1. The medical uses and synthesis of Doxycycline as a prescription antibiotic – by Molly
Winterbottom
Figure 1 – Skeletal structure of doxycycline molecule
So, what is Doxycycline? It is a common prescription antibiotic and semi synthetic derivative
of the tetracycline family which consist of a bacteriostatic property, meaning that it
prevents the growth of bacteria. It is a broad-spectrum antibiotic used to treat a wide range
of bacterial infections, such as severe acne or urinary tract infections 1
. It prevents and
treats these bacterial infections by inhibiting bacterial protein synthesis due to the
disruption of transfer and messenger RNA at ribosomal sites 30S, which is made up of a
1,540- nucleotide RNA and 21 proteins, and possibly the 50S ribosomal subunit site as well,
this binding will thereby block the binding of aminoacyl-tRNA to the mRNA-ribosome
complex, and therefore inhibit protein synthesis form occurring 2
.
Figure 2 – 3D image of ribosomal site 50S (on the left) and 30S (on the right)
Doxycycline is an isomer of tetracycline and differs in the placement of 1 hydroxyl group and
can be formally viewed as the result of transferring the C6 hydroxyl group of tetracycline to
C5.
2. Figure 3 – Skeletal structure of tetracycline molecule
Doxycycline can be synthesized in 2 ways, both from using oxytetracycline as a reactant.
One method (method 1) of synthesising doxycycline is by dehydrating the oxytetracycline
molecule at C6 by reducing the tertiary hydroxyl group using Rhodium on carbon catalyst.
Figure 4 – Synthesis of Doxycycline (method 1)
The second method (method 2) is analogous to that giving methacycline, which would
suggest an oxidation stage of the homoallyl system, except that N-chlorosuccinimide is used
as the oxidising agent which results in the formation of naphthacentetrahydrofuran
derivative. Reductive dichlorination of this product using sodium thiosulfate forms the
intermediate methacycline, and thiophenol is joined to the methyl group that carry out
radical reactions, forming the derivative. This product is reduced by hydrogen over a Raney
nickel catalyst, whilst this is happening reductive desulfurization takes place and therefore
giving doxycycline.3
3. Figure 5 – Synthesis of Doxycycline (method 2)
Doxycycline has a broad spectrum of activity and is effective against gram-positive (bacteria
that has a thick peptidoglycan layer and no outer lipid membrane) and gram-negative
(bacteria that has a thin peptidoglycan layer and an outer lipid membrane), aerobic and
anaerobic bacteria, spirochetes (spiral shaped bacteria), and mycoplasma (type of bacteria
that commonly causes mild infection of the respiratory system)4
. Doxycycline is currently
the most commonly used tetracycline and is considered an essential drug by the WHO
(World Health Organization) and has been used in medicine for more than 40 years.
Although some tetracyclines have been synthesised chemically, they are not generally
available in commercial quantities.
It has a variety of applications to treat common respiratory and genitourinary tract
infections, but also amongst atypical infections, such as malaria, rickettsial infections,
leptospirosis, brucellosis and some of the bioterrorist agents, including anthrax cytostatic
and cytotoxic activity as shown against cell lines of various tumour origins.
Figure 6 – 100mg box of doxycycline capsules for oral use
It is a well-tolerated drug that is bacteriostatic, and which is generally given at a dose of
100mg daily of twice daily. Doxycycline is well absorbed and has generally good tissue
penetration. The serum half-life is 18-22 hours depending on the dosage ingested. An
4. antibiotics half-life needs to be as long as possible to stay in the body as a concentrated
substance to attack the bacteria. Major side effects are gastrointestinal and dermatological,
and it is generally contraindicated in pregnancy or childhood since there is positive evidence
of human foetal risk, most common risk is that it can affect growing teeth and if taken whilst
pregnant or under the age of 12 it can cause discolouration of the teeth5
.
Figure 7 – 100mg Doxycycline capsule
The capsule is made from hard gelatine with an opaque pale green cap and opaque green
body as seen above in figure 7, in some circumstances the green capsule may have “100mg”
printed in white or black ink. The capsules are usually packed in blister packs made of one
sheet of 200-micron rigid, opaque white polyvinyl chloride and a second sheet of 20-micron
aluminium ranging in packs sizes of 8, 10, 14 and 50 capsules. Each capsule contained
100mg doxycycline base as doxycycline hyclate as seen in figure 8 shown above, also
containing sucrose, which can be digested and absorbed in the small intestine. Doxycycline
is almost completely absorbed and is not subject to presystemic metabolism, the mean
bioavailability being approximately 93%. Almost all of the product is absorbed in the upper
part of the digestive tract.6
More common side effects of taking doxycycline are headaches, feeling or being sick, it can
also make your eyes and skin sensitive to the sun. However, serious side effects can include
Diarrhoea that contains blood or mucus, ringing or buzzing in your ears, yellow skin or the
whites of your eyes turning yellow which could be a sign of liver problems and intracranial
hypertension.7
To conclude, doxycycline is a common antibiotic in treating various infectious diseases and is
widely used over the globe as a 40-year-old antibiotic, therefore showing its significant
medical uses as a prescription antibiotic as beneficial both medically and financially to those
who need it as a treatment, being an over-the-counter drug.
Figure 8 – Contents Inside a 100mg
Doxycycline Tablet
5. 1
Clinical infectious diseases, volume 38, Issue 6, 15 March 2004, Pages 864-970
2
URL:
http://ncit.nci.nih.gov/ncitbrowser/ConceptReport.jps?dictionary=NCI_Thesaurus&ns=NCI_Thesaursus&code=
C457 Doxycycline (accessed on 20/11/20)
3
R.S. Vardanyan, V.J. Hruby, in Synthesis of Essential Drugs, chapter 32 – antibiotics, 2006
4
Applications of Nanocomposites Materials in Drug Delivery, Chapter 6 Development of injectable in situ gelling
systems of doxycycline hyclate for controlled drug delivery system, Jignesh P. Raval, Dharmesh R. Chejara, Ketan
Ranch, Parth Joshi, 2018
5
Ruben Vardanyan, Victor Hruby, in Synthesis of Best-Seller Drugs, chapter 30, 2016
6
http://www.medicines.org.uk/emc/product/4063/smpc (accessed on 10/12/2020)
7
http://www.nhs.uk/medicines/doxycycline/ (accessed on 27/11/20)
