Therapeutic drug monitoring in hair samples. Principles and practice

Analysis of Antiretrovirals in Single Hair Strands for Evaluation of Drug Adherence with Infrared-Matrix-Assisted Laser Desorption Electrospray Ionization Mass Spectrometry Imaging

Adherence to a drug regimen can be a strong predictor of health outcomes, and validated measures of adherence are necessary at all stages of therapy from drug development to prescription. Many of the existing metrics of drug adherence (e.g., self-report, pill counts, blood monitoring) have limitations, and analysis of hair strands has recently emerged as an objective alternative. Traditional methods of hair analysis based on LC-MS/MS (segmenting strands at ≥1 cm length) are not capable of preserving a temporal record of drug intake at higher resolution than approximately 1 month. Here, we evaluated the detectability of HIV antiretrovirals (ARVs) in hair from a range of drug classes using infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry imaging (MSI) with 100 μm resolution. Infrared laser desorption of hair strands was shown to penetrate into the strand cortex, allowing direct measurement by MSI without analyte extraction. Using optimized desorption conditions, a linear correlation between IR-MALDESI ion abundance and LC-MS/MS response was observed for six common ARVs with estimated limits of detection less than or equal to 1.6 ng/mg hair. The distribution of efavirenz (EFV) was then monitored in a series of hair strands collected from HIV infected, virologically suppressed patients. Because of the role hair melanin plays in accumulation of basic drugs (like most ARVs), an MSI method to quantify the melanin biomarker pyrrole-2,3,5-tricarboxylic acid (PTCA) was evaluated as a means of normalizing drug response between patients to develop broadly applicable adherence criteria.

Regulated drug bioanalysis for human pharmacokinetic studies and therapeutic drug management

Regulated drug bioanalysis (i.e., determination of drug concentrations in biological matrices for regulated studies) usually refers to animal toxicokinetics, bioavailability/bioequivalence and clinical pharmacokinetic studies. However, there is another important regulated drug bioanalysis – therapeutic drug management (TDM). In the USA, TDM is regulated by Clinical Laboratory Improvement Amendments. In this article, we review and compare human pharmacokinetic sample analysis and TDM sample analysis. The US FDA/Bioanalytical Method Validation Guidance and the American Association for Clinical Chemistry/TDM Roundtable Recommended Generic Assay Validation Guidance are also compared. Some regulated drug bioanalysis issues, such as terminology, validation concepts and acceptance criteria, are discussed. Fostering interaction between bioanalysts from pharmaceutical science and clinical chemistry and reducing the regulatory gaps between different agencies for drug bioanalysis is our objective.

Microanalysis of the antiretroviral nevirapine in human hair from HIV-infected patients by liquid chromatography-tandem mass spectrometry

Sufficient drug exposure is crucial for maintaining durable responses to HIV treatments. However, monitoring drug exposure using single blood samples only provides short-term information and is highly subject to intra-individual pharmacokinetic variation. Drugs can accumulate in hair over a long period of time, so hair drug levels can provide drug exposure information over prolonged periods. We now report on a specific, sensitive, and reproducible liquid chromatography-tandem mass spectrometry method for measuring nevirapine (NVP), a widely used antiretroviral drug, levels in human hair using even a single short strand of hair. Hair samples are cut into small segments, and the drug is extracted in methanol/trifluoroacetic acid (v/v, 9:1) shaken at 37 °C in a water bath overnight, followed by liquid-liquid extraction under alkaline conditions. The extracted samples are then separated on a BDS-C(18) column with a mobile phase composed of 50% acetonitrile containing 0.15% acetic acid and 4 mM ammonium acetate with an isocratic elution for a total run time of 3 min and detected by triple quadrupole electrospray multiple reaction mode at precursor/product ion at 267.0 > 225.9 m/z. Deuterated nevirapine-d5 was used as an internal standard. This method was validated from 0.25 to 100 ng/mg using 2 mg hair samples. The accuracies for spiked NVP hair control samples were 98-106% with coefficients of variation (CV) less than 10%. The CV for incurred hair control samples was less than 7%. The extraction efficiency for incurred control hair samples was estimated at more than 95% by repeated extractions. This method has been successfully applied to analyze more than 1,000 hair samples from participants in a large ongoing cohort study of HIV-infected participants. We also showed that NVP in human hair can easily be detected in a single short strand of hair. This method will allow us to identify drug non-adherence using even a single strand of hair.

