Isadore Kanfer

Analysis of macrolide antibiotics

The following macrolide antibiotics have been covered in this review: erythromycin and its related substances, azithromycin, clarithromycin, dirithromycin, roxithromycin, flurithromycin, josamycin, rokitamycin, kitasamycin, mycinamycin, mirosamycin, oleandomycin, rosaramicin, spiramycin and tylosin. The application of various thin-layer chromatography, paper chromatography, gas chromatography, high-performance liquid chromatography and capillary zone electrophoresis procedures for their analysis are described. These techniques have been applied to the separation and quantitative analysis of the macrolides in fermentation media, purity assessment of raw materials, assay of pharmaceutical dosage forms and the measurement of clinically useful macrolide antibiotics in biological samples such as blood, plasma, serum, urine and tissues. Data relating to the chromatographic behaviour of some macrolide antibiotics as well as the various detection methods used, such as bioautography, UV spectrophotometry, fluorometry, electrochemical detection, chemiluminescence and mass spectrometry techniques are also included.

Impact of African herbal medicines on antiretroviral metabolism

We examined the effects of two African herbal medicines recommended for HIV/AIDS patients on antiretroviral metabolism. Extracts from Hypoxis and Sutherlandia showed significant effects on cytochrome P450 3A4 metabolism and activated the pregnane X receptor approximately twofold. P-glycoprotein expression was inhibited, with Hypoxis showing 42–51% and Sutherlandia showing 19–31% of activity compared with verapamil. Initiating policies to provide herbal medicines with antiretroviral agents may put patients at risk of treatment failure, viral resistance or drug toxicity.

Pharmacokinetics of Oral Decongestants

Only three drugs are commonly used as oral decongestants—phenylpropanolamine (PPA), pseudoephedrine (PDE), and phenylephrine (PE). They are all chiral drugs that exist as stereoisomers. It is possible that each enantiomer can reflect significant enantioselective differences with regard to both pharmacokinetic and pharmacodynamic effects. Both PPA and PDE are readily and completely absorbed, whereas PE, with a bioavailability of only approximately 38%, is subject to gut wall metabolism and is thought to be absorbed erratically. Peak concentrations are reached between 0.5 and 2 hours after administration. All three drugs are extensively distributed into extravascular sites (apparent volume of distribution between 2.6 and 5.0 L/kg). No protein‐binding data in humans are available. Whereas PPA and PDE are not substantially metabolized, PE undergoes extensive biotransformation in the gut wall and the liver. Elimination of PPA and PDE is predominately renal, with urinary excretion being pH dependent. Half‐lives are relatively short, approximately 2.5 hours for PE, 4 hours for PPA, and 6 hours for PDE. Elimination of PPA and PDE may be rapid in children, and the agents should be used with caution in patients with renal impairment. In addition, PPA increases caffeine plasma levels and decreases theophylline clearance. Reduced metabolism of PE occurs with concurrent administration of monoamine oxidase inhibitors. No direct relationship between nasal decongestant effect and plasma concentration has been established.

The challenges of involving traditional healers in HIV/AIDS care

In sub-Saharan Africa, traditional healers play a major role in providing for the needs of people, particularly in rural areas where western health care is unavailable. Despite a paucity of reliable figures to determine the prevalence of traditional medicine usage, it is estimated that some 70% of sub-Saharan Africans access traditional healers. There is now mounting evidence of the importance of involving traditional healers in the management of the HIV/AIDS epidemic – both for their potential benefits, although poorly researched and understood, and to reduce the impact that some traditional healing interventions may play on the spread of HIV/AIDS and unsafe treatment of infected patients. While there are few collaborative projects between traditional healers and biomedical health providers, there is an enthusiasm on the part of traditional healers to collaborate and learn from their western-trained counterparts. Collaboration is essential, given the changing epidemic of HIV and the dynamic relationship between the two health sectors.

