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Solubility of weakly acidic and basic drugs

Weakly basic drugs demonstrate higher solubility at lower pH, thus often leading to faster drug release at lower pH. The objective of this study was to achieve pH-independent release of weakly basic drugs from extended release formulations based on the naturally occurring polymer sodium alginate 1. j pharm sci. 1964 nov;53:1346-8. solubilization of weakly acidic and basic drugs by aqueous solutions of polysorbate 80. rippie eg, lamb dj, romig pw Cocrystals of a weakly basic drug (nevirapine) with acidic coformers are shown to alter the solubility dependence on pH, and to exhibit a pH max above which a less soluble cocrystal becomes more soluble than the drug. The cocrystal solubility advantage can be dialed up or down by solution pH Sometimes a combination formulation requires the admixture of acidic and basic drugs. One example (Septrin infusion) is discussed here. Because sulfamethoxazole (XVIII) is a weakly acidic substance and trimethoprim (XIX) is a weakly basic one, for optimal solubility basic and acidic solutions, respectively, are required. In consequence, in an. Weakly basic BCS class II drugs such as carvedilol (Fig. 1) exhibit a complex solubility pattern due to the pH gradient in the gastrointestinal (GI) fluid during transition from the stomach to the intestine. This class of drugs favors ionization and adequate solubilization in the stomach at low pH (4)

formulations. Most of drugs weakly acidic and weakly basic with poor aqueous solubility. Hence various techniques are used for the improvement of the solubility of poorly water-soluble drugs include micronization, chemical modification, pH adjustment, solid dispersion, complexation, co‐solvency, micellar solubilization, hydrotropy etc Most of the drugs are available as weak acids or weak bases. The weak base is absorbed at a faster rate from the intestine (pH 7.50 - 8), this is because the basic substances can't be ionized in basic medium. So the uncharged substances can be passed easily due to its lipid solubility As has been stated before, most of the drugs used in medicine behave insolution as weak acids, weak bases, or sometimes as both weak acids andweak bases. In this chapter we will explore the reasons why drugs behaveas acids or bases and what effects ionisation has on the properties of thedrug, and develop strategies to separate mixtures of drugs on the basis ofchanges in their solubility in various solvents

Strategies to overcome pH-dependent solubility of weakly

Independent of the pH value of the dissolution medium, the pH inside the tablet matrix was expected to be acidic and thus the solubility of the weakly basic drug to be high. In this case, drug release should be pH-independent Generally speaking the pH of extracellular fluid is always going to be within some decimal fractions of 7.4, and so drugs with a pKa under 7 (i.e. weak acids) will usually be water-soluble Salt formation is the most common and effective method of increasing solubility and dissolution rates of acidic and basic drugs. In this article, weakly acidic compounds under gastrointestinal. What the reader will gain: How could the inclusion of the pH the pH modifiers in the solid dispersion system change drug structural behaviors, molecular interactions, microenvironmental pH, and/or release rate of pH modifiers, relating with the enhanced dissolution of weakly acidic or weakly basic drugs with poor water solubility? These.

A soluble acid salt of a weakly basic drug will cause the pH to drop as the salt is added to the solution. This pH drop will, in turn cause more drug to dissolve, and this process will continue until the pH of maximum solubility is reached (see Fig. 4) Weakly basic drugs and their salts exhibit a drop in aqueous solubility at high pH conditions, which can result in low and incomplete release of these drugs from sustained release formulations. The objective of this study is to modulate matrix microenvironmental pH by incorporation of acidic polymers and thus enhance the local solubility and. The dependence of the solubility of a weakly acidic or basic active on the pH of the solvent used Similarly, for a weakly basic active it can be shown pH - pK a = log 10 [S 0/ (S - S 0)] (7) or S = S 0 [1 + 10-(pH - pK a)] (8) log S p

Solubilization of Weakly Acidic and Basic Drugs by Aqueous

  1. Enhancement of solubilization and bioavailability of poorly soluble drugs. By venkatesh rudra. Solubility enhancement techniques with special emphasis on hydrotrophy. By Renu Kumari. BIOAVAILABILITY ENHANCEMENT: A REVIEW HIMANI BAJAJ*, SEEMA BISHT2, MAYANK YADAV1 AND VINOD SINGH3
  2. Start studying IPS Drug Ionization, Lipophilicity and Solubility. Learn vocabulary, terms, and more with flashcards, games, and other study tools. A compound with both acidic and basic groups on the same molecule. Drugs as Weak Acids and Weak Bases
  3. ation: • When a weakly acidic or basic drug partially ionizes in GI fluid, generally, the unionized molecules are absorbed quickly