Collection of biological samples in forensic toxicology

Forensic toxicology is the study and practice of the application of toxicology to the purposes of the law. The relevance of any finding is determined, in the first instance, by the nature and integrity of the specimen(s) submitted for analysis. This means that there are several specific challenges to select and collect specimens for ante-mortem and post-mortem toxicology investigation. Post-mortem specimens may be numerous and can endow some special difficulties compared to clinical specimens, namely those resulting from autolytic and putrefactive changes. Storage stability is also an important issue to be considered during the pre-analytic phase, since its consideration should facilitate the assessment of sample quality and the analytical result obtained from that sample. The knowledge on degradation mechanisms and methods to increase storage stability may enable the forensic toxicologist to circumvent possible difficulties. Therefore, advantages and limitations of specimen preservation procedures are thoroughfully discussed in this review. Presently, harmonized protocols for sampling in suspected intoxications would have obvious utility. In the present article an overview is given on sampling procedures for routinely collected specimens as well as on alternative specimens that may provide additional information on the route and timing of exposure to a specific xenobiotic. Last, but not least, a discussion on possible bias that can influence the interpretation of toxicological results is provided. This comprehensive review article is intented as a significant help for forensic toxicologists to accomplish their frequently overwhelming mission.

Sensitive analysis of anti-HIV drugs, efavirenz, lopinavir and ritonavir, in human hair by liquid chromatography coupled with tandem mass spectrometry

A highly sensitive and selective method using liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) was developed and validated for the measurement of three antiretroviral agents, efavirenz, lopinavir and ritonavir, in human hair. Hair samples from adherent HIV-infected patients on antiretroviral therapies were cut into about 1 mm length segments and drugs were extracted by first shaking the samples with methanol in a 37 degrees C water bath overnight (>14 h), followed by methyl tert-butyl ether/ethyl acetate (1:1) extraction under weak alkaline conditions. The extracted lopinavir and ritonavir were separated by reversed-phase chromatography and detected by tandem mass spectrometry in electrospray positive ionization mode with multiple reaction monitoring (MRM), while efavirenz was monitored in negative ionization MRM mode. This method was validated from 0.01 to 4.0 ng/mg hair for ritonavir and 0.05-20 ng/mg hair for lopinavir and efavirenz by using 2 mg of a human hair sample. The interday and intraday assay precision (coefficients of variation, CV) for spiked quality control (QC) samples at low, medium and high concentrations were within 15% and accuracy ranged from 89% to 110%. Assay reproducibility was also demonstrated by analysis of incurred hair QC samples (CV <14%). No significant matrix ionization suppression was observed. This developed method allowed for the monitoring of these target medications in the hair samples of HIV-infected women on antiretroviral therapy in an observational study using small amounts of hair.

Spectrophotometric determination of a thiobarbituric acid-reactive substance in human hair

A simple and sensitive spectrophotometric method for the determination of a thiobarbituric acid-reactive substance (TBARS) in human hair has been developed. The proposed method is based on the formation of a red-colored product by the reaction of products of lipid peroxidation with thiobarbituric acid in an acidic medium. The absorbance of the resulting red product was measured at 534 nm. The linear dynamic range was between 1.0 and 20 micromol/L. The recoveries were 98.3-105.0%, and the relative standard deviations (RSD) were 0.32-1.24, respectively. TBARS in digested hair sample was stable for 3 days at room temperature. It was found that, using this method, the hair TBARS concentration in smokers (0.116 +/- 0.030 micromol/g, n = 30) was significantly higher than that in non-smokers (0.096 +/- 0.015 micromol/g, n = 30) (p < 0.05).

Usefulness of Saliva for Measurement of 3,4-Methylenedioxymethamphetamine and Its Metabolites: Correlation with Plasma Drug Concentrations and Effect of Salivary pH

Background: Saliva is an alternative biologic matrix for drugs-of-abuse testing that offers the advantages of noninvasive, rapid, and easy sampling. We studied the excretion profile of 3,4-methylenedioxymethamphetamine (MDMA) and its metabolites in both saliva and plasma, as well the effect of the drug on salivary pH.

