The bioequivalence study design recommendations for immediate-release solid oral dosage forms in the international pharmaceutical regulators programme participating regulators and organisations: differences and commonalities

Bioequivalence (BE) studies are considered the standard for demonstrating that the performance of a generic drug product in the human body is sufficiently similar to that of its comparator product. The objective of this article is to describe the recommendations from participating Bioequivalence Working Group for Generics (BEWGG) members of the International Pharmaceutical Regulators Programme (IPRP) regarding the conduct and acceptance criteria for BE studies of immediate release solid oral dosage forms. A survey was conducted among BEWGG members regarding their BE recommendations and requirements related to study subjects, study design, sample size, single or multiple dose administration, study conditions (fasting or fed), analyte to be measured, selection of product strength, drug content, handling of endogenous substances, BE acceptance criteria, and additional design aspects. All members prefer conducting single dose cross-over designed studies in healthy subjects with a minimum of 12 subjects and utilizing the parent drug data to assess BE. However, differences emerged among the members when the drug's pharmacokinetics and pharmacodynamics become more complex, such that the study design (e.g., fasting versus fed conditions) and BE acceptance criteria (e.g., highly variable drugs, narrow therapeutic index drugs) may be affected. The survey results and discussions were shared with the ICH M13 Expert Working Group (EWG) and played an important role in identifying and analyzing gaps during the harmonization process. The draft ICH M13A guideline developed by the M13 EWG was endorsed by ICH on 20 December 2022, under Step 2.

A Survey of the Criteria Used for the Selection of Alternative Comparator Products by Participating Regulators and Organizations of the International Pharmaceutical Regulators Programme

The safety and efficacy of a generic product are partly based on demonstrating bioequivalence to the innovator product; however, when the innovator product is no longer available as a comparator product, a survey conducted within the Bioequivalence Working Group for Generics (BEWGG) of the International Pharmaceutical Regulators Programme (IPRP) indicated that the criteria for selecting an alternative comparator product varies. For most members of the BEWGG, an existing marketed generic that was approved based on a comparison with the locally registered innovator product can be used, contingent on criteria that ranges from allowing any generic to be used, to allowing only specific criteria-defined generics to be used. Notwithstanding the acceptability of a generic as an alternative comparator, it is not always the preferred comparator for several jurisdictions. Some jurisdictions require the use of a locally sourced alternative innovator comparator (e.g., the same medicinal ingredient manufactured by a different company) or a foreign innovator comparator. Unlike the other members of the BEWGG, the European Union (EU) has no such options available, rather mechanisms are in place to allow manufacturers to develop a new comparator. The criteria described herein regarding the use of an alternative comparator product can also be applied to scenarios where a specific strength of a series of strengths or an innovative fixed dose combination are discontinued. The results of the survey demonstrate that while criteria for selecting alternative comparator products are not harmonized among the BEWGG participants, the common concern for all jurisdictions is to select a comparator product that meets the safety and efficacy standards of the original innovator product.

A Survey of the Regulatory Requirements for the Waiver of In Vivo Bioequivalence Studies of Generic Products in Certain Dosage Forms by Participating Regulators and Organisations of the International Pharmaceutical Regulators Programme

The requirements to waive in vivo bioequivalence studies for immediate release solid oral dosage forms based on the Biopharmaceutics Classifications System (BCS) are well known, and biowaivers[1] for other types of oral dosage forms based on pre-defined criteria may also be acceptable. Similarly, biowaivers for dosage forms such as injectable products may also be allowed if certain criteria are met. The current paper summarises the biowaiver requirements for oral solutions and suspensions, soft gelatin capsules and injectable products (intravenous injections, subcutaneous and intramuscular injections, emulsions for injection and micellar solutions for injection) among the participants of the Bioequivalence Working Group for Generics (BEWGG) of the International Pharmaceutical Regulators Programme (IPRP). A review of the requirements indicated that there was a trend towards convergence when the dosage form became less complex; however, the most common approach used by each of the jurisdictions was a case-by-case approach given that most jurisdictions do not have well defined guidelines to support all possible scenarios. Even in the simplest case of intravenous solutions, the acceptability of qualitative changes in excipients differ between the IPRP members.  Notwithstanding the differences, the dissemination of the information is a first step towards regulatory convergence regarding biowaivers for certain dosage forms and should be useful for pharmaceutical companies currently developing generic medicinal products for IPRP jurisdictions.  

