natural pdt, quality Flashcards
why is cocaine classified as an alkaloid
1 nitrogen atom in an amine ring structure
due to the N found in the ring structure
pdts from cocaine hydrolysis
Basic conditions. Hydrolyse ester linkages
Form benzoic acid + methanol + ecgonine
Soxhlet extraction of cocaine
- Leaves packed into extraction thimble
- Solvent evaporates and condenses into the thimble
i. Type of solvent used: use diff volatility, polarity
* methanol— ethanol — chloroform – hexane
ii. Thimble here also acts like a filter (Very porous) - Solvent extracts the cocaine and drip into solvent flask
i. Continuous process - ROTATORY EVAPORATION obtains crude cocaine
i. Under vacuum to pull out solvent. Residue is component (cocaine) - Recrystallization to obtain pure cocaine
* Test residual in diff acids –> HPLC (purification)
* Qualify/ identify and quantify compounds found
coca plant consists of
Majority (40-50%) is cocaine
Tropacocaine, cinnamoylcocaine, methylecognine
analgesic property of cocaine is due to ___
- Rapidly absorbed by mucus mem (due to lipophilic grps, promote mem PERMEATION pka 8.6) – most are unionised
a. Local anesthetic effect
b. Can be used topical application - Paralyse sensory ends of nerves + block Na ion channels in neuromem
a. Protonated cocaine is able to inhibit the Na+ channel intracellularly
essential functional grps for cocaine MOA analgeisc
i. Aromatic carboxylic acid ester
ii. Basic amino grp
iii. Lipophilic hydrocarbon ring
SE of cocaine
○ Allergic reactions
○ addiction, withdrawal sx
§ euphoric property (leads to dependence and withdrawal)
○ Tissue irritation
○ Poor stability in aq sol.
Structural modifications (improve analgesic/ decr SE) of cocaine
1) Benzoyltropine/ Tropacaine = REMOVAL of carboxymethyl COOCH3 ester grp (position 2)
* less addictive SE, good anesthetic property, but low solubility
benzocaine discovery
2) Benzocaine = simplified ester grp at position 3 + Add -NH2 grp para position of benzene
* lower solubility, less therapeutic effect
*intramolecular H bond, pKa 2.8 (weak acid)
procaine discovery
3) procaine = replace position 3 ETHYL –> 3* amine
* improve solubility (when 3* protonated)
* retain therapeutic effect, less toxic SE (systemic & local)
* shorter DOA, hydrolysed
discovery of isogramine
cocaine –> isogramine
- Fused heterocycle
- Tropine (N cycle) –> dimethyl amine (3*)
discovery of lidocaine
- Open heterocylce, add in O
- Forms amide functional grp next to phenyl ring
□ Improves stability (less likely to be hydrolysed)
□ Dimethyl (CH2 CH3) structure also acts as steric hindrance to block H2O access for hydrolysis - Good local anesthetic, less allergenic
why amide linkage improve stability
- less likely to be hydrolysed (double bond, compared to ester)
- less likely to be hydrolysed due to dimethyl grps, steric hindrance
- better solubility (lp on N delocalise into O, forms resonance structure which is charged)
3 Activity of drugs based on intermediate chain:
- Ester = local anesthetic
- Amide = local anesthetic
○ Longer DOA (more stable, harder to hydrolyse) - Amino ETHER, KETONE = rare
3 parts of SAR for cocaine-derived local anesthetics
1) aromatic part, lipophilic
2) intermediate part (DOA)
3) amino grp, hydrophilic
1) aromatic part, lipophilic
- Essential for activity – facilitates permeation across neuromem
- Log P value
2) intermediate part (DOA)
- Ester/ amide (followed by 1-3C chain)
- Determines chemical stability and influence duration of action
- Amide > ester (more resistant to hydrolysis)
- But if DOA too long, can reduce LA activity
less common (ketone, ether)
3) amino grp, hydrophilic
- 2* or 3* amine or N part of heterocycle
- Basic and ionisable to form cation – affinity to Na+ channel (specific action)
- Facilitates formulation of INJ
- pKa of 7.5 - 9
ideal Local anesthetic agent
- reversible blockade
- selective for sensory neuron, no effect on motor neuron
- rapid onset
- sufficient DOA
- chemically stable when sterilised
- no systemic toxicity
- wide margin of safety
- compatible w/ other drugs
- absence of ADR
- inexpensive
LA with higher lipid solubility and lower pKa values = faster onset, lower toxicity