Methods: Saliva and plasma samples were obtained from eight healthy MDMA consumers after ingestion of a single 100-mg dose of the drug. Concentrations of MDMA and its main metabolites, 3,4-methylenedioxyamphetamine (MDA) and 4-hydroxy-3-methoxymethamphetamine (HMMA), in saliva and plasma were measured by gas chromatography-mass spectrometry. Apparent pharmacokinetic parameters for MDMA in saliva were estimated, and the saliva-to-plasma ratio at each time interval was calculated and correlated with salivary pH.

Results: MDMA, MDA, and HMMA were detected in saliva. Salivary concentrations of MDMA were 1728.9–6510.6 μg/L and peaked at 1.5 h after drug intake. This was followed by a progressive decrease, with a mean concentration of 126.2 μg/L at 24 h. The saliva-to-plasma ratio was 32.3–1.2, with a peak of 18.1 at 1.5 h after drug administration. Salivary pH seemed to be affected by MDMA administration; pH values decreased by 0.6 units (mean pH values of 6.9 and 6.8 at 1.5 and 4 h after drug administration vs predose pH of 7.4).

Conclusions: Measurement of MDMA in saliva is a valuable alternative to determination of plasma drug concentrations in both clinical and toxicologic studies. On-site testing is also facilitated by noninvasive and rapid collection of salivary specimens.

Comparative dispositions of ofloxacin in human head, axillary, and pubic hairs

The distribution of ofloxacin (OFLX) along the shaft of each of three hair types, i.e., head, axillary and pubic, was investigated and compared among five healthy male volunteers 1 to 4 months after ingestion of OFLX for 1 or 2 days (total dose, 200 or 600 mg). Five strands of each hair type were sectioned together into successive 0.5-cm lengths starting from the dermal end, over a length of < or = 6 cm, and the OFLX concentration in each hair section was measured by high-pressure liquid chromatography with fluorescence detection. The distribution of OFLX along the head hair shaft was narrow, having a single peak even 3 to 4 months after administration, suggesting a rather uniform growth rate among hair strands. On the other hand, the OFLX distribution along axillary or pubic hair shafts tended to be broad, even having two apparent peaks, and the growth rate did not seem uniform. Since axillary hair seemed to stop growing after having gained a length of < or = 4 to 5 cm, it was suggested to enter a resting stage after the growth of < or = 3 cm over the 2 to 4 months after OFLX incorporation. These findings indicate that head hair is the most suitable for analysis of individual drug use and the larger growth rate and cycle stage variabilities of strands of the other types of hair should be taken into account.

Incorporation of drugs for the treatment of substance abuse into pigmented and nonpigmented hair

Hair analysis for drugs may be useful for the long-term monitoring of recidivism and treatment compliance. L-alpha-Acetylmethadol, buprenorphine, and methadone are drugs that are used for the treatment of substance abuse. The purpose of this study was to study the relationship between dose, plasma concentration, hair concentration, and hair pigmentation for these compounds and their major metabolites in an animal model. Male Long-Evans rats received either L-alpha-acetylmethadol (1 and 3 mg/kg; n = 6), buprenorphine (1 and 3 mg/kg; n = 5), or methadone (4 and 8 mg/kg; n = 5) by intraperitoneal injection daily for 5 days. Fourteen days after beginning drug administration, newly grown hair was collected and analyzed for either L-alpha-acetylmethadol and two metabolites (L-alpha-acetyl-N-normethadol and L-alpha-acetyl-N,N-dinormethadol), methadone and two metabolites (D,L-2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolinium and D,L-2-ethyl-5-methyl-3,3-diphenyl-1-pyrroline), or buprenorphine and one metabolite (norbuprenorphine). The plasma time course (AUC) for each compound was also determined after a single administration of each drug at the specified doses. There was an approximate dose-dependent increase in measured hair concentration of each parent drug in pigmented hair. The concentrations of L-alpha-acetylmethadol, methadone, and buprenorphine in nonpigmented hair were significantly less than that measured in pigmented hair at either the high or low dose. The metabolites L-alpha-acetyl-N-normethadol and D,L-2-ethyl-1,5dimethyl-3,3-diphenylpyrrolinium were detected at lower concentrations than their respective parent compounds (L-alpha-acetylmethadol or methadone) in pigmented hair. However, the L-alpha-acetyl-N,N-dinormethadol metabolite concentrations in pigmented hair were significantly greater than those of the parent drug after either the low or the high L-alpha-acetylmethadol dose. These data demonstrate that L-alpha-acetylmethadol, methadone, buprenorphine, and metabolites are distributed into hair in a dose-related manner with a preference for pigmented hair.

