Moclobemide excretion in human breast milk

Assessment of Infant Exposure to Antidepressants through Breastfeeding: A Literature Review of Currently Available Approaches

Despite the prevalence of depression in lactating mothers, there is a lack of knowledge about the excretion of antidepressants into breast milk and its potential adverse effects on infants. This creates concern, making depressed lactating mothers more likely to avoid pharmacological treatment. Clinical lactation studies are the most accurate and direct method to predict and demonstrate the excretion of antidepressants into human breast milk, and results from clinical studies can be included in drug labels to help physicians and patients make decisions on antidepressant use during lactation. However, there are limited clinical trials and studies on the pharmacokinetics of antidepressants in lactating women because of a lack of enrollment and ethical and confounding factors, creating a lack of knowledge in this area. To bridge this gap in knowledge, alternative methods should be sought to help estimate the antidepressant concentration in breast milk, which is used to assess the safety and transfer of antidepressants into breast milk. We provide a comprehensive review of the usage of these cost-effective, time-efficient, and ethically feasible methods that serve to provide a valuable estimation of the safety and transfer of antidepressants into breast milk before conducting clinical studies.

Antidepressant transfer into amniotic fluid, umbilical cord blood & breast milk: A systematic review & combined analysis

OBJECTIVE

Data regarding the ability of antidepressants to enter fetal, newborn and infant fluids have become gradually available, but mechanisms of antidepressant transfer remain poorly understood. Here we calculated penetration ratios in an array of matrices from combined samples of pregnant/breastfeeding women taking antidepressants.

METHOD

We performed a systematic literature search of PubMed and EMBASE to identify studies with concentrations of antidepressants from maternal blood, amniotic fluid, umbilical cord blood and/or breast milk. Penetration ratios were calculated by dividing the concentrations in amniotic fluid, umbilical cord plasma or breast milk by the maternal plasma concentration. When data from multiple studies were available, we calculated combined penetration ratios, weighting the study mean by study size.

RESULTS

Eighty-five eligible studies were identified. For amniotic fluid, the highest penetration ratios were estimated for venlafaxine (mean 2.77, range 0.43-4.70 for the active moiety) and citalopram (mean 2.03, range 0.35-6.97), while the lowest ratios were for fluvoxamine (mean 0.10) and fluoxetine (mean 0.11, range 0.02-0.20 for the active moiety). For umbilical cord plasma, nortriptyline had the highest ratio (mean 2.97, range 0.25-26.43) followed by bupropion (mean 1.14, range 0.3-5.08). For breast milk, the highest ratios were observed for venlafaxine (mean 2.59, range 0.85-4.85), mianserin (mean 2.22, range 0.80-3.64) and escitalopram (mean 2.19, range 1.68-3.00).

CONCLUSION

We observed considerable variability across antidepressants regarding their ability to enter fetal, newborn and infant fluids. Measuring antidepressant concentrations in a maternal blood sample can provide a reliable estimate of fetal/infant exposure, although further evidence for concentration-dependent effects is required.

Which antidepressants are safe to use in breast-feeding mothers?

As postpartum depression can occur in up to 10% of mothers, antidepressants will often be required in mothers who are breast-feeding. The judicious use of antidepressants is important since all psychotropic drugs cross into the breast milk. Drug excretion into breast milk occurs primarily by passive diffusion. Small, highly lipid soluble, unionised drugs diffuse more rapidly than other drugs. It must be remembered, however, that for those drugs with a high volume of distribution, such as the highly lipid soluble drugs, most of the drug is outside the plasma compartment, leaving only a small proportion free to transport from plasma to milk. Also, most lipophilic drugs are concentrated in hind milk which is richer in fat than fore milk. All of the antidepressants are highly lipid soluble with large volumes of distribution.

