R. L. Jayakody

Absence of effect of calcium antagonists on endothelium-dependent relaxation in rabbit aorta.

1 The effect of chronic feeding of New Zealand White rabbits with nicardipine (60 mg kg−1 daily for 5 weeks) on the endothelium‐dependent relaxation (EDR) to acetylcholine (ACh) was examined in vitro. The effect of acute exposure to nicardipine and diltiazem (10 μmol l−1) in the tissue bath was also examined. 2 A bioassay system for endothelium‐dependent relaxation factor (EDRF) in which a rabbit aortic ring with endothelium removed was used as recipient and a segment of rabbit aorta with endothelium as donor (producing EDRF in response to ACh) was developed. This system enabled the effect of nicardipine on the synthesis/release and on the relaxation to EDRF to be studied separately. 3 The maximum relaxations to ACh in control and nicardipine‐fed animals were 43.6 ± 5.5 and 53.8 ± 6.7% (mean ± s.e.mean) of the contractile response to noradrenaline (NA, 1 μmol l−1) (n = 6, P > 0.05). Similarly the EDR to ACh was not significantly altered by acute exposure (30 min) to nicardipine or diltiazem. The maximum relaxations without and with nicardipine were 32.4 ± 4.2% and 28.0 ± 3.1% of the contraction to NA (1 μmol l−1) (n = 11, P > 0.05). The corresponding data for diltiazem were 42.1 ± 5.7 and 36.4 ± 7.3% respectively (n = 11, P > 0.05). 4 Both calcium antagonists inhibited the contraction induced by potassium (100 mmol l−1). Nicardipine and diltiazem in concentrations of 100 μmol l−1 reduced the potassium‐induced contraction to 33.0 ± 9.0% and 53.8 ± 6.7% of control respectively (n = 6, P < 0.05). 5 In the bioassay experiments the infusion of nicardipine on (a) the recipient tissue only and (b) the donor and the recipient tissue had no significant effect on the relaxant response observed in the recipient tissue when superfused with Krebs‐bicarbonate buffer containing ACh via the donor tissue (n = 6, P > 0.05). 6 These results indicate that nicardipine and diltiazem had no significant effect on synthesis/release and the relaxant response to EDRF in the rabbit aorta. Thus the translocation of Ca2+ accompanying the EDR to ACh in the rabbit aorta is likely to utilize Ca2+ channels not blocked by these calcium antagonists.

Prevalence and predictors of self-medication in a selected urban and rural district of Sri Lanka

Background: Self-medication is widely practised in many developing countries. The determinants of self-medication need to be understood to design adequate medicine information policies and patient-dispenser education strategies. Hence, the prevalence of medicine use and predictors of self-medication were determined in Sri Lanka. Methods: In a community-based cross- sectional study, data were collected from 1800 adults selected from Gampaha and Polonnaruwa districts respectively. Study participants were sampled using a multistage cluster sampling technique. Trained public health midwives administered the questionnaire. Two Likert scales provided information on access to medical care and satisfaction with available pharmacy services. About 95% of the sampled population participated in the study. Results: Overall, prevalence of medication use (allopathic, traditional, home remedies) in urban and rural population was 33.9% and 35.3%, respectively. Self-medication prevalence of allopathic drugs in the urban sector (12.2%) was significantly higher than in the rural (7.9%) sector(p<0.05). In the urban sector, small household size and preference to have medicines from outside the pharmacies predisposed to self-medication. The higher acceptability of medical services and regularity of medical care decreased the likelihood of self-medication. In the rural sector, lower satisfaction about the healthcare providers’ concern for clients, lower satisfaction about affordability of medical care and higher satisfaction with technical competence of the pharmacy staff increased the likelihood of self-medication. In both urban and rural sectors, when symptom count increased, tendency to self-medicate decreased. Conclusions: Self-medication prevalence was higher in urban compared to rural areas in Sri Lanka. Some aspects of access to medical care, satisfaction with pharmacy services and perceived severity of the disease were found to be important determinants of self-medication.

Effect of calcium antagonists on adrenergic mechanisms in canine saphenous veins.