Clinical outcome of smoking-cessation trial of nicotine chewing gum evaluated by analysis of nicotine in hair

The axial distribution of nicotine along the hair shafts was examined in 21 subjects enrolled in a placebo-controlled, double-blind trial of nicotine chewing gum (Nicorette) for validating their self-reported smoking behavior and their physicians' assessments. Hair samples obtained from the subjects once during the 3-month follow-up period (n = 10 for placebo and n = 11 for Nicorette ad libitum) were analyzed for the cm x cm distribution of nicotine along the hair shafts. Hair analysis results were compared with the monthly self-reports and with the plasma concentrations of thiocyanate (SCN-) measured at 1-month intervals. A gradual decrease in nicotine content along the hair shafts generally corresponded to the decrease in self-reported number of cigarettes smoked daily by the subjects who reported that they abstained from smoking or decreased the number of daily cigarettes in placebo and nicotine chewing gum groups. Because nicotine may dissociate slowly from hair follicle cells, nicotine in the hair did not mark a sudden decrease or cessation of smoking and, therefore, hair analysis tended to underestimate the real decrease of smoking. However, physician assessment seemed to depend solely on self-reporting because the time profile of changes in serum SCN- concentration did not correspond necessarily to the changes in the self-reported number of cigarettes used daily.

High-performance liquid chromatographic determination of carbamazepine and metabolites in human hair

To study the use of hair analysis in monitoring drug compliance and historical changes in pharmacokinetics we developed a method for the quantitative determination of the anti-epileptic drug carbamazepine (CBZ) and trans-10,11-dihydro-10,11-dihydroxy-carbamazepine (CBZ-diol) in hair from carbamazepine users. Digestion by 1 M NaOH was found to be the best method for isolating CBZ and CBZ-diol from hair, followed by solid-phase extraction and reversed-phase HPLC with UV detection. Recoveries from spiked hair samples were 76-86%. Within-day precision (C.V.; n = 10) for CBZ and CBZ-diol in hair of a CBZ user containing 10.9 microg/g CBZ and 3.2 microg/g CBZ-diol were 1.7 and 5.0%, respectively. Sectional hair analysis of a patient on a constant dosage of CBZ demonstrates an exponential decrease in hair concentrations of CBZ and CBZ-diol with increasing distance from the root, probably caused by shampooing. No CBZ-10,11-epoxide (CBZ-epox) could be detected. However, one component in the chromatogram is probably CBZ-beta-hydroxythioether, an adduct of CBZ-epox with cysteine, or acridinethioacetal, its rearrangement product. The concentration of this component does not decrease with increasing distance from the root.

Simultaneous determination of phenytoin and carbamazepine in human hair by high-performance liquid chromatography

Drug detection in human hair has been regarded as a potentially useful technique for therapeutic drug monitoring and for the assessment of therapeutic compliance. An isocratic high-performance liquid chromatography (HPLC) assay for the simultaneous measurement of phenytoin and carbamazepine in human hair was used to assess therapeutic compliance in a population of patients with epilepsy. After alkaline digestion, phenytoin and carbamazepine were separated on a reverse-phase column by using a mobile phase of acetonitrile/methanol/water (9:37:54) and monitored at a wavelength of 214 nm with methylphenyl-5-phenylhydantoin as internal standard. The assay was linear in the range from 0 to 66.66 ng/mg hair, and recoveries of both drugs at concentrations of 8.33, 33.3, and 66.66 ng/mg hair from the hair matrix ranged from 91.2 to 104.0%. Inter- and intraassay coefficients of variation for both drugs (assessed at three concentrations in the calibration range) were < 10%. The limits of detection for phenytoin and carbamazepine were 2.0 and 1.33 ng/mg hair, respectively.