Palpitations and narrow-complex tachycardia

A 56-year-old patient with a history of Parkinson's disease presented with palpitations and an apparently irregular narrow-complex tachycardia on electrocardiogram. The discrepancy in ventricular rate between the limb and precordial leads was the result of myopotentials from his tremors mimicking the QRS complexes in the limb leads. These myopotentials can be differentiated from true QRS complexes by the fact that they are usually variable in amplitude and occur at a frequency similar to that of limb tremors.

Human bone marrow-derived adult stem cells for post-myocardial infarction cardiac repair: current status and future directions

Stem cell-based cell therapy has emerged as a potentially therapeutic option for patients with acute myocardial infarction (AMI) and heart failure. With the completion of a number of trials using bone marrow (BM)-derived adult stem cells, critical examination of the overall clinical benefits, limitations and potential side effects of this revolutionary treatment will pave the way for future clinical research. At present, clinical trials have been conducted almost exclusively using BM stem cells. The primary endpoints of these trials are mainly safety and feasibility, with secondary endpoints in the efficacy of post-myocardial infarction (MI) cardiac repair. Intervention with BM-derived cells was mainly carried out by endogenously-mobilised BM cells with granulocyte-colony stimulating factor, and more frequently, by intracoronary infusion or direct intramyocardial injection of autologous BM cells. While these studies have been proven safe and feasible without notable side effects, mixed outcomes in terms of clinical benefits have been reported. The major clinical benefits observed are improved cardiac contractile function and suppressed left ventricular negative remodelling, including reduced infarct size and improved cardiac perfusion of infarct zone. Moderate and transient clinical benefits have been mostly observed in studies with intracoronary infusion or direct intramyocardial injection of BM cells. These effects are widely considered to be indirect effects of implanted cells in association with paracrine factors, cell fusion, passive ventricular remodelling, or the responses of endogenous cardiac stem cells. In contrast, evidence of cardiac regeneration characterised by differentiation of implanted stem cells into cardiomyocytes and other cardiac cell lineages, is weak or lacking. To elucidate a clear risk-benefit of this exciting therapy, future studies on the mechanisms of cardiac cell therapy will need to focus on confirming the ideal cell types in relation to dosage and timing for post-MI cardiac repair, developing more effective cell delivery techniques, and devising innovative cell tracking modalities that could unveil the fates of implanted cells such as survival, engraftment and functionality.

Electrocardiographical case. Young woman with epilepsy

A 24-year-old Chinese woman was referred for evaluation of palpitations. She had a background history of epilepsy. A 12-lead electrocardiogram (ECG) showed prolonged rate-corrected QT of 600 ms and a T-U complex. The ECG findings with her typical history suggest a diagnosis of congenital long QT syndrome. Diagnosis and treatment options are discussed.

Electrocardiographical case. A young man with chest pain

A 31-year-old Chinese man presented with complaint of acute chest pain. 12-lead electrocardiogram (ECG) showed sinus rhythm, with widespread upward concave ST segment elevations. The ECG changes along with a history of acute chest pain in a young man with minimal coronary risk factors are suggestive of acute pericarditis. He subsequently developed a pericardial effusion. Diagnosis, treatment and complications of acute percarditis are discussed.

Echocardiographic advances in atrial fibrillation and supraventricular arrhythmias

Advances in echocardiography have paved the way for the development of intracardiac catheters with ultrasound transducers mounted on its tip. With this technology it has become possible for the interventional electrophysiologist to perform continuous echocardiographic examination during a procedure without the need for general anaesthesia or additional staff. Intracardiac echocardiography (ICE) allows the monitoring of catheter movement in real-time, assessment of catheter-tissue contact and potentially prevents and recognizes complications like thrombus formation and pericardial effusion. In addition recent technologies allow acquiring the full spectrum of Doppler-imaging permitting evaluation of haemodynamic data during the procedure. All these advances have made ICE an ideal tool for the interventional electrophysiologist, serving as a diagnostic and imaging tool during invasive electrophysiological procedures. This review will summarize currently available technology of ICE and its indications and applications in electrophysiological procedures.

Catheter ablation for atrial fibrillation

Recent advancements in our understanding of atrial fibrillation have led to the development of catheter ablation techniques that feasibly could achieve a cure for AF.

