MAOIs and transdermal delivery.

Although not currently considered a first-line treatment for depression due to safety and tolerability concerns, MAOIs are effective antidepressants, particularly for atypical or treatment-resistant depression. FDA-approved oral MAOIs inhibit both MAO-A and MAO-B; inhibition of MAO-A in the brain is required for an antidepressant effect, but inhibition in the intestinal tract can allow excessive absorption of tyramine, which can lead to hypertensive crisis. A transdermal formulation of selegiline delivers the medication directly into the circulatory system, bypassing the first-pass metabolism of the GI system and substantially reducing the risk for tyramine-related adverse events. The skin patch allows for a lower dose of the drug to achieve an antidepressant effect, maintains a steady dose of the medication over 24 hours, and avoids the need for dietary restrictions at the minimum effective dose of 6 mg/24 hours. MAOIs are useful treatment options for patients who have not responded to first-line treatments, and understanding their mechanism of action can help clinicians to accurately and safely prescribe these medications.

The transdermal delivery system of monoamine oxidase inhibitors.

Monoamine oxidase inhibitors (MAOIs) were once widely used as effective treatments for major depressive disorder, particularly for patients with atypical or treatment-resistant depression. Today, MAOIs have largely been replaced by newer antidepressants because of concerns over potential serious side effects due to their mechanism of action. Monoamine oxidase (MAO) is an enzyme that metabolizes serotonin, norepinephrine, and dopamine, the neurotransmitters that are most associated with depression; inhibiting MAO, therefore, makes more of these neurotransmitters available for synaptic action. However, MAO also metabolizes tyramine, a trace amine found in some foods that acts as a sympathomimetic. Allowing excess tyramine to accumulate via MAO inhibition can result in hypertensive crisis due to the release of norepinephrine; therefore, patients taking an MAOI have had to follow dietary restrictions to avoid tyramine-rich foods. Hypertensive crisis may also be precipitated by using MAOIs in conjunction with other drugs that have vasoconstrictive properties, that act as sympathomimetics, or that inhibit the reuptake of norepinephrine. Serotonin syndrome is another serious adverse effect that can potentially occur when using an MAOI with another drug that inhibits the reuptake of serotonin. In this article, the mechanism of action of MAOIs is reviewed, along with that of a newer MAOI formulation that lessens the need for dietary restrictions and has a greater safety and tolerability profile than the older oral formulations.

Evaluation of the potential for pharmacodynamic and pharmacokinetic drug interactions between selegiline transdermal system and two sympathomimetic agents (pseudoephedrine and phenylpropanolamine) in healthy volunteers.

Selegiline transdermal system is a recently approved monoamine oxidase inhibitor antidepressant. Medications that inhibit monoamine oxidase type A can augment the pressor effects of sympathomimetic amines, increasing the potential for hypertensive crisis. This study examined the potential for drug-drug interactions during treatment with selegiline transdermal system and pseudoephedrine or phenylpropanolamine. Two studies were conducted with 25 healthy volunteers to assess changes in blood pressure and heart rate during administration of pseudoephedrine or phenylpropanolamine alone or together with selegiline transdermal system. No significant differences in mean maximum changes in vital signs occurred with pseudoephedrine. No significant differences were found in mean maximum changes in systolic heart rate with phenylpropanolamine; however, 4 of 12 subjects each experienced 1 isolated protocol-defined minimal pressor response without concurrent adverse effects (1 with phenylpropanolamine alone; 3 with phenylpropanolamine + selegiline transdermal system). Pharmacokinetic parameters obtained following selegiline transdermal system and pseudoephedrine or phenylpropanolamine were unremarkable. The results suggest that selegiline transdermal system 6 mg/24 h does not significantly alter the pharmacodynamics or pharmacokinetics of either pseudoephedrine or phenylpropanolamine when administered to healthy volunteers; however, it is prudent to avoid coadministration of selegiline transdermal system and sympathomimetics.

Effects of a tyramine-enriched meal on blood pressure response in healthy male volunteers treated with selegiline transdermal system 6 mg/24 hour.

BACKGROUND: Monoamine oxidase inhibitors are well recognized as effective antidepressant agents but are rarely used due, in part, to the risk of hypertensive crisis following the ingestion of foods high in tyramine ("cheese reaction"). A selegiline transdermal system (STS) was developed to provide antidepressant concentrations of selegiline in the brain, while preserving the gastrointestinal monoamine oxidase A (MAO-A) barrier. The present study was conducted to determine the effect of the STS 6 mg/24 hour on cardiovascular safety following the ingestion of approximately 400 mg of tyramine consumed as a component of aged cheeses. METHODS: In this open-label, single-center phase I study, cardiovascular vital signs were recorded following tyramine challenges during placebo and STS 6 mg/24 hr treatment. Subjects were observed for clinical signs and symptoms of a pressor response and/or potential hypertensive crisis during and following the challenges. RESULTS: Ingestion of tyramine-enriched meals following 13 consecutive days of treatment with the STS 6 mg/24 hr (pharmacokinetic steady-state) produced no clinically significant changes in cardiovascular vital signs in 12 healthy adult male subjects. No evidence of a tyramine pressor effect on systolic blood pressure or evidence of hypertensive crisis occurred during the STS treatment. CONCLUSION: These results suggest that STS 6 mg/24 hr may be administered without concern for dietary tyramine consumption.