How cocrystals of weakly basic drugs and acidic coformers

  1. Pharmaceutics Final L13 Solubility. STUDY. PLAY. Solubility of a solid is defined as. the dissolved concentration of a solute in equilibrium with excess solid solute. drug in solid <--> drug in solution. Dissolution definition. process where solute molecules leave the solid phase and enter the solution phase. precipitation definition
  2. istered traginto the body 19 improve the solubility of weakly acidic and weakly basic drugs, they can be converted into sats by deprotonaton pilaration This conversion can increase the solubility product Ki, which is the equilibrium constant for dissolution of.
  3. ates. When the pH is greater than the pK.
  4. Drugs which are basic are ionized in acidic media (pH < 7) The ionized form of the drug provides it with improved water solubility But the unionized form generally passes nonpolar membranes more readily. Acidification of urine increases reabsorption and decreases excretion of weak acids and decreases reabsorption of weak bases

The solubility of drugs Basicmedical Ke

1.3 Solubility of salt form of drugs Salt formation of weak acidic or basic drugs is one of their solubility increasing methods since the ionized species have greater solubility in water and other polar solvents and a number of drugs are marketed as their salt forms. The most common salts used for sal Example: drugs like aspirin (weak acid) can cause ulcer by this phenomenon only. So, the drugs which favours gastric emptying can enhance the absorption of aspirin from ileum due to large surface area than stomach, despite the fact that the acidic pH of stomach helps to absorb weak acid However, some weakly acidic and neutral drugs can extended the definition of acids and bases to include dissolution theoretically be absorbed from the stomach,12 although clear events in nonaqueous solvents not involving free protons, i.e., examples of gastric absorption only (in the absence of intestinal Lewis acids as electron pair acceptors.

pH-Dependent Solubility and Dissolution Behavior of

  1. Weakly basic drugs that exhibit high solubility in acidic gastric pH and low solubility in the basic intestinal environment tend to precipitate (crash out) upon gastro-intestinal transition. Intestinal precipitation of weakly basic low solubility drugs is a well known phenomenon ( 20 )
  2. The ionized form of acidic or basic drug is considered as soluble whereas unionized from as insoluble. A weakly basic drug is more soluble in acidic medium and an acidic drug is more soluble in basic medium because these can ionize properly, and are insoluble in their relevant medium due to poor ionization (due to common H+ or common OH- ). 10
  3. Factors such as the use of salts of either weakly acidic or weakly basic drugs, or esterification of neutral compounds, can influence solubility and dissolution rate. Crystalline form of solid. The presence of polymorphs, hydrates, solvates or the amorphous form of the drug can all have an influence on dissolution rate
  4. Hence an acidic pH dramatically increases the solubility of virtually all sparingly soluble salts whose anion is the conjugate base of a weak acid. In contrast, pH has little to no effect on the solubility of salts whose anion is the conjugate base of a stronger weak acid or a strong acid, respectively (e.g., chlorides, bromides, iodides, and.
  5. The solubility of weak acids increases as the pH is increased. C. The solubility of weak acids in pharmaceutical formulations may be affected by the presence of counterions. d. All weakly acidic therapeutic agents exhibit an isoelectric point 2. Regarding weakly basic drug molecules, which of the following statements are true? a

Drugs that are weakly acidic and weakly basic, generally undergo ionization (Yang et al., 2012). Mostly drugs are developed as salts of weak bases or weak acids to have good solubility and absorption. These salt forms are ionizable and therefore their solubility is pH dependent When esterification of drug occur solubility decreases. 2. If weak acid is converted into its salt, its ionic dissolution in water increase in Poorly soluble drugs are dissolved in a mixture of water and alcohol. 5. Effect of complex formation: As most of the drugs are either weakly acidic or weakly basic in nature, therefore they are. Drug Class: example of a weak acid (RCOO-+ H + ↔ RCOOH) Pharmacokinetics: Almost all drugs are filtered by the glomerulus. The protonated form of a weak acid is the neutral, more lipid-soluble form. If a drug is in a lipid-soluble form during passage through the renal tubule, a significant fraction will be reabsorbed by passive diffusion. The observed difference between low and high pH behavior of weak acid drugs was the rationale behind the i.d. administration to find out the potential of sodium and potassium salts of AZ'403 (pK a 8.4). Now, when confirmed successful, an enteric coating formulation would be the next step to avoid low pH conditions and precipitation in the. Solubility of a weakly acidic or basic drug depends on the ____of the solution. pH of the surrounding fluid Many weakly acidic and basic drugs, are subjected to ionization in the gastrointestinal tract; therefore, solubility, dissolution, and absorption of a weak acidic or basic drug are very much influenced by the _____