Experiments were designed to investigate the effect of two calcium antagonists, diltiazem and nicardipine (concentration range: 10(‐7)‐10(‐4) M), on the contractile responses to transmural nerve stimulation, exogenous noradrenaline and tyramine in isolated canine saphenous vein rings. Both diltiazem and nicardipine inhibited the contractile response to transmural nerve stimulation in a non‐competitive, concentration‐dependent manner. At a concentration of 10(‐4) M, diltiazem and nicardipine inhibited the maximum contractile response to transmural nerve stimulation to 0.8 +/‐ 0.8% and 20 +/‐ 10% of control respectively. Effects of diltiazem and nicardipine (up to 10(‐4)M) on the contractile response to exogenous noradrenaline were minimal. The only significant difference observed was a 30% depression of the maximum contractile response with a shift in ED50 at high concentrations of nicardipine. Diltiazem (up to 10(‐4) M) had no significant effect on concentration‐effect curves for tyramine. Nicardipine inhibited the response to tyramine in a non‐competitive manner with the maximum response depressed to 46% of control at 10(‐4) M‐nicardipine. Release of [3H]noradrenaline during transmural nerve stimulation was reduced by both calcium antagonists in a concentration‐dependent manner. However, release of [3H]noradrenaline produced by the indirect sympathomimetic agent tyramine was not significantly inhibited by nicardipine. These experiments suggest that the calcium antagonists diltiazem and nicardipine inhibit the contractile response to transmural nerve stimulation in the canine saphenous vein predominantly by inhibiting the release of endogenous noradrenaline. However, nicardipine appears to have an additional post‐synaptic inhibitory effect on the responses to exogenous as well as endogenous noradrenaline.

Genetic variants in the cytochrome P450 2D6 gene in the Sri Lankan population

INTRODUCTION: Cytochrome P450 2D6 (CYP2D6) enzymes are involved in the metabolism of a large number of commonly prescribed drugs such as antidepressants and cardiovascular drugs. The CYP2D6 *3, *4 and *14 variants associated with the loss of enzyme function; CYP2D6 *10 and *17 variants with reduced enzyme function; and CYP2D6 *2 variant with no effect on enzyme function. Establishing the frequency of these variant alleles in Sri Lankan population would be useful for optimizing pharmacotherapy with CYP2D6-substrate drugs. OBJECTIVE: The objective of this study was to determine the prevalence of CYP2D6 *2, *3, *4, *10, *14 and *17 variants in the main ethnic groups in the Sri Lankan population. MATERIALS AND METHODS: A total of 90 deoxyribonucleic acid (DNA) samples (30 each from Sinhalese, Tamils and Moors) were selected from a DNA resource at the Human Genetic Unit, Faculty of Medicine, University of Colombo. This collection had been made for population genetic studies from a random population based volunteers. Genotyping was performed using published polymerase chain reaction/restriction fragment length polymorphism methods. RESULTS: The prevalence of the CYP2D6 variants in Sinhalese, Sri Lankan Tamils and Moors respectively were CYP2D6 *2: 37%, 41.6% and 37.9%; CYP2D6 *3: 60.3%, 45% and 30%; CYP2D6 *4: 21.6%, 6.6% and 8.3%; CYP2D6 *10: 40%, 35% and 44%. CYP2D6 *14 and *17 variants were not identified. CONCLUSION: CYP2D6*3, *4 and *10 variants, which are associated with reduced or loss of CYP2D6 enzyme function were found in our population in significant frequencies. CYP2D6*4, which is reported to be a Caucasian variant was also found in all three ethnic groups.