alkaloids from poppy plant
- Opium is air-dried milky exudate (latex) obtained from capsule of Papaver somniferum
- Alkaloids found in the latex belong to class of benzyltetrahydroisoquinolone
- Alkaloids in opium comprise: morphine, codeine, thebaine, papaverine, noscapine, narceine
- Morphinan: Morphine, codeine, thebaine (diff grp attached to benzyl grp, position 3. elimination reaction to form C=C)
Narcotic analgesic eg
1) morphine
2) codeine (most are semi-synthesised)
3) semi-synthesis of morphine derivatives (pholcodine, dihydrocodeine, diamorphine)
4) synthetic (pentazocine, pethidine, fentanyl, alfentanil/ remifentanil, tramadol, methadone)
pholcodine (from morphine)
alkylation w/ N-(chloroethyl)morpholine
- antitussive
dihydrocodeine from morphine/ codeine
1) morphine –> codeine (3* O-CH3 instead of OH)
2) reduce C7-8 double bond –>cyclohexane
H2 + catalyste
diamorphine/ heroin from morphine
esterification of Diacetate of morphine 3-, 6-
- incr lipophilic = better transport, absorption + ADDICTION
narcotic antagonist
1) nalbuphine (mixed agonist-antagonist)
2) naloxone (anta > agonist)
3) naltrexone (anta > agonist)
Morphine
- Powerful analgesic and narcotic. Hosp use (risk of resp depression)
- Unintended SE: Euphoria and mental detachment w/ regular use
- ADR: constipation, NV, tolerance, withdrawal
- Metabolised at 2 diff sites
○ Glucuronidation at position 3: antagonistic to analgesic effects of morphine
○ Glucuronidation at position 6: agonist
□ More effective and longer lasting analgesic, fewer SE > morphine
Codeine
- 3-O-methyl ether (of morphine) widely used and 1/10 potency of morphine
- PO. In many analgesic prep (Panadeine = paracetamol 500mg + codeine 8mg)
- ADR: constipation
- Unintended SE: non addictive medium analgesic (relatively safe)
- Indication: antitussives (relieve and prevent cough)
○ Depress cough centre, raise the threshold for sensory cough impulses
Pentazocine
- Morphine-like structure
○ Ether bridge omitted
○ Cyclohexane ring –> simple methyl grp - Good analgesic, non-addictive. But can induce withdrawal sx
Pethidine
○ Less potent than morphine.
○ Produces prompt, short acting analgesia
○ ADR: less constipating than morphine, less resp depression effect (good for outpt use)
○ Unintended SE: addictive
○ Only aromatic ring and piperidine systems retained
fentanyl
- 4-phenyl-piperidine structure –> 4-anilino structure
○ 50-100x more active > morphine
□ Higher lipophilicity
□ Excellent transport properties
○ Rapid acting, used in operative procedures
Alfentanil, remifentanil
○ Further variants of fentanyl structure
Rapid acting, used in operative procedures
Tramadol
- Produce analgesia by opioid mechanism and by enhancement of 5HT & NE pathways
- Few typical opioid SE
- Has 3-methoxy phenyl cyclohexane
Methadone
- No longer have: piperidine ring system
○ Has diphenylpropylamine derivative that can mimic piperidine ring conformation - PO active, similar activity to morphine, longer DOA
- ADR: less euphorigenic
- Unintended SE: potentially addictive (as morphine)
○ Diff withdrawal sx, less severe - Indication: tx and rehabilitation of heroin addicts
Narcotic antagonist
N-alkyl derivatives related to oxymorphone/ oxycodone
Nalbupine (less SE & abuse potential)
naloxene (heron addicts children, opioid poisoning)
naltrexone (similar activity)
QA processes
Controls overall methods and procedures at system level
Process oriented. Focus on quality of manufactured pdts
Strictly adhered to
- external inspection (HSA)
- Good laboratory practice (GLP)
- Good manufacturing practice (GMP)
QC processes
Controls parts in processes that manufacture the pdts
Product orientated. Focus on quality of manufactured pdts
- batch inspection, pdt sampling
- internal inspection
Good manufacturing processes
- Raw/ starting materials used in manufacturing must be pure
○ Pharmacopeia specific. Not contaminated with impurities - Premises and equipment used for manufacturing must be maintained for operational readiness
○ Premises, walls. Positive P, rounded walls
○ People involved: gowns, coverings
○ Equipment: run for 24hr.