Ph, Solubility, Ionization affecting absorption PharmaTuto

Any drug to be absorbed must be present in the form of an aqueous solution at the site of absorption. Water is the solvent of choice for liquid pharmaceutical formulations. Most of the drugs are either weakly acidic or weakly basic having poor aqueous solubility -The VAST majority of drugs are filtered out by the glomerulus -If the drug is in a neutral lipid-soluble form, like a weak acid in acidic urine, it will be REABSORBED -If the drug is in a polar form, like a weak acid in alkaline urine, it will be water-soluble; and water-soluble drugs will BE TRAPPED IN THE URINE Figure 1. The Effect of pH on the Solubility of an Acidic or Basic Extractable; conditional solubility (S e) as a function of solution pH for an acidic or basic extractable with a pKa of 5.0 and an intrinsic solubility (S 0) of 100 (arbitrary units).As the pH increases, the solubility of the acidic extractable increases, and as the pH decreases, the solubility of a basic extractable increases Salt formation is the most common and effective method of increasing solubility and dissolution rates of acidic and basic drugs. In this article, physicochemical principles of salt solubility are presented, with special reference to the influence of pH-solubility profiles of acidic and basic drugs on salt formation and dissolution + Solubility expressions The USP lists the solubility of drugs as: the number of ml of solvent in which 1g of solute will dissolve. E.g. 1g of boric acid dissolves in 18 mL of water, and in 4 mL of glycerin. Substances whose solubility values are not known are described by the following terms: Term Parts of solvent required for 1 part of solute.

Drug/CD complexes, especially those of the natural CDs, have tendency to self-assemble in aqueous solutions to form aggregates (Figure 1).At elevated CD concentrations these aggregates can become large and precipitate as solid microparticles [].In addition, the natural CDs and their complexes have limited solubility in aqueous solutions Supersaturated solutions of poorly aqueous soluble drugs can be formed both in vivo and in vitro. For example, increases in pH during gastrointestinal transit can decrease the aqueous solubility of weakly basic drugs resulting in supersaturation, in particular when exiting the acidic stomach environment. Recently, it has been observed that highly supersaturated solutions of drugs with low. administered drugs is a consequence of this 'first pass effect [2-4]. Many drugs, being weak bases, acids or salts thereof demonstrate pH-dependent release from extended release formulation, for example coated pellets. At the low pH in the stomach, weakly basic drugs are freely soluble resulting in fast release rates. However 80 drug was to improve aqueous solubility. Due to acidic nature of the drug, basic counter ions with 81 pKa value of >10.4 is likely to form pharmaceutically acceptable salts. Therefore, strong basic 82 counter ions like NaOH is needed for a desirable salt of phenytoin. Salts with weakly basic counte The micro-environmental conditions for the dissolution of the weakly acidic drug were kept almost constant, thus resulting in pH-independent drug release. Compound release from mini matrix tablets prepared by wet granulation was faster compared to the drug release from tablets prepared by direct compression

Effect of pH on weakly acidic and basic model drugs and

16.4: The Effects of pH on Solubility - Chemistry LibreText

Some drugs have both acidic and basic functional groups, and therefore can act as a base, an acid, or amphoteric (= both acidic & basic properties) HN N N CO 2 H O F neutral acidic alkyl amine basic aryl amine weakly basic aromatic amine weakly basic Ciprofloxacin The location of the compound in the body will determine the overall charge of the. The present invention is directed to pharmaceutical compositions, and methods of making such compositions, wherein the compositions comprise a plurality of TPR and RR particles, wherein: the TPR particles each comprise a core coated with a TPR layer; the core comprises a weakly basic, poorly soluble drug and a pharmaceutically acceptable organic acid separated from each other by an SR layer.

