Salivary excretion of lithium. I. Human parotid and submaxillary secretions

Saliva testing as a means to monitor therapeutic lithium levels in patients with psychiatric disorders: Identification of clinical and environmental covariates, and their incorporation into a prediction model

OBJECTIVE

The narrow therapeutic window of lithium medications necessitates frequent serum monitoring, which can be expensive and inconvenient for the patient. Compared to blood, saliva collection is easier, non-invasive, requires less processing, and can be done without the need for trained personnel. This study investigated the utility of longitudinal salivary lithium level monitoring.

METHODS

We measured salivary lithium levels using ICP-OES in n = 169 passive drool samples, collected both as single observations and longitudinally for up to 18 months, from a multi-center cohort of n = 75 patients with bipolar disorder or other psychiatric conditions.

RESULTS

Saliva and serum lithium levels were highly correlated. Adjustment for daily lithium dose, diabetes, and smoking improved this relationship (r = 0.77). Using the adjusted intersubject equation and a patient's salivary lithium value, we observed a strong correlation between the predicted vs. observed serum lithium levels (r = 0.70). Most patients had highly stable saliva/serum ratios across multiple visits, with longitudinal variability significantly greater with age. Use of the intrasubject saliva/serum ratio from a single prior observation had similar predictive power to the use of the adjusted intersubject equation. However, the use of the mean intrasubject ratio from three prior observations could robustly predict serum lithium levels (predicted vs. observed r = 0.90).

CONCLUSIONS

These findings strongly suggest that saliva could be used for lithium monitoring, and open the door for the development and implementation of a point-of-care salivary lithium device for use at home or the clinic. We propose that the use of saliva will dramatically improve treatment opportunities for patients with mood disorders.

A study on the bioequivalence of lithium and valproate salivary and blood levels in the treatment of bipolar disorder

Lithium (Li) and valproate (VPA) are used in the treatment of bipolar disorder (BD), with narrow therapeutic window requiring periodic control of serum levels. This prevents intoxication, lack of efficacy due to low serum concentrations, and allows monitoring adherence. We aimed at evaluating the bioequivalence of salivary and blood levels of LI or VPA in a sample of adult BD patients. Secondarily, lithium bioequivalence was evaluated across different patients' lifespans. BD patients treated with either Li or VPA underwent contemporary standard serum and salivary measurements. Blood levels of both drugs were taken according to standard procedures. Li salivary levels were performed by an adapted potentiometric method on the AVL9180 electrolyte analyzer. VPA salivary levels were taken with an immune-assay method with turbidimetric inhibition. A total of 50 patients (38 on Li, 12 on VPA) were enrolled. Blood-saliva bioequivalence for VPA was not found due to a high variability in salivary measures. Li measures resulted in a high correlation (r=0.767, p<0.001), showing no partial correlation with age (r=0.147, p=0.380). Li salivary test is a reliable method of measuring Li availability and is equivalent to serum levels. Potential advantages of Li salivary testing are its non-invasive nature and the possibility of doing the test during the usual appointment with the psychiatrist.

The use of oral fluid for therapeutic drug management: clinical and forensic toxicology

One of the underlying tenets of clinical pharmacology is that only free drugs are pharmacologically active. It is thought that only free drugs can cross biological membranes to interact with a given receptor to alter its function, and that drug responses, both efficacious and toxic, are a function of unbound concentrations. The rationale for measuring drugs in oral fluid is that the free fraction of a drug in plasma reaches equilibrium with the drug in saliva. Although reports concerning the appearance of organic solutes in saliva have been in the literature for over 70 years, it has only been in the past 30 years that there has been emphasis on the appearance of drugs. Although many assumptions for drug level monitoring in saliva are made, the primary requisite for salivary monitoring to be useful is a constant or predictable relationship between the drug concentration in saliva and the drug concentration in plasma. Measurement of oral fluid drug levels for the purpose of managing patients and making dosage adjustments may be useful for select drugs or drug classes. However, it does not appear to be useful for the majority of drugs therapeutically monitored. Some work with antipsychotic medications has indicated that although the measurement of drug concentrations themselves may not be useful for dosage adjustment, the ratio of parent drug to metabolite may reflect altered metabolic status due to either pharmacogenetic variation or other clinical conditions. Furthermore, analysis of saliva may provide a cost-effective approach for the screening of large populations.

Dialysis of saliva improves accuracy of saliva lithium determinations

BACKGROUND

Saliva lithium (Li) determinations have been explored as a potential alternative to plasma levels. Unfortunately, this method has been shown to be unreliable. Saliva has two major components: the aqueous and the mucopolysaccharide portions.

METHODS

Since Li is likely to distribute only in the aqueous fraction, we dialyzed the saliva through a 3000 Da filter to isolate the aqueous component and determine the Li level in it.

RESULTS

Lithium levels in the dialyzed saliva agreed more closely with plasma levels (Spearman's rho = 0.901, p < 0.001) than did whole saliva (Spearman's rho = 0.775, p = 0.012).

CONCLUSION

Dialysis of saliva may contribute to more accurate saliva Li levels.