Determination of in-vitro Equivalence of Paracetamol Tablets

Bioequivalence studies are the usually accepted method to determine the therapeutic equivalence of two drug products. Because in-vivo bioequivalence studies are time consuming and expensive to conduct, major regulatory authorities have introduced biowaivers for some selected medicines belonging to BCS class 1 and III drugs. Comparative dissolution tests are used in biowaiver procedure to waiver the bioequivalence requirement. We performed this study to see whether two brands of paracetamol tablets are bioequivalent using the in-vitro methodology. In the first stage of this research study, British Pharmacopeia 2012 quality tests were performed on the two selected paracetamol tablet products to determine whether they are pharmaceutically equivalent. In the second stage in-vitro equivalence of the two products was determined using the biowaiver testing procedure given by the World Health Organization. Dissolution profiles were generated at pH values, 1.2, 4.5 and 6.8. Results were compared through two model independent methods, difference factor (f1) and similarity factor (f2). The two paracetamol tablet products tested, complied with all the quality requirements of the British Pharmacopeia 2012. For the two products, the difference factor (f1) was below the 15 and similarity factor (f2) was above the 50 in all dissolution test conditions. These results confirm that the two products are pharmaceutically equivalent. The test product is also bioequivalent to the reference product in-vitro, and therefore they can be interchangeable during clinical use. This study shows that in-vivo bioequivalence testing can be waived using the in-vitro method, for some pharmaceutical products such as paracetamol tablets.

Regulatory requirements for the registration of generic medicines and format of drug dossiers: procedures in Sri Lanka in comparison with selected regulatory authorities

BackgroundThe regulatory requirements for approval of generic medicines and the format of compiling drug dossiers vary among regulatory authorities. The variation is particularly wide between High-income countries (HIC) and lower and middle-income countries (LMIC) with different regulatory frameworks. In this study, document requirements for approval of generic products, approval timelines, and consideration of bioequivalence and/or biowaiver data by Regulatory Authorities (RAs) of 10 selected jurisdictions was studied.MethodsThe guidelines and procedures from 5 purposively chosen RA of HIC and4 regional RAs relevant for Sri Lanka were compared with the Sri Lankan National Medicines Regulatory Authority (NMRA). Information available in the official websites of the selected RAs, published journal articles and via personal communication was collected in2016. Drug approval timelines achieved in Sri Lanka was obtained from data available from another study.ResultsCommon technical dossier (CTD) format of the International Council on Harmonization (ICH) for registration of pharmaceuticals (ICH:CTD) or the Association of South East Asian Nations (ASEAN) CTD format (ACTD) was used by all RAs studied except Sri Lanka which use its own dossier format. Nine out of ten RAs studied request BE data or justification for not submitting BE data for generic medicines. Sri Lanka requested BE studies only for antimicrobials, antiepileptic drugs and narrow therapeutic index drugs. Biowaivers are allowed for Biopharmaceutics Classification System (BCS)-based Class 1drugs in Singapore and India. USA, EMA, Canada and South Korea allowed biowaiver for BCS Class1and Class 3drugs but Sri Lanka does not accept BW at present. Nine NMRAs out of the ten studied reported legislated timelines for approval of generic pharmaceuticals except Sri Lanka.ConclusionsStreamlining the drug regulatory systems in LMIC such as Sri Lanka with that of HIC would facilitate an effective drug regulatory system based on reliance on decisions made by stringent regulatory authorities. Findings of this study encourage Sri Lanka to adopt a CTD format for regulatory submission of drug dossiers. Expanding the BE requirement drug list and accepting BCS-based biowaivers for BSC class 1 and 3 drugs during registration of generic drugs when it is scientifically justified is also recommended for Sri Lanka.

Endothelium Dependent Relaxation and Atherosclerosis

In 1980, Furchgott & Zawadzki demonstrated that the endothelium of the rabbit aorta releases a factor(s) with vasodilator properties in response to acetylcholine (1). This discovery helped to explain two phenomena that had remained pharmacological “paradoxes” — (i) the potent contractile effect of acetylcholine on non-vascular smooth muscle and the concurrent vasodilator action in-vivo on most peripheral vascular beds and (ii) the inability of acetylcholine to relax isolated preparations of blood vessels in-vitro. Furchgott’s group showed that the lack of relaxation to acetylcholine in helical strips of rabbit aorta (which was the standard in-vitro preparation at the time) was the result of unintentional removal of the endothelium during mounting. It was found that with care taken to avoid damage to the intima, any in-vitro preparation (whether a helical strip, a ring or a transverse strip) always relaxed to acetylcholine. Conversely, intentional removal of the intima always resulted in the loss of the relaxatory response of the preparation to acetylcholine.