Mapping and ablation of ventricular fibrillation

Sudden cardiac death frequently results from ventricular fibrillation (VF). While VF is frequently the eventual mode of death in patients with abnormal ventricular substrates, it has also been described in patients with structurally normally hearts. Until recently, the management of patients who have survived sudden cardiac death has focused on treating the consequences by implantation of a defibrillator. However, such therapy remains restricted in many countries, is associated with a prohibitive cost to the community, and may be a cause of significant morbidity in patients with frequent episodes or storms of arrhythmia. Evidence emerging from the study of fibrillation both in the atria and the ventricle suggests an important role for triggers arising from the Purkinje network or the right ventricular outflow tract in the initiation of VF. Initial experience in patients with idiopathic VF and even those with VF associated with abnormal repolarization syndromes (LQT or Brugada syndrome) or myocardial infarction suggests that long term suppression of recurrent VF may be feasible by the elimination of these triggers. With the development of new mapping and ablation technologies, and greater physician experience, catheter ablation of VF, with the ultimate aim of curing such patients at risks of sudden cardiac death, may not be an unrealistic goal in the future.

Critically ill elderly who require mechanical ventilation: the effects of age on survival outcomes and resource utilisation in the medical intensive care unit of a general hospital

INTRODUCTION

Advanced age has been a criterion for denying admission to the medical intensive care unit (MICU) due to the perceived poorer outcome and increased resource utilisation. We studied the relationship between age and outcome of the critically ill mechanically-ventilated patients admitted to the MICU.

MATERIALS AND METHODS

This prospective study included patients admitted to the MICU for mechanical ventilation between 1994 and 1998. These were divided into 2 cohorts, with 206 patients aged 65 and above and 159 below 65 years. Outcome measures were MICU and hospital mortality and length of stay (LOS) in the MICU and hospital. Logistic and linear regression analyses were performed to determine the association between age and MICU and hospital mortality, as well as MICU and hospital LOS. Factors adjusted for included gender, smoking history, pre-hospitalisation functional status, ambulatory status, use of inotropes and APACHE II (m) scores (APACHE II scores were modified to exclude age points).

RESULTS

Multivariate analysis revealed no statistically significant relationship between age and MICU or hospital mortality and LOS. However, APACHE IIM scores were significantly related to both MICU and hospital mortality (OR, 1.1; CI, 1.07-1.14 and OR, 1.1; CI, 1.09-1.18 respectively), but did not predict MICU or hospital LOS.

CONCLUSION

Severity of acute illness and chronic co-morbidities, but not age, are predictors of MICU and hospital mortality in elderly ventilated patients.

A case series of sotalol-induced torsade de pointes in patients with atrial fibrillation--a tale with a twist

INTRODUCTION

Sotalol is a potent antiarrhythmic often used in patients with atrial fibrillation. However, it has been associated with a risk of provoking other potentially dangerous arrhythmias, especially if used in high doses and in patients with uncorrected electrolyte imbalance or impaired renal and cardiac function.

CLINICAL PICTURE

We present 4 patients with atrial fibrillation treated with sotalol who developed torsade de pointes due to marked prolongation of the QT interval. While 1 patient had renal failure, all had normal left ventricular function. One patient had been treated with sotalol for more than 10 months before developing torsade de pointes precipitated by hypokalaemia, while another had tolerated sotalol for a 3-month period before the drug was discontinued, and only developed torsade de pointes when the drug was restarted 2 years later. Significantly, the doses used in all patients were relatively low, in contrast to most other reported cases where higher doses were used.

CONCLUSION

As with all antiarrhythmic therapy, these cases illustrate the need for close follow-up of patients treated with sotalol, even if relatively low doses are used. In addition, patients who had previously tolerated the drug well are still susceptible to its proarrhythmic effects.

Treatment of heart failure--role of biventricular pacing for heart failure not responding well to drug therapy

OBJECTIVE

Patients with heart failure may have conduction abnormalities in up to 30%, further aggravating cardiac output. Drugs worsen these abnormalities and resynchronisation therapy with biventricular pacing improves cardiac function by effecting a more coordinated and efficient ventricular contraction. We report here the technique of biventricular pacing and its results.

METHODOLOGY

Patients with NYHA Class III to IV heart failure, widened QRS (> or = 130 ms) complex on the ECG and impaired LVEF < or = 40% were enrolled.