Weak Acids and Weak Bases . When gastric pH is raised by ARAs, the solubility of weak acids generally increases . For clinical doses of weakly acidic drugs that are not completely dissolved in gastric fluid at physiologic pH, an increase in gastric pH may lead to an increased dissolution and likewise subsequent absorption rate and/or extent A drug like phenytoin & barbiturate when pka is larger than 7 is-A. Ionised at all pH B. unionised at pH C. Ionised at pH 8 D. Unionised at pH 6 Ans. D9. A drug where pka is 7 & unionised at all pH it is-A. Weak acidic B. Very weak acidic C. Weak basic D. Very weak basic Ans. B10. Dissolution & pka helps in drug-A. ionization & solubility

Sustained and controlled release drugs

Effect of pH on weakly acidic and basic model drugs and

This enhanced lipid solubility of API-ILs is illustrated in Figure 2 for four weakly basic APIs, namely cinnarizine (T m = 118°C), itraconazole (T m = 170°C), halofantrine (T m = 79°C-82°C) and dextromethorphan (T m = 111°C). In each case, when combined with an acidic lipophilic counterion, an API-IL was formed that, in turn, exhibited. Pharmacokinetics: General Principles-Lecture I, slide 2; press above to begin the lecture. Download and install current free versions of Quicktime, if needed, to support lecture series audio!. Figure Developed by Dr. Steve Downing, University of Minnesota, illustrating the many membrane barriers even within a single cell Hydrochloride, mesylate, hydrobromide, acetate, and fumarate are the most common counterions that are used for basic chemical entities in the past 20 years , while sodium, calcium, and potassium continue to be the most common counterions for weakly acidic drugs. Increases in aqueous solubility have been achieved by most of these counterions

Drug Absorption - Clinical Pharmacology - MSD Manual

Urine pH, which varies from 4.5 to 8.0, may markedly affect drug reabsorption and excretion because urine pH determines the ionization state of a weak acid or base (see Passive diffusion).Acidification of urine increases reabsorption and decreases excretion of weak acids, and, in contrast, decreases reabsorption of weak bases Papaverine HCl is an opium alkaloid antispasmodic drug, used in the treatment of visceral spasm and vasospasm [1]. The drug belongs to the class of weakly basic drugs - such as Verapamil HCl, Propiverine HCl, Dipyridamole or Dabigratran. These drugs show higher solubility at lower pH, thus often leading to faster drug release at lower pH The solubility of orally-administered drugs is dependent on their chemical properties and often by the intragastric pH the drug is exposed to in the process of absorption: 1. Weakly basic drugs may show decreased absorption, while the absorption of weakly acidic drugs may increase at higher intragastric pH. 1-3 (2010). Dissolution-modulating mechanism of pH modifiers in solid dispersion containing weakly acidic or basic drugs with poor water solubility. Expert Opinion on Drug Delivery: Vol. 7, No. 5, pp. 647-661

How do you tell if a drug is an acid or base

Over 50% of all drug molecules used in medicine exist as salts, most frequently as the hydrochloride, sodium, or sulfate salts. Drugs are often formed as a weak acid or base, but this drug form is not always optimal for dissolution or absorption into your body. Without absorption, a drug cannot have a therapeutic effect, so some forms require a. a. Aspirin (pka = 3.5) is 90% in its lipid-soluble, protonated form at pH = 2.5 b. The basic drug promethazine (pka = 9.1) is more ionized at pH = 7.4 than pH = 2 c. Absorption of a weakly basic drug is likely to occur faster from the intestine than from the stomach d. Acidification of the urine accelerates the secretion of a weak base, pka = 8 e N2 - It has been previously shown that the interaction of some weakly basic drugs with oppositely charged fatty acids during digestion can influence the solid-state form of the drug if it precipitates. The present study hypothesized the opposite effect for weakly acidic drugs