Pharmacokinetics of Moclobemide in Male, Virgin Female, Pregnant and Nursing Rats

The disposition of moclobemide, a reversible inhibitor of monoamine oxidase isoenzyme A was studied in male, virgin female, pregnant and nursing rats. The average clearance in control rats (male and female) was 36 mL min−1 kg−1, the initial volume of distribution 1·4 L kg−1, the volume of distribution at steady state 2·3 L kg−1 and the terminal half-life 59 min. The blood-to-plasma concentration ratio of moclobemide was 0·84 giving rise to an average blood clearance of 30 mL min−1 kg−1. The clearance values in rats were higher than in man but as a fraction of hepatic blood flow were similar (36 vs 45%). The volume of distribution at steady state was approximately twice as high as in man while the half-life was similar. Pregnant and nursing rats showed no statistically significant differences in their disposition parameters for moclobemide compared with virgin female rats. Nursing rats had statistically significantly lower concentrations of the moclobemide N-oxide metabolite than did pregnant and control rats. Generally lower concentrations of the lactam metabolite were also found in this group although the differences did not reach statistical significance. Moclobemide as well as the N-oxide and lactam metabolites were found in the amniotic fluid suggesting that moclobemide is capable of crossing the placental barrier.

A validated high-performance liquid chromatographic method for the determination of moclobemide and its two metabolites in human plasma and application to pharmacokinetic studies

A rapid and sensitive reversed-phase high-performance liquid chromatographic method (RP-HPLC) with ultraviolet detection has been developed for the determination of moclobemide and its metabolites, p-chloro-N-(-2-morpholinoethyl)benzamide N'-oxide (Ro 12-5637) and p-chloro-N-[2-(3-oxomorpholino)ethyl]-benzamide (Ro 12-8095), in human plasma. The assay was performed after single liquid-liquid extraction with dichloromethane at alkaline pH using phenacetin as the internal standard. Chromatographic separation was performed on a C(18) column using a mixture of acetonitrile and water (25:75, v/v), adjusted to pH 2.7 with ortho-phosphoric acid, as mobile phase. Spectrophotometric detection was performed at 239 nm. The method has been validated for accuracy, precision, selectivity, linearity, recovery and stability. The quantification limit for moclobemide and Ro 12-8095 was 10 ng/mL, and for Ro 12-5637 was 30 ng/mL. Linearity of the method was confirmed for the range 20-2500 ng/mL for moclobemide (r = 0.9998), 20-1750 ng/mL for Ro 12-8095 (r = 0.9996) and 30-350 ng/mL for Ro 12-5637 (r = 0.9991). Moreover, within-day and between-day precisions and accuracies of the method were established. The described method was successfully applied in pharmacokinetic studies of parent drug and its two metabolites after a single oral administration of 150 mg of moclobemide to 20 healthy volunteers.

Use of psychotropic medications in treating mood disorders during lactation : practical recommendations

Many new mothers who need antidepressant or mood-stabilising drug treatment may wish to breastfeed their infants, but are hesitant to do so because of possible harmful effects of the medication on the infant. This article reviews current data on drug excretion into breast milk and the effects on the breast-fed child, and provides recommendations for the use of the different psychotropic drugs in lactating women. Relevant literature was identified through systematic searches of MEDLINE, EMBASE and the Science Citation Index Expanded (ISI) from 1966 to February 2005. The present knowledge is based on the accumulation of case studies. No randomised controlled trials in breast-fed infants have been performed and there is a lack of long-term follow-up studies. Use of SSRIs and TCAs (except doxepin) is compatible with breastfeeding. However, if treatment with an SSRI is started in the postpartum period, fluoxetine and citalopram may not be drugs of first choice. With regard to other antidepressants, such as venlafaxine, trazodone, mirtazapine, reboxetine, moclobemide and other MAOIs, very little knowledge exists. Breastfeeding should be avoided while using lithium. Carbamazepine and sodium valproate (valproic acid) are generally better tolerated by the breast-fed infant than lithium. Data on lamotrigine are still sparse. Knowledge is also scarce on the novel antipsychotics and thus recommendations in lactating women cannot be made for these agents. It is unwise to expose infants unnecessarily to drugs that may have severe adverse effects. As such, clozapine should probably be avoided because of the risk of agranulocytosis. Our knowledge of the impact of drug exposure through breast milk is still limited. Infant drug exposure is, however, generally higher during pregnancy through placental passage than through breast milk. Despite the low dosage transferred to the infant through breast milk, premature infants and infants with neonatal diseases or inherited disturbances in metabolism may be vulnerable to such exposure.

