Microbial Pharmaceuticals

MICROBIAL SPOILAGE OF PHARMACEUTICALS

Microbial spoilage:

nIt is defined as

“deterioration of pharmaceutical products by the contaminant microbe is called microbial spoilage.

nAn elegant & efficacious medicine which is both stable & acceptable by the patient may be contaminated & spoiled due to growth of microbes which can enter the product during its manufacture or during its use by the patient or medical staff. Such as using of creams ointments ,tooth pastes etc.

nSuch spoilage may cause financial problems to the manufacturer either as immediate loss of the product or increased cost of litigation that whether the spoilage will cause damage to the user.

Chemical & physicochemical deterioration of pharmaceuticals:

nMicroorganisms form a major part of the natural recycling process for biological matter in the environment.

nMixed natural communities are more effective biodeteriogens than the individual species alone & sequence of attack of complex substrates occur where initial attack by one group of microorganisms render them susceptible to further deterioration by secondary & subsequent microorganism.

nThe overall rate of deterioration of a chemical depends upon

nIts molecular structure.

nThe physicochemical properties of a particular environment.

nThe type & quantity of microbe present.

nWhether the metabolites produced can serve as source of usable energy & hence the creation of more microorganism.

nSome naturally occurring ingredients are particularly sensitive to microbial attack.

Pharmaceutical ingredients susceptible to microbial attack

1. Organic polymer

2. Surface active agent

3. Therapeutic agent

4. Humactant

5. Fats and oils

6. Sweetening agents

7. Preservative and disinfectant.

nOrganic polymers:

nMany of the thickening & suspending agents used in pharmaceutical formulations are subject to microbial depolymerization by specific classes of extracellular enzymes yielding nutritive fragments & monomers. These include amlyses( starches),pectinases( pectins) cellulses( carboxymethylcelluloses) dextranases( dextrans) & proteases( protein) . synthetic polymers are resistant but cellophane( modified cellulose) is susceptible under some humid conditions.

nSurface active agents:

nAnionic surfactant e.g. alkali metal & amine soaps of fatty acids are generally stable due to the slightly alkaline pH. Alkyl benzene sulphonates & sulphate esters are metabolized by omega oxidation.

nWith the increase in chain length & complexity of branching of alkyl chain degradation decreases.

nNon ionic surfactants such as alkyl phenol polyoxyethylene alcohol are attacked by microorganisms but more resistant as compared to alkyl polyoxyethylene alcohol.

nThe cationic surfactants used as antiseptics & preservatives in pharmaceutical applications usually only slowly degrade but pseudomonas have been found growing readily in quaternary amm. Aniseptic solution.

nTherapeutic agents:

nThrough spoilage, active drug constituents may be metabolized to less potent or chemically inactive forms.

nMaterials including alkaloids( morphine, strychnine, atropine) analgesics( aspirin, paracetamol) barbiturates, steroid esters & mandelic acid can be metabolized & serve as substrate for growth

ne.g. metabolism of atropine in eye drops by contaminating fungi.

n Inactivation of penicillin injections by beta lactamase producing bacteria.

nChloramphenicol deactivation in an oral medicine by a chloramphenicol acetylase producing contaminant.

n Microbial hydrolysis of aspirin in suspension by esterase producing bacteria.

nHumectants:

nLow molecular weight materials such as glycerol & sorbitol are included in some products to reduce water loss & may be readily metabolized unless present in high concentrations.

nFats & oils:

nThese hydrophobic materials are usually attacked extensively when dispersed in aq. Formulations such as O/W emulsions aided by high solubility of oxygen in many oils.

nFungal attacks has been reported in condensed moisture films on the surface of oils or where water droplets have contaminated the bulk oil phase.

nGlycerol & fatty acids liberated by the rupture of triglycerides undergo beta oxidation of alkyl chains & produce odiferous ketones.

nSweetening, flavoring & coloring agents:

nMany of the sugars & other sweetening agents used in pharmacy are ready substrates for microbial growth. But used in very high concentrations to reduce water activity in aq. Products & inhibit microbial attack.

nAt one time coloring agents ( tartrazine & amaranth) & flavoring agents( peppermint water) were kept as stock solution for extemporaneous dispensing exhibit support for the growth of pseudomonas spp. Including Ps. Aeruginosa.

nPreservative & disinfectant:

nMany preservative & disinfectants can be metabolized by a wide variety of gram negative bacteria but at concentration below their effective use levels.

nGrowth of pseudomonas in stock solution of quaternary amm. Antiseptics & chlorhexidine resulted in infections of patient. Pseudomonas spp. Have metabolized 4 hydroxy benzoate ester preservatives contained in eye drops & cause serious eye infection.