pH-independent release of a weakly basic drug from water

Many important drugs belong to the class of weak acids and bases. They react with strong acids and bases and, within definite ranges of PH, exist as ions that are ordinarily soluble in water. Acidic drugs are more soluble in alkaline solutions where the ionized form can be obtained from the following equation. PH−PKa=log⁡ [ionized] [unionized The solubility of weakly acidic & weakly basic drug as a function of pH can be predicted with the help of eqn. S = So {1 + (K 1 / [H +])} ----- for weak acids. So weakly basic drug which are given as HCl salts have decreased solubility in acidic solution. Eg. Chlortetracycline, Papaverine, Bromhexine, Triamterene, etc Elimination of Weak Acid and Weak Base Drugs As a drug passes through the renal tubules, it will be either reabsorbed or eliminated in the urine. Which path it takes depends on the pKa of the drug and the pH of the urine. pKa is used to describe the strength of acids (the lower the pKa, the stronger the acid) Changes in solubility brought about by alterations of solvent pH can be predicted by the pHp equation. The pHp is the pH below which an acid or above which a base will begin to precipitate. where, e.g. Calculate the pHp of a 1% sodium phenobarbital solution. From Merck Index: (i.e. 1% phenobarbital will precipitate at or below a pH of 8.3 103 and/or area under the concentration time curve (AUC)) of absorptionf or weak-acid drugs with 104 low solubility at pH 1-2 and increased solubility at elevated pH. However, based on curren

Establishing the pH of Extraction Solvents Used to

DRUG SOLUBILITY: IMPORTANCE AND The use of surfactants to improve the dissolution performance of poorly soluble drug products is probably the basic, primary, and the oldest method. Surfactants reduce surface tension and related to complexation involving a weak interaction between the hydrotrophic agents like sodium benzoate, sodium. -differentiate acidic from basic drugs -predict ionization of a drug at different pH -estimate acidity/basicity of a drug solution -predict solubility, absorption and distribution of a drug at different body compartment -discuss the effect of acidity, size, shape, and stereochemistry of a drug on its activit Acid-Base Properties • Most drugs used today can be classified as acids or bases. • A drug's acid-base properties can greatly influence its biodistribution and partitioning characteristics. • the acid-baseddefinition have been developed, acidas a proton donor and a baseis defined as a proton acceptor.

Salts of acidic and basic drugs have, in general, higher solubilities than their corresponding acid or base forms. For solid dosage forms, dissolution rates of salt forms of several weakly acidic compounds under gastrointestinal (GI) pH conditions were much higher than those of their respective free acid forms Timolol is formulated as the salt of Maleic acid. The salt form of this drug is a conjugate acid of a weak base and has ACIDIC character. Question #4: The functional groups that enhance solubility are those that can interact with water via H-bonding or dipole/dipole interactions. The secondary alcohol, the secondary amine, th The rate of absorption depends upon the ratio of the two forms at a particular site and is also a factor in distribution and elimination. The protonated form of a weak acid is non-ionized, whereas the protonated form of a weak base is ionized. The pKa is the negative log of the ionization constant, particular for each acidic or basic drug Therefore, the aqueous solubility of a drug can be used as a first approximation of its dissolution rate. Drugs with low aqueous solubility have low dissolution rates and usually suffer from oral bioavailability problems. The aqueous solubility of weak acids or bases is governed by the pKa of the compound and the pH of the medium. For a weak aci

Factors which determine the lipid solubility of drugs

Basic drugs tend to accumulate in tissues and fluids with pH values lower than the pK a of the drug; conversely, acidic drugs concentrate in regions of higher pH, provided the free drug is sufficiently lipid soluble to penetrate the membranes that separate the compartments. Even small differences in pH across boundary membranes, such as those. It is good for the absorption of weakly acidic drugs; the pH of gastric juice is 0.9-1.5, and weakly acidic drugs can be absorbed in the stomach; the pH of the intestinal cavity is 4.8-8.2, and the intestines are healed The lower the pH is, the higher the pH is, and the weak acid and weak base drugs are easily dissolved and absorbed Domperidone was selected as a model drug due to its pH-dependent solubility. When a controlled-release dosage form of a weakly basic drug having pH-dependent solubility is exposed to an environment of increasing pH, the drug in the dosage form precipitates and can no longer be released from the dosage form (6, 12). Ther

Drug excretion lecture 10

Dissolution-modulating mechanism of pH modifiers in solid

For many weakly basic or weakly acidic API structures for which salt formation was pursued, salt hydrolysis to free form entity is a latent risk especially during formulation process, if for instance a wet granulation process is utilised or alkaline excipients are involved in the formulation (e.g. magnesium stearate as lubricant) The solubility of weakly basic drugs within passage though GI tract leads to pH-dependent or even incomplete release of these drugs from extended release formulations and consequently to lower drug absorption and bioavailability. The aim of the study was to prepare and evaluate hydrophilic-lipophilic (hypromellose-montanglycol wax) matrix tablets ensuring the pH-independent delivery of the.