Drugs that affect the fetus and newborn infant via the placenta or breast milk

In general, drugs that are taken by a mother during pregnancy or after birth may be transferred to the fetus or the infant (through breast milk). Many factors are involved that determine the amount of drugs that are transferred and their potential effects on the fetus or infant. A careful assessment of the risk versus benefit is necessary and should be individualized. In the breastfed infant, many measures can be undertaken further so that the amount of drug transferred to the infant is minimized.

Moclobemide: evolution, pharmacodynamic, and pharmacokinetic properties

The benzamide moclobemide is a reversible inhibitor of monoamine-oxidase-A (RIMA). It has been extensively evaluated in the treatment of a wide spectrum of depressive disorders and less extensively in anxiety disorders. While clinical aspects will be presented in a subsequent review, this article focuses primarily on moclobemide's evolution, pharmacodynamic and pharmacokinetic properties. In particular, the effects on neurotransmission and intracellular signal transduction, the neuroendocrine system, the tyramine pressure response and animal models of depression are surveyed. In addition, other CNS effects are reviewed with special respect to experimental serotonergic syndrome, anxiolytic and antinociceptive activity, sleep, cognition and driving performance, neuroprotection and seizures.

Antidepressants and breast-feeding: a review of the literature

For every antidepressant so far investigated in the breast milk of mothers prescribed these medications, findings indicate that some amount of drug will be excreted into the breast milk. Nursing infants will be exposed to some, usually a very low, amount of drug and drug metabolites. Levels of drug exposure to infants for the many antidepressants available are examined, discussing milk to plasma drug concentration ratios and the infant dose as a percentage of the maternal dose. Drug concentrations in infant plasma and adverse effects of drug exposures to infants are reviewed. Factors influencing the decision on whether to breast or bottle feed an infant nursed by a mother taking antidepressants are discussed, concluding that the decision needs to be made on an individual basis. The lactating mother, in consultation with her doctor, should be in a position to make an informed decision on whether or not to breast feed. Under certain circumstances the decision to bottle feed may be wise, but more commonly the advantages of breast-feeding will outweigh the very low risk of an adverse event from drug exposure to the infant.

Use of psychotropic medications in breast-feeding women: acute and prophylactic treatment

OBJECTIVES

The postnatal period is a time of increased onset and relapse of mental illness. It poses a clinical dilemma, as many mothers requiring medication acutely or prophylactically will also choose to breast feed. The present paper first reviews the safety of psychotropes in breast-fed infants and the usefulness of prophylaxis for women at risk of postpartum affective relapse and, second, provides guidelines in the use of psychotropic drugs in breast-feeding women.

METHODS

A Medline review was conducted reviewing all papers published during the period 1993-1998 (and their associated bibliographies) on the use of psychotropes in breast-feeding women and the prophylactic usefulness of medications in women at risk of affective postpartum relapse.

RESULTS

Findings are based on case reports and small, mostly uncontrolled studies. Both tricyclic antidepressants (TCA) and specific serotonin re-uptake inhibitors (SSRIs) appear to be relatively safe in breast feeding. Antidepressants commenced in the early postpartum period may reduce depressive relapse. While prophylactic lithium appears to significantly reduce relapse of affective psychosis in the puerperium, there have been no studies of the anticonvulsants in the puerperium. Finally, high dose antipsychotics should be avoided, as they may be associated with long-term adverse sequelae in the infant.