Hair analysis for nicotine and cotinine: evaluation of extraction procedures, hair treatments, and development of reference material

Analysis of nicotine and cotinine in human hair can provide information on nicotine intake and exposure to environmental tobacco smoke over a long period of time. Nonetheless, to better assess the usefulness of hair analysis to determine smoking habits or exposures, all procedures have to be standardized. Various solvents were tested as washing solvents to eliminate external contamination from nicotine. Dichloromethane was found effective when used for two washes prior to the extraction. Basic and acid digestion of hair followed by solid phase extraction with Extrelut-3 glass column using dichloromethane:isopropyl alcohol (9:1) as eluting mixture both gave good recoveries of nicotine and cotinine, when compared with extractions reported in the literature. The extraction method was free from substances, which could interfere in the chromatographic analysis. Furthermore, the addition of methanolic HCl to the eluting mixture prevented the loss of nicotine during the evaporation step before chromatography. Chromatography was performed using a reversed-phase column and a U.V. detection at 254 nm. Furthermore, hair treatments (dyes, permanent wave, hydrogen peroxide) caused a major decrease in the nicotine content in hair, and a smaller effect on cotinine levels. However, the effect of various treatments was not reproducible. Several attempts to produce reference materials were carried out. Nicotine and cotinine standard solutions at different concentrations were added to blank hair soaked in dimethylsulfoxide, methanol and water.

Evidence for saturable incorporation of methadone into rat hair: relationships among oral dose, plasma concentration, and hair content

Six groups of six male Wistar rats were administered methadone in their drinking water over the concentration range 0-0.25 mg/ml. Hair and trunk blood samples were collected after a 6-week period of drug administration. Immunoreactive methadone was measured by radioimmunoassay and methadone and its major metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidene (EDDP), by gas chromatography in plasma and alkali digests of hair. Plasma methadone concentration increased with increasing oral dose. The mean hair concentration of methadone increased to a maximum of 5.1 ng/mg at a drinking water concentration of 0.1 mg/ml corresponding to a plasma level of 14.0 ng/ml. No further significant rise in hair content was seen with higher drinking water concentrations despite a continuing increase in oral drug intake and in plasma methadone concentration. EDDP was not detected in plasma but was present at > 2 ng/mg in 25% of hair samples. The mean EDDP concentration in hair peaked at 3.2 ng/mg at the lowest dose level of methadone administered. The data suggest that methadone is incorporated into rat hair via a capacity-limited process that becomes saturated at plasma levels of some 14 ng/ml. Competition for uptake into hair between methadone and EDDP may occur.

The measurement of caffeine concentration in scalp hair as an indicator of liver function

Caffeine concentration in plasma and scalp hair has been determined for subjects consuming normal daily amounts of caffeine and the results used as an indicator of individual hepatic metabolic capacity. Daily exposure to caffeine was assessed in six healthy Japanese volunteers by direct HPLC measurement of the concentrations of caffeine in aliquots of all caffeine-containing beverages consumed by the subjects. The measurements were repeated on three different occasions for each subject and caffeine consumption (mean +/- s.d.) was calculated as 178.0 +/- 84.3 mg day-1 with an intra-individual variability of 23.8 +/- 6.3% as coefficient of variation. A survey of daily caffeine consumption in 121 adult Japanese by means of a questionnaire revealed a similar value (231.8 +/- 177.8 mg day-1). Caffeine concentration in the plasma sampled during an overnight caffeine-free interval was measured by HPLC and a comparison made between healthy subjects and patients with liver disease (0.71 +/- 0.32, 0.77 +/- 0.45 and 3.92 +/- 1.91 micrograms mL-1 for healthy volunteers (n = 6), patients with hepatitis (n = 11) and those with liver cirrhosis (n = 4), respectively). Strands of scalp hair were collected from six healthy subjects and six patients with liver cirrhosis. Caffeine in hair was identified and measured by gas chromatography-mass spectrometry after digestion of the hair matrix with protease and extraction of the caffeine with chloroform. Caffeine concentration in hair collected from patients with liver cirrhosis (26.5 +/- 5.04 ng mg-1 hair) was significantly higher than that in hair sampled from healthy subjects (7.21 +/- 3.11 ng mg-1). These findings suggest that the determination of caffeine concentration in the plasma and hair of subjects consuming normal daily amounts of caffeine-containing beverages provides a practical assessment of individual liver metabolic capacity.