§ The cleaning also need to follow the guidelines. Procedural & documented SOP - People involved in manufacturing process must be trained to competent level
○ Weigh properly, proper documentation - Manufacturing procedures must use latest technology and science
○ New tech need to be verified for use - Processes must be documented to show compliance
Who overlooks quality for medicines
International Conference on Harmonisation of technical Requirements for Registration of Pharmaceuticals for Human Use (ICH)
ICH standardises
- Org that standardises the requirements for medicines regulation throughout the world
- Standardise validation of analytical procedures
- indicates that validation requried for
○ Identification tests
○ Quantitative tests for impurities
○ Limit tests for control of impurities
○ Quantitative tests of API, drug pdt and selected compounds (excipients) in drug pdt
Sources of impurities
- Raw materials (contaminants)
- Method of manufacture
- atmospheric contaminants
- manufacturing hazards
- inadequate storage conditions
Method of manufacture
- Reagents employed in process
- Reagents added to remove other impurities
- Solvents
○ Eg: chloroform. Need to be completely removed, limited amt of residual - Reaction vessels (if washed, residual detergent may be left behind)
atmospheric contaminants
- CO2 dissolve –> carbonic acids (affect pH)
- Dust
manufacturing hazards
- Particulate contamination
○ Esp w/ injection formulation - Process errors
- Cross-contamination
○ Cannot use same facilities/ machines to make diff drugs - Microbial contamination
○ Esp in solutions, syrups (water = growth) - Packing errors
inadequate storage
○ Filth, environment, humidity (hydrolysis)
○ Chemical instability, light exposure
○ Reaction with container materials
○ Physical changes
○ Temp effects
Limit tests types and purpose
- Designed to identify and control small qty of impurity which may be present in drug sub
- May be quantitative or semi
1) comparison (semi-qty)
2) quantitative determination
1) comparison (semi-qty)
Chlorides, sulphates, iron, heavy metals
1) Standard is set up with definite amt of impurity
- At same time
- Same conditions as test exp
2) Compare test and standard solution
- Turbidity
- No ppt
2) Quantitative determinations
- Limits if insoluble matter
- Limit of soluble matters
- Limits of moisture, volatile matters, residual solvents
- Limits of non-volatile matter
- Loss on ignition
○ Limits of residue on ignition
○ Ash values - Precipitation methods
ash test (Qty)
Ash test: measure total ash remaining after incineration.
High ash value indicates:
○ Contamination, substitution or carelessness in preparing the crude drugs
○ Presence of inorganic salts of carbonates, phosphates, silicates — Na, K, Ca, mg
1) Incinerate crude drug
2) Weigh the amt of ash after cooled (in a dry environment)
3) Compare weight to pharmacopeia
Identification tests eg
Monograph of pharmacopeia usually have multiple methods to identify chemical drug sub
1) infrared absorption test
2) UV absorption test
3) TLC (thin layer chromatography) test
Infrared absorption test
- Compare the IR spectrum of test sample & USP reference standard
- MOA: Molecules absorb IR waves, gains energy based on the bonds in diff functional grps in structure
- Bonds can be bend/ stretched
- Appear as a peak
○ Allows identification of functional grps - Has fingerprint region (600-1400 cm-1) of IR spectrum
○ Unique to molecule. Can identify molecule if have same absorbent spectrum within this value
UV absorption test
- UV absorption measured of a test sol and standard sol
- Use 1 cm cell, over 200-400nm
- Compare the UV spectra of test and standard sol
- Determine the absorptivity and absorbance ratio as indicated in monograph
- Requirements are met if UV absorption spectra of test and standard sol exhibit maxima and minima at same wavelength
- Absorptivity and/or absorbance ratios are within specified limits
TLC
- Develop a TLC using silica gel chromatographic plate impregnated with suitable fluorescing sub
- Apply 10uL test sol and 10uL standard sol (prepared from USP reference standard)
- Use TLC developing solvent
- 180:15:1 (chloroform, methanol, water) mixture
- Rf value of principal spot obtained from test sol ~corresponds~ to that from standard sol
= positive identity to standard reference
Rf = distance travelled by SOLUTE/ SOLVENT
quantify purity of analyte by 2 methods
1) titrimetric analysis
2) HPLC
1) titrimetric analysis eg
direct acid/base titration
- argentometric titration
indirect titration
- blank titration
Argentometric titration (direct)
Complexometric titration
Redox titration
Non-aqueous titration
Potentiometric titration
1) Titrimetric analysis principles and application
- Principles: the amt of a standard reagent of precisely known conc is used to react chemically with an analyte such that the amt of the standard reagent used can be used to estimate the purity of the analyte
- Application: Used in pharmacopeia assays to determine the purity of active content of API in a dosage form, purity of raw materials for medicinal pdt prep
titrimetric ADV & DISADV
ADV:
i. Capable of high degree of precision and accuracy
ii. Methods are generally robust
iii. Analyses can e automated and cheap to perform (esp for countries that may not have suff resources)
DISADV:
i. Method may not be selective
ii. Time-consuming
iii. Require large amts of sample and reagents
Indirect titration in aqueous phase mechanism
Involve addition (from pipette) an excess of standard volumetric sol (VS) to weighed amt of analyte.