RESULTS

Biventricular pacing was performed in 29 patients (26 males, three females) from August 1999 to December 2001. The mean age of the patients was 59.6 +/- 12.8 years and 62% had underlying ischemic heart disease. All were in NYHA class III or more. Twenty-three had LBBB, four RBBB and two had widened paced QRS complex. The QRS duration was 161 +/- 21 ms and LVEF was 22 +/- 8%. All the left ventricular leads were implanted successfully. The procedure time was 167.0 +/- 79.6 mins and the fluoroscopy time was 43.8 +/- 41.4 mins. There were no significant complications. The NYHA class improved from a mean of 3.1 to 2.0 and exercise time from 252 +/- 95 seconds to 392 +/- 152 seconds at six months post implant (p=0.049). On follow-up (one month to 28 months), 25 (86%) patients had improvement in heart failure symptoms and 26 (90%) of the patients remained alive.

CONCLUSION

Biventricular pacing can be safely performed and results in improvement in symptoms and exercise tolerance in heart failure patients with ventricular dyssynchrony not responding to drug therapy.

Immediate and mid-term safety and efficacy of single lead VDD pacemakers for patients with atrioventricular block and normal sinus node function--a single centre experience

INTRODUCTION

Single lead atrial synchronous ventricular pacing (VDD) is increasingly being used in place of conventional dual chamber pacing (DDD) for patients with atrioventricular block and preserved sinus node function. Compared to the latter, VDD pacemakers provide similar haemodynamic benefits derived from atrial synchronous pacing, with the added benefit of an easier implant procedure.

OBJECTIVE

To review the use, safety and efficacy of VDD pacing in a single tertiary referral centre.

MATERIALS AND METHODS

A review of all patients with atrioventricular block and normal sinus node function implanted with a VDD pacemaker over a 2-year period at a local tertiary cardiac referral centre. Data on complications, atrial sensing performance and maintenance of atrioventricular synchrony during implant and at subsequent follow-up visits were obtained from a prospectively maintained registry and analysed.

RESULTS

Forty-one patients (17 males, 24 females) with a mean age of 72 +/- 9 years received VDD pacing for various forms of high-grade atrioventricular block. The average implantation time was 46.8 +/- 17.1 minutes, and a pneumothorax in 1 patient was the only complication. Electrical measurements at implantation and subsequent follow-up visits revealed an initial rapid decrease in atrial signal amplitude (mean atrial P wave at implant 3.1 +/- 1.1 mV, predischarge 1.9 +/- 1.3 mV) which began to stabilise after 3 months, reaching a mean atrial P wave value of 1.3 +/- 0.3 mV at 24 months. The atrial sensing performance (percentage of atrial synchronous ventricular complexes) was 97% over a mean follow-up period of 9.9 months. Four patients (10%) developed paroxysmal atrial tachyarrhythmias. Sinus node dysfunction was not observed in any of our patients during the follow-up period.

CONCLUSION

In patients with atrioventricular block and preserved sinus node function, single lead VDD pacing is safe and effective in maintaining a physiological atrial synchronous pacing mode.

Clinical outcomes of patients with diabetes mellitus and acute myocardial infarction treated with primary angioplasty or fibrinolysis

OBJECTIVE

To compare the early and late outcomes of primary percutaneous transluminal coronary angioplasty (PTCA) with fibrinolytic treatment among diabetic patients with acute myocardial infarction (AMI).

DESIGN

Retrospective observational study with data obtained from prospective registries.

SETTING

Tertiary cardiovascular institution with 24 hour acute interventional facilities.

PATIENTS

202 consecutive diabetic patients with AMI receiving reperfusion treatment within six hours of symptom onset.

INTERVENTIONS

Fibrinolytic treatment was administered to 99 patients, and 103 patients underwent primary PTCA. Most patients undergoing PTCA received adjunctive stenting (94.2%) and glycoprotein IIb/IIIa inhibition (63.1%).

MAIN OUTCOME MEASURES

Death, non-fatal reinfarction, and target vessel revascularisation at 30 days and one year were assessed.