CONCLUSIONS

On the basis of current knowledge, the use of SSRIs, TCA, carbamazepine, sodium valproate and short-acting benzodiazepines in breast feeding is relatively safe. If lithium is to be used, close collaboration with a paediatrician is essential. The long-term risks of antipsychotics, especially at high doses, remain to be clarified. Before a decision can be made, the risk-benefit ratio must be clearly outlined and discussed with the mother and her partner.

A guide to the safety of CNS-active agents during breastfeeding

For most agents with CNS activity, there are limited data regarding their safety in breastfeeding. Any decision to institute treatment for a neurological or psychiatric disorder must weigh the benefits of maternal treatment against the potential harm to the breastfeeding mother of withholding medication which may improve her illness. For the neonate, one must balance the risk of medication exposure against the benefit of receiving breast milk. Most tricyclic antidepressants can be used in lactating women. Because of the limited data, selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors should only be used with due consideration of the potential adverse effects. Breastfeeding is best avoided by women who require lithium therapy, because of both the immature excretory systems in the infant and relatively high doses received by the infant. There is little information about the safety of antipsychotic medications in breastfeeding. Concerns include toxicity and abnormal neurological development in the infant. These agents may be used with caution. Most agents which cause depression of the CNS, including opiates and sedatives, can be used in small doses and for short courses in breastfeeding mothers. Most anticonvulsants can be used in lactating women. Reference texts and consultation with experts are useful adjuncts to discussion of the risks and benefits of therapy with the patient. The scope of this review is limited to drugs with therapeutic uses, thus drugs of abuse are not discussed, nor are caffeine and alcohol (ethanol).

Postpartum psychiatric disorders : guidelines for management

Psychiatric disorders, in particular depression, are common Postpartum and have potential long term implications for the woman and her family. Critical to management is identification and early intervention. Management needs to be multifaceted, including hospitalisation in severe cases, psychotherapy (supportive at least) and organisation of community support. A number of factors need to be considered with respect to medication, in particular if the woman is breastfeeding. Women with puerperal psychosis may require antipsychotics, antidepressants and mood stabilisers; ECT achieves good results when available and acceptable. Women with postpartum depression can generally be managed with antidepressants alone. Management needs to take into account that these disorders may be long lasting, with risk of recurrence after subsequent childbirth, and may have significant effects on child development.