Followed by determination of excess unreacted VS
indirect titration used for.
1) Volatile sub (NH3, volatile oil)
◊ Evaporates off, not very accurate
◊ Add reagent to prevent sub from evaporating off
2) Insol sub (CaCO3)
3) Sub for which quantitative reaction proceeds rapidly only in excess of a reagent
◊ Excess reagent to make reaction. Back titrate the remaining excess reagent
4) Sub which requires heating with volumetric reagent during determination in which a decomposition / loss of reactants or pdts would occur in the process (aspirin)
◊ Heating can cause other rxn
blank titration (also an indirect)
- Blank titration to standardize conditions in both blank and sample determination
- involve heating a lq containing excess of standard alkali, cooling and back titrate excess
◊ Heating and cooling affects strength of excess reagent
◊ Need to account for it. So blank and analyte undergo same conditions
Argentometric titration (direct)
- Quantitative precipitation used for volumetric determinations, provided the point at which PPT is complete can be determined
NaCl + AgNO3 –> AgCl (ppt) + NaNO3
- NaCl sol can be determined by: titration with AgNO3 (AgCL ppt)
- Excess AgNO3 reacts with Potassium Chloromate (indicator – red coloration = end point)
Considerations for titration
- primary standards
- correction factor
primary standards
- Stable chemical compounds that are available in high purity
- Used to standardise the standard sol used in titrations
- Eg: titrant (NaOH) standardised against Potassium hydrogen phthalate (available in high purity)
- Use to determine the correction factor (f)
correction factor (f)
- Usually used in volumetric analysis to simplify calculations
- Factor is calculated as a ratio (Actual conc/ Desired, nominal conc)
* Tells us how much a given sol differs from the nominal/ true conc
f = 1, prep sol is prepared precisely to desired conc
Actual conc = (0.5 N) x 0.96 (factor) = 0.48N
f < 1
prepared sol is of lower conc than what was desired – usually (absorb water, moisture)
f > 1
prep sol is of higher conc than what was desired
HPLC
- analyses based on calibration with external standard
- Analyses using calibration against an internal standard
external standard
* Put in “x” amt, get “ x” amt
- Plot area under curve and varying conc
- Recovery is complete then can use EXTERNAL standard
Analyses based on single point calibration
i. If recovery complete: peak of analyte compared with calibration curve of standard analyte
* When TDM, how much drug present by HPLC – assay with internal standard used
* If cannot retrieve an “x” amt of drug than recovery incomplete, maybe mostly bound to proteins
calibration with external standard
conc against peak area graph
adv of external standard
- used when sample does not interfere with analysis
- simpler to use
- does not ened reference standard for every sample
disadv of external standard
- relatively accurate if have wider range of concentration used to make calibration curve
- affected by instrumental performance
internal standard
- Should be closely related in structure to analyte
- Should be stable
- Should be chromatographically resolved from analyte and excipients present
- Elute as CLOSE AS POSSIBLE to analyte with restrictions above
- For given weight should produce a detector response similar to that produced by analyte
- Same time, but more dissolved peak, not overlap same
calibration with internal standard
conc of unknown = Peak area of INTERNAL x (peak area ratio unknown)/ (peak area ratio of known)
peak area ratio =
(unknown/ INT standard)
(known/ standard)
calibration with internal standard
conc of unknown = Peak area of INTERNAL x (peak area ratio unknown)/ (peak area ratio of known)
peak area ratio =
(unknown/ INT standard)
(known/ standard)
adv of internal standard
- any variations in sample prep or instrument response are corrected by comparing the peak area / height of the analyte to that of the internal standard
- more accurate and precise measurement
disadv of internal standard
- difficulty selecting appropriate internal standard
- requires reference standard for every sample
why we do internal standard
If we want to quantify drug substances from biological fluids
Most methods in pharmacopoeia don’t use internal standards, as already use very ‘clean’ analyte VS biological fluids like blood
E.g., TDM (plasma concentration - biological system) need internal standard to check extraction method