solution when it is dissolved in an acidic or a basic medium is proportional to the solubility of the drug. Many drugs have different solubilities at different pHs. These pH-dependent solubility differences lead to pH- -dependent dissolution profiles. The solubility-pH pro-file of drugs or amines has already been reported by many authors [4-13] This is actually the case for many weakly acidic drugs. The converse argument, of course, would apply to weakly basic drugs. We would expect their absorption from the stomach to be poor. Consider the three barbituric acid derivatives thiopental, secobarbital, and barbital with respective pKa of 7.6, 7.9, and 7.8. These drugs are very weak acids A basic drug will be ionized in an acidic environment. Both acidic and basic compounds may be ionized to some extent (depending on their acid/base strength, i.e., pKa or pKb) in a neutral environment. Compounds which contain neutral functional groups are not ionizable. Compounds or drugs that are ionized are soluble in polar solvents especially.

Salt selection for basic drugs - ScienceDirec

According to the pH partition theory, a weakly acidic drug will be absorbed more likely from the stomach, because the drug exists primarily in the: Un-ionized, more lipid-soluble form Ionic form, which facilities diffusion Ionized, more water-soluble form Form of weak acid and more soluble in acid mediu Weak Acid and a Weak Base Drug Compound The dissolution rate of a sparingly soluble weak electro-lyte drug is proportional to the total solubility (6, 8) where the total solubility, S total, for a weak acid drug compound, RCO 2H, in the microenvironment is defined by S total = [RCO 2H] o + [RCO 2-] o = [RCO 2H] o(1 +K a drug /[H+] o) (7) where. after parenteral administration. Water soluble and ionized from of weakly acidic and basic drugs are excreted in GIT. Example are nicotine and quinine are excreted in stomach. Drugs excreted in GIT are reabsorbed into systemic circulation & undergo recycling The sulfonamide group is weakly acidic and the pKa of the group is usually too high to affect solubility at pH 7.4. Examples Sulfony phosphoramidic acid derivatives of the selective COX-2 inhibitor, Cimicoxib show good solubility at neutral pH, enabling formulation as aqueous solutions for parenteral administration Most organic drugs contain one acid group, usually a carboxylic acid, -COOH, or one basic primary, secondary, or tertiary amino group, NC 1-3, [3,22,27,28,29] that determines the acid-base.

Solubility (Physical Pharmacy)Dissolution and In Vitro In Vivo Correlation (IVIVC)

The degree of dissociation is related to the drug constant and the pH of the absorption site. For example, the stomach is the site for the absorption of weak acidic drugs, and intestine is the site for the absorption of the weak alkaline drug. On the other hand, for cell membranes, it takes longer to absorb as well as excrete strongly acidic. Hasselbalch equation for the ratio of solubility for the weak acid or weak base? a) Aqueous diffusion b) Lipid diffusion c) Carrier molecules d) Endocytosis and exocytosis 5.4) Which of the following drug permeation mechanisms is used for peptides, amino acids, glucose, and other large or insoluble molecules? a) Aqueous diffusion b) Lipid diffusio Figure 1.7. Solubility of the basic drug NVP and its cocrystals with acidic coformers: (1:1) cocrystal NVP-MLE, and (2:1) NVP-SAC and NVP-SLC as a function of pH. The symbols represent solubilities determined from the solutions saturated with NVP and/or cocrystal at 25ºC. The pH values correspond to equilibrium pH Because of the weak basic properties and an acid dissociation constant (ie, the pH at which equilibrium is reached between the ionized and the nonionized form) near the stomach pH range of 1 to 4 (erlotinib pK a = 5.4), intragastric pH shifts lead to a more significant shift toward the nonionized (less-soluble) form and subsequent lower. How cocrystals of weakly basic drugs and acidic coformers might modulate solubility and stabilit Theoretically, weakly acidic drugs (eg, aspirin) are more readily absorbed from an acid medium (stomach) than are weakly basic drugs (eg, quinidin ). However, whether a drug is acidic or basic, much of the absorption can occur in the small intestine because the surface area is larger and membranes are more permeable