The Role of Metabolites of Antidepressants in the Treatment of Depression

Recognition of the role of active metabolites in mediating therapeutic and/or adverse effects of many antidepressants is an important part of understanding the mechanisms of action of these medications. While virtually all antidepressants except lithium undergo extensive hepatic metabolism, the profile of activity of the resulting breakdown products varies considerably.The metabolites of some antidepressants share the primary biochemical actions of their parent compounds and appear to contribute to the therapeutic efficacy of those medications. Examples of this are the tricyclic antidepressant (TCA) nor-triptyline, the selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor (SSRI) fluoxetine and the serotonin-noradrenaline (norepinephrine) reuptake inhibitor venlafaxine. Less commonly, the activity of the primary metabolite may differ from that of the parent drug. An example is clomipramine. This drug is a potent serotonin reuptake blocking TCA, but its demethyl-metabolites are noradrenaline reuptake inhibitors. On the other hand, a number of effective anti-depressants, including most of the SSRIs other than fluoxetine, lack active metabolites.On the negative side, antidepressant metabolites may add to the adverse effect burden presented by their drugs of origin. At sufficiently high doses, the amphetamines resulting from the metabolism of some monoamine oxidase inhibitors, e.g. selegiline (deprenyl), may directly produce toxicity from the pharmacodynamic interaction with the parent antidepressant. While hydroxy-nortriptyline produces lesser anticholinergic effects than its parent compound, this metabolite may block the therapeutic action of nortriptyline when present in high concentrations. Excessive plasma concentrations of the major metabolite of amfebutamone (bupropion) have been associated with nonresponse and clinical worsening in some patients.Amfebutamone also illustrates the importance of pharmacokinetic factors in determining the magnitude of the influence of metabolites on antidepressant action. Active metabolites that have long elimination half-lives may predominate over the parent compound in plasma and CSF, exerting considerable clinical impact. With several of the newer drugs, notably amfebutamone, venlafaxine and nefazodone, the presence of active metabolites with half-lives approaching 1 day suggests that once-daily administration may be sufficient.The formation of most antidepressant metabolites is under strong genetic control and the metabolites themselves often exert effects on hepatic enzyme systems. This can lead to the possibility of drug-drug interactions. A key example is norfluoxetine, which is associated with potent inhibition of the cytochrome P450 isozyme 2D6 (and, consequently, reduced metabolism of drugs such as TCAs). This effect lasts for weeks even after fluoxetine discontinuation, due to the fact that norfluoxetine has a half-life of up to 2 weeks.The clearance of most antidepressant metabolites is ultimately dependent on elimination by the kidneys. Therefore, these substances tend to accumulate in states of reduced renal function, including normal aging. The relative increase in TCA hydroxy-metabolite concentrations in the elderly may contribute to the cardiovascular and other toxicities of these antidepressants in this vulnerable patient population.Attention to the existence and implications of active metabolites from the earliest stages of antidepressant drug development may help optimise the benefit: risk ratio of this valuable class of psychotropic medications.

Antidepressant use during breastfeeding

Women who suffer from postpartum depression require treatment. Caution must be exercised if any antidepressant is used. These agents concentrate in the central nervous system; therefore, serum concentrations and breastmilk: plasma ratios may not accurately predict infant drug exposure. Since there is no absolute contraindication to breastfeeding during antidepressant use, recommendations should be made on a case-by-case basis limited to healthy term infants. When possible plasma antidepressant concentrations, including metabolites, should be measured in the infant. Frequent developmental follow-up, not only during the treatment period but throughout childhood, should be performed on these infants.

Clinical pharmacokinetics of the monoamine oxidase-A inhibitor moclobemide

There has been a resurgence of interest in the use of monoamine oxidase (MAO) enzyme inhibitors for the treatment of depression. Unlike the first-generation MAO inhibitors, the current drugs are readily reversible in their action, resulting in far less concern about interactions with certain foods and drugs which could lead to serious pressor effects. Furthermore, the current drugs are far more selective in their actions as a result of the ability to affect either the MAO-A or the MAO-B isoenzyme. Moclobemide is an example of a reversible MAO-A inhibitor which has been extensively studied and whose pharmacokinetic, clinical pharmacological and toxicological profiles have been thoroughly defined. Moclobemide has a short disposition half-life and intermediate values for systemic clearance and volume of distribution; half-life increases somewhat with dose. The drug is completely metabolised by the liver. Moclobemide is rapidly and completely absorbed following oral administration in a variety of dosages and forms. The drug has a high intrinsic (apparent oral) clearance which results in a substantial hepatic first-pass effect and, while there is marked interindividual variation, differences within an individual are small. A time- and dose-dependence is observed with multiple oral administration: clearance decreases with administration during the first week and thereafter remains constant. The exact mechanism of this effect is not known, but it may reflect inhibition of elimination by metabolites (the kinetics may always be described as being first-order). Moclobemide disposition is not affected by renal disease, nor is there substantial alteration with advanced age. Liver disease causes a dramatic reduction in clearance; dosage must be adjusted for patients with liver disease. There is minimal transfer of the drug into breast milk, such that breast-feeding neonates are exposed to only a very small dose of the drug. Moclobemide administration results in a minimal interaction with exogenous amines (e.g. tyramine and pressor amine drugs); the so-called 'cheese effect' is therefore of little concern. As a result, the drug has an excellent tolerability profile both within the therapeutic dose range and in overdose (no deaths have been attributed to moclobemide intoxication per se). Cimetidine inhibits the elimination of moclobemide. Moclobemide appears to affect several isoenzymes of the cytochrome P450 (CYP) system (CYP2C19, CYP2D6 and CYP1A2). The adverse events profile of moclobemide indicates only mild and transient effects at a relatively low rate of occurrence.

