Agriculture Business Week

Halquinol is an old drug but still is useful for nonspecific treatment of scouring or diarrhea in livestock and poultry. Although it is quite commonly used in pig and poultry production, many raisers still needs to know the nature of this drug.

What is halquinol?
Halquinol is the generic name of the active ingredients of Quixalud, a product of Novartis Animal Health. Halquinol is also available as generic products from different sources.

Is halquinol an antibiotic?
In the strictest sense, halquinol is NOT an antibiotic, but it kills microbes that may cause disease.

If it’s not an antibiotic, what is it then?

The best classification for halquinol according to how it is used is “intestinal antiseptic”, which is like a disinfectant but used in living tissues instead of inanimate objects. It however has other action than just antiseptic. Chemically it belongs to 8-hydroxyquinolines, whose general chemical structure is like this:

The most active component of halquinol is an 8-hydroxyquinaline like the one shown above but with chloride (CI) attached to carbon (position) 5 and 7, making it a 5, 7-dichloro-8-hydroxyquinoline (see the following illustration). This specific component is also called chlorquinol.

So, are halquinol and chlorquinol one and the same?
Not really. While chlorquinol is halquinol’s

main component, halquinol also contains 5-chloro-8-hydroxyquinoline (designated A below) and 7-chloro-8-hydroxyquinoline (designated B below).

Halquinol is actually a mixture of three forms of chlorinated 8-hydroxyquinoline, is that correct?

That’s correct.

Is there a specific or optimum ratio of these chlorhydroxyquinolines in a product preparation of halquinol?
Yes. More than half of halquinol should contain the most active component which is 5,7-dichloro-8-hydroxyquinoline. Specification for halquinal (Quixalud) should be as follows: 5,7-dichloro-8-hydroxyquinoline 57-74%, 5-chloro-hydroxyquinoline 23-40%, and 7-chlorohydroxyquinoline minimum of 3%. The best antimicrobial effect is this ratio only which is present in Quixalud.

What kinds of microbes are affected by halquinol?
Halquinol is effective against (1) protozoan parasites such as Giardia, Balantidium, and Entamoeba, (2) fungi, and (3) bacteria (Gram-positive, Gram-negative, aerobes and anaerobes including E.coli and Salmonella causing diarrhea).

Is halquinol used for treatment of specific infectious disease?

Halquinol is used as a nonspecific gastrointestinal antiseptic or preventive rather than as treatment of specific infections.

Halquinol has been used in treating chronic diarrhea of unknown origin in horses. Fecal consistency in these horses changed from “cow-like” to formed feces with 1-2 days. Similar observation has been made in pigs and poultry. Body weights improved most probably because of improved hydration and absorption of nutrients.

In human and pet animal medicine, some ointment or cream for skin wounds may contain halquinol or another 8-hydroxyquinoline as skin antiseptic.

What is the most common use of halquinol in animal agriculture?

Halquinol is used in pigs and poultry production as non-specific anti-scour, and as a non-antibiotic performance enhancer. They are also approved for the same reasons in ruminants.

How does halquinol act?
The specific mechanism of action of halquinol is not known, but it has been suggested that as nonfunctional analogue of Coenzyme Q, it blocks the transport of electrons down the respiratory chain in the process of making ATP (energy) in the mitochoria of bacteria, fungi and protozoa. Coenzyme Q is a functional form of electron carrier in this process. In short, halquinol prevents microbes from making energy to stay alive.
It has also been suggested that the beneficial effect of halquinol is related to its action on colonic microbial fermentation activity. Volatile fatty acids produced from colonic fermentation participate in controlling water absorption and secretion balance across the wall of the large intestine.

Also, halquinol may “chelate” or in other words “trap” microbial toxins, heavy metals, and other harmful substances within the gut, and are excreted in the feces rather than absorbed. Chelation refers to the formation of complexes through ring systems, often 5- to 6-membered ring. An example of “chelation” with halquinol is shown below; TX represents the chelated substance.

Would you consider halquinol a “growth promotant” or “performance enhancer”?
Yes, because improved growth rate and feed efficiency are almost always observed with the use of Quixalud.

How does halquinol improve performance?
The mechanism is not specifically known as with other “growth promotant”, but it could be any or all of the following,
a. Inhibit growth or metabolism of harmful gut organisms.
b. Decrease elaboration of toxic substances (Quixalud “chelates” toxins).
c. Reduce bacterial destruction of essential nutrients.
d. Improve efficiency of nutrient absorption by modifying the gut wall by reducing intestinal thickness for more efficient nutrient absorption.
e. Reduce intestinal epithelial cell turnover.
f. Reduce intestinal motility by the direct action on smooth muscle. This allows more efficient nutrient absorption.

Is halquinol absorbed from the gut? Quixalud is very minimally absorbed. Its effect is confined to the gut. It is excreted directly in the feces.

Do microorganisms develop resistance to halquinol?
The development of resistance to any drugs that affect microorganisms is always possible, but in the case of halquinol the likelihood of microbial resistance is very low.

Is halquinol compatible with other antibiotics?
Halquinol has no adverse reaction with other antibiotics. It can be administered together with other antimicrobial drugs in feed.

How stable is halquinol in the feed?

Halquinol is stable in premix and in pelleted feed for at least 3 months.

How safe is halquinol to medicated animals?
At the recommended inclusion rate and duration of treatment, Halquinol is safe.

Does halquinol cause drug residues in meat and other food products?
Since halquinol is minimally, if at all, absorbed, the bulk of ingested halquinol stays and act in the gut and is excreted in the feces. Since it is not absorbed, there is no chance of developing drug residues in meat. However, the law requires that at least 2 days of withdrawal period must be observed.

What differentiates Quixalud from other preparations of halquinol?
The most important difference would be the assurance of the right proportion of the active components in Quixalud.