Qualitative and Quantitative Evaluation of Multi-source Piroxicam Capsules Available in Nigeria

The qualitative and quantitative evaluation of eleven brands of piroxicam capsules marketed in Nigeria is presented. The disintegration time, dissolution rate and absolute drug content were determined in simulated intestinal fluid ( S F ) and simulated gastric fluid (SGF) without enzymes. Weight uniformity test was also performed according to official methods. Data obtained from the dissolution profiles in both media ( S F and SGF) were mathematically treated according to the model proposed by Khan (with slight modification) and the resulting predicted availability equivalent (PAE) was used to quantitatively assess1 predict bioavailability of piroxicam from the various brands. Our results indicate variable PAE with pH. In SGF, four out of the eleven (1 1) brands could be adjudged to be bioequivalent with the innovator drug, Feldene (Neimeth, Nigeria); In SIF, only three out of the eleven (1 1) were equivalent with the innovator drug. All the capsules (except one brand) generally disintegrated within 15 min. in both SIF and SGF. The weights were also very uniform with insignificant variations. However, the variation in absolute drug contents were generally wide, with all the capsules having drug contents that are above the label claim


Introduction
The influx of multisource (generic) drug products of various classes into the Nigerian market is increasing daily at an alarming rate.This calls for concern especially as it has been observed that the quality ofmedicines available in some less developed countries (including Nigeria) are poor in terms of level content of active ingredients (Taylor el al, 200 1 ; Shakour, el al, 1997;Kibwage el al, 1992).
Multisource piroxicam capsules abound in the Nigerian open market.Diverse brands from India, China, Malaysia, Belgium, Germany and others are actively competing with the innovator brand (FeldeneR, Pfizer) in terms of price.These brands are relatively cheaper than FeldeneR and as such economically appeal more to the generality of consumers.Even the innovator brand has about two variations with strikingly different prices.A current health concern therefore should be to ascertain the quality (in terms of content of active ingredients) and the potential therapeutic benefit in terms of bioavailability of these multisource piroxicam capsules marketed in Nigeria.
Multisource drug products must satisfy the standards of quality, efficacy and safety as those applicable to the innovator's product (Feldene").It is usually not enough to ascertain just the quantity ofactive constituent (label claim) of the product.This is because biopharinaceutical studies have shown that bioavailability, and hence therapeutic efficacy of most drugs are significantly affected by formulation factors such as binder type or concentration and1 or method of incorporating (intra-and or extra granularly), lubricant type and concentration, particle size of active components, etc (Babalola et al, 2001a;2001 b;Proudfoot, 1988;Jones et al, 1988).Since these factors vary significantly from one manufacturing firm to another, the possibility of differential bioavailability of drugs from similar dosage forms produced by different companies is very high.Using either in vitro or in vivo designs, several workers in Nigeria have demonstrated differential (variable) release and bioavailability of various drugs from multi-source (generic) dosage forms   al, 2000).
Ideally, bioavailability studies should be carried out in vivo.However, econon~ic and ethical reasons demand alternative in vilro methods since in many developing countries (like Nigeria), in vivo bioavailabilityl bioequivalence testing remains an impracticably costly proposition (Olaniyi,200 1).Therefore, in vitro drug availability methods that could predict in vivo availability of suitable drugs are becoming very popular.One of such tests, based on the conventional dissolution studies, has been successfully used by Ofoefule el a1 to predict the in vivo bioavailability of some commercially available brands ofperfloxacin and ciprofloxacin marketed in Nigeria (Ofoefule el 01, 200 1 ; Ofoefule el al, 2000).
The current study attempts to investigate the quality of 1 1 brands of piroxicam marketed in Nigeria vis-ir-vis pharmacopoeia1 'requirements for content uniformity, weight uniformity, disintegration time and by es-timating their possible in vivo availability using a modification of the concept of dissolution efficiency proposed by Khan (1975).

Materials:
Drug san~ples-: Reference sample of piroxicam powder was kindly supplied by Pfizer Nigeria, Plc (now Neimeth Nig, Plc).

Clrertr i d s :
Concentrated hydrochloric acid (BDH), and methanol (Mallinckrodt) were purchased locally from chemical stores in Nsukka.