Tyramine pressor sensitivity during treatment with the selegiline transdermal system 6 mg/24 h in healthy subjects.

The oral tyramine pressor test was administered to healthy males during treatment with a selegiline transdermal system (STS; 6 mg/24 h). The tyramine sensitivity factor (TSF) was calculated from the ratio of baseline and on-treatment tyramine pressor doses. The tyramine sensitivity factor value following 9 days of treatment with the selegiline transdermal system was 1.85 +/- 0.10. Extended treatment, 33 days, produced a small, clinically non-meaningful increase in this value. The tyramine sensitivity factor for the selegiline transdermal system was similar to that following treatment with 10 mg/d of oral selegiline capsules but more than 20 times less than observed during tranylcypromine treatment. A larger increase in the tyramine sensitivity factor was observed following extended selegiline transdermal system treatment at a higher dose (12 mg/24 h), which was significantly decreased following coadministration of tyramine capsules with a meal. These results suggest a wide tyramine safety margin for the selegiline transdermal system and provide evidence that the 6-mg/24-h selegiline transdermal system can be administered safely without dietary tyramine restrictions.

Tyramine pharmacokinetics and reduced bioavailability with food.

Tyramine challenge studies have demonstrated that it requires approximately twice the amount of tyramine administered with a meal compared to administration after a fast to elicit the same effect, suggesting a reduction in bioavailability of tyramine when administered with food. The pharmacokinetics of tyramine when administered in a fasted versus a fed state were studied. A single 200-mg dose of tyramine was administered orally to healthy subjects both after an overnight fast and during a meal. Systemic exposure to tyramine was reduced by 53% (p < 0.05), and the maximum concentration of tyramine was reduced by 72% (p < 0.05) when the dose was administered during a meal. Tyramine maximum serum concentration was observed between 20 minutes and 1 hour when the dose was administered after an overnight fast and appeared to be delayed and/or prolonged by administration during a meal. Tyramine oral clearance was 135 +/- 55.4 L/min, maximum observed serum concentration was 37.7 +/- 26.01 ng/mL, and tyramine elimination half-life was 0.533 (range: 0.330-0.668) hours after administration to fasted subjects. Tyramine bioavailability was significantly reduced when administered with a meal compared to after a fast. The results suggest that larger amounts of dietary tyramine will be required to induce a pressor response equivalent to that following encapsulated tyramine administered in the fasted state.

Pharmacokinetics of fluvoxamine in relation to CYP2C19 phenotype and genotype.

OBJECTIVE: To evaluate the pharmacokinetics of fluvoxamine (FLV) in poor metabolizers (PMs) versus extensive metabolizers (EMs) of cytochrome P450 (CYP)2C19. METHODS: This was a prospective, open-label study conducted at the Clinical Research Unit School of Pharmacy. Fifty-seven healthy, nonsmoking volunteers aged 21-40 years participated. Subjects abstained from caffeinated products 12 hours prior to and during each testing period. To assess CYP2C19 activity, blood samples were collected from each subject prior to and two hours after a single dose of omeprazole 20 mg. Once PMs were identified, a sample population of EMs were selected for comparison between the two groups regarding FLV disposition. A single 100 mg FLV dose was given to EMs and PMs; blood samples for FLV analysis were obtained prior to drug administration and 0.5, 1, 2, 3, 4 6, 8, 12 and 24 hours later. A blood sample one day prior to FLV administration was also obtained for CYP2C 19 and CYP2D6. RESULTS: Four PMs were identified with the omeprazole phenotype probe and had a mean +/- SD hydroxylation index of 1.335 +/- 0.271. Nine EMs were selected based upon a hydroxylation index between 0.100 and 0.400 (mean 0.193 +/- 0.079). FLV pharmacokinetic parameters (AUC, elimination half-life, Cmax and Tmax) did not significantly differ between the two groups. Genotype analysis for CYP2C19 revealed a mutant allele for the *2 which confirmed phenotype detection of PM status. Genotype analysis for CYP2D6*3 and *4 alleles showed that all PMs of CYP2C19 were EMs of CONCLUSIONS: FLV disposition and dosing is unlikely to be affected by CYP2C19 polymorphism.