Application of dermal microdialysis for the evaluation of bioequivalence of a ketoprofen topical gel

The purpose was to investigate dermal microdialysis (DMD) for the assessment of the bioavailability of a ketoprofen topical gel formulation and to evaluate this technique as a tool for the determination of bioequivalence. Four microdialysis probes were inserted into the dermis on the volar aspect of the forearms of 18 human subjects and the probes were perfused with normal saline for 60 min. A ketoprofen (2.5%, m/m) gel formulation (50mg) was applied to the skin directly overlying the probes and samples were collected at 30 min intervals for 5h. With the probes still in place in the dermis each site was scanned by ultrasound to determine the implantation depth of these probes. Ketoprofen concentration in dialysates was determined by LC-MS/MS. The area under the curve obtained from the concentration-time profiles from pairs of application sites in each subject was evaluated in order to assess bioequivalence. Ninety percent confidence intervals were calculated using the two one-sided test procedure and limits of 80-125% based on log-transformed data were used as acceptance criteria to declare bioequivalence. The intra-subject variability was 10% between probes whereas inter-subject variability was 68% (n=18). Bioequivalence was confirmed with a power greater than 90%.

Evaluation of the proposed FDA pilot dose-response methodology for topical corticosteroid bioequivalence testing

AbstractPurpose. The American FDA has recently released a Guidance document for topical corticosteroid bioequivalence testing. The purpose of this study was to evaluate the recommendations of this document for appropriateness. The new specifications require a dose-vasoconstriction response estimation by the use of a Minolta chromameter in a preliminary pilot study to determine the parameters for use in a pivotal bioequivalence study. Methods. The visually-assessed human skin blanching assay methodology routinely practiced in our laboratories was modified to comply with the requirements of the pilot study so that visual and chromameter data could be compared. Two different cream formulations, each containing 0.12% betamethasone 17-valerate, were used for this comparison. Results. Visual data showed the expected rank order of AUC values for most dose durations whereas the chromameter data did not show similar results. The expected rank order of AUC values for both chromameter and visual data was not observed at very short dose durations. In fitting the data to pharmacodynamic models, equivalent goodness of fit criteria were obtained when several different parameter estimates were used in the model definition, however the visual data were best described by the sigmoid Emax model while the chromameter data were best described by the simple Emax model. Conclusions. The Emax values predicted by the models were close to the observed values for both data sets and, in addition, excellent correlation between the AUC values and the maximum blanching response (Rmax) (r > 0.95) was noted for both methods of assessment. The chromameter ED50 values determined in this study were approximately 2 hours for both preparations. At this dose duration the instrument would not be sensitive enough to distinguish between weak blanching responses and normal skin for bioequivalence assessment purposes.

Potential pharmacokinetic interactions between antiretrovirals and medicinal plants used as complementary and African traditional medicines

The use of traditional/complementary/alternate medicines (TCAMs) in HIV/AIDS patients who reside in Southern Africa is quite common. Those who use TCAMs in addition to antiretroviral (ARV) treatment may be at risk of experiencing clinically significant pharmacokinetic (PK) interactions, particularly between the TCAMs and the protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Mechanisms of PK interactions include alterations to the normal functioning of drug efflux transporters, such as P-gp and/or CYP isoenzymes, such a CYP3A4 that mediate the absorption and elimination of drugs in the small intestine and liver. Specific mechanisms include inhibition and activation of these proteins and induction via the pregnane X receptor (PXR). Several clinical studies and case reports involving ARV-herb PK interactions have been reported. St Johns Wort, Garlic and Cats Claw exhibited potentially significant interactions, each with a PI or NNRTI. The potential for these herbs to induce PK interactions with drugs was first identified in reports of in vitro studies. Other in vitro studies have shown that several African traditional medicinal (ATM) plants and extracts may also demonstrate PK interactions with ARVs, through effects on CYP3A4, P-gp and PXR. The most complex effects were exhibited by Hypoxis hemerocallidea, Sutherlandia frutescens, Cyphostemma hildebrandtii, Acacia nilotica, Agauria salicifolia and Elaeodendron buchananii. Despite a high incidence of HIV/AIDs in the African region, only one clinical study, between efavirenz and Hypoxis hemerocallidea has been conducted. However, several issues/concerns still remain to be addressed and thus more studies on ATMs are warranted in order for more meaningful data to be generated and the true potential for such interactions to be determined.