RESULTS

Baseline characteristics were similar in these two treatment groups except that the proportion of patients with Killip class III or IV was considerably higher in those treated with PTCA (15.5% v 6.1%, p = 0.03) and time to treatment was significantly longer (103.7 v 68.0 minutes, p < 0.001). Among those treated with PTCA, the rates for in-hospital recurrent ischaemia (5.8% v 17.2%, p = 0.011) and target vessel revascularisation at one year (19.4% v 36.4%, p = 0.007) were lower. Death or reinfarction at one year was also reduced among those treated with PTCA (17.5% v 31.3%, p = 0.02), with an adjusted relative risk of 0.29 (95% confidence interval 0.15 to 0.57) compared with fibrinolysis.

CONCLUSION

Among diabetic patients with AMI, primary PTCA was associated with reduced early and late adverse events compared with fibrinolytic treatment.

Two case reports on incessant left ventricular tachycardia: curative therapy with radiofrequency ablation

INTRODUCTION

Incessant ventricular tachycardia is a rare arrhythmia which can be life threatening. Treatment with anti-arrhythmic agents may occasionally fail.

CLINICAL PICTURE

We report 2 cases of incessant ventricular tachycardia. The first case was a young man with idiopathic left ventricular tachycardia who was in incessant ventricular tachycardia despite treatment with multiple anti-arrhythmic drugs and developed dilated cardiomyopathy. The second case was an asymptomatic girl with the incidental finding of an incessant ventricular tachycardia which originated from the left ventricular outflow tract.

TREATMENT AND OUTCOME

Both patients underwent electrophysiologic study and radiofrequency ablation with complete termination of the tachycardia.

CONCLUSION

Radiofrequency catheter ablation in experienced centres should be the first-line therapy for incessant ventricular tachycardia.

Cardiac marker point-of-care testing: evaluation of rapid on-site biochemical marker analysis for diagnosis of acute myocardial infarction

INTRODUCTION

Up to 40% of patients with acute myocardial infarction (AMI) present with non-diagnostic electrocardiograms (ECGs). The diagnosis in such cases is usually made with the aid of biochemical markers. Newer and more rapid assays for such markers have now enabled testing to be done on-site instead of in the laboratory. This potentially enables the clinician to rapidly diagnose and triage patients. We evaluated the diagnostic precision of this point-of-care testing strategy using one such analyser, the Stratus CS (Dade Behring) in a prospective study.

MATERIALS AND METHODS

The study population consisted of 51 consecutive patients admitted for suspected AMI with non-diagnostic ECGs. Two blood samples from each patient were drawn simultaneously on admission. The first sample was assayed for myoglobin, troponin I (TnI) and creatine kinase-MB (CKMB) mass by the point-of-care instrument (Stratus CS), and the second sample was sent for standard testing for AMI, comprising a troponin-T (TnT) qualitative test and the analysis of CKMB by the hospital laboratory. Utilising the recommended cut-off values for the individual assays, the results of these 2 sets of tests were evaluated based on whether they were positive or negative for AMI and compared against the patient's final diagnosis at discharge. Various combinations of markers were assessed.

RESULTS

On evaluation of individual markers, myoglobin was the most sensitive (75%) at 0 to 6 hours after onset of symptoms, while TnI (95%), TnT (80%) and CKMB-mass (90%) performed better at 7 to 12 hours. Point-of-care testing utilising a combination of markers was highly sensitive and specific. Both dual-marker panels of myoglobin with TnI and myoglobin with CKMB-mass yielded equivalent overall sensitivities and specificities of 90% and 95% respectively. A triple-marker panel of myoglobin, TnI and CKMB-mass had a sensitivity of 93% and specificity of 95%. All point-of-care testing panels had good positive and negative predictive values, and showed comparable diagnostic efficacy with the standard testing presently utilised for the diagnosis of AMI. The average time for results to become available was up to 26 minutes for point-of-care testing and 65 minutes for standard testing.

CONCLUSION

Point-of-care testing utilising a panel of 2 or 3 cardiac markers has comparable diagnostic precision to the presently utilised testing strategy for AMI, with earlier availability of results.

Hypertension in the young adult--come feel the pulse

Hypertension occurring in teenagers and young adults is uncommon. Though the most common form is still essential hypertension, secondary causes are more commonly found here than in older adults. Renal, cardiovascular and endocrine diseases constitute most of these causes. Coarctation of the aorta is the most common cardiovascular cause of hypertension, and its importance lies in the fact that it is correctable, and that its persistence often leads to dangerous complications and early death. The cardinal sign of differential pulse and blood pressures between the upper and lower limbs can be detected clinically. Hence, the importance of a detailed physical examination in all young hypertensives, including palpation of all the pulses, cannot be overemphasized. We present 2 hypertensive young men who were found to have isolated coarctation of the aorta. The lesion in the first patient was located postductally just distal to the left subclavian artery. This area has been found to be the most common site of coarctation. The second patient had an unusual mid-thoracic coarctation. The clinical and radiological features as well as complications are highlighted. In young hypertensive patients, a high index of suspicion may enable the physician to make a timely diagnosis and hence avert the potentially disastrous complications that may arise in undetected cases.