Methods: Preparation of dissolutiorr Media:
Simulated gastric fluid (SGF) without enzymes was prepared by adding 42.4 ml of concentrated HCl (36.5%) to 2.0 litres of portable water; log of NaCl was added to this solution and mixed until complete dissolution occurs.The solution was then made up to 5.0 litres with portable water.
Simulated intestinal fluid (SIF), without enzymes was prepared by dissolving40g of sodium hydroxide and 34 of monobasic potassium phosphate in 2.0 litres of portable water.The solution was made up to 5 litres with portable water.

Weight Uniform ity Test:
Ten capsules were randomly selected from each brand.The intact capsules were opened one after the other and the entire content weighed, making sure that no powder is lost.The mean weight of the capsules and standard deviations in weight was computed.

Disirrtegratiort Tinre Test.
The BP (2001) method was adopted using the Erweka disintegration apparatus.Simulated gastric fluid (SGF) or simulated intestinal fluid (SIF) was used as disintegration medium.The temperature of the apparatus was maintained at 37OC + 1°C).One capsule from each brand was placed in 500 ml of either SIF or SGF and the motor switched on.The time taken for the capsule to disintegrate, such that no residue (except fragments of the capsule) remained on the screen, was monitored with a stopwatch.The experiment was repeated twice and the mean time taken.'The BP (2001) method was similarly adopted using the Erweka Dissolution Unit with in-built paddle and thermostated electric water that was set to regulate the temperature of the dissolution medium at 37'C + 1°C.

Dissoliitiorl Rate of Capsdes
A 500 ml quantity of freshly prepared dissolution medium (SGF or S F ) was equilibrated to a temperature of 37+1°C.From each brand, one capsule was randomly selected and put into the dissolution medium.At various time intervals ranging between 5-120 min, lml of solution was withdrawn from dissolution media and replaced with equivalent quantity of fresh media.The withdrawn sample was filtered, and the filtrate diluted with 9 ml of methanolic HC1 (made from0.77ml of conc.HC1 to 250 ml of methanol to form 0.1N solution HC1 in methanol).The absorbance of the resulting solution was measured at 242 nm, against a blank methanolic hydrochloride solution.The concentration of piroxicam was estimated mathematically from the Beer-Lambert's plot.

Beer-Lambert ' s plot:
Varying concentrations of the reference sample of piroxicam ranging from 0.003 1 -0.1 mg% in methanolic hydrochloride were prepared and their absorbances at 242nm determined.
A graph of absorbance versus concentration of piroxicam was plotted and represented as standard Beer-Lambert's plot for piroxicam in methanolic hydrochloride.The AUC is estimated mathematically using either Simpson s or trapezoid rule.Differences in PAE of the various brands were ascertained by subjecting the data to statistical analysis (student' t test at 5% level of significance

Results and Discussion
All the brands had fairly uniform weights, with % standard deviation generally very much less than 10%.According to the Europian Pharmacopoeia (2000) specification, capsules with weight deviation less than 10 % have passed the weight uniformity test., 2001).All the capsules therefore passed the disintegration test i both media.However, leis time (faster disintegration) was observed in SGF was observed in SGF The area under the dissolution -tjme curve was computed mathematically from dissolutio profile (release rates) of piroxicam from the various brands of piroxicam in SGF and SIF and use. to estimate the prediclcd availability Equivalence (PAE) according to the relationship:

