks. With complete blockade of the panic attack, the anticipatory anxiety will reduce and, based on the clinical experience of many including this author, the patient will be less reluctant to enter phobic situations. If the patients panic is blocked in these situations, the phobic avoidance may decrease. As noted above, benzodiazepines are frequently used in conjunction with SSRIs to avoid the activation. Besides activation, SSRI side effects that may be troublesome in the treatment of panic disorder are nausea, heartburn, diarrhea, insomnia, and sexual desire and performance problems.
Though paroxetine (Paxil) has been recently approved by the FDA for treatment of panic disorder, there are no studies to suggest that it has any special efficacy over the other SSRIs for this syndrome.
Although no controlled evidence exists for this approach, in many clinical settings a combination of a low-dose benzodiazepine and antidepressant is frequently given. In general, this combination is safe and beneficial as the drugs tend to complement each other by having differing effects on the aspects of panic disorder. Benzodiazepines block the activation of antidepressants in addition to alleviating anticipatory anxiety while antidepressants (which are slower to act) block the panic attack and also alleviate comorbid depressive symptoms.
The strategy is to hold the individual on low-dose benzodiazepines (e.g., alprazolam 0.25 to 0.5 mg tid or qid plus antidepressant) for four to eight weeks. When the patient's panic has abated and antidepressant levels are adequate, the benzodiazepine can be slowly withdrawn. For some individuals who experience symptom worsening upon withdrawal of the benzodiazepine, it may be necessary to continue the patient on the combination for longer periods of time.
For individuals who fail on monotherapy, a combination of TCA plus SSRI is occasionally used in the treatment of panic disorder (Coplan and colleagues). This requires an extremely cautious approach as SSRIs inhibit the hepatic cytochrome P450 2 D6 (as well as 3A4 and 1A2) system and interfere with the metabolism of TCAs, causing marked increases in TCA levels with the end result being severe cardiac toxicity. Though controversies exist as to the quantitative differences between the three SSRIs in elevating tricyclic levels (Preskorn and colleagues; Harvey and Preskorn; Nemeroff and others), it appears that fluoxetine and paroxetine elevate tricyclic levels more than sertraline does. Sertraline appears to have less inhibition of the hepatic TCA metabolism. For patients who receive a TCA-SSRI combination, TCA blood levels and electrocardiograms should be monitored frequently.
Clonidine (Catapres) at doses of 0.2 to 0.5 mg per day has been found to have some effects in the treatment of panic disorder in one open (Liebowitz and colleagues 1981) and one double-blind crossover study (Hoehn-Saric). (The main effect of clonidine in the Hoehn-Saric study was a decrease of anxiety attacks and "psychic" symptoms. Somatic symptoms were least affected. The conditions of 17 percent of the patients became worse with the medication- Ed.) Its usage, either alone or in combination, however, appeared somewhat limited secondary to such side effects as drowsiness, sedation, fatigue, weakness and dizziness.
Calcium channel blockers have found some success in the treatment of panic disorder. Goldstein noted some success for both diltiazem (Cardizem) (60 mg per day) and verapamil (Calan) (80 mg per day), and in a double-blind crossover study, Klein and Uhde noted some benefit for seven of 11 patients treated with verapamil. Because of the possibility of cardiac side effects, EKG, blood pressure and pulse should be monitored. Similarly, because of these effects, combination treatment with calcium channel blockers should be cautiously undertaken.
Anticonvulsants have recently gained some attention in panic disorder. Though an initial double-blind placebo controlled study found carbamazepine (Tegretol) ineffective for panic disorder, Tondo and colleagues noted improvement in 20 of 34 patients treated with 170 to 500 mg per day of carbamazepine for two to 12 months. Open and double-blind crossover studies with valproate have yielded some success in panic disorder (Lum and colleagues; Woodman and Noyes). Despite the small numbers, doses of valproate in the range of 1,000 to 2,000 mg per day have decreased the length and intensity of panic attacks with minimal side effects.
Length of Treatment
It is pretty clear that panic disorder is a life-long problem as 50 percent of patients suffer continuous symptoms despite adequate treatment (Peselow and colleagues). Though no firm evidence exists, many clinicians feel that patients who respond should be maintained on the treatment for nine months to two years (Coplan and others 1996). After this length of time, discontinuation can be considered.
Fyer and colleagues found high rates of relapse if the drug is withdrawn quickly. Consequently, a slow taper (from three to six months) is often indicated. Chances for a patient to be successfully withdrawn from medication completely are small. It has been often felt that cognitive behavioral therapy (CBT) in conjunction with pharmacotherapy may help with the discontinuation process and decrease the possibility of relapse (Black and others). In the event of relapse upon discontinuation, the medication should be restarted and continued over the same interval.