Pharmacokinetic optimisation of therapy with newer antidepressants

Since the early 1950s, when imipramine was first introduced, a whole series of antidepressants with differences in structures, neurochemical effects and pharmacokinetics have been developed. Structurally or functionally, they have been classified as tricyclic antidepressants (TCAs), tetracyclic antidepressants, monoamine oxidase inhibitors (MAOIs), or selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors (SSRIs). In addition, there is a series of antidepressants with unique structures. Many of the newer TCAs appear to have shorter half-lives than the standard TCAs (e.g. imipramine), allowing for the possibility of a more rapid response, but requiring the drugs to be given in multiple daily doses, which may reduce patient compliance. The short time to peak plasma concentration (tmax) can also lead to rapid onset of adverse effects. The tetracyclic antidepressants have longer elimination half-lives (t1/2) than the TCAs, but there is only very minimal evidence for a relationship between drug concentrations in the blood and clinical response. The triazolopyridines, like the newer TCAs, show pharmacokinetic evidence for rapid onset of adverse effects and the need for multiple daily doses due to short tmax and t1/2. The newer MAOIs are a significant addition to therapy, as the rapid binding action of these medications increases their safety margin with regard to tyramine interactions. Further information in this area is required. In addition, moclobemide has pharmacokinetic features that are clinically beneficial (e.g. aging and renal dysfunction have little effect on the elimination of the drug), but also features that are not beneficial (e.g. nonlinear pharmacokinetics). Among the SSRIs, there are a range of t1/2 values for the parent drugs, from relatively short t1/2 values of less than 24 hours (paroxetine, fluvoxamine) to among the longest found (e.g. 2 days for fluoxetine). Only 2 of the agents (sertraline and citalopram) have linear pharmacokinetics, and 1 drug has nonlinear pharmacokinetics within the usual therapeutic range (fluvoxamine). Once a therapeutic blood concentration is established, linearity is helpful in avoiding the small dose changes and repeated rechecking of concentrations of medications that would be required for those agents with nonlinear pharmacokinetics. Sertraline stands out as having the best effects on behaviour among all antidepressants. However, fluoxetine and fluvoxamine are least likely to penetrate into breast milk. All 3 of the structurally unique newer antidepressants [amfebutamone (bupropion), viloxazine venlafaxine] have relatively short tmax values (1 to 2 hours), which may relate to the early onset of adverse effects. Amfebutamone has the benefits of linear pharmacokinetics with potential for defined therapeutic blood concentrations, lack of effect of liver enzymes on metabolism of the drug, and lack of significant effects of either aging or hepatic dysfunction on elimination of the drug. Thus, the antidepressants best suited for pharmacokinetic optimisation of therapy are the following: desipramine, sertraline, fluvoxamine, citalopram and amfebutamone.

Excretion of psychoactive drugs into breast milk. Pharmacokinetic principles and recommendations