P . O . O S A D E B E & C . O . E S I M O N E
The PAE values of the various brands in SIF and SGJ? are presented in table-3.PAE values were generally higher in SGF than in S F .The PAE of Saldin 20, Diovin 20, Smwin and Neoxicam were not significantly different from that of the innovator drug FeldeneK (Neinlmeth, Nigeria Plc) and so were judged to be bioequivalent with FeldeneRl,In SIF, the PAE of the Saldin 20, Pixicam and Neoxicam were similarly judged to be bioequivalent with FeldeneR, based on the abovementioned criteria.
The absolute drug content is presented in table 4. Amongst the various brands, drug content varied in the two media (SIF and SGF).In SGF, all the capsules contained piroxicam above the label claim at levels above the acceptable compendial standard.In S F , only Felxicam, Diovin, Felvin, Pixicam, Saldin, Piroxy and Feldene, contained piroxicam within the range of the label claim.Our findings have revealed that multi-source piroxicam capsules marketed in Nigeria have varying Predicted Availability Equivalence (PAE) and content of the active ingredient.The label claim of all the samples of piroxicqm used for this study is 20 mg per capsule.However, the assayed quantity of the active drug for most of the products was very much higher than the label claim.Therefore, most of the products were substandard because of the higher quantity of the active drug far above the acceptable compendial standards.This finding is in consonance with those of many studies carried out with various drugs marketed in the developing countries (Taylor et al, 2001; Shakour el al, 1997; Kibwage et al, 1992).
The wide variation in the content uniformity of these studied brands of piroxicam might not be deliberate, but may rather be a reflection of the poor quality control and quality assurance during manufacture (Taylor et ul, 200 1).
The fact that manufacturing ,procedures and formulation excipients significantly affect biopharmaceutic properties of drug formulations is well established (Babalola, 2001; Proudfoot,  1988;Jones et al, 1988; Ofoefule et al, 200 1; Ofoefule et al, 2001; Olaniyi, 200 1).This is principally the reason for stringent evaluation of multi-source preparations in terms of their comparative dissolution efficiency.
The PAE used in our study can be theoretically related to the in vivo data because it is based on the assumption that the degree of absorption of a drug in vivo is proportional to the concentration of the drug in solution and the time this solution in contact with a suitable absorption region in the gastro-intestinal tract GiT (Khan, 1975).In in vitro dissolution studies, this could be represented as the area under the dissolution-time eurve.
Our results show that PAE values between 89-1 10% were not significantly different (P<0.05)l'rom that of the innovator drug (FeldeneK).Therefore, only Saldin 20, Diovin 20, Sanwin 20 pixicam and Neoxicam were judged to equivalent with FeldeneR in SGF while only Saldin 20, pixicam and Neoxicam were equivalent in S F .Predictably, dissolution media (and hence pH) affects drug release and hence bioavailability.Piroxicam is rapidly absorbed in the stomach (Pagan et ul, 1995) and so their likely in vitro availability will follow the release profile of the drug formulations in SGF.It Sollows therefore that only Saldin 20, Diovin 20, Sanwin and Neoxicam are really bioequivalent with h e innovator drug based on their statistically similar DAE values.Of these four brands, however, only Neoxicam has statistically similar absolute drug content with the innovator brand and hence complied with desirable compendial standard.The other brands have absolute drug content far above the compendial limits.
Although ilr vitro studies are not alternatives for in vivo studies, they do serve as cheap and rapid leads in the quality control of multi-source drugs (Ofoefule el al, 2001; Olaniyi, 2001).Very clearly therefore, many of the brands of piroxicam marketed in Nigeria may not strictly be switchable (substitutable) with the innovator drug.They may accomplish the therapeutic goal, but could also 1.csu1t in high-level toxicity (because of the higher concentration of the active constituents).
T h e observed non-compliance with pharmacopoeia1 standards ofmany brands of Piroxicam capsules marketed in Nigeria calls for caution in the prescription and in dispensing of these supposed i~lternatives.Since many of the piroxicam brands contain excess of the active ingredient above the compendial standards, they could actually relieve pain but the potential gastrointestinal risk might be quite high and dangerous.Most of these problematic products are usually brought into the country by unauthorized importers We advocate a multicentre study that will screen all the brands of piroxicam in the Nigerian market \\iith the view of listing suitable and unsuitable brands.
A modification of the concept of dissolution efficiency was employed to analyze the dissolution rate data.Conventionally, dissolution efficiency, DE is given by, DE = AUC at time x AUC over the entire time course of release where DE = dissolution efficiency AUC = Area under the release (dissolution) time curve.However, this concept has been slightly modified and Predicted availability equivalent(PAE) is more appropriately used and is given by, DEX = AUC of brand X AUC over the entire time curve DE'.' = AUC of innovator brand AUC over the entire time curve P A E = ~ = A U C O ~X DE'.' AUC of innovator brand

Table 1 :
Weight unifprmity of multi-sourced Piroxicam capsules marketed in Nigeria Brand

Table 2 :
Disintegration time of capsules in SIF and SGF The disintegration time of capsules in S F and SGF is shown in table 2. Officially, they are require to disintep-ate within 30 min (B.P.

Table 4 :
Absolute Content of Multi-sourced Piroxicam Capsules Marketed in Nigeria