Electrocardiographic case: diagnosis of acute myocardial infarction in the presence of left bundle branch block

The electrocardiographic features associated with acute myocardial infarction (AMI) are often easily recognised. However, interpretation is made more difficult in the presence of confounding patterns such as a left bundle branch block (LBBB). This may result in missed cases which may otherwise have benefited from acute revascularisation therapy. Though not straightforward, the diagnosis of AMI in the presence of LBBB can be made with a reasonable amount of accuracy. We report a case of acute myocardial infarction with LBBB that was appropriately diagnosed and underwent acute revascularisation by angioplasty. A detailed knowledge of the typical electrocardiographic features associated with LBBB, especially the ST segment morphologies, is very important. This will greatly aid recognition of an evolving AMI and help us decide on the most appropriate therapy.

Acute mercury vapour poisoning in a shipyard worker--a case report

Acute mercury vapour poisoning is a serious, potentially fatal but fortunately rarely encountered problem. It is most commonly due to industrial accidents. The vapour is a direct respiratory tract irritant as well as a cell poison, exerting its greatest effects in the lungs, nervous system, kidneys and liver. We present a case of mercury vapour poisoning in a shipyard workers presenting as an acute chemical pneumonitis, which resolved with aggressive supportive therapy. Further investigations later revealed transient mild neuropsychiatric symptoms, and residual peripheral neuropathy. No chelation therapy was instituted. The detailed investigative work that led to the discovery of the source of mercury is also presented. This case alerts us to the potential hazard to shipyard workers who may work in ships previously carrying oil contaminated with mercury. There have been no previous reports of mercury poisoning in shipyard workers. A high index of suspicion leading to early diagnosis and institution of appropriate supportive measures in suspected cases can be life-saving.

A case series of Paget's disease of bone: diagnosing a rather uncommon condition in Singapore

Paget's disease of bone is an uncommon condition in the Asian population, with only 2 cases reported in medical literature so far. We discuss 5 cases of Paget's disease who presented over an 8-year period with a wide and interesting variety of clinical features. Though 4 out of the 5 patients were asymptomatic, all of them had characteristic radiological features and elevated serum alkaline phosphatase levels of varying degrees. Diagnosis was based on the clinical features, the elevated serum alkaline phosphatase levels, and most importantly, the distinctive radiographic features, which are almost pathognomonic of the condition. The incidence of Paget's disease is probably under-reported in Asia and Singapore, as it is rarely encountered and can be easily overlooked due to its usually asymptomatic and benign nature. A high index of suspicion and an active search for its typical features are thus essential for its detection.

Binding of taxol to plastic and glass containers and protein under in vitro conditions

This study examined the stability and protein binding of taxol in aqueous solution and tissue culture medium. After storage for 19 h in 1% methanolic aqueous solution, the concentration of taxol declined to about 40% in 1.5 mL glass vials, 67% in 1.5 mL polypropylene tubes, and 55% in 1.5 mL siliconized polypropylene tubes. There was no difference in the decline at two initial concentrations of 0.18 and 1.8 micrograms/mL. The concentration declines were biphasic; the initial phase showed a half-life of 1-2 min and the second phase showed a half-life of 30-350 min. A methanol wash recovered 0%, 16%, and 31% of taxol from glass vials and unsiliconized and siliconized polypropylene tubes, respectively. In culture medium without fetal bovine serum, the concentration of taxol stored in polystyrene tissue culture plates declined to 73% after 24 h, whereas no concentration decline was observed in the presence of 9% fetal bovine serum (FBS). Protein binding of taxol in FBS-containing culture medium was saturable, varying from 79% at 0.5 microgram/mL to 20% at 15 micrograms/mL. These data indicated (a) rapid and nonspecific adsorption of taxol to plastic and glass surfaces, (b) stabilization of taxol in culture medium by FBS, and (c) saturable protein binding of taxol in culture medium.