The postpartum period is a time of great physical and emotional changes. The incidence of psychiatric illness is higher in this period than at any other time in a women's life. Therefore, the question of whether women receiving psychotropic drugs should continue breast feeding is an important one. Drug excretion in breast milk depends mostly on passive diffusion of the unionised unbound drug. Passive diffusion is affected mainly by the drug disposition in lactating mothers, by the physicochemical properties of the molecule and by the protein and lipid contents of breast milk. Indeed, breast milk can be considered as a compartment with bidirectional transfer rather than a reservoir into which drug accumulates. Benzodiazepines are the most prescribed psychotropic drugs. Generally there does not seem to be any contraindication to breast feeding after a single dose, provided the dose administered is relatively low. If higher doses are to be used or long term administration is required, then breast feeding should probably be discontinued, particularly with drugs with a long elimination half-life. On the basis of the average concentration of phenobarbital (phenobarbitone) in milk, breast feeding is not recommended. For glutethimide, breast feeding would appear to be safe for the infant when a single dose is taken occasionally. Zopiclone may also be prescribed on a short term basis to breast feeding mothers. Due to limited available data or to the large amount transferred to milk, administration of phenothiazines and nonphenothiazine tricyclic, butyrophenone, and benzamide antipsychotics to breast feeding mothers cannot be recommended. Breast feeding is not always considered an absolute contraindication to lithium therapy, but the mother should watch for signs of toxicity in her baby. Whether clomipramine should be contraindicated during breast feeding depends on the concentration of active metabolites in breast milk, and this has not yet been determined. It is probably safe for mothers to breast feed while receiving amitriptyline, but before more conclusive recommendations are made more infants should be studied. The available data suggest that the amount of doxepin and its metabolite in breast milk is small. However, the metabolite of doxepin may accumulate in the infant with risk of sedation and respiratory depression: therefore, an alternative antidepressant should be selected for breast feeding mothers.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemistry and pharmacology of reversible inhibitors of MAO-A agents: focus on moclobemide

Moclobemide, p-chloro-N-[morpholinoethyl]benzamide, is a prototype of RIMA (reversible inhibitor of MAO-A) agents. The compound possesses antidepressant efficacy that is comparable to that of tricyclic and polycyclic antidepressants. In humans, moclobemide is rapidly absorbed after a single oral administration and maximum concentration in plasma is reached within an hour. It is moderately to markedly bound to plasma proteins. MAO-A inhibition rises to 80% within two hours; the duration of MAO inhibition is usually between eight and ten hours. The activity of MAO is completely reestablished within 24 hours of the last dose, so that a quick switch to another antidepressant can be safely undertaken if clinical circumstances demand. RIMAs are potent inhibitors of MAO-A in the brain; they increase the free cytosolic concentrations of norepinephrine, serotonin and dopamine in neuronal cells and in synaptic vesicles. Extracellular concentrations of these monoamines also increase. In the case of moclobemide, increase in the level of serotonin is the most pronounced. Moclobemide administration also leads to increased monoamine receptor stimulation, reversal of reserpine induced behavioral effects, selective depression of REM sleep, down regulation of beta-adrenoceptors and increases in plasma prolactin and growth hormone levels. It reduces scopolamine-induced performance decrement and alcohol induced performance deficit which suggest a neuroprotective role. Tyramine potentiation with moclobemide and most other RIMA agents is negligible.

Prospective evaluation of a model for the prediction of milk:plasma drug concentrations from physicochemical characteristics

1. Milk:plasma (M/P) drug concentration ratios predicted by a model utilizing pKa, plasma protein binding and octanol:water partition coefficients have been compared with actual M/P values for 10 basic drugs. 2. There was a close relationship between predicted and observed M/P ratios with a coefficient of determination r2 of 0.97. However, there was a proportional error. 3. The data were transformed by taking logs of predicted and observed (M/P + 1) values. Regression analysis resulted in an r2 of 0.95, an intercept on the Y-axis not significantly different from zero and a slope not significantly different from one. 4. The 95% confidence interval around a single prediction revealed an error between 150% for the lowest and 23% for the highest M/P ratios. The error is therefore lowest for the drugs likely to have the greatest transfer into milk. 5. There was no significant bias in the predictions. 6. The model was refined by multiple linear regression analysis utilising the observed M/P ratios for the 10 basic drugs in addition to those of the original drugs. The revised equation resulted in an improvement in the explained variance. 7. Protein binding was the most important single predictor. 8. The results confirm that M/P ratios for basic drugs can be predicted accurately from their physicochemical characteristics.