Observable effects of microbial attack on pharmaceutical products

nMicrobial contaminants usually need to attack formulation ingredient & create substrates necessary for biosynthesis & energy production before they replicate to levels where obvious spoilage becomes apparent.

nGrowth & attack may be localized in surface moisture films or very unevenly distributed within the bulk of the viscous formulations such as creams.

nUnpleasant smelling & tasting metabolites such as “sour” fatty acids, “fishy” amines, “bad eggs” bitter, earth or sticky taste or smell indicates the spoilage.

nProducts may become unappealingly discolored by microbial pigments of various shades.

nThickening & suspending agents e.g. tragacanth, acacia or CMC can be depolymerized resulting in loss of viscosity & sedimentation of suspended ingredients.

nMicrobial polymerization of sugars & surfactant molecules can produce shiny, viscous masses in syrups, shampoos & creams & fungal growth in creams has produced gritty textures.

nChanges in the pH of the product also occur depending on whether acidic or basic metabolized are released.

nMetabolism of surfactant in o/w emulsions reduce stability & accelerate creaming of the oil globules. Release of fatty acids lower pH & encourage coalescence of oil globules & cracking of emulsion

Factors affecting microbial spoilage of pharmaceutical products.

n1) Nutritional factors:

nThe simple nutritional requirements & metabolic adaptability of many common spoilage microorganisms enable them to utilize many formulation components as substrates for biosynthesis & growth.

nIn a formulation containing crude vegetable or animal products provide additional nutritious environment.

nEven demineralized water prepared by ion exchange method normally contain sufficient nutrients to allow growth of some pseudomonas spp.

nAcute pathogens require specific growth factors which are often absent in pharmaceutical formulations so they do not multiply but remain viable & infective for an appreciable time.

n2) moisture contents: water activity (Aw):

nMicroorganisms require readily accessible water in appreciable quantities for growth.

nBy measuring product’s water activity proportion of uncomplexed water that is available in the formulation to support microbial growth can be obtained by using the formulae:

nGreater the solute concentration the lower is the water activity. Water activity of aq. Formulations can be reduced by the addition of high concentration of sugars or PEG or by drying.

nCondensed water films can accumulate on the surface of dry products such as tablets or bulk oils due to storage in damp atmospheres resulting in fungal growth due to high localized Aw.

n3) Redox potential :

nmicrobial growth in an environment is influenced by its oxidation-reduction balance as they require compatible terminal electron acceptor for their respiratory pathways to function.

nThe redox potential in viscous emulsions may be high due to the appreciable solubility of oxygen in fats & oils.

nStorage temperature:

nSpoilage of pharmaceuticals could occur potentially over the range of –20c to 60c.

nReconstituted syrup & multidose eye drop packs are instructed to store at 8-12c to reduce the risk of growth inadvertently introduced during use.

nWater for injection should be held at 80c after distillation & before packing & sterilization to prevent possible growth of gram negative bacteria.

nPH:

nExtremes of pH prevent microbial attack. Above pH 8(e.g. with soap based emulsions) spoilage is rare. In products with low pH levels e.g. fruit juice flavored syrups with a pH 3-4 mould or yeast attack is more likely. Yeast can metabolize organic acids & raise the pH where secondary bacterial growth can occur.

nPackaging design:

nPackaging can have a major influence on microbial stability of some formulations in controlling the entry of contaminants during both storage & use.

nSelf sealing rubber wads must be used to prevent microbial entry into multidose injection containers.

nWide mouthed cream jars have now been replaced by narrow nozzles & flexible screw capped tubes.

nProtection of microorganisms within pharmaceutical products:

nThe survival of microorganism in particular environments is sometimes influenced by the presence of relatively inert materials. Thus microbes can be more resistant to heat or desiccation in the presence of polymers such as starch, acacia or gelatin.