Salivary gland function in patients on chronic lithium treatment

Salivary gland function was studied in 14 manic-depressive patients treated with lithium carbonate (Li) for 4 to 120 months. Function level was evaluated by means of sialometry, dynamic salivary scintigraphy, and sialography. Daily Li dose, serum Li concentration, duration of Li therapy, and caries activity index were correlated with the salivary function parameters studied. Hyposalivation was noted in 71% of the patients, showing good correlation with the scintigraphic (r = 0.94) and sialographic (r = 0.87) results. Duration of Li therapy was poorly correlated with the degree of salivary gland dysfunction and with the caries activity index, whereas the correlation between duration of therapy and each of the three salivary function parameters was erratic. Because four of the patients exhibited normal salivation, we suggest that there are some additional factors (e.g., genetic or thyroid function level) that might be involved in salivary dysfunction connected with Li therapy.

Matrix modifiers in graphite furnace atomic absorption analysis of trace lithium in biological fluids

The use of KH2PO4/NH4NO3 as matrix modifier eliminates severe interference effects on the atomic absorption analysis of lithium in biological fluids. This enables determination of trace lithium in microliter size samples with absolute sensitivity (0.0044 absorbance) of 2 pg. There is no requirement for standard additions experiments to correct for interferences in specific matrices such as serum and saliva. The biological half-life of trace lithium was 16.9 +/- 2.8 h. Saliva lithium is a good estimate of serum level; the two are highly correlated (r = 0.97) and saliva level is about three times serum.

The monitoring of saliva drug levels: psychiatric applications

An overview is presented of the status of human saliva as a clinical monitoring medium in medicine and psychiatry. Despite the present controversy about the reliability of saliva lithium levels, an evaluation of the prospects of saliva for other pharmacokinetic estimations as well is recommended. The second part of the paper outlines the authors' attempt to expand the use of saliva monitoring in a depot neuroleptic clinic and a methadone maintenance program. This technique, well accepted by the patient populations, is found useful as a screening tool for drug use and compliance can be checked. It can also be indicated prior to the evaluation of the toxicity of prescribed medication as well as the assessment of drug interaction. On humanitarian, clinical and economical grounds, further investigation of the clinical applications of saliva in psychiatric practice is warranted.

Salivary lithium concentration--a tool for monitoring psychiatric patients

Salivary and serum lithium concentrations were measured simultaneously in 118 manic-depressive patients. Lithium concentration in saliva was 2.24 +/- 0.35 times higher than in serum. An equation to calculate serum lithium concentration from salivary measurements was derived: Li serum = 0.36 Li saliva + 0.13. Psychotropic drugs had no effect on the salivary:serum ratio. Eighteen patients were followed for several weeks. A significant correlation coefficient between salivary and serum lithium concentrations was found in thirteen of the eighteen patients studied.

Comparison between saliva and serum lithium concentrations in patients treated with lithium carbonate

The relation between serum and saliva lithium concentration was studied in patients treated with lithium carbonate. In 23 patients a highly variable saliva/serum ratio was found in simultaneous saliva and serum samples. In five patients studied during a period of 4-8 weeks three patients showed a high fluctuation in saliva/serum lithium ratio. In 20 patients saliva lithium concentrations varied unexpectedly in a second sample produced after 15 min. Although some authors report a high and stable relation between saliva and serum lithium concentration, we consider the saliva lithium level unreliable as a prediction of the serum lithium level in patients treated with lithium carbonate.

Lithium concentrations in saliva, plasma and red blood cells of patients given lithium acetate

Lithium concentrations in saliva, plasma and red blood cells were measured in: 1) six hospitalized patients under long-term lithium therapy, at 2, 5, 9 and 24 hours after oral doses of 24 mEq Li acetate and 2 or 12 hours after 8 mEq Li acetate; and 2) 10 outpatients under chronic lithium treatment at two occasions 8 days apart. With changing plasma concentrations, [Li] saliva varied without any notable time lag. [Li] saliva was always much higher than [Li] plasma. The ratio [Li] saliva/ [Li] plasma water averaged 3.2 +/- 0.2 in 62 determinations, but varied widely at different times after oral lithium in the same individuals and less widely between different individuals. "Prediction" of plasma lithium concentration from measured [Li] saliva appears hazardous, and may provide reliable indications only if [Li] saliva is measured repeatedly. Salivary lithium concentrations were not correlated with either potassium or sodium concentrations. Lithium concentrations in red blood cells were always lower than in plasma: [Li] red blood cell water/ [Li] plasma water averaged 0.37 +/- 0.03. With changing plasma concentrations, rise and fall of red blood cell lithium lagged considerably behind plasma changes. This resulted in a rise of the red blood cell/plasma concentration ratio from a very low value 2 hours after an oral dose to a rather high value 24 hours after an oral dose.

Usefulness of saliva lithium estimation

Estimation of lithium in 24 samples of serum and saliva show that there is a very high correlation between the lithium levels in serum and saliva (r= + 0-88). The ratio found in our patients is very similar to that reported from North America. Estimation of lithium in saliva at different periods of time show there is a good degree of stability for saliva lithium levels. Thus saliva can be used as a substitute for serum for lithium monitoring. The practical advantages of this are discussed.

Salivary excretion of lithium. II. Functional analysis

Salivary Li+ was actively secreted by the cat submaxillary gland, inversely to the rate of flow, at concentrations above serum level. Stop-flow studies indicated ductal secretion of Li+ by a HgCl2 and ouabain-sensitive mechanism. Salivary secretion of Li+ did not resemble Na+ but was similiar to K+ secretion.