Rapid UPLC–MS/MS method for the determination of ketoprofen in human dermal microdialysis samples

Dermal microdialysis (DMD) is a technique capable of determining the percutaneous penetration of drugs from topical formulations intended for local and/or regional activity. Typically, the concentrations of drug collected in dialysates are very low, generally in the ng/ml or even pg/ml range. An additional challenge is the very low volume of sample collected at each collection time and which can range from 1 to 30 microl only. Hence the objective was to develop and validate a rapid, accurate, precise, reproducible and highly sensitive LC-MS/MS method for the quantitative analysis of ketoprofen (KET) in dialystes following application of a topical gel product to the skin of human subjects. UPLC-MS/MS was used and KET was separated on an Acquity UPLC BEH C(18) column (100 mm x 2.1 mm i.d., 1.7 microm) and analysed in negative-ion (NI) electrospray ionisation (ESI) mode. The mobile phase (MP) consisted of acetonitrile:methanol:water (60:20:20, v/v/v) under isocratic conditions at a flow rate of 0.3 ml/min. Samples were extracted using ethyl acetate with ibuprofen (IBU) as internal standard (IS) and the organic solvent was then evaporated to dryness and the residue re-constituted in methanol. 5 microl samples were injected and analysis was performed at ambient temperature 22+/-0.5 degrees C. KET and IBU eluted at 1.07 and 1.49 min, respectively. KET and IBU responses were optimised at the transitions 253.00>209.00 and 205.00>161.00, respectively. Calibration curves were linear over the range 0.5-500 ng/ml with correlation coefficients>0.999. The accuracy and precision of the method were found to be between 99.97% and 104.67% (R.S.D.<2%) and the mean recovery of KET from normal saline was 88.03+/-0.3% (R.S.D.<2.20%). The LLOQ and LOD values were found to be 0.5 and 0.1 ng/ml respectively whereas the ULOD was set at 500 ng/ml. The method was successfully applied to determine the bioavailability of KET following application of topical KET gel, Fastum gel, to the skin of human volunteers.

Effect of Compressibility and Powder Flow Properties on Tablet Weight Variation

A powder flowmeter has been designed to provide both quantitative and qualitative data relating to powder flowability. Three directly compressible powders, Emdex, Emcompress and magnesium oxide as well as a three component powder mixture was assessed for flowability, angle of repose and particle size. Compressibility indices were determined for all the above materials as well as for the fractions of each which consisted of a particle size below 315 μm. Sieve analysis was performed on the above powders in order to establish groups consisting of cohesive, mildly cohesive and non-cohesive fractions and their respective flow-time profiles were subsequently determined. Scanning electron microscopic analysis was performed to obtain information on the particle size, shape and size distribution. The interrelationships between flow rate, angle of repose, compressibility index and coefficient of tablet weight variation were established using both a single punch and a high-speed rotary tabletting machine.A three-dim...

Simultaneous determination of trimethoprim, sulphamethoxazole and N4-acetylsulphamethoxazole in serum and urine by high-performance liquid chromatography

The simultaneous determination of trimethoprim, sulphamethoxazole and N4-acetyl-sulphamethoxazole in serum and urine by high-performance liquid chromatography using sulphafurazole as internal standard is described. The separation was achieved on a reversed-phase column employing acetic acid-methanol as the mobile phase with spectrophotometric detection at 230 nm. Precise simultaneous quantitative analysis of the relative components has been achieved at levels of 0.1 microgram/ml for trimethoprim and 1.0 microgram/ml for both sulphamethoxazole and its N4-acetyl metabolite using 1 ml of serum of urine.