Drug monitoring in nonconventional biological fluids and matrices

Determination of the concentration of drugs and metabolites in biological fluids or matrices other than blood or urine (most commonly used in laboratory testing) may be of interest in certain areas of drug concentration monitoring. Saliva is the only fluid which can be used successfully as a substitute for blood in therapeutic drug monitoring, while an individual's past history of medication, compliance and drug abuse, can be obtained from drug analysis of the hair or nails. Drug concentrations in the bile and faeces can account for excretion of drugs and metabolites other than by the renal route. Furthermore, it is important that certain matrices (tears, nails, cerebrospinal fluid, bronchial secretions, peritoneal fluid and interstitial fluid) are analysed, as these may reveal the presence of a drug at the site of action; others (fetal blood, amniotic fluid and breast milk) are useful for determining fetal and perinatal exposure to drugs. Finally, drug monitoring in fluids such as cervical mucus and seminal fluid can be associated with morpho-physiological modifications and genotoxic effects. Drug concentration measurement in nonconventional matrices and fluids, although sometimes expensive and difficult to carry out, should therefore be considered for inclusion in studies of the pharmacokinetics and pharmacodynamics of new drugs.

Testing human hair for carbamazepine in epileptic patients: is hair investigation suitable for drug monitoring?

Hair samples were obtained from 30 patients who had been taking carbamazepine in fixed daily doses for more than 6 months. Carbamazepine was extracted from the hair by enzymatic hydrolysis and quantified by gas chromatography-mass spectrometry. Concentrations ranged from 1.2 to 57.4 ng mg-1. The concentrations of carbamazepine were significantly correlated (P < 0.0001) with the daily dose and the correlation coefficient was 0.793. Although it had been suggested by several authors that the measurement of carbamazepine in hair might provide a better index of individual dosage history than the plasma level assays, the deviations observed in this study led to the conclusion that hair samples are not suitable for evaluating the quantity of drug consumed. However, hair testing may be useful for documenting clinical disorders by sectioning the shaft into segments corresponding to 1 month periods.

The axial distribution of nicotine content along hair shaft as an indicator of changes in smoking behaviour: evaluation in a smoking-cessation programme with or without the aid of nicotine chewing gum

1. Hair samples were obtained from subjects at the end of a 6 month smoking-cessation programme carried out with (n = 16) or without (n = 10) the aid of nicotine chewing gum. The axial distribution of nicotine along the hair shaft was determined and compared both with the self-report of smoking behavior and with the concentration of carbon monoxide (CO) in expired air measured at 1 month intervals. 2. A gradual decrease in nicotine content along the hair shaft corresponded to the decrease in self-reported number of cigarettes smoked daily in both the nicotine chewing-gum treated and untreated subjects and with the clinical assessment of abstinence. 3. There was reasonable agreement between the CO content of expired air, the self-reported number of cigarettes smoked daily and the axial distribution of nicotine in 22 of 26 subjects. In the other four subjects there was an apparent disagreement between the CO content of expired air and the other parameters. 4. This study showed that, as a routine marker of smoking status, hair analysis may be preferable to repeated CO measurements since only a single sample at the end of an abstinence programme might be sufficient. However, one problem is that nicotine may dissociate slowly from melanin to limit the ability to mark a sudden cessation of smoking. Also, some nicotine in hair might be attributable to nicotine adsorbed to the outside of hair.

Simultaneous determination of ofloxacin, norfloxacin and ciprofloxacin in human hair by high-performance liquid chromatography and fluorescence detection

A high-performance liquid chromatographic method for the simultaneous determination of ofloxacin, norfloxacin and ciprofloxacin in human hair is described. A reversed-phase C18 column and a fluorescence detector with switching fluorescence wavelengths were used together with solid-phase extraction of the drugs from hair dissolved in 1 M sodium hydroxide. Reproducibility and linearity studies yielded coefficients of variation of 0.2-2.2, 1.4-3.1 and 1.5-3.4%, and correlation coefficients of 1.000, 0.999 and 0.999 within the concentration range 0.3-100 ng/ml for ofloxacin, norfloxacin and ciprofloxacin, respectively. For validation, hair samples were obtained from six subjects who had been taking one or two of the three fluoroquinolones. Assuming a hair growth-rate of 1 cm per month fluoroquinolones could be detected in the hair section(s) that had grown approximately between the dates of drug administration and hair sampling.